DesigningSpacesforNaturalVentilationBuildingscanbreathenaturally,withouttheuseofmechanicalsystems,ifyoudesignthespaces properly. This accessible and thorough guide shows you how, inmore than 260color diagrams andphotographs illustrating case studies andCFD simulations.You canachievetrulynaturalventilationbyconsideringthebuilding’sstructure,envelope,energyuse,andform,aswellasgivingtheoccupantsthermalcomfortandhealthyindoorair.

By using scientific and architectural visualization tools included here, you can developventilationstrategieswithoutanengineeringbackground.Handysectionsthatsummarizethe science, explain rules of thumb, and detail the latest research in thermal and fluiddynamicswillkeepyourdesignssustainable,energyefficient,anduptodate.

UlrikePasseisanAssociateProfessorofArchitectureandtheDirectoroftheCenterforBuildingEnergyResearch(CBER)atIowaStateUniversity,USA.

FrancineBattaglia is a Professor of Mechanical Engineering and the Director of theComputational Research for Energy Systems and Transport (CREST) Laboratory atVirginiaPolytechnicInstituteandStateUniversity,USA.

‘Avirtualhandbookof theories,principles, andconcepts,DesigningSpaces forNaturalVentilation is an essential resource for designers, researchers, and students.The authorspresent both historical andmodern examples of successfully naturally ventilated spacesand offer discussions of recent research that challenge the perceptions of “coolth” andthermal comfort provided by air conditioning.’ – Alison G. Kwok, Department ofArchitecture,UniversityofOregon,USA

‘Through a comprehensive combination of traditional and contemporary case studies,clearlyexpressedbasicconcepts,andthestrategiestoimplementthem,thisbookprovidesa very useful guide to designing low energy, low carbon buildings using naturalventilation.Arecommendedreferencebookforbothstudentsandarchitects.’–PabloLaRoche, Professor of Architecture, Cal Poly Pomona University, Sustainable DesignLeader,RTKLAssociates,USA

‘Forfartoolongthedesignofnaturalventilationsystemshasrelieduponthearchitect’smagic arrow sketches or the engineer’s finite difference computations. Confusionregardingwhatanaturalventilationsystemcanrationallyaccomplishhasabounded.WiththepublicationofDesigningSpacesforNaturalVentilationbuildingdesignerswillfindavaluableguidetothislow-energyapproachtospacecoolingandairquality.Thejourneytonet-zero energy and carbonmitigationdemands such a resource.’ –WalterGrondzik,PE,Professor,DepartmentofArchitecture,BallStateUniversity,USA

DesigningSpacesforNaturalVentilationAnArchitect’sGuide

UlrikePasseandFrancineBattaglia

Firstpublished2015

byRoutledge

711ThirdAvenue,NewYork,NY10017

andbyRoutledge

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RoutledgeisanimprintoftheTaylor&FrancisGroup,aninformabusiness

©2015Taylor&Francis

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LibraryofCongressCataloguinginPublicationData

Passe,Ulrike.

Designingspacesfornaturalventilation:anarchitect’sguide/UlrikePasseandFrancineBattaglia.

pagescm

Includesbibliographicalreferencesandindex.

1.Naturalventilation.2.Windsandarchitecture.3.Architectureandclimate.I.Battaglia,Francine.II.Title.

TH7674.P372015

720’.47—dc23

2014032584

ISBN:978-0-415-81775-2(hbk)

ISBN:978-0-415-81777-6(pbk)

ISBN:978-0-203-58347-0(ebk)

AcquisitionEditor:WendyFuller

EditorialAssistant:GraceHarrison

ProductionEditor:EdGibbons

TypesetinAvenirby

ServisFilmsettingLtd,Stockport,Cheshire

ContentsListoffigures

ForewordbySueRoaf

Acknowledgments

Introduction:WhyDoweTalkaboutNaturalVentilationNow?

WhyweNeedNaturalVentilation

BenefitsofNaturalVentilation

NaturalVentilationandDesign

NaturalVentilationandEnergy

TheLiteratureGap

WhatIsVentilation,andWhatIsNaturalVentilation?

What’sintheBook?

TheAudienceofthisBook

TheOriginofthisBook

WhattoExpectfromtheBook

Part1TheoriesandScientificBackground

1. TheImportanceofSpaceforNaturalVentilation

1.1. ConnectedandDetachedSpaces

1.2. TheDrivingForcesofNaturalVentilationAreSpatial

1.3. HouseswithImpactontheGeometriesofFlow

1.3.1. SlidingSpace:TheAffleckHouse

1.3.2. BoltedSpace:TheHowHouse

1.3.3. IncorporatedSpace:TheEsherickHouse

1.3.4. TheAtrium

1.3.5. TheNorthernCourtyard

2. ThePhysicsofAirFlow

2.1. SolidsandFluids

2.2. LagrangianVersusEulerianDescriptionasFrameofReference

2.3. PropertiesofAir

2.4. MaterialDerivative

2.5. ConservationofMass–ConservationofMomentum

2.6. ForcesonFluidParticles

2.7. Navier-StokesEquations

2.8. Bernoulli’sEquation

2.9. BoundaryCondition

2.10. Turbulence

2.11. ReynoldsNumber

2.12. K-Epsilon(TwoEquation)Model

2.13. BuoyancyastheBasisforStackEffect

2.14. ForcedConvection

2.15. FluidDynamicsofWeather

2.16. AirandMoisture

2.17. WhatIsWind?WindandObstructions/WindinUrbanContext

2.18. TheImpactofFluidDynamicsPrinciplesonSpatialProportions

3. TheImportanceofFreshAirforOccupants’Health

3.1. WhatIsAir?

3.2. IndoorAirQuality

3.3. ABriefHistoryofAirandHealthSciences

3.4. HealthandWell-Being

3.5. Architecture,HealthandAir:AlvarAalto’sPaimioSanatorium,Finland

3.6. Breathing,Cooling,Cleaning,andVentilationRates

3.7. IndoorAirQualityTools

3.8. BuildingMaterialsandVentilation

4. NaturalVentilationandClimate

4.1. AtmosphericBoundaryLayer

4.2. TheScienceofAtmosphereandClimate

4.3. TheLaminarBoundaryLayer

4.4. EncyclopediaofClimates

4.5. WindasaResource

4.6. ABriefHistoryofWindNotations

4.7. PersonificationofWinds

4.7.1. WindNamesandtheirCharacters

4.7.1.1. Aeolus

4.7.1.2. Anemoi

4.7.1.3. Boreas

4.7.2. OtherMythologicalAiryCharacters

4.7.2.1. AngelsandSpirits

4.7.2.2. Ariel

4.8. CondensationandClouds

4.9. ImpactonBuildingsandInteriorSpaces

4.10. WindSystems

4.11. HowArchitectsCanInfluencetheImpactofWindontheBuildingVentilationPath

4.12. InformationforArchitectstoStarttheDesignProcess

4.12.1.Macro-ScaleInformation

4.12.2. RegionalScaleInformation

4.12.3.Micro-ScaleInformation

4.12.4. FinalScale:TheBuildingScale

4.13. ClimatesforNaturalVentilation

5. InheritedSpatialArchetypesforNaturalVentilation

5.1. SharedIdeasasArchetypes

5.2. TheImportanceofInheritedVernacularStrategiesforSustainableDesign

5.3. SpaceTypes:Cave,Courtyard,Chimney,Passage/Arcade/Loggia,Basket

5.3.1. UtilizingTemperature-InducedPressureDifferentials:Caves

5.3.1.1. ThekivaoftheAnasaziPeople

5.3.1.2. TheCorbelledDomesoftheHarranHousesinSoutheastAnatolia,Turkey

5.3.1.3. TheAeolianVillasinCostozza,Veneto

5.3.2. SimultaneouslyUtilizingTemperature-andWind-InducedPressureDifferentials:Courtyard

5.3.2.1. CourtyardasClimateDevice

5.3.2.2. TheCourtyardHouseinChina

5.3.2.3. Two-CourtyardsVentilationStrategy

5.3.3. HorizontalWindCatchers:Passage,Arcade,Loggia

5.3.4. Wind-InducedPressureDifferentials:WovenStoneBasket

5.3.5. Wind-InducedPressureDifferentials:WindCatcher

5.3.6. Temperature-InducedPressureDifferentials:Chimneys

5.4. InheritedBuildingTypesandClimate

5.5. TraditionalVernacularandContemporaryModernArchitecture

6. NaturalVentilationandThermalComfort

6.1. StandardizingComfort

6.2. Air-Conditioning

6.3. ComfortResearch

6.4. ThermalComfortParameter

6.5. AdaptiveComfortStandardforNaturalVentilatedBuildings

6.6. ThermalDelight

6.7. RelationshipofAirVelocityandComfort

6.8. ThermalComfortandMetabolism

6.8.1. EnergyofMetabolicRate

6.9. BehaviorandComfort

6.10. ClothingandComfort

6.11. OutdoorComfortandWind

6.12. OperativeTemperatureandComfort

6.13. VentilationandHumidity

6.14. TheConceptof‘Coolness’asaSocialRatherthanaHealthConcern

6.15. ThermalLimitsinaNaturallyVentilatedBuilding

6.16. ThermalPleasureVersusThermalBoredom:TheConceptofAlliesthesia

6.17. EvaluatingThermalComfortConditions:TheThermalComfortCalculator

Part2Parameters

7. PressureasIndicator

7.1. Temperature-InducedAirMovement

7.1.1. StackVentilationorThermalBuoyancyVentilation

7.1.2. PositionofNeutralPressureLevel

7.1.3. ClassificationofStackVentilationStrategies

7.2. Wind-InducedVentilation

7.2.1. Cross-Ventilation

7.2.1.1. BasicProportionsandStrategiesforWind-InducedCross-Ventilation

7.2.2. Single-SidedVentilation

7.3. WindPatternsintheUrbanClimateContext

7.3.1. PopulationinUrbanAreas

7.3.2. UrbanPatternsandtheModernMovement

7.3.3. UrbanMeteorology

7.3.4. UrbanTypology

7.3.5. WindandtheUrbanStreetCanyon

7.3.6. ObstaclestoFlow/FlowAroundBuilding

7.3.6.1. IsolatedRoughnessFlow

7.3.6.2. WakeInterferenceintheUrbanCanyon

7.3.6.3. SkimmingFlowRegime

7.3.6.4. FlowFieldsAbovetheCity

7.3.7. InfluenceofUrbanClimatologyonUrbanPlanningandArchitecturalDesign

7.3.7.1. ClimaticCoolingPotential(CCP)

7.3.7.2. ThermalInfluenceonUrbanAirFlow

7.3.7.3. InteractionofAirFlowintheUrbanBoundaryLayer(TheCity)withotherFactors

7.3.7.4. BoundaryLayerRoughnessLength

7.3.7.5. Zero-planeDisplacement

7.3.7.6. UrbanPollutants

7.3.8. UrbanGeometry

7.3.9. UrbanMorphometry

7.3.10. AirportWindDataandEnergyModelingTools

7.3.11. ModelingtheUrbanEnergyBalance

8. SpatialStrategies/Space-InducedAirMovement

8.1.DevelopingtheFlowPath

8.1.1. Path1:Cross-Ventilation

8.1.1.1.CasaadAppartamentiGiulianiFrigerio,Como,byGiuseppeTerragni(1939–1940)

8.1.1.2.KanchanjungaApartmentBuildingbyCharlesCorrea(1970–1983)

8.1.2. Path2:Single-Sided(Comfort)Ventilation

8.1.2.1.CommerzbankbySirNormanFoster

8.1.3. Path3:StackEffectVentilation

8.1.3.1. JudsonUniversityinElgin,Illinois,nearChicago

8.1.4. Path4:SolarChimneys

8.1.4.1. TheCharlesdeGaulleSchool

8.1.5. Path5:WindTowers–PassiveandHybridDowndraftCooling

8.1.5.1.HabitatResearchandDevelopmentCenter(HRDC)byNinaMaritzArchitects,Katatura,Windhoek,Namibia

8.1.6. Path6:CombinedStrategies

8.1.6.1. FreieUniversitätBerlinLibrary

8.2.ConnectingtheInnerFlowPathtotheOuterCondition

8.2.1. KfWWestarkade,Frankfurt,Germany,bySauerbruchHutton

8.2.2. SanFranciscoFederalBuildingbyMorphosis

9. FaçadeasFilter:FromWindowstoCurtainWallstoAdaptiveandSmartSkins

9.1. WindowVentilationinDifferentRegionsandClimates

9.1.1. FrenchDoors

9.1.2. EnglishSashWindows

9.1.3. HopperWindows

9.1.4. NorthernEuropeanBoxWindows

9.1.5. MultifunctionalRomanWindows

9.1.6. VentilationWindows

9.1.7. LaueferliinDavos

9.1.8. PivotWindows

9.1.9. WingWalls

9.1.10. VentilationHoles

9.2. ProportionalRulesforWindowOpeningsandDistribution

9.3. FaçadeProportionsandWindowVentilationStrategies

9.4. BenefitsofDouble-SkinFaçadesintheContextofNaturalVentilation

9.5. Innovations:AdaptiveandSmartSkinsforAirandLight

9.6. RoofVentilators,Coils,andWindCatchers

9.7. RoofElementstoEnhanceAirFlowbytheVenturiEffect

9.8. Louvers

9.9. TrickleVentilationandVentilationSkins

10. ControlofNaturalVentilation

10.1. Senses,Sensors,andtheirControls

10.1.1. SensingAirMovement

10.1.2. SensorsforAirMotion

10.1.2.1. TheToweroftheWinds,Vatican

10.1.2.2. AgeofAir

10.1.3.Actuators

10.1.4.Controls

10.1.4.1. OccupantsandControls

10.1.4.2. PredictiveControls

10.1.4.3. AirtightnessandInfiltration

10.1.4.4. UserInteractionandOverridingControls

10.2. DistinctNaturalVentilationStrategies

10.2.1. CoolingtheStructure:NighttimeVentilation

10.2.1.1. NighttimeVentilationCaseStudy:ThePaulWunderlichHaus

10.2.1.2. MaterialsforThermalMassinNighttimeCooling

10.3. LimitationsofNaturalVentilation

10.3.1. ClimaticLimitations

10.3.2. AcousticChallenges

10.3.3. IssueswithNoiseandPollution

10.3.4. IssuesofRiskandLifeSafetyforOpen-PlanSpacesandStackAtria

10.3.5. Screens,Louvers,andShades

Part3MakingAirVisible–ComplexScienceSummarizedforArchitectsandDesigners

11. OverviewofMethodsforCalculationandSimulation

11.1. ExperimentsandWindTunnelResearch

11.2. EmpiricalandAnalyticalModels

11.3. ComputationalModels

12. ComputationalFluidDynamics

12.1. NumericalModeling

12.2. GridResolutionandValidation

12.3. InitialandBoundaryConditions

12.3.1.Wind-DrivenFlows

12.3.2. Buoyancy-DrivenFlows

12.3.3. Pressure-DrivenFlows

12.4. VisualizingtheDrivingDynamicsofVentilation

AuthorBiographies

Bibliography

ImageCredits

TableCredits

Index

FiguresFigure0.1 Erde,Wasser,Luft(Earth,Water,Air),drawingbyPaulKleeforthePedagogicalSketchbook

(PädagogischesSkizzenbuch),originally1925,BauhausBücher,p.37.

Figure0.2 Theoperablewindowistheclassicmeansfornaturalventilation,ascanbeseenhereinAlvarAalto’sownhouseatRiihitieinMunkkiniemi,Helsinki.

Figure0.3Thethree-dimensionalityofspaceconnectingspacesverticallyandhorizontallyisessentialfornaturalventilation.ThisdrawingconceptualizesthecontinuingsurfaceofsuchaspaceforHausMarxeninGermanybyPasseKaelberArchitects,Berlin,2001.

Figure0.4 HVACenergyconsumptionbybuildingendusein2005(U.S.DepartmentofEnergy).

Figure0.5 Approachforachievingnet-zeroenergybuildings:onlywithreduceddemandwillitbepossibletocoverenergydemandwithrenewableresources.

Figure0.6 AirflowandturbulencemodeloftheViipurilibrarybyAlvarAalto,designedduringthelate1920sandearly1930sbasedona1927competitionentryandcompletedin1935.

Figure0.7 TraditionalwindcatchersinthecityofYazdinIran.

Figure0.8 HausMarxenbyPasseKaelberArchitects,Berlin(2001):externallyacompacttiltedcubecladintimberpanels.

Figure0.9 HausMarxenbyPasseKaelberArchitects,Berlin(2001):internallyanopencompositionofverticalandhorizontallyconnectedspaces.

Figure1.1 GrandCanyon,Arizona,USA,anaturallandscapeformedbythefluiddynamicsofwaterandwind.

Figure1.2FountainatVillaLanteatBagnaia,Italy,attributedtoJacopoBarozzidaVignola(sixteenthandseventeenthcentury)–specificallyshapedtoformturbulencesintheflowofwaterandwiththatshapethesoundsinthegarden.

Figure1.3 TheforcesofflowarereflectedintheconstructionoftheHooverDam(constructedbetween1931and1936).

Figure1.4 SteeproofsinhotandhumidclimatessupportstackventilationasinthispalaceinGoa,India.

Figure1.5 VillaMadamainRome,Italy,designafterRaffael,startedin1518:eachspacedevelopsitsowngeometryandthespacesareplacedinconnectedsequence.

Figure1.6 HistoricvisualizationofairmovementandenergydistributionbyLewisLeeds.

Figure1.7 GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:exteriorviewoftheslopebehindthehouseleadingtotheloweropenporch.

Figure1.8GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:theexteriorporchspacebelowthehousewiththebasinbelowandtheventilationopeningintothemainlivingspaceabove.

Figure1.9 GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:operablefloortoceilingwindowatthecornerofthemainlivingspace.

Figure1.10 DiagramofmainairflowpathintheAffleckHouse.

Figure1.11 DiagramofspatialcompositionintheAffleckHouse.

Figure1.12 WindroseforthelocationoftheAffleckHouse.

Figure1.13 ThesecretoftheAffleckHouseliesinthehorizontalwindowbetweenthelowerairporchandthemainlivingspace,whichallowsforanupdraftairmovement.

Figure1.14 JamesEadsHowHousebyRudolphM.SchindlerinLosAngeles,CA,constructedin1925:viewof

thehouseonthetopofthehill.

Figure1.15 DiagramofmainairflowpathintheHowHouse.

Figure1.16 DiagramofspatialcompositionintheHowHouse.

Figure1.17 WindroseforthelocationoftheHowHouse.

Figure1.18 EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:streetfaçadewithclosedshutters.Thedoubleheightlivingroomisontheright.

Figure1.19 EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:compositiondiagramofdoubleheightspacewithinthelargercubicvolume.

Figure1.20 EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:streetfaçadewithclosedshutters.Thedoubleheightlivingroomisontheright.

Figure1.21 DiagramofspatialcompositionintheEsherickHouse.

Figure1.22 WindroseforthelocationoftheEsherickHouse.

Figure1.23 CourtyardandgardenofPalazzoMediciRiccardibyMichelozzo(1396–1472),commissionedbytheFlorentineMedicifamilyin1444.

Figure1.24 CourtyardsintheworksofAlvarAaltorelatetotraditionalfarmsteadlayouts(fromtoplefttobottomright):Carelianfarmstead,AaltoHouse,VillaMairea,Säynätsalo,Muuratsalo.

Figure1.25 TownhallinSäynätsalobyAlvarAalto(1952–1953):viewuptheexteriorstairstotheraisedcourtyard,thechamberinthebackground.

Figure1.26 TownhallinSäynätsalobyAlvarAalto(1952–1953):raisedgreencourtyardinfullsunshineandshelteredfromthewinds.

Figure1.27 TownhallinSäynätsalobyAlvarAalto(1952–1953):lookingoutintothecourtyardfromtheinnercirculationarcade.

Figure1.28 DiagramofmainairflowpathintheSäynätsalotownhall.

Figure1.29 SectionofspatialcompositionofraisedcourtyardintheSäynätsalotownhall.

Figure1.30 WindroseforthelocationoftheSäynätsalotownhall.

Figure2.1 Thematerialvariablesofsolids,liquid,andgasesarevelocity,pressure,anddensity.

Figure2.2Differenceinmotionbetweensolidsandfluid:moleculesindifferentsectionsoffluidscanmoveindifferentdirectionsinoppositiontosolids.Allpartsofasolidobjectcanonlymoveinonedirectionbasedonthecenteroftheirmass.

Figure2.3 TheLangrangiandescriptionofflowfollowseachparticleofaflow,whiletheEuleriandescriptionofflowdeterminestheflowbasedonhowandwhentheflowpassesthroughagridpoint.

Figure2.4 Firstlawofthermodynamics:energycannotbelost,butchangesstatetransferredfrombodytobodylikewarminghandsonawarmobjectorfire.

Figure2.5 Propertiesofairaretemperature,pressure,volume,anddensity.

Figure2.6 Thelawofmassconservation.

Figure2.7 DepictionoftheBernoulliprinciple:anincreaseinfluidspeedoccurssimultaneouslywiththedecreaseinpressure.

Figure2.8 Theno-slipboundaryconditionindicatesthatparticlesclosetosolidboundariesoffluidlowdonotmove,but‘stick’totheboundary.

Figure2.9 Theturbulentflowisbestdepictedwhenverywarmairmixeswithfairlycoldair,ascanbeseenintheplumeoveracupoftea.

Figure2.10 Thebuoyancyeffect:warmairislighterandlessdenseandthusrisesoverwarmsurfacesorobjects.Thebuoyancyforcecanbestrongerthangravity.

Figure2.11 TheCorioliseffectdrivesthemovementofairintheEarth’satmospherebasedontherotationalforcesoftheEarthanditsgravity.

Figure2.12 Psychrometricchartdepictsthethermodynamicpropertiesofgas-vapormixtureinatmosphericair.

Figure3.1LewisLeedslectureonventilation,Fig.4,5,6,p.29:nineteenth-centuryvisualizationofairmovementinsideinteriorspaces.1

Figure3.2 Thecompositionofairasamixtureofgases.

Figure3.3 AnExperimentonaBirdinanAirPumpbyJosephWrightofDerby,1768,depictingtheexperiment,whereavacuumwascreatedinaflaskwhichcontainedabird,robbingthebirdofthebasisforlife:air.

Figure3.4 TheoriginalwindowdetailforPaimiosanatoriumprovidedtwopanesofglassforgentlypre-warmingtheincomingventilationairofthepatient’sroom.

Figure3.5 Providingopenspacesforthetuberculosispatient,theiconicroofterraceexposespatientstofreshair.Theterracewasglazedinthe1960s.

Figure4.1 Weather/climate:theverticalstructureoftheatmosphereandthetimeandspacescalesofvariousatmosphericphenomenacreatethecharacteristicdomainforboundarylayerclimateconditions.

Figure4.2 Windformsbetweenhighandlowpressurezonesinordertoevenoutthepressuredifferentialsbetweenthetwozones.

Figure4.3Thermodynamicsandclimate:thermalenergyisconstantlyexchangedbetweentheEarth’ssurfaceandtheatmospherebylong-waveradiation,whileshort-waveradiationfromthesunisabsorbedbytheEarth’ssurface.

Figure4.4 Laminarboundarylayer:veryclosetothesurfaceoftheEarththeflowislaminar.

Figure4.5Köppen–Geigermapofworldclimates:theseclimateclassificationsareusedworldwidetodeterminemajorclimatecharacteristicsofaregion.2

Figure4.6TheclimatemapsofASHRAE(AmericanSocietyforHeating,RefrigerationandAirConditioningEngineers)arebasedonheatingdegreedaysandusedtodetermineprescriptiveinsulationrequirements.

Figure4.7 USwindresourcemapaspublishedbytheNationalRenewableEnergyLaboratory(NREL);darkerbluecolorsindicatehigherwindpowerandvelocityonanannualaverage.

Figure4.8 AwindroseforChicago,IL,asderivedfromweb-basedClimateConsultantsoftwaretool.

Figure4.9 WindrosedepictedbyVincenzoScamozzi3(1548–1616)inL’architetturaUniversale.

Figure4.10 TheBirthofVenus(NascitadiVenere)bySandroBotticelli(1485/86),withapersonalizedwindgodblowingather.

Figure4.11 SculptedangelwithruffledfeatheredwingsinS.GiovanniinLateranobyFrancescoBorromini(1599–1667),around1646.

Figure4.12 Flowpatternaroundtopographicelementsandfeatures.

Figure4.13 Urbanflowpatternaroundbuildings.

Figure4.14 Flowpatternaroundandthroughbuildings.

Figure4.15 Climatezonesfornaturalventilation:mapofmeanclimaticcoolingpotentialinKWhpernightbasedonMeteonormdataforEurope.

Figure5.1 ReynerBanhamdescribestwotribesinhisArchitectureoftheWell-TemperedEnvironment,thosewhowouldusethefoundwoodtomakeafireandthosewhowouldbuildashelter.

Figure5.2 Thesemajorinheritedspatialtypologiesareanalyzedwithrespecttopromotionofairmovement:caves,courtyards,passage/loggia,baskets,windcatchersandchimneys.

Figure5.3 Anasazicavedwellingsdemonstratedsophisticatedventilationstrategiesastheywereidentifiedtoutilizewindcatchingtechnologies.

Figure5.4 TheHarranhousesinsoutheasternTurkeynearSanliurfa.Multipleopeningsinthemudbrickwallsandthetopofthecorbelledroofchannelairinhomes,whichresemblecool‘caves.’

Figure5.5CorbelledroofsareaveryspecifictechnologyutilizedmainlyintheMiddleEastinsoutheastTurkey,Syria,andIranandshowavarietyofmorphologicaldiversitybasedongeometry,scale,andcomplexity.

Figure5.6 Palladio’sVillaslikeVillaEmoshownhere,designedbyAndreaPalladioin1559,utilizesimilarventilationtechnologiesconnectingthelivingspaceswiththecoolairofthebasements.

Figure5.7 TheAeolianVillasinCostozzaVenetoareventilatedandcooledthroughconnectionwithcoolcaveairinsidetheBericiHills.

Figure5.8 Ventiductsdirectthecoolairfromthehillcavesdirectlyintothebasementofthevillafromwheretheairrisesupintothelivingquarters.

Figure5.9 TheventilationopeninginthefloorofVillaTrentoaCostozzashowselaboratelatticework.

Figure5.10 VentilationopeninginthecryptaofBorromini’sS.CarloalleQuattroFontane(1638–1641).

Figure5.11TheNordiccourtyard,recallingtheCarelianfarmstead,hasamuchlargerwidth-to-heightrelationshipandletsinsolarradiationwhileprotectingfromharshwinds,likehereinAlvarAalto’sExperimentalHouseinMuuratsalo(1952).

Figure5.12Chinesecourtyardschangesignificantlyinproportionbetweensoutherntropicalandnortherncolderlocations,ashasbeenanalyzedbyKnappin2005.4

Figure5.13 MuuratsaloExperimentalHouseseenfromtheoutside,whichhighlightstheproportionofthecourtyardspace.

Figure5.14 ThetheorythattwocourtyardsoperatetogetherhasbeenmadepopularbyHassanFathyandisnowvalidatedbymeasurementsofErnestandFordattheCasadePilatosinSevilla.

Figure5.15 ThegardenoftheRealesAlcazaresdeSevillaisconnectedtosmallershadedcourtyardsintheinteriorofthepalace.

Figure5.16 TheBelvedere,athreebayloggiaonthetopofPalazzoFalconieri,wasaddedtothepalacebyFrancescoBorrominiin1646.

Figure5.17 ThegrainstoragebuildinginLindoso,northernPortugal,areraisedstone‘baskets’providingventilationaccesstothegrainwhileprotectingthegrainfromintruders.

Figure5.18 TheGambleHouseinPasadenadesignedbyGreeneandGreenein1908providesaniconicexampleoftheCaliforniagardensleepingporches,raisedtimber‘baskets’opentotheventilationbreezes.

Figure5.19 ApairofwindcatchersinYazd,Iran.

Figure5.20 AhighlydecoratedpairofwindcatchersinYazd,Iran,showingtheroofareaasoccupiedspaceandindicatingtherelationshipofwindcatcherstothedemonstrationofwealthinYazd.

Figure5.21 ThiswindcatchershowstheproportionalvarietystillexistinginYazdtoday.

Figure5.22 Thesewindcatchersshownfromtheroofshowlessdetailandfewerventilationopenings.

Figure5.23 ThewindcowlsoftheoasthousesinKent,England,usedtodryhopsforbeerbrewing,areabletomovewiththechangingwinddirection.

Figure5.24 ThekitchenchimneysdominatetheappearanceofSintraNationalPalaceinSintra,Portugal,alreadyinthisearlysixteenth-centurydrawing.

Figure5.25 ThekitchenintheMonasteryofAlcobacaincorporatesanenormousfree-standingchimneyoverthecookingstation.

Figure5.26 TraditionalfarmhousesliketheSennhütteinDavoswerebuiltaroundacentralfurnaceandcooktop,whichresemblesanatrium.

Figure5.27 ChimneysalsodominatetheexteriorappearanceoftheSerailoftheTokapiPalaceinIstanbul.

Figure6.1 TherustichutasenvisionedbyMarcAntoineLaugierinhisEssayonArchitecture,writtenasanarchitecturalrulebookin1753,indicatestheprimaryneedforarchitecture:shelter.

Figure6.2 FireplaceinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

Figure6.3 InglenookinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

Figure6.4 GazeboinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

Figure6.5 UrbancourtyardinSanliurfa,Turkey,highlightsshade,water,andopeningsforventilation.

Figure6.6 Metabolicrate:thehumanbodyconstantlyexchangesthermalenergywithitsenvironment.

Figure7.1 Definitionofneutralplane:theneutralplanedefinestheplaneintheheightofaventilationstack,whereinwardpullingairmovementforceschangetooutwardmovingforces.

Figure7.2 Solarchimney:increasingthetemperatureatthetopofthestackincreasesthepressuredifferentialandthustheairchangeratebystackventilation.

Figure7.3 Thepressuredifferentialactiveattheinlethastobestrongenoughtoovercomethefrictionofairmovingagainstthematerialsandgeometryattheventilationinletopeningarea.

Figure7.4 Theheightrequirementofthestackisdeterminedbythetemperaturedifference,whichcanbeexpectedbetweenallinletscombinedandtheoutlet.

Figure7.5 Stackterminaldevicescanbedesignedjustasoutletsorasacombinedsystemofwindcatcherandstackexhaust.

Figure7.6 SimulationoftheAffleckHouseshowingtemperatureandstreamlines.Enlargedviewsemphasizethewinddrawnintothefloorventandexitingthroughthewindowsanddoors.

Figure7.7Thespatialplacementforstackventilationinletandoutletcanfollowavarietyofcombinations,asdescribedbyLomasetal.:5Edgein–centerout/Edgein–edgeout/Centerin–centerout/Centerin–edgeout.

Figure7.8 Windpressuredistributionaroundastand-alonebuildingshowsthepositivepressureonthewindwardsideandthenegativepressureontheleewardsideandonsurfacesperpendiculartothewind.

Figure7.9 Anexampleforawindcoefficientdatamaponbuildingsurfacesdependingonheightandwidthofthebuilding.Thisinformationisavailableatavarietyofresources(adaptedfromCIBSE,p.54).

Figure7.10 Cross-ventilationisoftencombinedwithastackventilatedatriumtoincreasebuildingdepthandcoordinatewithdaylightingandcirculationstrategies.

Figure7.11 Wind-drivenflowforcross-ventilationinRoom1-2for(top)lowvelocity(V=0.5m/s)and(bottom)highvelocity(V=5m/s).

Figure7.12 Wind-drivenflowforcross-ventilationinRoom1-3for(top)lowvelocity(V=0.5m/s)and(bottom)highvelocity(V=5m/s).

Figure7.13 Wind-drivenflow(V=1.0m/s)forsingle-sidedventilationin(top)Room2-1and(bottom)Room2-2.

Figure7.14 AerialviewofaverydenseurbanenvironmentinaresidentialquarterofMumbai,India.

EbenezerHoward(1850–1928)describedthebenefitsoftheGardenCityinthisdiagramofthree

Figure7.15 magnets,wheretheGardenCityprovidesthebestofbothworlds:freshairandsocialopportunity.

Figure7.16 LeCorbusier’siconicmodelfortheRadiantCity(VilleRadieuse)incorporatestheobservationsofClAM’sCharterofAthensandreducestheurbandensity.

Figure7.17BasedonGrimmondandOke’surbanmorphometry,6weanalyzedtheurbanproportionofeightglobalcities(Ames,Iowa,Tokyo,London,CapeTown,Berlin,Chicago,Barcelona,SaoPaolo,andGenoa)andfoundthatallofthemhadaverysimilarstreetcanyonproportioninspiteofdiverseheightandwidthofblocks.

Figure7.18 UrbanCanyonsectionaldiagramshighlightingthediversityofsection.

Figure7.19 UrbanCanyonfiguregroundcomparisonandplandimensions.

Figure7.20Schematicsectionoftheurbanatmosphere,differentiatingbetweentheurbanboundarylayer(UBL)andtheurbancanopylayer(UCL)withroughnesssub-layerandmixedlayerastransitionzonesinbetween.

Figure7.21 Thedistinctzonesdevelopedbyairflowingaroundanobstacle:thedisplacementzone,thecavityzone,andthewake.

Figure7.22 Flowaroundsharpedgeobjectscreatesturbulence.

Figure7.23 Urbansurfaceenergybalanceandexchangeofheatbetweenurbanzoneandtheatmosphericsurfacelayerabove.

Figure7.24 Streetcanyonwindpatternschangesignificantlywiththegeometricrelationshipofprimarywindflowtostreetdirection.

Figure7.25 Isolatedroughnessflowoccursinurbanareaswithbuildingsspacedfarapart(H/Wratiolessthan0.3–0.5).

Figure7.26Wakeinterferenceflowintheurbancanyonoccurswithaspectratiosbetween0.5and0.65wherethezonebehindthebuildinginterfereswiththezoneinfrontofthenextbuildingtocreatefairlyturbulentmixingsituations.

Figure7.27 Skimmingflowregimeoccurswhenthebuildingsareclosertogetherandtheprimarywindflowskimsacrossthecanyonandthebulkofthefreshairflowdoesnotenterthestreetcanyon.

Figure7.28 Solarradiationenteringthestreetcanyonsignificantlyimpactsthecanyonflow.

Figure7.29Dependingontheroughnessoftheurbanenvironment,theverticalprofileofwindvelocityaboveterrainisshiftedupwardssignificantly,reducingthewindvelocityavailabletourbanventilationstrategies.

Figure8.1 LeCorbusier’sUnitéD’Habitationdevelopedthemosticonicsectionaldiagramforasplit-levelapartmentcirculationlayoutoverlappingwithacirculationcorridor.

Figure8.2 HansScharoun’sLedigenheim(homeforsingles)developedanevenmorecompactsectionallayoutforacross-ventilationpathoverlappingwithacirculationcorridor.

Figure8.3 CasaGiulianiinComobyGiuseppeTerragni:southernstreetfaçadeasthebuildingappearsin2012.

Figure8.4 CasaGiulianiinComobyGiuseppeTerragni:interiorviewofthecorridorbeneaththeventilationwindow,2012.

Figure8.5 CasaGiulianiinComobyGiuseppeTerragni:easternstreetfaçadewiththewindowsofthecorridorvisiblebeneaththekitchenventilationwindow,2012.

Figure8.6 WindroseforComo,Italy,showingtheprevailingwinddirectionsthroughouttheyear.

Figure8.7 SectionthroughthecentralapartmentofCasaGiulianishowingthelocationofthekitchenwindowabovethecorridor.

Figure8.8 SpatialcompositionofapartmentsatCasaGiulianidevelopingtheflowpath.

Figure8.9 VolumetriccompositioncreatingtheflowpathwithinCasaGiuliani.

Figure8.10 CFDsimulationsofflowpaththroughthecentralapartmentseenfrominletside.

Figure8.11 KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:viewofthetowerasitsitsinthecityscape.

Figure8.12 KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:differenttwo-storysplit-levelapartmentsarecomposedasinterlockingvolumesformingonecubictower.

Figure8.13 KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:thecornersoftheapartmentsarelargedoubleheightloggiastomodulatetheincomingairflowfromthebreezeoftheArabicSea.

Figure8.14 WindroseforMumbai,India,showingtheprevailingwinddirectionsovertheyearoverlaidwiththesiteplanoftheKanchanjungaApartmentBuilding.

Figure8.15 Volumetriccompositioncreatingtheflowpathforcross-ventilationatKanchanjungaApartmentBuilding.

Figure8.16 SpatialcompositionofKanchanjungaApartmentBuildingdevelopingtheflowpath.

Figure8.17 CommerzbankTowerasitappearsabovethestreetcanyonofFrankfurt/Main.

Figure8.18 ViewuptheinteriorcourtyardofCommerzbankTowershowingoneofthehorizontalglassscreens,whichcreatetheboundarybetweenthemultipleskygardens.

Figure8.19 Close-upviewoftheCommerzbankfaçadeshowingthedouble-skinfaçadeandtherecessedvolumeoftheskygarden.

Figure8.20 WindrosediagramforFrankfurt/MainshowinghowthevolumeoftheCommerzbankTowersitswithintheprevailingwinds.

Figure8.21 SectionthroughtheCommerzbankTowershowingthediagonallyconnectedinterlockingcompositionoftheskygardensconnectingtheinnerflowpathofthebuilding.

Figure8.22 Volumetriccompositionofofficesectionandskygardens,whichfacilitatetheoverallventilationpath,whileeachofficeindividuallyisconnectedtotheflowpaththroughsingle-sidedventilationstrategy.

Figure8.23 WindrosediagramforHarare,Zimbabwe,showinghowthevolumeoftheEastgateshoppingcentersitsperpendiculartotheprevailingwinds.

Figure8.24 VolumetricspatialcompositionofEastgateshoppingcenter.

Figure8.25SectionthroughEastgateshoppingcenterinHarare,Zimbabwe,showingthetwocentralventilationstacksaswellasthecourtyard,whichreducestheflowpathdepthandaddsdaylightingcapacitytoeachfloor.

Figure8.26SouthfaçadeoftheHarmA.WeberAcademicCenteratJudsonUniversityinElgin,Illinois,highlightingthephotovoltaicarrayonthetopoftheventilationstackswarmingtheupperlevelofthestacktoincreasethepressuredifferencebetweeninletandoutlet.

Figure8.27 InteriorcourtyardoftheHarmA.WeberCenteratJudsonUniversitydoublingupasventilationflowpathanddaylightingdevice.

Figure8.28 VentilationexhaustdeviceontheroofofHarmA.WeberCenteratJudsonUniversity,addinganiconicfeaturebehindthephotovoltaicarray.

Figure8.29 WindrosediagramforElgin,Illinois,showinghowthevolumeoftheHarmA.WeberCentersitsperpendiculartoaprettydiversedistributionofprevailingwindsforbothsummerandwinter.

Figure8.30Flowpathdiagramofthelibrarybuildingshowingthespatialcompositionalrelationshipbetweenthestackventsinsidethedouble-skinfaçadeandtheinternalcoveredatriumattheHarmA.WeberCenterofJudsonUniversity.

Figure8.31 SectionthroughtheHarmA.WeberCenterhighlightingtheverticalstackspacesinbetweentheactualvolumesofthebuildingcomposition.

Figure8.32 LycéeCharlesdeGaulleinDamascus,Syria:overviewofthecompositionofbuildingandcourtyardspaces.

Figure8.33 LycéeCharlesdeGaulleinDamascus,Syria:detailofsolarchimney.

Figure8.34 LycéeCharlesdeGaulleinDamascus,Syria:courtyardwithtrees.

Figure8.35 WindroseforDamascus(Beirut,Lebanon)showingtheprevailingwesterlywindsoftheregion.

Figure8.36 VolumetricdiagramhighlightingtheflowpathandspatialcompositionofLycéeCharlesdeGaulleinDamascus.

Figure8.37 HabitatResearchandDevelopmentCenter(HRDC)inWindhoek,Namibia:thecenterwithitswindtowersinthelandscape.Stackventilationwindowsarealsovisibleatthetopofthebuilding.

Figure8.38 HRDCinWindhoek,Namibia:oneofthewindtowersasseenfromtheexteriorpassageways.

Figure8.39 HRDCinWindhoek,Namibia:thetopofthewindtoweriscoveredbyasheetmetalroof,whichhelpstoinducetheVenturieffectandincreasestheairvelocityatthetopofthetower.

Figure8.40 WindroseforWindhoek,Namibia,showingtheprevailingwindsinthelocation.

Figure8.41 SectionthroughthemainspaceoftheHDRCshowingtheinteractionofcross-ventilationandwindcatcherventilation.

Figure8.42 AxonometricviewoftheoverallspatialcompositionoftheHRDC.

Figure8.43 Volumetricflowpathdiagramsshowingthespatialcompositionofthewindtowers,whichareintegratedintothemainspatialvolumeasanedgein–edgeoutflowpathcomposition.

Figure8.44 PhilologicallibraryoftheFreieUniversitätBerlin:interiorviewofthebuildingskin.

Figure8.45 PhilologicallibraryoftheFreieUniversitätBerlin:interiorviewoftheventilationopeningsinthebuildingskin.

Figure8.46 PhilologicallibraryoftheFreieUniversitätBerlin:exteriorviewoftheall-encompassingbuildingskin.

Figure8.47 WindroseforBerlin,Germany,showingtheprevailingwesterlywindofthelocation.

Figure8.48 VolumetricdiagramhighlightingtheflowpathandspatialcompositionofthePhilologicallibraryattheFreieUniversitätBerlin.

Figure8.49 SectionaldiagramofthePhilologicallibraryattheFreieUniversitätBerlinshowingtherelationshipofskin,core,andventilationflowpathinbetween.

Figure8.50 KfWWestarkadeFrankfurt,Germany:exteriorviewofthetowerfromthewest.

Figure8.51 KfWWestarkadeFrankfurt,Germany:viewupthetoweredgewithventilationwingsopen.

Figure8.52 KfWWestarkadeFrankfurt,Germany:detailedviewofthebuildingenvelopewithventilationwindowsopen.

Figure8.53 WindroseforFrankfurt,Germany,showinghowtheshapeofthetowerislocatedwithintheprevailingwesterlywindofthelocation.

Figure8.54 VolumetricdiagramhighlightingtheflowpathandspatialcompositionoftheKfWWestarkadebuildinginFrankfurt.

Figure8.55 VolumetricdiagramhighlightingtheseasonallychangingflowpathfornaturalventilationintheKfWWestarkadeFrankfurt.

Figure8.56 FederalBuildingSanFrancisco,California,USA:exteriorviewofthetowerfromthenortheast.

Figure8.57 FederalBuildingSanFrancisco,California,USA:exteriorviewofthetowerslabfromthesoutheastshowingthesolarshadingscreen.

Figure8.58FederalBuildingSanFrancisco,California,USA:detailedviewofthebuildingenvelopefromthenorthwest.

Figure8.59 WindroseforSanFrancisco,California,USA,showinghowtheshapeofthetowerislocatedwithintheprevailingwesterlywindofthelocation.

Figure8.60 VolumetricdiagramhighlightingtheflowpathandspatialcompositionoftheFederalBuildinginSanFrancisco,California.

Figure8.61 SectionhighlightingtheflowpathofthenaturalventilationflowoftheFederalBuildingSanFrancisco,California.

Figure9.1Differentopeningstylesforwindowsdirectlyinfluencetheventilationinletflowdirectionoftheflowpathinsidethebuilding.Fromlefttoright:horizontalpivot,verticalpivot,tophung,sidehung,tiltandturn,verticalsliding,horizontalsliding,louvers.

Figure9.2a Frenchwindows,asseenherefromtheexteriorofatypicalhouseintheParisregion,reachfromclosetothefloortoclosetotheceiling,aresplitinthemiddle,andaresidehungandusuallyopeninward.

Figure9.2b AninteriorviewofaFrenchwindow.

Figure9.3Englishsashwindowsaredoublehung,horizontallysplitandslideupanddown,allowinggradualchangesintheopeningsize,anddonotprotrudeintotheoccupiedspace;thustheydonotredirecttheflow.

Figure9.4 Hopperwindowsaresmallwindowflapsopeningoutwards,ashereintheIowaInterlockHouse.

Figure9.5 NorthernEuropeanboxwindowscanopeninwardsoroutwardsandarecomposedoftwosetsoffourwindows,whichencloseanairspaceinbetween(phototakeninTallinn,Estonia).

Figure9.6

ThisRomanwindowatPalazzoCenci,theISUCollegeofDesignstudioinPiazzadelleCinqueScole,Rome,Italy,includesthreelayers:anouterlayer,whichactsasashadingdevice,butalsoasaventilationlouver,theactualwindowwithglass,andaninnerlayer,whichcansecludethewindowfromtheinsidefortotalprivacy.

Figure9.7 TheventilationopeninginAlvarAalto’sownhousewindow,whichhedesignedwithhisfirstwifeandpartnerAinoAalto,separatestheventilationfunctionclearlyfromtheviewwindow.

Figure9.8Theso-calledLaeuferliinDavosdescribesafairlysmallventilationslider,whichisintegratedinalargercomposition,whichwasbroughttoattentionbyAndresGiedion7inhisbookontheDavosAlphuette.

Figure9.9 WalterGropius’famousglassfaçadeattheBauhausbuildinginGermanyfrom1926connectsaseriesofpivotwindowsthroughamechanicalopeningmechanism.

Figure9.10 Wingwallscandirecttheairflowpatternsandinfluencethewayfreshairmixeswithstaleairininteriorspace.

Figure9.11 VentilationholefromMeixiun,China,shapedlikeagourd.

Figure9.12 Thesizeofopeningdirectlyinfluencestheairflowrateinrelationtowindvelocity.

Figure9.13 Overhangstraphotandhumidairinfrontofventilationopeningsandshouldbeavoidedinhotandhumidclimates.Movableshadingdeviceswillbemorebeneficial.

Figure9.14 Thesmallestopeningdeterminestheoverallairflowrate.

Figure9.15 EsherickHousefaçadewithhighlightedventilationshutters.

Figure9.16 ThespatialcompositionoftheEsherickHousejuxtaposesadoubleheightspacewithtwosinglestories.

Figure9.17 TheCFDanalysisoftheEsherickHousehighlightstheimportanceoftheheightofthespaceforcoolingpurposes.

Figure9.18 CFDanalysisoftheEsherickHouse:fourtimestepsofcoolingcase.

Figure9.19Double-skinfaçadeintheUnileverBuildinginHafenCityHamburg,Germany,wherethesingleouterlayerofplasticfilmclearlyservesthepurposeofslowingdownthewindvelocityatthiswindylocationinthemiddleoftheportattheElberiver.

Figure9.20 ThedoubleglassfaçadeoftheGSWbuildinginBerlinfacilitatesthecross-ventilationbyprovidingastack.

Figure9.21 Thetextureofagolfballfacilitatesitsmovementthroughairbyreducingtheresistanceofairagainstitsflow.

Figure9.22 Balconiesorotherelementsontheoutsideofthefaçadeactasroughnesselementsandcansignificantlyaltertheairvelocityaroundabuilding.

Figure9.23 ThiswindcowlatNottinghamJubileeCampusisagoodexampleofpurposelydesigneddevicesenhancingnaturalventilation.

Figure9.24 TheroofwingonthetopoftheGSWbuildinginBerlin,Germany,increasestheairvelocityabovethebuildingandthusfacilitatestheventilationdriveinthestackfaçadeonthewest.

Figure9.25 Atrickleventactslikethisfinemeshedshadingscreen,whichletsinairataconstantrate,butaverylowvelocity.

Figure9.26WindowpanesinhistoricalpalacesandvillasinGoa,India,madefromoystershellsfilterlightaswellasair.

Figure9.27 ThisstreetfaçadeinMumbai,India,completelymadeupofventilationopeningsfilterslightaswellasair.

Figure9.28 AMashrabiaisascreenwhichdoesnotallowaviewintotheinteriorofthebuilding,butpermitsfilteredlightandairinside,asseeninthisstreetfaçadeinMumbai,India.

Figure10.1 AlexanderCalder(1898–1976):VerticalFoliage.1914.Sheetmetal,wire,andpaint,57.5x167.6x142.2cm.

Figure10.2 ThewindvaneandcupanemometeraspartoftheweatherstationatIowaStateUniversity’senergyefficiencyresearchlaboratory:theInterlockHouse.

Figure10.3 Ahotwireanemometerdetectswindvelocityanddirections.

Figure10.4 ThewindvaneintheSalaMeridianaoftheTorredeiVentisituatedonthetopoftheSecretArchiveoftheVaticanconnectstoaceilingfrescoandaninteriorwinddial.

Figure10.5Winddirectioncanbedetectedwithasmokepen,asshownhereduringanexperimentattheIowaNSFEPSCoRcommunitylab,theInterlockHouse,originallyconstructedasIowaStateUniversity’s2009entryfortheU.S.DOESolarDecathloncompetition.

Figure10.6 ThewindowsintheBauhauslinedupinabandarealloperatedbyonejointactuator.

Figure10.7 Thecontrolalgorithmsforsummerandwinterventilationneedadjustmentfordifferentopeningsizes.

Figure10.8 AcommerciallyavailableblowerdoortestkitwasusedtotesttheairtightnessoftheIowaNSFEPSCoRInterlockHouse.

Figure10.9 Advancedcontrolsystemsneedtoadjustfortheinteractionandfeedbackloopbetweencomplexparameters.

Figure10.10 Nightflushventilationcoolsdownthethermalmassofthebuildinginteriorwithcoolnightairanddemandstheclosureofwindowsduringtheday.

Figure10.11 ThePaulWunderlichHausinEberswalde,Germany,asitsitsinsidetheprevailingwinddirection,utilizesoperablewindowsforcross-ventilationandnightflushcooling.

Figure10.12 SiteplanofthePaulWunderlichHausinEberswalde,Germany.

Figure10.13 ThecourtyardbetweenthefourbuildingsconnectedtoformthePaulWunderlichHaus.

1

2

3

4

5

6

7

Figure10.14 TheentrancespacetothePaulWunderlichHaus.

Figure10.15 Thebioclimaticchartshowingtheclimaticlimitationsfornaturalventilationstrategies.

Figure10.16 Acousticbufferingisnecessarywhentheventilationinletissituatedclosetostreetswithhightrafficorothersourcesofdisturbingnoise.

Figure10.17 TheventsattheJudsonUniversityHarmA.WeberAcademicCenteraredirectedtowardsthenorthsideandtheparkinglot.

Figure10.18 Openatriumspaces,forexamplehereintheUnileverHouseHamburgbyBehnisch&Behnisch,requirespecificprotectiveelementsagainstfireandsmoke.

Figure10.19 TheFederalBuildinginSanFranciscobyMorphosisrequiresoperablewindowsandsolarprotectivescreens.

Figure10.20 ThedistancebetweenmosquitoscreenandinletwindowasinaMidwesternporchisimportanttomediatethereducedairflowratethroughthescreen.

Figure12.1 (a)CADmodeloftheAffleckHouseand(b)themeshusedtomodelthemaininterior.

Figure12.2EnlargementofgridresolutionfortheAffleckHouseusingaviewrotated180°,asshowninFigure12.1.

Figure12.3 (left)ComputationaldomainusedtomodeltheMahajanexperimentsand(right)gridresolutionvalidationstudycomparingvelocityprofileinthedoorway.

Figure12.4 Buoyancy-drivenflowforwarmambientconditionscomparingtemperatureandstreamlinesforcross-ventilation:Room1-2andRoom1-3.

Figure12.5 Pressure-drivenflowtimesequenceoftemperatureandstreamlinesforcross-ventilation:Room1-2.

Figure12.6 (left)Pressure-drivenflowand(right)wind-drivenflowcomparingvelocityfieldandstreamlinesforsingle-sidedventilation:Room2-1.

Figure12.7 Pressure-drivenvelocityflowfieldandstreamlinesforsingle-sidedventilation:Room2-2.

Figure12.8 Three-dimensionalviewof(topleft)roomlayoutandtemperaturecontoursimposedwithstreamlinesfor(topright)warmambienttemperatureand(bottom)coldambienttemperature.

Figure12.9 Two-dimensionalviewsoftemperaturecontourssuperimposedwithvectorsandstreamlinesfor(top)warmambienttemperatureand(bottom)coldambienttemperature.

Figure12.10 CADmodeloftheViipuriLibraryandtwoimagesoftemperatureandstreamlinesastimeelapsestodemonstratepassivecooling.

NotesLewisW.Leeds,LecturesonVentilation:BeingaCourseDeliveredintheFranklinInstituteofPhiladelphia(NewYork:Wiley&Sons,1868).

Seehttp://koeppen-geiger.vu-wien.ac.at/usa.htm.

VincenzoScamozzi,L’ideaDellaArchitetturaUniversale,2Vols(Ridgewood,NJ:GreggPress,1964).

RonaldG.Knapp,ChineseHouses:TheArchitecturalHeritageofaNation(Singapore:Tuttle,2005).

K.J.Lomas,“ArchitecturalDesignofanAdvancedNaturallyVentilatedBuildingForm,”EnergyandBuildings,39(2),2007,pp.166–181.

C.S.B.GrimmondandT.R.Oke,“AerodynamicPropertiesofUrbanAreasDerivedfromAnalysisofSurfaceForm,”JournalofAppliedMeteorology,38(9),1999.

AndresGiedion,DieArchitekturDerDavoserAlphütten:ErnstLudwigKirchners“AlteSennhütte”UndIhrVorbild(Zürich:Scheidegger&Spiess,2003).

ForewordInourrapidlychangingbuildingmarkets,nowisagreattimeforsomearchitectstotakestockofwhatproductstheyoffertheirclients,workouthowtheycanaddvaluetotheirdesignrepertoire,andbroadentheirskillsbasetoreflecttheirchosendirectionoftravel.Nearthetopofmany‘musthave’listswillincreasinglybetheabilitytodesignsuccessful,naturallyventilatedbuildings.IsaysomearchitectsbecausefromwhereIamstandingtheprofessionappearstobebroadeningoutintobeingmanysub-professions.Somearchitectsaredestinedtospendtheir livesasCADoperativesinlargepractices,achosenfewwillfindworkasgraphicartistsgivingformtothegranddesignsofambitiousarchitectsanddevelopers,manywill flowout into jobs other than architecture,while the restmay beluckyenoughtodesign,orrefurbish,actualbuildings.Ifyouareoneofthelatterandkeentokeepupwithmarkettrends,probablyworkinginaverysmalltomediumsizedpractice,then this book is essential reading for you because the buildings of the future willincreasingly,foratleastpartoftheyear,benaturallyventilated.

The reasons for this inevitable growth of natural ventilation are many and clearlymanifestingthemselvesgloballyasenergypricessoar,poweroutagesproliferateandmoreextreme weather events often render twentieth-century comfort solutions inadequate.Peoplemay think theywant tobe livingorworking inhighly insulated, air-tight, light-weight buildings with unopenable windows over a long hot summer with full air-conditioning systems belting out comfort, but many are thinking again for two mainreasons: cost and energy insecurity.For instance, those living inAdelaide,Australia, inJanuary 2014will have thought again, after the heatwave summer of 2013/2104whenagainst a background of months of rising temperatures, a record was set with fiveconsecutivedaysof42°Candabovewithnighttimetemperaturesfallingonlyto31°C.Our twentieth-century responsewouldbe ‘turnon theair-conditioning’,butmanycouldnotafford itshighcost in theirhomes,particularlyatpeak tariffsat thehottest timesofday,andotherswhocouldafforditcouldnotenjoyitbecauseoftherollingpoweroutagesthat were experienced across the city. The association of power failures with extremeweathereventsisnowafactoflifeinthetwenty-firstcentury,asituationthatwillonlygetconsiderably worse with the rising temperatures forecast for the future in the FifthAssessmentReportonclimatechangepublishedbytheIPCCinApril2014.1Soinmanypartsof theworldincludingtheUSAthenameofthegameis increasinglytobeabletodesignclimate-resilientbuildingsthatkeeptheiroccupantssafeevenwhenthepowerdoesfail.2

Theoptimalcoolingsolutionduringmanyseasonsandatmanytemperatures,inmanycitiesandbuildingsaroundtheworld,istoopenthewindowandletthelocalbreezesdothework.Itisalsothecheapestone.Thisisparticularlythecaseinhousing,whereenergycostscanbeacriticalissue,withmorepeoplefallingintofuelpovertyannuallyandwithgreater economic consequences as peoplehave tomake their ownchoiceofwhether topaytocoolorheatthehouseinextremeweatherorpayforthemortgage.3In‘developed’nationsaclearrelationshipisemergingbetweenthecostofenergy,GDP(grossdomestic

product,orthewealthofacountry),andthequalityoflifeofcitizens,withtalkgrowingaround theworld of the disappearingmiddle classes.4 The speed of the polarization ofincomes and wealth globally over the last decade has amazed many pundits, and itsimplications are far-reaching; even for the comfortably off professional classes such asmyself,thetendencytocutcornersoncomforttolowerheatingbillsseemsstrongertome,year on year. For businesses, the idea that energy is a low priority for boardroomdeliberationsisfastdisappearing,asthecostsforenergybegin,forsome,toapproachthecosts of employing staff. On top of that, the drive to reduce carbon emissions frombuildingsisputtingenergyissuesandcostswayuponthemanagementagenda,evenforthe global corporates for whom corporate social responsibility issues are increasinglyassociated with ‘brand’ value, in a fickle marketplace increasingly steered by theenvironmentconcernsofa social-media-literategeneration.All thesedrivers to increasetheuseofnaturalventilationmaycomeasarealshocktoasystemwherearchitectsandengineersarenolongertaughthowtonaturallyventilatebuildings,andincultureswherewhole generations of building occupants are addicted to, and adapted to, the artificialindoorclimatesthatair-conditioningproduces.

However, the architectural challenge is not only to achieve affordable, comfortablebuildings,buttodesignbetterbuildingsusingnaturalventilation,toprovide‘delight,’astheauthorsexplaininChapter6.Thesensuallyexquisitefeelingofasoftbreezecoolingtheskininsummer,theheadyfeelingofopeningawindowandinhalingthefreshcoldairofspringorautumn,orthewelcomewarmthbeingpumpedintoahomefromasunlightconservatoryonawinter’sdayishardtobeat.Thegreatestofthetraditionalandmodernbuildingsthatarerunforasmuchoftheyearaspossibleonfreedelightfulenergyareinessence themselves great natural ventilation machines that are powered by heat(temperaturedifferences)andpressure(winddirectionsandspeeds).Attimesofthedayoryear and in places where the ambient, outdoor air is healthy to breath, well-designed,naturallyventilatedbuildingsgenerallyprovideinfinitelysuperiorclimateexperiencestothose produced in mechanically conditioned buildings. They also provide that highlydesired linkbetween thebuildingoccupantsandnature, beyond thewalls andwindowstheyareenclosedin.Buttodesignagoodnaturallyventilatedbuildingtakesrealskill,andthat iswhy, if youwant tokeepupwith twenty-first-centurybuildingmarket demands,youshouldreadandabsorbthecontentsofthisbook.

PasseandBattagliahavesetoutsystematicallytoprovideacomprehensiveintroductionto the history, theory, and application of natural ventilation principles and practices inbuildingdesign.Theyuselanguagethatarchitectsarefamiliarwith,andmathematicalandcomputingtoolsthattheycanassimilateandapply,andprovidecleardirectionsonhowtointegrate the chosen air-flow and thermal storage systems into local climate contexts,ensuring that particular buildings in particular climateswill be successful. It helps thatUlrike Passe is an award-winning architect and teacher who benefitted from anarchitectural education in Berlin, Germany, where most buildings are still naturallyventilated,beforemovingontobeaneducator in theUSAin2006, takingonboardthearchitectural ethos embodied inAmerican building practices.Her co-author is FrancineBattaglia, amechanical engineer specializing in air and fluid flows,who in her current

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role as Director of the Computational Research for Energy Systems and Transport(CREST) Laboratory specializes in using computational fluid dynamics and models toexploreissuesrelatedtothethermalsciences,includingthenaturalventilationofbuildingsand thefireandcombustioneffectswithin them.Thecombinationof these twoskillsetsproducesabookthatisarchitectfacing,andyetrigorousinitsengineeringapproach.

The book covers all the bases a practicing architect needs to know about whendesigning a successful naturally ventilated building, from the basic principles of howpeopleadaptthemselves,theirventilationsystemsandtheirbuildingstoachievethermalcomfortindifferentclimates,tothethree-dimensionaldesignofroomsandbuildingswiththeir internal air pathways, to their envelope andwindow design, themechanics of airmovement and control and the thermodynamics of heat and coolth management andstoragewithinbuildings.The theory is illustratedandclarifiedwitha richarrayofcasestudy buildings that will enable architects to envisage and extend their own palette ofnatural ventilation applications, opportunities, and approaches. The advice proffered onthecorrectmodellingofventilationisvitalforagenerationofcomputer-literatedesignerswhoneedonly the steps to follow to successfully capture the performanceof buildingsthatarenaturallyventilated, and theextensive images throughout thebookarenotonlyeducationalbutalsoofteninspiring.

Itisinevitablethatbuildingswillincreasinglyberunonnatural‘ambient’energyforaslong as possible, using appropriate combinations of diurnal or seasonal energy storage,and an expanded range of human behaviors to adapt to changing climates and risingenergycosts.Thisbookprovidesathorougharchitecturalfoundationfromwhichtocreatetheconditionsnecessary todesignsuccessfulnaturallyventilatedbuildings that functionwellinpractice.If,asastudentorpracticingarchitectyourself,youwanttodesignlow-energy, low-carbon,andtrulysustainablebuildings,andyoudon’tknowhowtoachievethisalready,pleaseput‘learnhowtodesignfornaturalventilation’atthetopofyour‘addvalue – to do’ list and buy, read, and apply the vital lessons contained in this book. Indoing so, then enjoy – because you will, at heart, be learning how to design betterbuildings,andthatinitselflendsdelighttothewholeprocess.

SusanRoafApril2014

NotesSeeT.F.Stockeretal.(eds),ClimateChange2013:ThePhysicalScienceBasis.ContributionofWorkingGroupItotheFifthAssessmentReportoftheIntergovernmentalPanelonClimateChange(Cambridge:CambridgeUniversityPress,2014).

TheResilientDesignInstitute(www.resilientdesign.org)isaNewYork-basedgroupworkingtopromote‘PassiveSurvival’developments.

S.Roaf,“TransitioningtoEco-Cities:ReducingCarbonEmissionswhileImprovingUrbanWelfare,”in:Young-DooWangandJohnByrne(eds),Secure&GreenEnergyEconomies(Washington:TransactionPublishers,2014).

B.Plumer,“Here’sWhereMiddle-ClassJobsAreVanishingtheFastest,”WashingtonPost,8/27/2013,http://www.washingtonpost.com/blogs/wonkblog/wp/2013/08/27/heres-where-middle-class-jobs-are-vanishing-the-fastest/.

AcknowledgementsDesigningSpaces forNaturalVentilation is theoutcomeofa ten-year investigation intothe relationship of spatial composition and themovement of air,which startedwith thedesign and construction of HausMarxen by Passe Kaelber Architects. Ulrike Passe isgratefultoherdesignpartnerandfriendThomasKälberforenhancingherunderstandingofarchitectural spaceand indebted toher fatherHermannPasse,whoprovidedayoungBerlinarchitecturefirmwiththechallengeandopportunity todesignaspacefornaturalventilationandwishedtoretireinahousewithoutdoors.

Turningtheseideasandconceptsintothisbookwouldnothavebeenpossiblewithoutthe generous support of Iowa State University, who granted Ulrike Passe a facultyprofessionaldevelopmentassignment(FPDA)infall2014totaketimeawayfromfacultydutiestodevelopthemanuscript.TheDepartmentofArchitectureprovidedfundswiththeVernon Stone Grant, which provided opportunities for undergraduate students SuncicaJasarovic, ShuaibuKenchi andMattDarmour-Paul towork on the diagrams.The bookwillhopefullygivebackinmanywaystoIowaStateUniversity,thestateoflowaandthearchitecture profession. Thanks go to Gregory Palermo and Deborah Hauptmann,Department Chairs during the time of writing, for agreeing to a release from teachingduties, as well as to the College of Design Dean Luis Rico-Gutierrez, who providedremainingfundstocompletethedrawingsinthisbook.

ThedrawingsneededthecreativemindsofSuncicaJasarovic,ShuaibuKenchiandMattDarmour-Paul to turn ideas and scribbles into legible drawings and adapt researchconducted invarious fields intoourownvisual language,whichwehopewillappeal tothemainreadership:designingarchitects.

UlrikePasseverymuchappreciates the suggestions and support ofmany friends andcolleagues:

Karen Bermann, Clare Cardinal-Pett, Ingrid Lilligren, Jamie Horwitz, JelenaBogdanovic, Dusan Danilovic, Baskar Ganapathysubramanian, Umesh Vaidya, EugeneTakle, and Krishna Rajan, Iowa State University; Jonathan Hill, Bartlett School ofArchitecture; Katerina Ruedi-Ray, Bowling Green State University; Ro Spankie,University ofWestminster;LawrenceC.Bank,HillaryBrown andChristianVolkmann,CityCollegeNewYork;DaphnaDrori,TechnionHaifaIsrael;AlisonKwok,UniversityofOregon;GudrunSack,NaegeliSackArchitekten;HolgerKleine,RheinMainUniversitätWiesbaden; Robert Demel, Willi Hasselmann Beuth Hochschule; Gail Brager and EdAhrens,CBEUCBerkeley;EvyatarErell,BenGurionUniversity of theNegev, Israel;JuliaFishandRichardRezac,Chicago; IrenaFialova,TechnicalUniversityPrague;UtePoerschke, Penn State; Yasemin Somuncu and Pinar Menguc, Oezegyn University,Istanbul;BulentYesilata,HarranUniversity;DruryCrawley,BentleySystems;ASHRAETechnicalCommittee4.2and4.10;andAtilaNovocelac,UniversityofTexasatAustin.

Generousassistanceandadvicewasofferedbythefollowingarchitectsandengineers,whoprovided informationabout their buildings:AlanShort,MatthiasSauerbruch,Nina

Maritz, Keelan Kaiser and David Ogoli at Judson University, Matthias Rudolph andThomas Lechner at Transsolar, and Scott Bowman of KJWW in Des Moines. PhilippPlowrightofLawrenceTechnologyUniversityprovideddrawingsfortheAffleckHouse.

NoelieDaviau,ShanHe,MattDarmour-Paul,PiaSchneiderandIrenaVezinsupportedthebookbyprovidingphotographsoftheirimmediateenvironmentsinIowa,Rome,ParisandGoa.

ChristineStrohmreadthefinalmanuscriptandgavesolidandmuchappreciatedadviceonthefinalphrasingsandstyle.

Dr. Francine Battaglia wishes to express her gratitude to her graduate students, whocontributedtotheworkasfollows.ThankstoPrestonStoakesforhavingfaithandmovingfromIowatoVirginiatoengageinoneofthefirstdetailedCFDstudiesofwholebuildingswithme; toMichaelDetaranto forhis timeandcommitmenthelpingus tovisualize themyriadofnaturalventilationbuildingscenarios; toDavidParkforcontributinghisM.S.researchonstackventilationandforhisunwaveringdevotiontoearninghisdoctorate;andto theComputationalResearch forEnergySystems andTransport (CREST)Laboratoryresearchersfortheirhelp,advice,andpatience.Finally,thankyoutomyfamily,especiallymyhusbandJavid,fortheirsupportandencouragementduringthewritingprocess.

Thank you toWendy Fuller, GraceHarrison, and EdGibbons at Routledge for theircontinuoussupportinmakingthisbookareality.

IllustrationsConsiderableefforthasbeenmadetotracecopyrightholdersofimages.Theauthorsandpublishersapologizeforanyerrorsandomissions,and,ifnotified,willendeavortocorrecttheseattheearliestopportunity.

IntroductionWhyDoWeTalkaboutNaturalVentilationNow?

WhyWeNeedNaturalVentilationAir is one of the four major classical elements and vital to human life. Ventilating aninterior space is essential, yetmost people know very little about the reasonswe needconstantairexchangesinbuildings.Itisnottheoxygenweneed–aircontainsplentyofoxygen, andonly in very tightly sealed spaceswouldwe runout of oxygen eventually.Veryrarelydospacesstillcontainsourcesoftoxiccarbonmonoxide,althoughthiswasamajorconcernwhenengineeredventilationlaunchedasafieldofresearchinthesecondhalfofthenineteenthcentury.Today,indoorairquality,thermalcomfort,andenergyaremoreimportantissuesinoccupiedspaces.Ventilationisessentialtoremoveodorparticlesand volatile organic compounds (VOCs) as well as humidity (90 percent of humanexhalation is humidity),which are themost annoying indoor air quality disturbances tooccupants.1 It is also necessary to dilute CO2, which can make occupants drowsy.Foremost,weventilatetoremoveexcessheatthataccumulatesinsidebuildings.

Figure0.1

Erde,Wasser,Luft(Earth,Water,Air),drawingbyPaulKleeforthePedagogicalSketchbook(PädagogischesSkizzenbuch),originally1925,BauhausBücher,p.37.

Theamountofairneededtotransportheatismuchlargerthantheamountneededforalloftheabovestatedreasons.Inourcontemporarymechanizedworld,mostofthisheatisremovedusingforcedaircooledbyrefrigerationtechnologythatreliesoncompressionrefrigerationmachineryconsuminglargeamountsofelectricalenergy.Infact,deliveringplentifulfreshairintoaspacewithaslittleenergyaspossibleisacomplexendeavorandcan be tricky.But natural ventilation is truly underrepresented and could pick upmuchmoreoftheloadthenincurrentpractices.Thereasonthishasnotyethappenedhastodobothwiththewaybuildingsaredesignedandengineeredandwiththelackofacceptanceof dynamic conditions. Control strategies are becoming more complex in hybridsituations, where natural ventilation and mechanical air conditioned cooling alternate.

Building occupants now commonly expect homogeneous and constant interior thermalconditions. The availability of fairly cheap comfort through air-conditioning makesoccupants forget that there are times during the day or year when opening a windowwouldprovidesimilarcomfortableconditions.Ontheotherhand,theengineeringrequestto control thermal comfort led tomanyofficebuildingsbeingdesignedandconstructedwithoutoperablewindows.

Slowly,thoroughresearchfindsitswayintostandards,andthecreationofan“adaptivethermal comfort model”2 enables a better understanding of thermal comfort underdynamic weather conditions and a closer relationship between exterior conditions andinteriorcomfortacceptance.

BenefitsofNaturalVentilationThe direct benefits of natural ventilation are manifold. Ventilation itself is essential tohumanhealth,comfort,andwell-being.Naturalventilation,ifdoneright,canachievealltheabovewithmuchlessenergythanmechanicalventilationsystems.Naturalventilationremovesheatthroughtemperature-orwind-drivenpressuredifferences(oracombinationof both), while providing fresh air (good indoor air quality) by removing or dilutingparticle load, odors, humidity, and Volatile Organic Compound (VOC) concentrations.Utilizingnaturalforces,aircanremoveheatthathasbuiltuporwasemittedbyoccupants.Naturalventilationasasubstituteformechanicalsystemshelpsreducecostforequipment,forductwork,andforthespacetohouseboth.Naturalventilationcanalsocooldownthebuildingfabricovernightbyremovingheatfromthermalmassandprovidingadditionalenergystoragecapacityforthedaytime.Theairvelocitycanalsocoolahumanbodybyevaporation,directlyaffectinghumanthermalcomfortperceptionandincreasingtoleranceforslightlyhigherairtemperatureswithslightlyhigherairvelocity.

NaturalVentilationandDesignWhenusedproperly,naturalventilationcanprovidealargeamountoftherequiredenergyforfree,withoutharmtoclimateandatmosphere.Naturallyventilatedbuildingsneed tobedesigned,operated,andcontrolleddifferently thanmechanicallyventilatedbuildings.Schedulingandcontrolcanbecomeamajorconcern,whenoperationalchangesneed tooccurat inconvenient timesforoccupants.Nighttimeventilation,forexample,mayonlybe feasible from2.00a.m.until8.30a.m.when theairoutsidehas finallycooleddownenoughtoallowabreezethroughthebuilding,butoccupantsareeitherawayfromtheirworkspace or asleep. Very few energy-saving advocates are actually so committed toactively and manually activate this change. Therefore, complex control strategies areneeded.Control strategies are directly related to human behavior and are probably bestexecutedbysmartcontrolsystemsthatstillneedtogiveoccupantsindividualinfluenceaswell, because current research shows that occupants are far more tolerant to thermalconditions in naturally ventilated spaces and in spaces overwhich they have individualcontrol.2Theperceptionofhumancomfortchangeswithhigherairvelocityprovidedbycarefullydesignednaturalventilation.

Figure0.2

Theoperablewindowistheclassicmeansfornaturalventilation,ascanbeseenhereinAlvarAalto’sownhouseatRiihitieinMunkkiniemi,Helsinki.

Figure0.3

Thethree-dimensionalityofspaceconnectingspacesverticallyandhorizontallyisessentialfornaturalventilation.ThisdrawingconceptualizesthecontinuingsurfaceofsuchaspaceforHausMarxeninGermanybyPasseKaelberArchitects,Berlin,2001.

Buildingdesignstrategiesoftendonotyetintegratedynamicperformanceexpectations,becauseappropriatedesigntoolsarestillindevelopment.Howcandesignersensurethatwindow openings are optimized for all possible wind directions? If performance isconsidered at all, usually only intuition and experience drive performance predictionduring the design process.Natural ventilation and daylight are complex, uncertain, anddynamicphenomena, design experience takes time to accumulate, andmechanization isoften chosenbecauseof the lackof basic design experience andguidelines. In order toprovide sufficient air exchange rates that comply with minimum performancerequirementsforusercomfort,mostspacesaremechanicallycooled,artificiallylit,orlitpoorly with natural light. With the goal to achieve high-performance, net zero energybuildings,architectsneedtobebetterequippedduringtheearlydesignphaseswithbothknowledgeanddesigntoolstopredictdynamicperformancesoflightandairmovement.

NaturalVentilationandEnergyThearchitectureandengineeringcommunityiswellawareofthefactthatalargeportionofbuildingenergyconsumptionisusedtoconditiontheindoorenvironmentofbuildings(by heating or cooling outdoor air to provide thermal comfort and improved indoor airquality). Much of this wasteful consumption could be avoided by changing the waybuildingsaredesigned.Thenumbershavenotchangedmuchinrecentyears:in2009,USresidential buildings consumed 39 percent of primary energy to condition the indoorenvironment.3Since1949,energyconsumptionintheUnitedStateshasrisenfrom32×1015(quadrillion)BTUto102×1015(quadrillion)BTUin20074andisnotpredictedtodecline any time soon.The combinationof increased energy cost and energyusagehascaused energy spending in theUSA to increase from$83 billion to $1 trillion between1970and2005.5Afteradjustingforinflation,thisisstillanincreaseof250percent.Itisurgent for both the economy and the community to conserve energy and reduce CO2emissionsinordertomitigatetheimpactsofglobalclimatechange.

The best way to reduce energy consumption is to design for human comfort byexploitingnaturalforcesaroundthebuildingsite.

Avoidingorreducingheatgainsandlosseswhilestillmaximizingqualitydaylightisthefirststep.Newreportsongooddaylightingtechniquesandtoolshaverecentlyemerged.6Utilizingnaturalforcesonsitethroughanintegrateddesignprocessisthesecondsteptoreducing energy consumptionbynatural ventilation and spatial strategies.Finally, thesestrategiesshouldalsoleadtomorerefinedarchitecture.

With the development of mechanical air-conditioning, building typology and thedevices for heating and cooling have been separated in the design process.7 Moderntechnology seemed to make every form possible. This development is currently beingquestioned and tools are needed to allow and verify more sensible design strategies.

Interestingly,mechanicalventilationdoesnotfullysatisfybuildingoccupants.Theyoftenfeelthattheenvironmentistoohotortoocold,toodraughtyortoostuffy,andnotalwayshealthy.8 Complete user satisfaction is hard to achieve and is rarely found in post-occupancyevaluations.Ventilatingbuildingswithnaturaldrivingforcesismorecomplexthan it seems.Eversincegreendesignstrategiesaimedatsavingenergyandfossil fuel,thereisacertainurgencytore-establishnaturalventilationflowsinarchitecturaldesign,andtheevaluationofnaturalairmovementbecomesmoreandmorerelevant.

Figure0.4

HVACenergyconsumptionbybuildingendusein2005inquads(10tothepowerof15BTUsorapprox.25milliontonsofoil)(U.S.DepartmentofEnergy).

Figure0.5

Approachforachievingnetzeroenergybuildings:onlywithreduceddemandwillitbepossibletocoverenergydemandwithrenewableresources.

TheLiteratureGapWhile a growing number of contemporary architects desire the integration of natural

ventilationflowintoarchitecturaldesignconcepts,theevaluationofnaturalairmovementand related energy performance is still difficult because of the complexity of theunderlyingphysics.There isanapparentgapbetweenengineeringknowledgeofnaturalventilationand its implementation into spatialdesign strategiesbyarchitects.Thus, twomajorissuesbasedonourcurrentresearchandteachingbackgroundandexperienceledtothisbook.

For one, although there are a variety of books onmechanical and natural ventilationavailable for engineers, providing current engineering research, no in-depth guidelinesactuallyexistfordesigningarchitects.Existingliteraturecommunicatesinaverytechnicalmanner and contains mathematical formulae many architects are ill equipped toincorporateforlackofknowledge,patience,ortime.Althoughintegrativedesignisontherise,thefirstsketch,whichsitesthebuildinginthelandscape,almostalwaysdeterminesthesuccessofthedesignfornaturalventilation.

Figure0.6

AirflowandturbulencemodeloftheViipurilibrarybyAlvarAalto,designedduringthelate1920sandearly1930sbasedona1927competitionentryandcompletedin1935.

The second issue is related to the complexity of thermodynamics. The interaction ofnatural ventilation flow with thermal heat transfer properties in solid materials iscomputationallyvery intensiveand thusnotwell integrated intoengineeringanddesignpredictiontoolsyet.Airvelocityandthermalcapacityofmaterialsaredifficulttosimulatein one equation system, and turbulences in larger spaces cannot be predicted withcertainty.Forexample,currentenergyevaluationtoolssuchasEnergyPlusdonotmodelthermal stratification of air temperature. Therefore, further research into architecturaldesignandfluiddynamicsisneeded.Itisverycomplexincomputationalfluiddynamics

(CFD)tomodelflowsbetweensolidmaterialsandaircurrents.9

WhatisVentilation,andWhatisNaturalVentilation?Ventilation describes the means to introduce fresh quality air into a space and extractexhaust, stale, polluted, or odorous air out of the space. Fresh air replenishes oxygen,althoughnottothedegreegenerallybelieved.Unlessoccupyingasubmarineformultipledays,peoplewillnotrunoutofoxygen.DilutingCO2isadifferentmatter,andincreasedCO2 levels can make occupants feel drowsy. Without proper ventilation we will notsuffocate,butairwillstarttofeelhotandsmelly.Theuseofnaturaldrivingforcesisanunderutilized design strategy to control the indoor environment. It is dynamic, alwayschanging,butnotalwaysreliable.Air isalsoameans to transport thermalenergyeitherforheatingorforcoolingtomoderatethermalcomfort.

Figure0.7

TraditionalwindcatchersinthecityofYazdinIran.

Air movement is caused by pressure differences, either in the form of wind on anatmosphericscaleorintheformofstackeffectscreatedbytemperaturedifferences.Thedifferenteffectsarebasicallyamatterofscaleandbuilduparoundthebuildingorwithinanopening,aroom,orashaft.Naturalconvectioniscausedbythermalgradientswithinthebuildingorbetweenthebuildingandtheatmosphere.Naturaldrivingforcesarethusintrinsicallyspatial.

In buildings designed to exploit natural ventilation, air must be able to flow freelythroughthebuilding.Spatiallayout,theideaofhowdifferentareasofabuildingconnect,is very important when considering flow through a building. Thus, natural ventilationneedstobedesignedattheconfluenceofstructure,buildingenvelopeproperties,energyuse,andformaswellasoccupationalpatterns,humancomfort,andhealth(goodindoorairquality).Mostimportantly,naturalventilationneedstobedesigned;itcannotbeadded

later.

What’sintheBook?This book ismeant to serve as a handbook for architects to design spaces that can benaturally ventilated as long as outside conditions allow. It will show how to enhancearchitectural performance with the use of novel computational fluid dynamics (CFD)simulation tools. It is currentlynotpossible for eachandeveryarchitect to individuallyconductCFDevaluationsforeachproject.Therefore,thebooksetsouttobridgethegapbetweenthescienceoffluiddynamicsandarchitecturaldesignbymeansofscientificandarchitecturalvisualizationtools.Ventilationisnotonlythemainmeanstointroducefreshqualityairintospacesandextractstaleandpollutedairoutofthespace,butalsoamajormeanstotransportenergywithinabuilding.

The reason why natural ventilation has been so difficult to evaluate is its complex,dynamic, three-dimensional nature. Temperature and air velocity distributions within abuilding are especially dynamic when natural convection is combined with externalfactorssuchaschangingwindpatterns,whichdirectlyinfluencetheflowpatternswithinabuilding. In buildings designed to exploit natural ventilation, air must be able to flowfreelythroughthebuildingandopeningsizesshouldbeadjustable.

Ventilationisusuallydesignedtoprovideminimumairexchangeratestandards.Ratesare considered more a quantitative than a qualitative issue, and therefore more anengineering concern than a concern for design. Natural ventilation needs to become adesigndisciplineagain,likedaylighting,andbetaughtindesignstudiosandnotjustinthetechnology classes as an add-on. The question is: How to achieve a certain healthyventilation ratewith naturalmeans and how to achieve healthy air exchange rateswithminimum energy consumption? Designing a building with natural ventilation requiresknowledgeofprevailingwinddirectionsandweatherdata,aswellassolarorientationandradiation intensity. However, constant good performance cannot always be guaranteedbecauseoftheunpredictablenatureofwind.

Turbulenceresultingfromwindinteractingwithobstacles,suchasbuildings,isoneofthe last unsolved problems of classic physics.Depending on friction and velocity, theyoftenoccurinsideandaroundbuildingsandinductwork,andresultinpressurelosses.10Turbulencecanenhanceorblocknaturalflows.

Movement of sound, heat, energy, and fresh airwithin or through a space needs thepotentialforexpansion.Airisconstantlyinmotion,evenifweonlyperceivethemotionbeyondacertainthreshold.11Thusairexchangeratesforcomfort,energy,andindoorairqualitypurposesareafunctionofgeometry,scale,andsizeofapertures.Smalleropeningsincreasetheairvelocity;largeopeningsslowairdown.Thebasicassumptionsarebasedonthelawofconservationofmass:Whatentersononesidehastoleaveattheotherside.But what goes on between the inlet and the outlet is important to know. Air flowinvestigations need to consider how exactly the shapes of interlocking volumetricconnectionsaffecttheflowofairinthreedimensions.Thecomplexityofchoicescanbeenormous. How to design for all eventualities?Which strategy for the combination of

openingsisbest?

Each space and site is different, and predictions of the interrelationship of thecomponents of air flowpatterns, for example theVenturi effect, buoyancy, stack effect,andcross-ventilationareintuitivelyintegratedintothedesignproposalbasedonrulesofthumb,12butaresofardifficulttoquantifywithcommerciallyavailabledesigntoolsthatcouldeasilybe integrated into thedesignprocess.13While the scales for solar radiationand light are not affected by size, wind and air velocity have scales for which datagatheredfromscaledmodelshastobereevaluatedforsituationsatfullscale.Withinthisbook, the readerwill findanoverviewofdesignstrategiesandadvice regardinghowtoapproachaniterativeprocessofeventualities.

TheAudienceofthisBookTheIndianarchitectCharlesCorreapointsoutthatinthetwentiethcentury,

architectshavedependedmoreandmoreonthemechanicalengineertoprovidelightandairwithinthebuilding.ButinIndia,wecannotaffordtosquanderresourcesinthismanner–whichisofcourseactuallyanadvantage,foritmeansthatthebuildingitselfmust,throughitsveryform,createthe‘controls’whichtheuserneeds.Sucharesponsenecessitatesmuchmorethanjustsunanglesandlouvers;itmustinvolvethesection,theplan,theshape,inshort,theveryheartofthebuilding.14

In this approach architecture truly serves as apassive-energydevice, and its integrationintoaspecificculturebecomesvitallyunderstood.

Mechanicalventilationontheotherhandworksagainstthesenaturalflowsbytryingtomixhotandcoldairbyforce,whiletheairisattemptingtoseparateandstratifybynature.Ahomogenous interiorclimateas imaginedbyBuckminsterFullerorYvesKlein in the1960s15isanillusionanddoesnotcomplywiththephysicsoffluidflowandmotion.LeCorbusieralsoembracedmechanicalsystemsandpromoted‘exactair’ inVilleRadieuse(Radiant City)16 as a means to provide healthy indoor air quality. The opposite hashappened: indoor air quality has become amajor problem leading to the sick buildingsyndromeorotherbuilding-relatedillnesses.17

Thus,thecontentofthisbookwasdevelopedwiththedesigner,student,orprofessionalarchitectinmind.Ofcourseitshouldalsobeabletospeaktotheengineer,andprovideanoverview for the educated and interested amateur. The book is an attempt to translateengineeringknowledgeintoarchitecturaldrawingsandcasestudies.Naturalventilationisa key factor in green, energy-efficient, climate-responsive design both in the developedand especially in the developingworld. It should be read globally and applies tomanyclimate regions. It should work well as a support for the intersection of technologyteaching and the design studio because it touches on both sides of the architecturespectrum. The book will make fairly complex knowledge accessible to students andpracticingreaders,andfunctionasaneducationalandteachingtool.

TheOriginofthisBook

HausMarxen18 was built in 2000/2001 by Passe. Kaelber Architects in Germanywithspatially interconnected volumes to support the air flow to such a degree that thetemperaturewaskeptwithinanacceptablerange.Inthisapproach,architectureservesasapassive-energydevice.UnderlyingHausMarxenisaclearspatialstructure,whichisbasedona three-dimensionalgeometricgridof3×3×3 timber framebays.Thisstructure isoverlaidbyaspatialcompositionusingvolumetricproportionsoftheFibonaccisequence,which connects rhythms and sequences of space on three different levels, opening upspatialconnectionsforvisionandmovementasintuitivelypredictedbythearchitectandexperienced by the user during the occupancy over the last ten years. Anecdotalinformation shows that natural ventilation flows in this house support the cooling andheatingof thebuilding.Yet,at thetimeofdesignandconstruction, therewerenoeasilyaccessibledesigntoolstoquantifythespatialeffectonthisflow.Thissparkedthedecisiontoembarkonaten-yearjourneytorevealthehiddenphysicsofnaturalventilationtothedesigningarchitect.

Figure0.8

HausMarxenbyPasseKaelberArchitects,Berlin(2001):externallyacompacttiltedcubecladintimberpanels.

WhattoExpectfromtheBookThestudyofcurrentlyavailableengineeringandscientificliteratureledtotheapproachtoconvey this knowledge through case studies and diagrams. Advocating the design ofpleasurable spatial atmospheres and experiences, the chapters were developed with thefollowingthoughtsinmind.

Part 1: Theory and scientific background. This will narrate and highlight keybackgroundparameters,startingwiththeimportanceofspace.Ventilationstrategiesstart

with the flow path, issues of health, vernacular and historic precedents, climate, andthermalcomfort.Thissetsthestageforfurtherinvestigationsofthedifferentelementsoftheflowpath.

Figure0.9

HausMarxenbyPasseKaelberArchitects,Berlin(2001):internallyanopencompositionofverticalandhorizontallyconnectedspaces.

Part 2 highlights the important parameters, starting with the driving forces behindnaturalventilation:“pressureasindicator”windandtemperaturedifferences,whichformthebasistounderstandtheflowrate.Chapters7and8thendiscusstheproportionoftheflowpathandissuesofspatialresistance.Theyhighlightthestrategiesinaseriesofcasestudy projects. Spatial strategies determine the main design parameters to develop acontinuousventilationpath,andtheresistanceandtheflowcanbeinvestigatedtogether.Chapter9focusesonthe“façadeasfilter.”Thefaçadeopeningsareonecrucialparametertodeterminetheflowrateandarethereforehighlightedintheconcept.Chapter10followsupwithcontrolstrategies.

ThefirstchaptersofthebookusewhatisexplainedinPart3inmoredetail:thetoolstounderstandandvisualizeair–“makingairvisible.”Asthisisatextbookorguide,readerswhoarejustinterestedinthesimulation,rules,guidelines,andsooncanalwaysrefertoPart 3. It can be handled as an insert or parallel to the first chapters, which have anarrative. For every problem related to fluid motion by pressure (wind-induced) ortemperaturedifference (convection) it is important todefine theboundary conditionsoftheventilationsystemtobestudied.Therefore,theanalysisofcasestudyprojectsandthedevelopmentofthree-dimensionaldiagramsascommunicationtoolswerechosen.

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For some readers, these final chapters might actually be themost interesting.WhenHausMarxenwasdesigned,thearchitectscouldonlydreamofthesimulationtoolsnowbecomingavailabletothedesigningcommunityatfairlylittlecost.Sincethemid-2000s,computationaltime,whichwaspreviouslythemajorlimitation,hasbecomemorereadilyavailableandthusledtotheaccessibilityofthesenewdesigntoolsforabroaderaudience.However,onlyfewtoolsareinusetoevaluatedesignbeyonditsvisualimpactandenergyperformance.Thereaderwillfindalistofcommonlyusedtoolsattheendofthebook,butasthefieldisrapidlychanging,thelistwillneverbecomplete.

Architectural space, which shapes air to enhance comfort, has had little place in thecriticaldiscourseaboutairandaboutarchitecture,andhowitshapesairisonlymarginallytaught inschoolsofarchitecture.Thus, inanidealsense, this isabookbetweenscienceandvisualizationandabookaboutspaceandair.

NotesVarisBokaldersandMariaBlock,TheWholeBuildingHandbook:HowtoDesignHealthy,EfficientandSustainableBuildings(London;Sterling,VA:Earthscan,2010),p.117.

G.SchillerBragerandR.deDear,“AStandardforNaturalVentilation,”ASHRAEJournal,42(10),2000,pp.21–27.

InternationalEnergyAgency,“Buildings,”2010,http://iea.org/subjectqueries/buildings.asp(accessed1/5/2011).

U.S.DepartmentofEnergy,AnnualEnergyReview2007(Washington,D.C.:EnergyInformationAdministration).

U.S.DepartmentofEnergy,2007BuildingEnergyDataBook(OfficeofPlanning,BudgetandAnalysis,EnergyEfficiencyandRenewableEnergy,preparedbyD&RInternationalLtd,2007).

PeterTregenzaandMichaelWilson,Daylighting:ArchitectureandLightingDesign(NewYork:Routledge,2011).

ReynerBanham,ThearchitectureofaWell-TemperedEnvironment(Cambridge:MITPress,1969).

FergusNicol,MichaelHumphreys,andSusanRoaf,AdaptiveThermalComfort:PrinciplesandPractice(NewYork:Routledge,2012),p.3.

PrestonStoakes,UlrikePasse,andFrancineBattaglia,“PredictingNaturalVentilationFlowsinWholeBuildings.Part1:TheViipuriLibrary,”BuildingSimulation,4(3),2011.

ChristianGhiausandFrancisAllard,“NaturalVentilationinanUrbanContext,”in:M.Santamouris(ed.),SolarThermalTechnologiesforBuildings(London:James&James,2003).

M.vonPettenkoferandA.Hess,TheRelationsoftheAirtotheClothesWeWear,theHousesWeLivein,andtheSoilWeDwellon:ThreePopularLectures(N.Trübner&Company,1873).

AlisonG.KwokandWalterGrondzik,“TheLoganHouse:MeasuringAirMovement,”in:Proceedingsof24thNationalPassiveSolarConference(Portland,ME,1999)andadditionalpublicationsonthisbuildingatthefollowing25thand27thconferencesin2000and2002.

FrancisAllard(ed.),NaturalVentilationinBuildings(London:James&James,1998);ChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005);M.Santamouris(ed.),SolarThermalTechnologiesforBuildings(London:James&James,2003).

CharlesCorrea,“BlessingsfromtheSky,”in:CharlesCorreaandKennethFrampton,CharlesCorrea(London:ThamesandHudson,1996).

UlrikePasse,“AtmospheresofSpace:TheDevelopmentofAlvarAalto’sFreeFlowSectionasaClimateDevice,”ArchitecturalResearchQuarterly(ARQ),12(3/4),2008.

LeCorbusier,TheRadiantCity:ElementsofaDoctrineofUrbanismtoBeUsedastheBasisofOurMachine-AgeCivlization(NewYork:OrionPress,1967),p.49.

OlliSeppaenen,“TheEffectofVentilationonHealthandOtherHumanResponses,”in:M.SantamourisandPeterWouters(eds),BuildingVentilation:TheStateoftheArt(Sterling,VA:Earthscan,2006),pp.247–264.

UlrikePasseandThomasKaelber,“CasaaMarxen,”L’architetturanaturale,30,March2006,pp.62–65.

Part1 TheoriesandScientificBackground

Chapter1

TheImportanceofSpaceforNaturalVentilationEnvironmental forcescreate shapesand formsasdemonstratedby the forcesexertedbywind andwater that formed theGrandCanyon inArizona over a long period of time.While objects created tomove through air are designed to lower resistance against air,buildingsdesignedfornaturalventilationneedtobuildupresistanceinordertofacilitatetheflow.

Shapes and forms can thus be created to enhance and support the effects of naturalforces.Knowledgethattheflowofwaterfollowstherulesofgravityunlessunderpressureledtothedesignofroofsthatguiderainwaterdownwards.However,aircanmoveinalldirectionsdependingonspatialpressuredifferences.

Onlywiththeadventofmechanicalfan-poweredcoolingwereengineersabletocreateinternalclimateconditionswithoutusingtheforcesofwindandbuoyancy.ForcesofflowareevidentinmanyengineeredformsandsystemssuchastheHooverDam.

Although air flow exerts less impacting forces, the forces of natural ventilation haveplayed an integral part in the formation of architectural typology, visible in manyarchitectural structures invariousclimate regions. In thehot-humidclimateofSouthernIndia,interiorceilingsinGoa1areornamentedtoformabrokengrid,allowingwarmairtorise into the height of the roof space, while windows and porches are constructed asbreathablesurfacesforcross-ventilation.

Figure1.1

GrandCanyon,Arizona,USA,anaturallandscapeformedbythefluiddynamicsofwaterandwind.

Figure1.2

FountainatVillaLanteatBagnaia,Italy,attributedtoJacopoBarozzidaVignola(sixteenthandseventeenthcentury)–specificallyshapedtoformturbulencesintheflowofwaterandwiththatshapethesoundsinthegarden.

1.1

Figure1.3

TheforcesofflowarereflectedintheconstructionoftheHooverDam(constructedbetween1931and1936).

Figure1.4

SteeproofsinhotandhumidclimatessupportstackventilationasinthispalaceinGoa,India.

ThedesiretoenhancenaturalventilationalsoshapedmultiplebuildingsintheeraoftheModernMovement,andanalysisofthesespatialconceptswillintroducethefullspectrumofpossibleapproachestoenhancenaturalventilationinbuildingstoday.

ConnectedandDetachedSpacesCooling strategies based on natural ventilation are intrinsically spatial.Air passes fromspacetospacethroughconnectingapertures.Theoverallairexchangerateisonlyaslargeasthesmallestpassageallows.Airflowthusdoesnotworkwellwithsingular,enclosedcellspaces,butneedsinterconnectivity.Dependingonthedesignstrategy,acorridorcanhaveaconnectingoradisconnectingfunction.Itcanconnectseparatespaceswithanairstack or it can separate thewind from the leeward side, blocking airmovement.Ventsneed toallowair topass throughdoorsorwalls.Air isnotpushed throughaspace,butpulledoutofthespacebyanegativepressuredifference.

PrivacyasknowninthecontemporaryWesternworldisaninventionofmodernity.Thecorridor is themainarchitectural feature thatguaranteesprivacybyseparatingfunctionsandspacesfor individuals. In interconnectedspatialsituations, twoissuescanget in theway of privacy: sound and vision. Full acoustic and visual privacy is in directcontradiction to thedevelopmentofacomplete flowpath throughabuilding.Whereairflows, vision is possible and sound can penetrate. Thus air-conditioning supported theseparation of individual spaces in buildings, a development Robin Evans describes indetailinFigures,DoorsandPassageways.2LisaHeschongtakesonthesameobservationof social separation through spatial means in Thermal Delight in Architecture.3 Evanstracesthedevelopmentofresidentialfloorlayoutstosocialpatterns,beginningwithVilla

1.2

Madama in Rome with its sequences of all interconnected rooms to functional roomsseparated by corridors as spaces without quality of inhabitation in nineteenth-centurymansions,whileHeschong analyzes the relationshipof thermal convenience and spatialcomposition.

Figure1.5

VillaMadamainRome,Italy,designafterRaffael,startedin1518:eachspacedevelopsitsowngeometryandthespacesareplacedinconnectedsequence.

AccordingtoEvans,thecorridorwasoriginallyinsertedintotheEnglishcountryhometoseparatedomesticservantsfromtheiremployersandconsequentiallyledtothenotionof privacy of modern life. In most contemporary buildings, the corridor separatesindividual,personalizedcomfortzones.

TheDrivingForcesofNaturalVentilationAreSpatialNatural ventilation needs natural forces to drive airmovement and a three-dimensionalflowpaththatleadsfreshairintoandstaleairoutofthebuilding.Designingthisflowpathis amatter of space connectivity dominated by either vertical connection or horizontalconnection, or a combination of both. The path should connect the areas within thebuilding that promise the creation of the largest possible pressure gradient. Therefore,designingfornaturalventilationstartswithsiteplanningandtheinvestigationofexternalforces. The intensity of those forces is distinctly different in urban and rural contextconditions.

Naturalventilationisdrivenbytwomajorexternalforcesbasedonpressuredifferences:wind(hydrostaticpressuredifferences)andthestackeffect(densitypressuredifferences).Inner city wind patterns and temperatures require very different approaches other thanopensites.Macro-andmicroclimatesalsoneedtobeconsidered.Theoverallresultsaredeterminedby the interactionbetween these forces and resistances andobstacleswithinthe flow path, which are determined by the building and its openings, as well as therelationship of the building and its context. The condition in an urban context, itsroughnessorsmoothness,willinstantlyrelatetothevelocityanddirectionandseasonaloreven daily patterns of wind. Natural ventilation cannot be added later as an add-ontechnology,butcanonlybeimplementedduringthearchitecturaldesignprocess.Natural

1.3

ventilationisdirectlyrelatedtothespatialcompositionoftheflowpathandthedirectionandintensityofthedrivingforces.

Theresistancetoflowinthepathisdeterminedbythebuilding’sshape,form,height,orientation, and internal spatial composition and the pressure building up against theseobstacles. Ventilation through the building is determined by these variables and theobstruction to air flow they create. The ventilation rate is determined by the pressuredifferenceactingacrossaventilationpathandtheresistanceofthatpath.4

Airis‘lighter’andlessdensewhentemperaturesincrease,andrisinghotairmayleadtotemperaturestratification.Takingthesephysicalpropertiesintoconsideration,itisobviousthatspatialcompositionplaysacrucialroleinenablingthemovementofair.Thespatialanalyses of volumetric compositions of selected buildings identify the types ofoverlappingfree-flowopenspacesthatconstitutethemainflowpotentials.Flowpathsaretrulythree-dimensionalinalldirectionsofspace.

Free-flowopenspace,asdistinguishedfromfree-planarchitecture,5isdefinedasspatialcomposition that addresses flow and continuity along all three axes of space. Wallapertures,openpassageways,niches,stairways,splitlevel,interiorwindows,galleriesordoubleheightspacesconnectsuchspaces.Enablinginterlockingconnectionsinplanandsection,free-flowopenspaceblurstheboundariesbetweenindividualroomsandbetweeninsideandoutsidesurroundingspace.Usingtheconceptofpartialenclosure,intermediatespaces are created that belong to more than one system of spatial relations and offermultiple possiblemovement patterns for air, light, people, and vision.Architects of theModernMovement, suchasLeCorbusier,oftenachieved thesimultaneityof insideandoutside through a solely visual connection. This apparent visual flow is achieved bysealingtheinterioroftheglassboxfromitsexteriorclimate.The“humansubjecthasbeendisplaced,” as Beatrix Columina has aptly pointed out: displaced from nature and itsenvironmentalforceswithpositive(comfort)aswellasnegative(energyuse)impact.Shecites Le Corbusier “A window is to give light, not to ventilate! To ventilate we usemachines;itismechanics,itisphysics.”6

HouseswithImpactontheGeometriesofFlowAventilationpathisspatial,becausewindandbuoyancymostlyactincombination.Asaresult, air can move up, air can move down, air can move across, and air can pivot,dependingontheintensityofthedrivingforcesandcombinationsofotherinfluencesonlypartiallydrivenbygravity.Infact,airisconstantlyinmotion,evenifwecannotactuallyperceivethismotionatvelocitiesbelowtwometerspersecond(395feetperminute).Thisphysical property of air was already known to early researchers such as Max vonPettenkofer,whoselecturesonair7wereinitiatedbyapublicoutreachrequestforpublichealtheducationandarestillvalidinformation.ThesamecanbesaidaboutLewisLeeds’LecturesonVentilation;8theselectureswerealsotheresultofhealthconcernscausedbybadairqualityinsidepublicbuildingslikeschoolsandhospitals.

Spacehas tobe composed todevelop apressuredifferencebetween two sidesof the

building.Itisnecessarytoprovideaconnectionbetweenthetwosidestoallowtherightamount of flow. Ideally the amount of flow can be altered by changing the size and/ordirectionofopenings.Theheightofthespacethusmatters.Spaceitselfisimportant,buthowdo theshapesof these interlockingvolumetricconnectionsaffect theflowofair inthreedimensionswhentheair insideisconstantlyinflux?Inordertotakeadvantageofthephysicalpropertiesofair–mass,pressure,temperature,andthusflow–interiorspacemust takemore thanoneclimatic/seasonalcondition intoconsideration.Allcontributingfactors need to be considered in the design process. A designer needs to develop aniterativeparametermatrix andapply thebasicprinciplesof the relationshipbetweenairflowandgeometricproportion.Elementsshouldbedeterminedbyvolumetricproportions,notbyplanarcompositionandnumbersalone.Naturalventilationhastobedesignedwithdynamicvariationsinmind.

There are three major spatial principles that enhance natural ventilation; they arerepresentedinthreeiconicbuildingsoftheModernMovement:thewindcatcher,thestackeffect,andcross-ventilationasrepresentedbytheAffleckHousebyFrankLloydWright(1940)(anexampleofaUsonianHouse),alsorepresentedbytheHowHousebyRudolphM.Schindler(1925)andtheEsherickHousebyLouisKahn(1961).

These three breathing houses utilize all basic spatial themes: the stack chimney, thewindcatcher,andcross-connections,aswellasacombinationofallthree.Dependingontheoutsideconditions,thechimneyandwindcatchercanreversewithinthesamespace,ifdesigners arenot carefulor actwithoutproperguidance.Whether a tall space acts as awindcatcherorastackchimneydependsonmultiplefactors:windcatchersalwayshavetobedirected towards thewindwardsideandstackexhausts to the leewardside,wherelow pressure zones can pull the hot air out of the stack space. But wind direction canfrequently change and so inlet and outletmight also change and reverse the flow path.Second,itisimportanttounderstandthedensitydifference(temperaturedifference).Thehottertheairwillbeattheupperendofthespace,themoreitislikelytoactasachimney,notawindcatcher.

1.3.1

Figure1.6

HistoricvisualizationofairmovementandenergydistributionbyLewisLeeds.

SlidingSpace:TheAffleckHouseFrank LloydWright (1867–1959) established an architectural concept for theMidwestclimateinitiallywithhisprairiehousesintheearlyteensofthetwentiethcenturyandlaterinthe1940swiththeUsonianHouses.TheAffleckHousewasbuiltin1940inBloomfieldHills, a suburb ofDetroit,Michigan. F. L.Wright developed the concept for the housefollowingacallforproposalsfromLifeMagazinefora‘DreamHouse.’HenamedhisideaUsonianHouse,whichturnedintoaprototypeforlow-costsuburbanhouses.TheideaoftheUsonianHouseisintrinsicallyrelatedtothehistoryofUSAmericansuburbanizationand thedreamofmaking low-costsingle-familyhousesaccessible foreverybody.ThesehousesrepresentthestartofWright’ssecondmajorcareerfromthelate1930sonward.

Figure1.7

GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:exteriorviewoftheslopebehindthehouseleadingtotheloweropenporch.

The main features of the house are a modular approach to the construction, visiblematerial patterns, and the development of a spatial kit of parts. Rosenbaum9 notes that“anothercontribution to thefeelingofspaciousness is thevisible two-by-fourmodule,agrid that is etched into the concrete floor and the fiberboard ceiling… this grid alsocomplements thehorizontal transomwindow, theboard andbattenwall units.”Anotherimportantcharacteristicwasintendedby“theindoor-outdoorqualitieswhich…glorifiednature.”10Thisrelationshipisnotonlyvisual,butexperientialowingtomultipleoperablewindowsandaverticalshaft.

Twohorizontallylayeredcubicvolumesareplacedatrightanglesasifslidingpasteachother.Thesetwoperpendicularspacesofdifferentheightarejoinedbyavolumeofdoubleheightthatopensupattheintersectiontothelandscapebelowandallowsairtobecooledover a stream of water below and be pulled up into the space, where the two slidingvolumesmeet.

Wind-driven air flow over a building induces positive (inward-acting) pressure onwindwardsurfacesandnegative (outward-acting)pressureon leewardsurfaces; thus thebuildingcreatesapressuredifferenceacrossthesectionthatdrivescross-ventilation.Thewindvelocityincreaseswiththeheightofthebuilding.Airentersthebuildingononeside,sweepstheindoorspaceandleavesthebuildingontheotherside.11

Figure1.8

GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:theexteriorporchspacebelowthehousewiththebasinbelowandtheventilationopeningintothemainlivingspaceabove.

Figure1.9

GregorS.andElizabethB.AffleckHousebyFrankLloydWright,constructedin1940:operablefloortoceiling

windowatthecornerofthemainlivingspace.

Figure1.10

DiagramofmainairflowpathintheAffleckHouse.

Figure1.11

DiagramofspatialcompositionintheAffleckHouse.

Figure1.12

1.3.2

Windrose(inm/s)forthelocationoftheAffleckHouse.

Figure1.13

ThesecretoftheAffleckHouseliesinthehorizontalwindowbetweenthelowerairporchandthemainlivingspace,whichallowsforanupdraftairmovement.

BoltedSpace:TheHowHouseRudolphM.Schindler(1887–1953),whocametotheUSAfromViennain1914,designedtheHowHouse inLosAngeles,California, in1925forDr. JamesEadsHow.Schindlerbasedthevolumetricstructureofthebuildingonasequenceofstrategicdecisions,whichwere strongly related to the Californian climate, which he described as “paradise onearth.”12TheHowHouseisoneofSchindler’smostspatiallycomplexbuildings,andinitsdesignheelaboratedonthe‘Raumplan’concept,a‘volumeplan’13firstintroducedbythe Viennese architect Adolf Loos (1870–1933) as a spatial composition strategy. The‘Raumplan’intheHowHouseiscomposedasaspatialflowofcubicvolumesofvariousheightsandscalealignedonadiagonalaxis in space.At thecentral junction,averticalshaftorwellisboltedthroughallothermainvolumes,openingthehousetotheelements,thus enhancing natural ventilation on thismountainous site. This is a unique feature inmodernarchitecturalcompositions,applicableonlyinthemildCalifornianclimate,whichhas little precipitation.Themain ventilation space is open to the venting airmovementwithout barriers created by glass or other architectural materials. The diagonal space

actuallycatchesthemainwinddirectionsperpendiculartotheslopewithoutbuildingupresistancetotheflowofairalongtheflowpath,allowingconstantairmovementat lowvelocity.

Figure1.14

JamesEadsHowHousebyRudolphM.SchindlerinLosAngeles,CA,constructedin1925:viewofthehouseonthetopofthehill.

Figure1.15

DiagramofmainairflowpathintheHowHouse.

Schindlerwasawareofthepotentialofbuildingstoshapetheflowofairashestronglyconsideredtherelationshipofairflowandspaceasahealthissueinhistheoreticaltexts.In an article published in theLosAngelesTimes parallel to the completion of theHowHousein1926entitled“CareoftheBody,Ventilation,”14Schindler laidouthis intrinsicconceptforventilation:“thebuildingneedssmallopeningsonallsidesofthebuildingatvarious heights. It should be built in the concept of a basket. The openings should beformedassuch that theyreduce theairvelocity toenableaconstanthardlyexperientialexchangeofairthroughoutthewholehouse.”ThestructureoftheHowHouseisthereforean elaboration on his own invention, the ‘Schindler Frame,’15 a modification of thewooden frame traditionallyused for residences throughout theUSA.Herehedevelopedthe ‘Raumplan’ concept, which was originally conceived for solid massive masonrystructures in Central Europe, into a planar wooden construction system andmodulatedheights. Overall, the resulting spatial composition typically acts as a traditional windcatcher,pullingcolderairofhighervelocityfromhighupdownintothelivingspacestoventilateouthotaironthelowerlevels.

1.3.3

Figure1.16

DiagramofspatialcompositionintheHowHouse.

Figure1.17

Windrose(inm/s)forthelocationoftheHowHouse.

IncorporatedSpace:TheEsherickHouseWhenaconnectingdoubleheight space is incorporated inanall-encompassingvolume,spatialcontinuityisachievedinacompactverticalandhorizontalvolumetriccomposition.Warmairrisesbyconvection,enablingstackeffectsbecauseofthehighspatialvolume.Thehigher thespaces, thefurtherawaytheexhaustairmovefromthecomfortspaceoftheinhabitantsbeforecollectingattheceiling,whereitcanbeexhausted.Windcanassistthestackeffectbyblowingover thestackandincreasingthepressuredifferential.Stackeffectsandwindcanthusworkwitheachotheroragainsteachotherdependingontheirdirection,whichisanimportantmattertodistinguishasanarchitect.Thistopiciscovered

furtherinChapter7.

This compositional strategy of ordering space and air can be evaluated in the housebuiltbyLouisI.Kahn(1901–1974)forMrs.EsherickinChestnutHill,Philadelphia,PA,in 1961. Its spatial composition is intentionally designed for natural ventilation and thefaçadeincludeswoodenshutterstomodifytheflow.Theseshuttersalsocontributetothecompositional complexity of the façade, as they are set back in the volumetric surface.Thus, the volume of thewall is shading the surface of the shutterwhile air velocity isincreasedat thesame timebecauseof thebottleneckeffectof the inletpoint.Toreduceheatgain,thesealedglasssurfacesareshadedwithexteriorblinds.16

Figure1.18

EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:streetfaçadewithclosedshutters.Thedoubleheightlivingroomisontheright.

Figure1.19

EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:compositiondiagramofdoubleheightspacewithinthelargercubicvolume.

Kahn’s architecture has often been described as a composition of volumes or spacesdivided between server and served spaces. This analytical view indicates a distinctionbetweenthespacesthathaveacontrolledenvironmentandthosethathelptoenhanceandcontrol this environment. In the Esherick House, this distinction of spaces is notapplicable.Serverandservedspaceareoneandthesame,becausethespacesofthehouseare designed to enhance natural ventilation. The spatial composition explores theconnection of two single spaces and one double height space incorporated within acompact volume,which in itself is subject to a complexgeometric composition. In thishouse, structure, space, light, and vents are intertwined in the same volumetriccomposition, enhancing immaterialmovements of air and light.The spatial envelope inthe Esherick House mediates the flow of light and air in a very distinct way, whilechangingtherelationshipbetweeninsideandoutside.

Kahn’s work is mainly known for its elaborate mathematical precision and beautyachievedby the implementationoforderingprinciplesandusingspatialstructureon thebasisofdimensionandgeometry.Gast17 developed a plan analysis of shifting axis andgeometricproportion,butdidnotincludethespatialheighttoelaborateonthevolumetricproportion,whichgreatlycontributetothespatialcomplexityandairflowcapacityofthehouse.

Figure1.20

EsherickHouseinChestnutHill,PA,designbyLouisKahnandconstructedin1961:streetfaçadewithclosedshutters.Thedoubleheightlivingroomisontheright.

InordertoanalyzeairflowintheEsherickHouse,theunderstandingofspaceneedstogobeyondtheobviousestablishedreadingofthegeometriccomposition,whichhasbeenextensivelydescribed as complexplanar geometry.Rykwert18 noted that thebuilding isdesigned as a cubic volumetric composition of 9 × 9 (+1) modules with verticalproportionsof1×2×1and2×2modules.

Size and placement of openingsmanipulate airmovement in space.A change in therelationshipbetweeninletandoutletopeningshassignificantimpactonthevelocityofair,allowing for themanipulation of air flow. It is crucial to understand the relationship ofnatural ventilation and space to be able to strategically place openings. In theEsherickHouse, openings for air and openings for light are designed not as one but as separateentities,whichalsoenhancesthechangingrelationshipbetweeninteriorandexterior.AsButtiker19noted,closingthewoodenshutters,whichactasventilationopenings,hidestheviewtothegardenandleadstoawithdrawalintoaninnerworld.Inthisscenario,onlytheclerestorywindowhighupprovidesdaylightandviewstothesky.Openingtheventilationdoor refers the occupant back to the exterior view, opening the view to the garden, theweather, and the changing seasons. This situation enables the interior to be part of thegreaterflowofnatureandair.Thehousecanthusbeseenasaphysicalobstacle,whichdistorts the laminar flow into unpredictable turbulent eddies through and around thebuilding.

1.3.4

Figure1.21

DiagramofspatialcompositionintheEsherickHouse.

Figure1.22

Windrose(inm/s)forthelocationoftheEsherickHouse.

TheAtrium

Greek,Roman, andRenaissance atrium houses, public buildings, and palaces have hadwidespreadinfluenceonthebuildingtypologyintothemoderneraandtothisday.

Figure1.23

CourtyardandgardenofPalazzoMediciRiccardibyMichelozzo(1396–1472),commissionedbytheFlorentineMedicifamilyin1444.

AlvarAaltoandCharlesCorreasharea strongmotivation inarchitecture tocreatean“opening to the sky.”20 Both refer to the Pompeian patio house typology as theirfundamentalsource,where thehouse isshapedaroundanopening to theskyorasemi-opencourtyardasaclimate-modifyingdevice.

In his essay “Blessings from the Sky,” Charles Correa takes a similar approach.“Throughouthumanhistory, theskyhascarriedaprofoundandsacredmeaning…thusthegreatHindutemplesofSouthIndiaarenotjustacollectionofshrinesandgopurams,butamovementthroughtheopen-to-the-skypathwaysthatliebetweenthem.”21Withthisinmind,heestablishestheopen-to-the-skyspaceasamainfeatureofdesignexplorationinhisKanchanjungaApartmentbuildinginMumbai,India,wheretheporousenvelopeissupposedtoallowthebreezeoftheArabianSeatonaturallyventilatetheapartments(seethecase study inChapter8).BothAlvarAalto andCharlesCorreanever allow this in-between space to be enteredon center; it is always enteredoff-axis, relating the spatialconfiguration strongly to social patterns and cultural functions. This is also the mosteffective flow path, as it allows the air stream to reach all parts of the room. Thetypological interrelationship to the garden and hearth as the two main sources for theintermediate,interstitialspaceisevident.Mumbai-basedCharlesCorreahadtobuildwithless mechanical technology to meet requirements for user comfort. He seems to have

found a synthesis of his Western formation (Correa was trained at the MassachusettsInstituteofTechnology–MIT)andthearchitecturaltraditionsofhishomecountry,India,where he practices. His strong theme of a processional unfolding of spaces is also areinterpretation of the pleasure garden, an equivalent to the paradiso inMediterraneanarchitecture.

Figure1.24

CourtyardsintheworksofAlvarAaltorelatetotraditionalfarmsteadlayouts(fromtoplefttobottomright):Carelianfarmstead,AaltoHouse,VillaMairea,Säynätsalo,Muuratsalo.

Thecourtyardoratriumactsasaninterfacetocreateanintermediatemicroclimate.Thismicroclimate mediates between the severe outside climate and the more moderate,comfortable,orevendelightful interior.Tobecomethisinterface, thecourtyardneedstobe a protected in-between space thatmediates the buildingmass required to create themicroclimate. Thus the courtyard has to be surrounded by building mass, in order toprotect these spaces inside thismass.Air and its ventilation patterns,which are shapedthrough the spatial composition, create a climaticmembrane,whichacts as amediatinginterface.Glazedstreets, loggias,verandas,orarcadeshavethesamemediatingfunctionofrelatingtheinhabitedspacetoitsclimaticcounterpart.

1.3.5

Figure1.25

TownhallinSäynätsalobyAlvarAalto(1952–1953):viewuptheexteriorstairstotheraisedcourtyard,thechamberinthebackground.

TheNorthernCourtyardOneofAlvarAalto’smajorworksofthe1950s,theSäynätsaloTownHallwithitsgreenraisedcourtyard, captures the sun,protects from thewind, andhasa lowheight-to-arearatio,which allows the lowangle of the northern sun to penetrate andwarm thewholeinner space.Courtyards are known in the respective literature as employing “ingeniousnaturalcoolingstrategies.”22

Aalto’searlywritings(“Porraskiveltäarkihuoneesen”)fortheAitta1926sampleissue23hinge on the idea of inner paradise, using Fra Angelico’s (1400–1455) painting L’Annuziazione as ametaphor to describe and envision the inside–outside relationship ofspaceandclimateinhisbeginningdesignwork.

InthisessayAaltoexpresseshisconcernaboutthewayoneentersaroomandhowtheroom one enters into is connected to the exterior climate and the light of the sky.OnecouldsaythattherooflightshefirstexploredatPaimioandTurkuSanomat,andfurtherelaborated at Viipuri Municipal Library, are the open sky over a modern version of aclassicalamphitheater.HisbiographerGoeranSchildtarguesthatAalto’saimistoletthisentrancespaceappearliketheinsidespacebetweenotherspacesratherthanthesculpturalsurfaceofaninsidespace.24Itisaninnerexterior,asifenteringthelongPompeianroomopentothesky:theancientatriumortheformlessEnglishdomestichallreferringtoopenspaceasifitwereopenair.25

Figure1.26

TownhallinSäynätsalobyAlvarAalto(1952–1953):raisedgreencourtyardinfullsunshineandshelteredfromthewinds.

Figure1.27

TownhallinSäynätsalobyAlvarAalto(1952–1953):lookingoutintothecourtyardfromtheinnercirculationarcade.

Figure1.28

DiagramofmainairflowpathintheSäynätsalotownhall.

Figure1.29

SectionofspatialcompositionofraisedcourtyardintheSäynätsalotownhall.

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4.

5.

6.

7.

Figure1.30

Windrose(inm/s)forthelocationoftheSäynätsalotownhall.

A courtyard in northern climates can also provide protection from detrimentalwindsand create a sheltered space.Studies of the relationshipbetweenwindvelocity, pattern,and direction with respect to the proportions of the courtyard itself (height andwidth)support this approach. A courtyard creates a microclimate and protects from excessivewindwhile still enablingnatural ventilation from thewarm inner courtyard through thecirculation space into the surrounding rooms.Contemporarydouble-skin façadeshaveasimilarcalmingeffect.

Furtherreferencetoinheritedspatialstrategiessuchaswindcatchers,atria,anddoubleheight spaceswillbe furtherelaborated inChapter5 after introducing thedetailsof thephysicsbehindthephenomenonofflow.

NotesHelderCarita,PalacesofGoa:ModelsandTypesofIndo-PortugueseCivilArchitecture(London:Cartago,1999).

RobinEvans,“Figures,DoorsandPassageways,”in:TranslationsfromDrawingstoBuildings(London:ArchitecturalAssociation,1997).

LisaHeschong,ThermalDelightinArchitecture(Cambridge,MA:MITPress,1979).

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationManualAM10(London:CIBSEPublications,2007).

BeatrizColominaandMaxRisselada(eds),RaumplanversusPlanLibre:LeCorbusierandAdolfLoos1919–1930(NewYork:Rizzoli,1988).

BeatrizColomina,“Window,”in:PrivacyandPublicity:ModernArchitectureasMassMedia(Cambridge,MA:MITPress,1994).

MaxvonPettenkofer,TheRelationsoftheAirWeBreathetotheClothesWeWear(London:Trübner&Co,1873).

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

LewisLeeds,LecturesonVentilation(NewYork:JohnWileyandSons,1968).

AlvinRosenbaum,Usonia:FrankLloydWright’sDesignforAmerica(Washington:PreservationPress,1993),p.149.

Ibid.,p.191.

ChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005).

JamesSteele,R.M.Schindler:HowHouse(London:AcademyEditions,1996),p.17.

WecontinuetousetheGermanwordRaumplanbecausethedirecttranslationspaceplaninEnglishdoesnotapplytothesameconcept.

ManfredKovatsch(ed.),RudolphM.Schindler1887–1953,exhibitioncatalogue(Munich:MuseumVillaSuck,1985),p.18.

JamesSteele,R.M.Schindler:HowHouse(London:AcademyEditions,1996),p.20.

PrestonStoakes,UlrikePasse,andFrancineBattaglia,“PredictingNaturalVentilationFlowsinWholeBuildings.Part2:TheEsherickHouse,”BuildingSimulation,4(4),2011.

Klaus-PeterGast,LouisI.Kahn:TheIdeaofOrder(Basel;Berlin;Boston:Birkhaeuser,1998),pp.45–51.

JosephRykwert,LouisKahn(NewYork:HarryN.Abrams,2001),pp.53–54.

UrsButiker,LouisI.Kahn:LightandSpace(NewYork:Birkhaeuser,1994),pp.90–95.

CharlesCorrea,“BlessingsfromtheSky,”in:CharlesCorreaandKennethFrampton,CharlesCorrea(London:Thames&Hudson,1996).

Ibid.

DanaRaydan,CarloRatti,andKoenSteemers,“Courtyards:ABioclimaticForm?”in:BrianEdwards,MagdaSibley,MohamadHakmi,andPeterLand(eds),CourtyardHousing:Past,PresentandFuture(NewYork:Taylor&Francis,2006).

GöranSchildt,AlvarAalto:TheEarlyYears(NewYork:Rizzoli,1984),p.214.

Ibid.,p.223.

UlrikePasse,“Free-FlowOpenSpace,ClimateandSustainability,”in:K.Wingert-PlaydonandH.Neuckermans(eds),EmergingResearchandDesign,proceedingsoftheInternationalARCC/EAAEConference(Philadelphia,2007).

Chapter2

ThePhysicsofAirFlowThephysicsofairflowisacomplexscientificfield,asisthedeterminationofitsdrivingforces, which are based on pressure differences caused by wind, temperature, or acombination of both. In urban areas where street canyons create their own climate oftemperaturedifferentialsandwindpatterns,thisbecomesevenmorecomplex.Theforcesin nature and their relationships and proportions can be expressed in mathematicalformulaebasedonspecific lawsofphysics,but theycanalsobeexpressed inspatialorgeometric proportions and thus have a direct relationship to architecture and designdecisions.

This chapter is an attempt to ‘translate’ the basics of fluid dynamics for a non-scientificallytraineddesignaudienceandtoexplainthemajortermsandunitsthatprovidethe basis for the physics of natural ventilation based on existing literature.1 For thoseinterested inamore formaldescription,Chapter11presents themathematical equationsthatdescribeairflowandtemperaturerelationships.

Inordertofullyunderstandthephysicsofnaturalventilation,severalsystemsandlawsofphysicsneedtobeconsideredandintegrated.Theyincludefluidflowandwindpatternsand how they affect each other – in particular, how natural forces are influenced andchangedbyobstacles inspace that in turnneed tobeventilated.Mostof these lawsarecoveredbythefieldofphysicscalledfluiddynamics,whichattemptstodescribefluidsinmotion.Fluidscanbeliquidsandgases,thatis,everythingnon-solid.

Fluid dynamics examines velocity, pressure, density, and temperature as functions ofspace and time, all of which can change within the same flow field. An Euleriandescriptionoftheflowfieldprovidesaframeofreferencefortheflowfieldandfocuseson one location in space and observes how the fluid flows through as time passes.ChristianGhiausandFrancisAllard2elaboratethatbysuitabledifferentiationwithrespecttotime,theaccelerationofafluidparticlecanbedeterminedatanypositionandtime,ascan the displacement of the particle from its position at an earlier time by integration.Pressure (p) and density (ρ) are also considered functions of position and time. Abuilding’sinteriorspaceisconsidereda‘vessel’inwhichaircanmovefreelyundercertainboundaryconditionsattheinletsandoutlets.Mathematicallyspeaking,velocity,pressure,and density are the dependent variables of flow that are functions of the independentvariablespositionandtime.

2.1

2.2

Figure2.1

Thematerialvariablesofsolids,liquid,andgasesarevelocity,pressure,anddensity.

Figure2.2

Differenceinmotionbetweensolidsandfluid:moleculesindifferentsectionsoffluidscanmoveindifferentdirectionsinoppositiontosolids.Allpartsofasolidobjectcanonlymoveinonedirectionbasedonthecenteroftheirmass.

SolidsandFluidsAccordingtoGhiausandAllard,3thebasicdifferencebetweensolidbodiesinmotionandfluidsisthatallpartsofasolidbodymovetogetherwithrespecttothecenterofitsmass,either by movement along its coordinates or by rotation. A fluid can also move inrelationshiptoitsmasscenteranditisimpossibletofolloweachfluidparticle,andfluiddynamicsfocusesonthevelocityofaparticleatagiventime.However,particlesinafluidcanalsomoveatdifferentvelocitieswithrespecttoeachotherandcreateaflowfield.

LagrangianVersusEulerianDescriptionasFrameofReference

Lagrangian and Eulerian descriptions use different ways to describe the flow within afield. TheLagrangian description of flow follows themotion of one particle,while theEulerian description explains the characteristics of a flow relative to fixed grid points,calledlaboratorypoints, throughwhichtheparticlepasses.Inmathematical terms,Euleruses a fixed coordinate system to describe themovement of a particle,whileLagrangeusesamovingcoordinatesystemtodescribetheparticle’spath.Lagrangiandescriptionsofmovementareverywellappliedtothemovementofsolidobjects,whiletheEuleriandescriptionofflowismorepracticalforthemotionoffluids.

Figure2.3

TheLangrangiandescriptionofflowfollowseachparticleofaflow,whiletheEuleriandescriptionofflowdeterminestheflowbasedonhowandwhentheflowpassesthroughagridpoint.

Airisnothomogenousanditspropertieschangewiththefactorsmentionedearlier;itisa transient and dynamicmatter. This behavior led to formulae withmultiple variables;therefore obtaining precise information about fluid flow is an extremely difficult task.Someresearchersevencallitthelastmajorunsolvedphysicsquestion.4

Newton’s three lawsofmotionset thebasis forclassicalmechanicsand they indicatethe relationship between force or velocity of an object and the inertia of the object.Accelerationofanobject isdeterminedbyanexternal forceand themassof theobject.Oneoftheforcesactingonabodyisgravity.Othersarepressureandviscosity.Forcescanalsoactonfluidsand,evenmorecomplexly,forcescanactwithinfluids.Theaccelerationofabodyisdirectlyproportionalto,andinthesamedirectionas,thenetforceactingonthebody,andinverselyproportionaltoitsmass.

2.3

1.

2.

3.

4.

5.

Figure2.4

Firstlawofthermodynamics:energycannotbelost,butchangesstatetransferredfrombodytobodylikewarminghandsonawarmobjectorfire.

Thelawsofthermodynamicsareanotherveryimportantsetoflawsthatdescribefluidmotion.Thefirstlawisparticularlyimportanthere:energycannotbelost;itcanonlybetransferredtoadifferentstate.

PropertiesofAirThemajorpropertiesofairaredependentoneachother.The idealgas lawrelates theseproperties:

Pressure

Volume

Density

Mass

Temperature

Temperature is a measurement of the kinetic energy of molecules in a substance. Airpressureistheforcetowhichobjectsareexposedwhenairmoleculeshitthem.Thus,withan increase in temperature molecules move faster and in turn the pressure on othersurfaces increases. When the volume increases, density decreases. With a decrease involume, temperature also decreases.There is thus a direct relationship between volumeand temperature. So,when pressure increases for the same volume andmass of air, itsdensityincreasesaswell.

2.4

2.5

Figure2.5

Propertiesofairaretemperature,pressure,volume,anddensity.

Thedensityofairatsealeveland15°C(60°F)isapproximately1.29kg/m3(0.08053lb/ft3).Thus,theairinsideaboxwiththedimensionsof1×1×1m3contains1kgofair.Onetonofairhasthevolumeofapproximately10×10×10m3,whichisaboutthesizeofasmallresidentialhouse.Theonlyreasonthehousecanwithstandandholdthisweightisthatthepressureoftheairinsideapproximatelyequalsthepressureoftheairoutside.Whenthatisnotthecase,forexampleatanopening,theairmovesinandoutattheotherend.Thedensityofairisapproximately1.5timeslargerat-40°C(1.514kg/m3or0.095lb/ft3)asitisat100°C(0.9461kg/m3or0.06lb/ft3).

Whenairisinmotion,avelocityfieldiscoupledtothosefivemajorproperties.Becauseairmoleculescanmoveagainsteachother,aparcelofwarmaircanmoveupwardsinaspaceatthesametimeasaparcelofcooler(heavier)airwilldescend.

MaterialDerivativeNewton’s law ofmotion and the laws of thermodynamics applied to a fixedmass of aknownmatteronlyprovidethepropertychangesovertime.Forthisdescriptionofmotion,theLagrangiandescriptionisused,becauseitdescribesthehistoryofanidentifiedmovingparticle.However,theEuleriandescriptionisaconvenientwaytodescribetheLagrangianviewpointfromafixedframeofreference.TheEuleriandescriptionisusedforamovingfluid,andthisleadstotheneedtoestablishthe

Eulerian expression of the rate of change of any property of a fluid particle as itmoves through the flow field. The time rate of change of a fluid property, asmeasuredbyanobservermovingwiththeparticle,iscalledthematerialderivativeofthatproperty.5

ConservationofMass–ConservationofMomentumThelawof‘massconservation’basicallystatesthatthemassofasystemremainsconstantovertime.Conservationofmasscandescribetheamountofmassmovingthroughanareaataparticularvelocity(referredtoasmassflowrate).Forexample,ifavolumeofmovingair needs to go through a smaller opening, its velocity increases, conservingmass. If a

2.6

2.7

force is executed on this fluid system, conservation of momentum indicates that thevelocityofthesystemhastoincrease.

ForcesonFluidParticlesFluid particles are exposed to two different types of force: the surface of a particleexperiences theforceperunitarea,alsocalledstress.Thesestressesaredue topressureandviscouseffects.Theothertypeofforceiscalledthebodyforce,becausethisforceactsontheentireparticle,notjustthesurface.Averyimportantbodyforceisthegravitationalforce,whosemagnitudeistheproductofthemassofthefluidelementmultipliedbythegravitationalacceleration.Dependingon thealtitudeof the location,objects fallwithanacceleration between 9.78 and 9.82 m/s2 or approximately 32 ft/s2. Also, air and theEarth’s atmosphere are exposed to thegravitational forceof theEarth.For avolumeoffluid, themass is related to itsdensity so that thegravitational forceperunitvolume iscomposedofthegravitationalforceandtheaccelerationmultipliedbythemass.

Figure2.6

Thelawofmassconservation:withthesameamountofpressurefluidstravelfasterthroughsmalleropeningsasopposedtolargeropenings,asshowninboth1A/2Aand1B/2B,where1Ahasawiderdiameterandthearrowsareshorter,and1Bhasasmallerdiameterwithlongerarrows.Notethatthelengthofarrowsdenotesspeed.

Navier-StokesEquationsInphysics, theNavier-Stokesequations,6 namedafter theFrenchengineerandphysicistClaude-LouisNavier (1785–1846)and the IrishphysicistandmathematicianSirGeorgeGabriel Stokes (1819–1903), describe the motion of fluid substances. These equationsarise from applying Newton’s second law to fluid motion and account for the forcesdescribedinSection2.6.,togetherwiththeassumptionthatthestressesinthefluidarethesumofadiffusingviscous term(proportional to thegradientofvelocity)andapressureterm–hencedescribingviscous flow.Viscosity indicates the resistanceof amaterial to

2.8

2.9

2.10

flow. Oil for example has a much higher viscosity than water. The Navier-Stokesequationsarethemajormathematicalbasisofallcomputationalfluiddynamicspracticestoday.FurtherinformationisprovidedinChapter11.

Bernoulli’sEquationInfluiddynamics,Bernoulli’sprinciplestatesthat“foraninviscidflow,anincreaseinthespeed of the fluid [that is, kinetic energy] occurs simultaneously with a decrease inpressureoradecreaseinthefluid’spotentialenergy.”Theterm‘inviscid’herereferstoanideal fluid that has no viscosity.Bernoulli’s principle is named after theSwiss scientistDanielBernoulli(1700–1782),whopublishedthisprincipleinhisbookHydrodynamicain1738.7 The Bernoulli equation is very important for understanding the change of airvelocityatinletsandoutletsofbuildings.

BoundaryConditionIn order to understand viscous flow behavior, the physical conditions limiting the flowalong its boundaries, the so-called ‘boundary conditions’ need to be taken intoconsideration.Iftheflowistime-dependent,thereisan‘initialcondition’whichneedstobe determined and fromwhich the flow is evaluated.A variety of boundary conditionsmust be determined in order to characterize a certain flow scenario: inflow boundary,outflow boundary, or no-slip conditions along walls for example. A typical inflowboundaryconditionisprescribingavelocitysuchasthewindvelocityintoanopening.Anappropriate outflow boundary condition is specifying pressure such as atmosphericpressure. The no-slip boundary condition of viscous fluids along a solid surfacemeansthattheoutermostparticlesofthefluidsticktothesurfaceofthesolidboundaryandhavezerorelativevelocity,implyingthatthefluiddoesnotmoveatthesurface.

TurbulenceMost flows are actually unstable and thus exhibit turbulent behavior. The atmosphericboundary layer, jet streams in the upper troposphere, andmost cloud formations are inturbulentmotion.Mostnaturalventilationstrategiesalsoinvolveturbulentairmovement.Laminar,straightparallelflowisactuallyanexceptioninnature.Non-turbulentflowsareextremely rare, because most flows are unstable, in particular when they encounterobstacles.Because air canmove in different directions reacting to pressure differences,turbulence can occur between two different flow fields and between fluids and solids.Laminarflowisseenonlyinsmallflowfieldswithhighviscosity.Movingwaterinrivers,the wakes of ships, moving cars, and airplanes have flow patterns that are turbulent.Turbulentmotion is characterized by disorder, irregularity, and randomness in time andspace. It isdifficult ifnot almost impossible topredictwhenandwhere turbulencewilloccur;itisalsodifficulttodeterminetheformandshapeofturbulentstructures.Thisleadsto a much more complex mathematical model for turbulence prediction, based onstatisticalanalysisoftheflowpattern.

Figure2.7

DepictionoftheBernoulliprinciple:anincreaseinfluidspeedoccurssimultaneouslywiththedecreaseinpressure.Pressurehasaneffectondiffusion,asshownhere.Bottle1hasahigherpressurethanbottle2;thusdiffusionoftheliquidfromtheheatedflaskismuchhigherinbottle2thaninbottle1.

Figure2.8

Theno-slipboundaryconditionindicatesthatparticlesclosetosolidboundariesoffluidflowdonotmove,but‘stick’totheboundary.

Anadvantageouscharacteristicofturbulentflowforventilationpurposesisthefactthatturbulent flow is very diffuse, which leads to very efficient mixing characteristics, forexample,offreshandexistingairtoimproveairquality.However,thismixingalsocreatesan increased rate of momentum, heat, and mass transfer. Turbulent flows cool morerapidlyowingtobettermixing.Inaddition,turbulentflowistrulythree-dimensional,andischaracterizedbyfluctuatingvelocitiesofahighorder.Flowinstabilitiessuchaseddiesandvorticesdevelopwhenfluidflowsencountersolidobjectsorotherfluidflows.Fluid

2.11

motion is a dynamic space-time problem; fluid flow and turbulence are driven by a“constant supply of energy to compensate the viscous losses.”8 This energy driving theflow can come from shear or buoyancy forces and fromwind.Because every turbulentflow is different and unique, the exact characterization of turbulence is an extremelydifficultproblem,butturbulentflowshavecommoncharacteristicsthatcanbeidentifiedandaccountedfor.

Thesteamplumerisingoverahotcupofteaorcoffeeisoneofthebest-knownvisualimages of a turbulent flow.Turbulence is necessary for themixing of air streams, thusessentialforgoodventilationthatreliesontheexchangeofair.

Figure2.9

Theturbulentflowisbestdepictedwhenverywarmairmixeswithfairlycoldair,ascanbeseenintheplumeoveracupoftea.

The characteristics of turbulence have been studied using numerical simulation andexperiments. Turbulence typically starts fairly small, with a primary instabilitymechanism.These instabilities cause eddies – airmovements turning in on themselves,creating secondary motions that are usually threedimensional and will again becomeunstable.Turbulence isconstantlycausingstrong, threedimensionaldiffusionofall flowquantities: temperature,velocity,pollutantconcentration,densities(duetotemperatures),and others. These properties are the basis for good air quality based on mixing anddilutionofpollutants,highhumidity,andheat.Turbulencereliesonoutsideenergyfromtheenvironment.Itisstillamajorresearchareainphysics,mathematics,aerospace,andother engineering fields.9 Further reading about turbulence can be found in FrancisAllard’saccount.10

ReynoldsNumberTheReynoldsnumberisanindicatorfortheratioofinertialforcestoviscousforces.TheReynoldsnumberisalsousedtocharacterizedifferentflowregimes,suchas laminarorturbulentflow.Laminarflowoccursat lowReynoldsnumbers,whereviscousforcesare

2.12

2.13

dominant; it ischaracterizedbysmooth,constantfluidmotion.TurbulentflowoccursathighReynoldsnumbersandisdominatedbyinertialforces,whichtendtoproducechaoticeddies,vortices,andotherflowinstabilities.Itisalmostimpossibletopreciselydescribeturbulent flows, as any airplane passenger will notice when experiencing unexpectedturbulence. Turbulence occurs randomly in time and space. It arises from instabilitieswithinthefluidflow.Reynoldsnumberscloseto600leadtounstableboundarylayersinzero-pressuregradients.11Asa ruleof thumb forboundary layer flowover a surfaceorobject, turbulencecanoccur at aReynoldsnumberof approximately200,000;however,flowinsideapipecanbecometurbulentataReynoldsnumberofapproximately2,300.

K-Epsilon(TwoEquation)ModelIn order to better understand turbulent flow, numerical models have been created toapproximate the outcome and characteristics of a turbulent flow.Themostwidely usedmodel for air flow simulations in interior rooms is the k-epsilon model, which wasintroducedbyHarlowandNakayamain1968.12Thismodelisbasedontwoequations:theturbulentkineticenergydissipationrateequation,whichreferstothekineticenergywithinthe turbulent flow, and the dissipation rate of the flow. Themodel determines that the“time-averagedturbulentenergyperunitmassis thecombinationofthekineticenergiesofmanyeddiesofmanysizes.”13Referring to thedifferentscalesofmotionswithin theflow, this kinetic energy is called the turbulent energy spectrum. The dissipation rateequationcontains twovariables,derivedbyacomplexformula: the turbulentgenerationrate and the turbulent viscosity. Both variables refer to space, time, and materialproperties,whichsubsequentlyallowthedeterminationofthemixingrateoftheturbulentflow.

These computation-intensive calculations between the largest and the smallest eddieswithina turbulent flowarestillachallenge,evenwith the largestand fastestcomputersavailable, and therefore present an obstacle to air flow quantification for naturalventilation strategies. Thus, all solutions that are obtained for turbulent flow fields areapproximations.

BuoyancyastheBasisforStackEffectThearchitectVitruvius(bornc.80–70BC,diedafterc.15BC)wasthefirsttomentionArchimedesofSyracuse’sEurekamoment,14describingthemomentwhenhediscoveredtherelationshipbetweenmass,volume,density,andbuoyancy.15Archimedes’principleisafundamentallawofphysics,usedinfluidmechanics.Thisphysicslawindicatesthattheupward buoyant force that is exerted on a body immersed in a fluid, whether fully orpartially submerged, is equal to the weight of the fluid that the body displaces. InVitruvius’9thBook,12inwhichhediscussestheinfluenceofthesciencesonarchitecture,heusedananecdotalstorytointroducethelawofArchimedes.16AccordingtoVitruvius,Archimedeswasrequestedbyhiskingtodeterminewhetheragoldsmithhadcheatedwiththe weight of gold in a crown he crafted. While sitting in the bath tub, Archimedesrealized that the water displaced by his body must be the same volume as his body.

2.14

2.15

Thereforehe immersed thecrown intowater inorder tomeasure thewater itdisplaced,knowingthatifthecrownhadsilvermixedintotheform,itwouldbebulkierthanapuregold crown and therefore displace more water. His measurement found the goldsmithguilty of fraud. It is not clear whether this story is actually true and took place asdescribed, but that is not important here.What is interesting is the fact that Vitruviusalreadyplacedimportanceontherelationsbetweenarchitectureandthephysicsofairandfluidsandhowtheymightrelateingoodproportiontoeachother.

Airisconstantlyinmotion,activatedbythermalenergyintheformofairtemperature.Heatedairbecomeslighterandrises,whilecoolairdescendstowardsthefloor.Oftenairisinmotionevenwhenwecannotperceiveit.Theso-calledstackeffectisbasedonthisbuoyancyeffect,wheretheweightoftheairandthegravitationalforcethatactsontheairarebalancing,andwiththebuoyantforcelargerthangravity,airwillriseupinaspace.

Figure2.10

Thebuoyancyeffect:warmairislighterandlessdenseandthusrisesoverwarmsurfacesorobjects.Thebuoyancyforcecanbestrongerthangravity.

ForcedConvectionIfanexternalforceisactingonthefluid,forexamplewiththehelpofafanorthewind,the transferofenergydue to temperaturedifferences isknownasforcedconvectionandcanalsobedescribedbythemass,momentum,andenergyconservationequations.17

FluidDynamicsofWeatherThemajor relationships in the fluiddynamicsof air form thebasis for thecreationandformation of weather phenomena and patterns such as clouds, wind, and rain. TheirmovementisdrivenbythefluiddynamicsofairtogetherwithgravitationalforcesandtheEarth’srotationalforce,whichcausestheso-calledCorioliseffect.18

Web Weather for Kids19 clearly depicts the elements that create the phenomena ofweatherdescribedbyatmosphericsciences. Interiorenvironmentalconditionsfollowthesame physical properties as weather. Weather can be explained as a combination oftemperature,pressure,volume,anddensityofairandsocanindoorclimate.Thefactthat

2.16

2.17

hot air rises is not only the key physical characteristic of natural air convection insidebuildings,butalsothekeydriverofweatherphenomena.Combinedwiththepropertyofair toholdmoremoisturewhen it iswarm, it explains theoriginof cloud formation aswellastheoriginofhumanthermalcomfortconditions.

Figure2.11

TheCorioliseffectdrivesthemovementofairintheEarth’satmospherebasedontherotationalforcesoftheEarthanditsgravity.

AirandMoistureTheabilityofairasamixtureofgasestoholdmoistureisanothermajorinfluenceontheformation of weather and building interior conditions. At normal conditions close toground, the pressure of hot air can hold more absolute humidity than cold air, as thepsychrometricchartinFigure2.12shows.Here, therelativehumiditylevel indicatesthecapacityofairatacertaintemperaturetoholdmoisture.Whenthetemperatureofawarmair sample drops and comes into contact with a cold glass surface, the water vaporcondenses out of the air and creates small water droplets on the surface. The level ofhumidityhas a strong impactonweather andbuildingclimatewith its effectonhumanthermalcomfort.20

WhatisWind?WindandObstructions/WindinUrbanContext

Windisformedbylargemassesofairmovingfromhigh-pressuretolow-pressurezones,which are created by temperature differentials. Wind is a large, atmospheric scale

2.18

1.

2.

3.

4.

5.

movementofairaroundtheEarth’sglobe.Windasaforcedoeshaveascale,butthesameforcesapplytowindastheyapplytosmall-scalemovementsofairinatestscenario.

Figure2.12

Psychrometricchartdepictsthethermodynamicpropertiesofgas-vapormixtureinatmosphericair.ThehorizontalaxisindicatestemperatureinFahrenheit,whiletheverticalaxisshowspoundsofwaterperpoundofdryair.

TheImpactofFluidDynamicsPrinciplesonSpatialProportions

Thisbriefreviewofthecomplexphysicalpropertiesofairmovementbasedonfluidflowmechanics shows the significanceof spatial proportions, andevenmoreof scale, to thephysicsofnaturalventilation.Naturalventilationflowpatternsarebasedonthecreationofpressureandtheresistancetopressureprovidedbythebuildinginordertochanneltheflowthroughtheintendedpath.Theflowenablesthemixingofinteriorandfreshexteriorair on its way, utilizing the forces of the flow itself (wind and buoyancy). Theseproportionalrelationshipskeeptheturbulenteddiesconstantlyinmotion,andtheairwillmixaslongasthereisanenvironmentalforceavailable.

NotesChristianGhiausandFrancisAllard,“ThePhysicsofNaturalVentilation,”in:FrancisAllard(ed.),NaturalVentilationintheUrbanEnvironment(London;Sterling,VA:Earthscan,2005),pp.36–80.

Ibid.,p.36.

Ibid.

PaulF.Linden,“TheFluidMechanicsofNaturalVentilation,”AnnualReviewofFluidMechanics,31(1),1999,pp.201–238.

ChristianGhiausandFrancisAllard,“ThePhysicsofNaturalVentilation,”in:FrancisAllard(ed.),Natural

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

VentilationintheUrbanEnvironment(London;Sterling,VA:Earthscan,2005),p.37.

IainG.Currie,FundamentalMechanicsofFluids,3rded.(BocaRaton:CRCPress,2002).

DanielBernoulliandJeanBernoulli,Hydrodynamics(NewYork:DoverPublications,1968).

ChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005),p.54.

GeorgeBatchelor,AnIntroductiontoFluidDynamics(CambridgeUniversityPress,1967).

ChristianGhiausandFrancisAllard,“ThePhysicsofNaturalVentilation,”in:FrancisAllard(ed.),NaturalVentilationintheUrbanEnvironment(London;Sterling,VA:Earthscan,2005),p.53.

Ibid.

F.H.HarlowandP.I.Nakayama,TransportofTurbulenceEnergyDecayRate,LosAlamosNationalLaboratory,ReportLA-3854(1968),doi:10.2172/4556905.

ChristianGhiausandFrancisAllard,“ThePhysicsofNaturalVentilation,”in:FrancisAllard(ed.),NaturalVentilationintheUrbanEnvironment(London;Sterling,VA:Earthscan,2005),pp.36–80.

Vitruvius,TheTenBooksonArchitecture(DeArchitectura),bookIX,introductionandtranslationMorisHickyMorgan(NewYork:DoverPublications,1960),pp.253–254.

T.L.Heath,TheWorksofArchimedes,booksI–II(CambridgeUniversityPress,1897).

DavidBiello,“FactorFiction?ArchimedesCoinedtheTerm‘Eureka!’intheBath,”ScientificAmerican,http://www.scientificamerican.com/article.cfm?id=fact-or-fiction-archimede.

ChristianGhiausandFrancisAllard,“ThePhysicsofNaturalVentilation,”in:FrancisAllard(ed.),NaturalVentilationintheUrbanEnvironment(London;Sterling,VA:Earthscan,2005).pp.36–80.

DepartmentofAtmosphericSciences(DAS)attheUniversityofIllinoisatUrbana-Champaign,“CoriolisForce:AnArtifactoftheEarth’sRotation,”http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/crls.rxml(accessed5/6/2014).

WebWeatherforKids,UniversityCorporationforAtmosphericResearch(UCAR),FriendsofUCARandBoulderValleySchoolDistrictScienceDiscovery,http://eo.ucar.edu/webweather/basic2.html(accessed5/6/2014).

MichaelJ.MoranandHowardN.Shapiro,FundamentalsofEngineeringThermodynamics(NewYork:Wiley,2000).

Chapter3

TheImportanceofFreshAirforOccupants’HealthAs Steven Connor elaborates in The Matter of Air: “The ancient world was familiar,indeed, preoccupied to the point of obsession, with various kinds of vapor, exhalation,fume and spirit,most ofwhichwewould nowadays characterize as aerosols or similarsuspensions of liquid or particulate matter in air.”1 Air had also become a concern ofphysiciansandpublichealthspecialistsduring theseventeenthcenturywith the increaseofpublicinstitutionssuchasschoolsandhospitalsandthedesiretopreventthespreadofdiseases. Steven Connor, meanwhile, notes: “Buildings sweat, age, excrete and theyrespire.”2We now understand that onemajor concern for indoor air quality is the off-gassing of building material in addition to occupant odors as well as the results ofoccupants’breathing.

TheheatingandventilationengineerLewisW.Leeds(1829–1896)in1868claimedthat“Man’sownbreathishisgreatestenemy.”3Thiswasthemottoofhis1868publicationinhisLecturesonVentilation, oneof the firstguidelinesonbuildingventilation strategies.Thewriting in these guidelines is crystal clear, and they contain fabulous color crayonillustrationsbasedon thephysicsof roomair circulationunderstood fromexperienceatthe time. Most of his recommendations for air inlet and outlet placement and theirrelationshipsstillholdtruetoday,becausetheyarebasedonthephysicalpropertyofhotair rising. However, Leeds’ statement created a very costly misconception stillencounteredtoday:thebeliefthatair-tightbuildingspreventgoodairquality.Theproblemisindeedfarmorecomplex.Goodairqualitywithlowerventilationratescanbeachievedespeciallywithfeweremissionsfrommaterials.

His lectureswerea response to thedeath rateassigned to foulair in largeEastCoastcitiesoftheUSAinthelatenineteenthcentury.Thesedeathsandthehealthconcernstheypromptedareconsideredthebeginningofventilationscience.Onecandrawaninterestingand maybe even frightening comparison to today’s large Asian cities and their smoglevels,whereasthmarates inchildrenareattributedtobadoutsideairqualitycausedbyindustryandcartraffic.4Whentheexteriorair isbad,wherecanhealthy,freshaircomefrom?Inaddition,Lewisalsopointedouttherelationshipbetweencombustionforheatingand theneed for ventilationwhenhe talks aboutManchester: “Wehavenothing in thiscountry [the USA] like this city [Manchester], where two millions of tons of coal areburnedannually, the smoke fromwhich fills theair and stretches like ablackcloud farintothecountry.”5

3.1

Figure3.1

LewisLeedslectureonventilation,Fig.4,5,6,p.29:nineteenth-centuryvisualizationofairmovementinsideinteriorspaces.3

WhatIsAir?Basedonresearchandexperimental resultsweknowthatair iscomposedof78percentnitrogen,20percentoxygen,2percentcarbondioxide(CO2),andafractionofinertgases.Water vapor content amounts to only about 1 percent. Exhaled air contains about 4–5percent less oxygen than inhaled air and 4–5 percentmoreCO2 than inhaled air. Thus,eveninair-tightbuildingswewillnotrunoutofoxygenthatsoon,althoughwemayfindtheair starting tosmellbad.Asaconsequence, the reductionofemissions isonemajorfactor inenergy-efficientventilation.Exhaledairhasarelativehumidityofclose to100percentaccordingtotheWholeBuildingHandbook.6 It iscommonlyunderstoodthatweventilatetohavesufficientoxygentobreatheandtogetridofexcessCO2.AlthoughCO2isused tomeasure ‘staleair’, theconcentrationswhicharedetermined toposea risk tohealth are hardly ever achieved, even in the most air-tight buildings.7 Ventilation isprimarilyrequiredtoadjusthumidityandremoveexcessheat,bodyodors,andmaterials’emissions(VOC),whicharemajorhealthconcerns.

3.2

1.

2.

3.

4.

5.

6.

7.

3.3

Figure3.2

Thecompositionofairasamixtureofgases.

IndoorAirQualityVentilation in general has two major goals: 1. cooling air and occupants throughtemperature reduction or cooling by evaporation using increased air velocity, and 2.maintaining appropriate air exchange rates to keep a proper composition of air,makingsure it isnotsmellyornauseatingwith too littleoxygenor toomanypollutantssuchasvolatile organic compounds (VOC). Ventilation at a to-be-determined rate removes ordilutes pollutants to an acceptable level. Next to cooling, indoor air quality or indoorenvironmentalquality(IEQ) is themajorreasonforventilationand thusalsofornaturalventilation.Thischapterdiscusseshealth-relatedventilationreasonsandprovidesashorthistoryoftherelationshipofairandhealthasabasisofventilationstudies.

Manyhealthissuesarerelatedtopollutionofindoorair:8

Infectiousdiseasescausedbyairbornevirusesorbacteria;

Growth of microorganisms in humid air, for example in humidifiers or within thebuildingenvelopeconstruction;

Allergiesandasthmacausedbyexposuretomoldthatthrivesathighhumidityindoors;

Lungcancercausedbyexposuretotobaccosmokeandradondecayproducts;

CancerandskinirritationaswellasallergiescausedbyVOCsandformaldehydesintheair;

Dizzinessandnauseacausedbyodors,whichcanleadtodissatisfactionwiththeindoorenvironment;

Sickbuildingsyndrome(SBS).

Manyresearchstudies9haveshownthatventilationratesbelow10l/s(20ft3/m)haveoneormoreofthosedetrimentalhealtheffectsonhumanoccupants.Childrenandtheelderlyareparticularlyvulnerabletoexposurestothesepollutantsathighlevels.10

ABriefHistoryofAirandHealthSciencesPriortoamodernscientificunderstandingoftheworld,evenmorepropertiesandailmentswereattributed to the influenceofair.11 InGreekphilosophy,airwasconsideredoneofthefourelements,togetherwithfire,earth,andwater.12Aristotle(384BC–322BC)added

“aether”asthefifthelementtothislist,andheassignedittothestars,astheycouldonlyhave beenmade of a different, divine substance. In hismajor treatise onmaterials,OnGenerationandCorruption,13Aristotlesearchedforthereasonwhymaterialscomeaboutandhowmaterialspassaway,howchangeshappen,howmaterialsgetaltered,andhowgrowthoccurs.Themovementofairandhowaircancomeoutofwaterwaspartofhisconsiderations.TheoriginofthefourelementsinclassicalthinkingmayevengobacktoBabylonianmythologyand theEnûmaEliš,14 a textwrittenbetween the eighteenth andsixteenthcenturiesBC.Itdescribesfivepersonifiedcosmicelements:thesea,earth,sky,fire,andwind.Thustheunderstandingthatairisitsownentityismanymillenniaold.TheGreek philosopher Plato (427BC–347BC) assigned properties to the elements, and heconsideredair tobehotandwet.Platowrites inTimaeus:“Soit iswithair: there is thebrightestvarietywhichwecallaether,themuddiestwhichwecallmistanddarkness,andother kinds forwhichwehave no name.”15Airwas at the same time considered to berelatedwiththespiritualbeginningoflifeandsoulasspiritualcenterofahumanbeing.

Table3.1Historicelementsacrosscultures

Source:http://en.wikipedia.org/wiki/Classical_element

Another health-related concept in antiquity was the Pneuma, also going back toAristotle.Pneuma indicatedspirit,breathing,and thepowerof life,andair is thusoftenconsidered synonymous with spirit and soul.Pneuma was the ancient Greek word forbreath and thus relates air as an element to the living body and the soul as an aerialspirit.16

The presocratic thinker Anaximenes (585 BC–525 BC) saw air as the “arche”, thebeginning of all things,17 relating “aer” to the very existence of humans, not justbiologically,butalsospiritually.Inaddition,airwasalsorelatedtotheimmaterial,butalsoconsideredthefoulbearerofallevil.

3.4

Othercultures,philosophies,andworldviewshadsimilarcategories.Buddha’steachingincludedfourelementsandconnectedairtovibrationandexpansion.18

In the Western scientific world, air became a subject of scientific study in the latesixteenth century,when the chemical composition of airwas stillmostly unknown andscientific inquiry circulated around the questionwhether a vacuumexisted andwhetherwhatcouldnotbeseencouldbeextractedtoachieve‘lessthannothingness.’Themeanstoinvestigateairinsciencewastheair-pump,andvacuumwasdiscoveredasascientificfactinabout1660byRobertBoyle(1627–1691).19Thephenomenonwasdepictedinthe1768paintingAnExperiment on a Bird in an Air Pump by JosephWright of Derby (1734–1797),nowdisplayedintheNationalGalleryinLondon.20

Figure3.3

AnExperimentonaBirdinanAirPumpbyJosephWrightofDerby,1768,depictingtheexperiment,whereavacuumwascreatedinaflaskwhichcontainedabird,robbingthebirdofthebasisforlife:air.

HealthandWell-BeingHealth and well-being are strong concerns in ventilation science, and the appropriateventilation rates required to provide a healthy environment are constantly debatedwithrespecttotheenergyandequipmentneededtoconditiontheair.

Forexample,indoorhumidityisconsideredawidespreadcauseofdiseasesinchildrenbecause high humidity in indoor air promotes mold growth. Therefore, removal ofhumiditycanreducehealthrisks,butithastobeclearthatitisnotthehumiditythatistheissue,butmoldgrowth.Ontheotherhand, if toomuchhumidity isremovedthedryairmaycauseotherdetrimentaleffectssuchasrespiratoryissues.

Historicallymanypathogenswereoriginallyconsideredtobespreadbyair,whichledto the depletion of urban environments during epidemics, as described vividly in the

3.5

Decameron by Giovanni Boccaccio (1313–1375).21 But modern research showed thatcholera epidemics, for example, were spread by contaminated water. Today, mostinfluenza viruses are spread with a handshake and not by air. But in the modernenvironment new particles linger in the air, having a negative health effect on humanoccupancy: VOCs (volatile organic compounds), carcinogenic particles, formaldehyde,andcombustionfineparticlescreatedassideproductsofgasburnersandmotorvehicles.22

Exposure tofreshand thushealthyairwasconsideredamajorcureof tuberculosis intheearlytwentiethcentury,whichledtotheconstructionofmajorsanatoriumbuildingsintheSwissAlps,butalso inFinland,exemplifiedby thePaimioSanatoriumdesignedbyAlvarAaltoin1932.23

Architecture,HealthandAir:AlvarAalto’sPaimioSanatorium,Finland

AlvarAalto’s(1898–1976)designforthePaimiotuberculosissanatorium(1932)marksahighpointinhisFunctionalistperiod.Tuberculosiswasconsideredadiseaseofthedense,urban,unventilatedenvironment.Tuberculosis is in fact an infectiousdiseasecausedbymicro-bacteria that affects the lungs and is transmitted through air.Therefore, sanatoriawere built in remote mountaintop regions such as Davos, Switzerland, and werehighlighted in the 1924 novelMagicMountain (Zauberberg) by ThomasMann (1875–1955).24 Pure forest locations such asFinlandwere also considered appropriate sites toexposetuberculosispatientstoplentifulfreshairandventilation.

SanatorialentthemselvesverywelltothenewModernMovementinarchitectureandthe development of Functionalist architectural features. The ventilation of the patientwards in Paimio brought fresh air without draught into the patients’ rooms through aspecially designed double pane glasswindow, oriented to the sun,which preheated theventilation air to a more temperate condition. The Paimio patient room windows canthereforebeconsideredaspredecessorsofthemanydouble-skinglasswallstocome.

Another iconicarchitectural featureof thebuilding is theopenbalconies,whichwereusedtoexposethepatientstoplentifulfreshairasahealingtreatment.

3.6

Figure3.4

TheoriginalwindowdetailforPaimiosanatoriumprovidedtwopanesofglassforgentlypre-warmingtheincomingventilationairofthepatient’sroom.

Figure3.5

Providingopenspacesforthetuberculosispatient,theiconicroofterraceexposespatientstofreshair.Theterracewasglazedinthe1960s.

Breathing,Cooling,Cleaning,andVentilationRatesMax von Pettenkofer (1818–1901), one of the founders of public practical hygiene,delivered three public lectures on hygiene in 1873 called The Relations of the Air WeBreathetotheClothesWeWear,theHouseWeLivein,andtheSoilWeDwellon.25Thedevelopmentofpublichealthasasubjectofscientific inquirystarted inEuropeand theUSAwith theadventof large-scalepublicbuildings,high-density livingconditions,andanaspirationtoconquerthedesolatelivingconditionsoftheurbanworkingpoor.

Withthesentence“Wewantairtonourishusandtokeepuscool,”26Pettenkoferstarts

his tripartite lecture by stating the incredible adaptability of the humanbody to variousclimatictemperatureconditionsandtheresultinghumanmetabolism.Whilehumansadapttoboththearcticandthetropics,humanbodytemperatureonlyvariesbyapercentageofadegreeFahrenheit,whetheritis30degreesFahrenheit(~0degreesCelsius)or105degreesFahrenheit(40degreesCelsius)outside.Coolingbyevaporationandconductionaccordingto Pettenkofer is a most significant and astounding means of cooling. He alreadyunderstood that cooling is supported by air movement until air movement turns toannoyance and draught. Here, the surrounding conditions matter as much as thetemperatureoftheairbreeze.

Currenthealth concerns related to indoor environmental quality in residential, public,andcommercialbuildings includeasthmaandcancer riskspotentiallycausedbyVOCs,radon,odorsandchemicals,allergies,ozoneirritation,andotherrespiratorysymptoms.Avibrantdebateisongoingaboutthebestapproachtoremovetheseparticlesfromtheair.The most obvious approach is to remove or reduce the source of the pollutant or toincrease the ventilation rate in order to dilute and dispose of particles and to keep itsconcentration below a proven acceptable range.27 However, these ranges have changedsignificantlyovertimeandarestillinflux.

Air change rates have become the most important validation parameter (next totemperature and humidity) for ventilation strategies. A ventilation strategy can only beimplementedifitcanprovidetherequiredventilationrateonacontinuousbasis.Thustherate in question becomes the minimum rate for a natural ventilation strategy, which isusuallydrivenbydynamicandnotbycontinuoushomogenousforces.

Currentventilationratesforhealthyindoorairqualityaredeterminedbythenumberofpeopleoccupyingaspace,theiractivity,andthevolumeandareaofthespace.Thereisnodistinctionmadebetweenthetypeofventilationsystemandtheenvironmentinwhichthebuildingissituated(forexampleurbanversusrural).Supplyairwillalwaysbeconsideredfreshairandwillreplaceordilutetheused/exhaustedairinagivenspaceindependentofwheretheairisdrawnfrom.

Recent findings indicate that there is very little evidence supporting the notion thathigherventilationratesactuallydoresultinhealthierindoorenvironments.28Consideringthefactthathighoutdoorairsupplyratesleadtohigherenergycost,thequestionisindeedcrucial.

Recent research indicates that inhabitants favor natural ventilation. Seppaenen andFisk29cametotheconclusionthat“buildingswithnaturalventilationareassociated lesswith SBS symptoms than buildingswith traditionalmechanical ventilation systems andare also well accepted by the users due to the potential for individual controls.”Hummelgardetal.30comparedusersatisfactionratesinnaturallyventilatedbuildingsandinmechanicallyventedbuildings,andalthoughtemperaturesandCO2levelswerehigher,satisfaction rateswere higher in naturally ventilated buildings. In addition, researchhasnoted that increased ventilation rates would increase productivity and thus increaseeconomicbenefitsduetosalarycostsforworkersandlesssickleave.31

Table3.2BreathingzoneoutdoorairflowratesaccordingtoASHRAE62.2-2031:Ventilationforacceptableindoorairquality(extractedfromTable6.2.2.1:MinimumVentilationRateinBreathingZone)

3.7

3.8

Notes:Thistablerepresentsadiverseselectionofoccupancycategories;foracompletelist,thestandarditselfshouldbeconsulted.Thetableisnotvalidinisolation;itmustbeusedinconjunctionwiththeaccompanyingnotespublishedinthestandard.Thenumbersarepublishedhereforinformationonly.

Source:ASHRAE62.2-2013withpermission

IndoorAirQualityToolsThe United States’ Environmental Protection Agency has developed two indoorair-quality-relatedprograms and tools: theEPA IndoorAirQualityBuildingEducation andAssessment Model (I-BEAM), a tool designed to provide guidance to buildingprofessionals and others interested in indoor air quality in commercial buildings, andIndoorairPLUS,whichprovidesavarietyofconstructionpracticesandtechnologiesfornew homes.32 Major construction and design features are covered including moisturecontrol; radonandpestbarriers;heating,ventilation,andair-conditioning(AC)systems;combustionpollutantcontrol;low-emissionmaterials;andhomecommissioning.

BuildingMaterialsandVentilationMaterial off-gassing is typically encountered with composites, glues, or adhesives andmaycausemajorhealthconcerns,whichcanbeaddressedbyincreasedventilationratesto

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dilute the often toxic particles. Themore effective approach in general and for naturalventilation design is to avoid harmful off-gassing from materials to the indoorenvironment in the first place. Environmental benign manufacturing33 is a growingmovement, which avoids various toxic compounds during the production process andsubsequentlyduringthelifetimeofamaterial.34

McDonough Braungart Design Chemistry’s “Parameters for MBDC’s MaterialsAssessmentProtocol”35providesasystemtoclassifymaterialpropertieswithregards tohealthandenvironmentalriskfactors.Itdistinguishesbetweenhumanhealthcriteriaandecologicalhealthcriteria.

Humanhealthcriteria:

Carcinogenicity

Teratogenicity

Reproductivetoxicity

Mutagenicity

Endocrinedisruption

Acutetoxicity

Chronictoxicity

Irritationofskin/mucousmembranes

Sensitization

Otherrelevantdata(skinpenetrationpotential,flammability,etc.)

Ecologicalhealthcriteria:

Algaetoxicity

Bioaccumulation

Climaticrelevance

Contentofhalogenatedorganiccompounds

Daphniatoxicity

Fishtoxicity

Heavymetalcontent

Persistence/biodegradation

Other(waterdangerlist,toxicitytosoilorganisms,etc.)

NotesStevenConnor,TheMatterofAir(London:ReaktionBooks,2010),p.27.

StevenConnor,“BuildingBreathingSpace,”in:MonikaBakke(ed.),GoingAerial:Air,Art,Architecture

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(Maastricht:JanvanEyckAcademie,2006).

LewisW.Leeds,LecturesonVentilation(NewYork:Wiley,1867),p.28.

DanaRayanandKoenSteemers,“UrbanEnvironmentalFactsToday,”in:M.Santamouris(ed.),EnvironmentalDesignofUrbanBuildings:AnIntegratedApproach(London;Sterling,VA:Earthscan,2006),p.2.

LewisW.Leeds,LecturesonVentilationBeingaCourseDeliveredintheFranklinInstituteofPhiladelphia(NewYork:Wiley&Sons,1868),p.5.

VarisBokaldersandMariaBlock,TheWholeBuildingHandbook:HowtoDesignHealthy,EfficientandSustainableBuildings(London;Sterling,VA:Earthscan,2010),p.117.

Ibid.

MattSantamourisandPeterWouters,BuildingVentilation:TheStateoftheArt(London:Earthscan,2006).

WilliamJ.N.TurnerandIainS.Walker,“UsingaVentilationControllertoOptimiseResidentialPassiveVentilationforEnergyandIndoorAirQuality,”BuildingandEnvironment,70(0),2013.

Ibid.

BarbaraKenda,AeolianWindsandtheSpiritinRenaissanceArchitecture:AcademiaEoliaRevisited(NewYork:Routledge,2006).

PhilipBall,TheElements:AVeryShortIntroduction(Oxford:OxfordUniversityPress,2004),p.33.

Aristotle,OnGenerationandCorruption(Raleigh,NC:AlexCatalogue,2000).

FrancescaRochberg,“AConsiderationofBabylonianAstronomywithintheHistoriographyofScience,”StudiesinHistoryandPhilosophyofScience,33(4),2002,pp.661–684.

Plato,Timaeus,ch.27,p.83.

BarbaraKenda,AeolianWindsandtheSpiritinRenaissanceArchitecture:AcademiaEoliaRevisited(NewYork:Routledge,2006).

DavidC.Lindberg,“TheGreeksandtheCosmos,”in:TheBeginningsofWesternScience(Chicago:UniversityofChicagoPress,2007),p.28.

DanLusthaus,BuddhistPhenomenology:APhilosophicalInvestigationofYogācāraBuddhismandtheCh’engWei-shihLun(NewYork:Routledge,2002),p.183.

RobertBoyle,NewExperimentsPhysico-Mechanical,TouchingtheSpringoftheAir,andItsEffects(Made,fortheMostPart,inaNewPneumaticalEngine)(Oxford:HallandRobinson,1662).

Seehttp://www.nationalgallery.org.uk/paintings/joseph-wright-of-derby-an-experiment-on-a-bird-in-the-air-pump(accessed3/5/2011).

DecameronWeb,“Texts”,http://www.brown.edu/Departments/Italian_Studies/dweb/texts/DecIndex.php?lang=eng(accessed5/7/2014).

MatSantamourisandPeterWouters,BuildingVentilation:TheStateoftheArt(London:Earthscan,2006).

Seehttp://www.alvaraalto.fi/net/paimio/paimio.html(accessed5/7/2014).

ThomasMann,DerZauberberg,ed.MichaelNeumann(FrankfurtamMain:S.Fischer,2002).

M.vonPettenkoferandA.Hess,TheRelationsoftheAirtotheClothesWeWear,theHousesWeLivein,andtheSoilWeDwellon:ThreePopularLectures(N.Trübner&Company,1873).

Ibid.

MartinHolladay,“VentilationRatesandHumanHealth:HaveResearchersFoundAnyConnectionbetweenResidentialVentilationRatesandOccupantHealth?”MusingsofanEnergyNerd,3/29/2013,http://www.greenbuildingadvisor.com/blogs/dept/musings/ventilation-rates-and-human-health.

Ibid.

O.SeppänenandW.J.Fisk,“AssociationofVentilationSystemTypewithSBSSymptomsinOfficeWorkers,”IndoorAir,12(2),2002.

J.Hummelgaard,P.Juhl,K.Saebjornsson,G.Clausen,J.Toftum,andG.Langkilde,“IndoorAirQualityandOccupantSatisfactioninFiveMechanicallyandFourNaturallyVentilatedOpen-PlanOfficeBuildings.”BuildingandEnvironment,42(12),2007,pp.4051–4058.

31

32

33

34

35

MatSantamourisandP.Wouters(eds),BuildingVentilation(NewYork:Routledge,2006),p.169.

UnitedStatesEnvironmentalProtectionAgency’sIndoorPlusProgram,http://www.epa.gov/indoorairplus/building_professionals.html.

T.G.P.Gutowski,WorldTechnologyEvaluationCenter,LoyolaCollegeinMaryland,andInternationalTechnologyResearchInstitute,WTECPanelonEnvironmentallyBenignManufacturing:FinalReport(InternationalTechnologyResearchInstitute,WorldTechnologyDivision,2001).

WilliamMcDonoughetal.,“PeerReviewed:ApplyingthePrinciplesofGreenEngineeringtoCradle-to-CradleDesign,”EnvironmentalScience&Technology,37(23),2003,pp.434A–441A.

Ibid.

4.1

Chapter4

NaturalVentilationandClimateEnvironmental andclimatic characteristics andconditionshave a tremendous impactonthe development of a spatial language for natural ventilation. Vernacular culturesmanifested themselves out of necessity through a response to atmospheric and climaticproperties,whichwere inscribed into architectural space.Humidity, dryness, heat, cold,and illumination intensityhave left theirmark in thebuilt form, in roof types, surfaces,andopeningproportionsofbuildings.Buildingswereoftenpositioned in relationship tothedirectionof thesun, theprevailingwinds,andother influences.Theneedforvision,light, heating, and cooling is always based on the interrelation between the exteriorclimateandinternalneeds.Thischapteroutlinesthemajorclimaticterminologyimportantto understanding the climate-related energy flow around buildings, which is critical inorder to determine the resources available to drive the ventilation energy flowwithin abuilding.

Climate isameancharacteristicofdailyandannualweatherpatternsdrivenbylarge-scale wind flow, precipitation, and the strong seasonal influence of solar radiation.Weatherdevelopsintheatmosphere’stroposphere,whichextendstoapproximately10km(6.2miles) away from the Earth’s surface. Long-termweather data is translated into apatternofclimatebasedon typicalannualscenariosandreoccurringcharacteristics (i.e.,seasonsandtheirpropertiesrelatedtocertainlocations).

Figure4.1

Weather/climate:theverticalstructureoftheatmosphereandthetimeandspacescalesofvariousatmosphericphenomenacreatethecharacteristicdomainforboundarylayerclimateconditions.

AtmosphericBoundaryLayerThe atmospheric boundary layer is the layer closest to and directly influenced by itsinteractionwiththeEarth’ssurface.Thisisthelayerinwhichwindsformandcloudsandprecipitation dominate the weather patterns. Wind flow is characterized by strong

turbulence in the low atmospheric layer that is generated by anygroundobstacle or bythermalairflowinstabilities.Thus,theEarth’ssurfaceinfluencestheweatherpatternsandthe weather patterns interact directly with the Earth’s surface. Weather is a complexphenomenon created between solid matter of the multifaceted Earth surface and itsvegetation, the oceans, and the gaseous shell of air enclosing the planet. Solar energy,gravity,andtheEarth’srotationalmovementcreatetheenergytoinitiatemotionoftheair.Air moves from high pressure to low pressure and thus the atmosphere is in constantmotionacrossthesurfaceoftheEarth.TheEarth’ssurfaceandtheairarewarmedbythesun;theairrisesduetobuoyancyandcarrieswithitmoistureevaporatedfromtheEarth’ssurface and its bodies of water. Air volumes moving across the Earth’s surface areconstantlydevelopingturbulenceclosetothesurface.Theseturbulentflowsdecreasewithincreasingheight.Windis thuscausedbyairmovementbasedondifferentairdensities.Mostoftenastatisticalapproachisusedtoapproximatethepossibilityofturbulenceandthepredictionofwhatkindofwindcanbeexpectedatwhattime.1

Figure4.2

Windformsbetweenhighandlowpressurezonesinordertoevenoutthepressuredifferentialsbetweenthetwozones.

Table4.1Aerodynamicpropertiesofnaturalsurfaces

Surface Remarks Roughnesslengthz0(m) Zeroplanedisplacement(m)

Water Still–opensea 0.1–10.0×10-5 –

Ice Smooth 0.1×10−4 –

Snow 0.5–10.0×10-4 –

Sand,desert 0.0003 –

Soils 0.001–0.01 –

Grass 0.02–0.1m0.25–1.0m

0.003–0.010.04–0.10

≤0.07≤0.66

Agriculturalcrops 0.04–0.20 ≤3.0

Orchards 0.5–1.0 ≤4.0

Forests Deciduous 1.0–6.0 20.0

1.

2.

3.

Coniferous 1.0–6.0

Source:AdaptedfromT.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),p.57

An important indicator of surface conditions is the roughness length,2 which isdetermined as a function of the nature of the ground and the geometry of existingobstacles,providinginformationonvariousterrainconditions.

Obviously, the forceofgravityplaysasignificant role in the formationofweather. Itholds the atmosphere around the Earth together and forms the counter force to thebuoyancyofrisinghotair.Atacertainpoint,thegravitationalforcewillbestrongerthanthebuoyancyforceofpressuredifferentialsandtheairwillstartmovingbacktowardstheEarth’ssurface.

The second important force influencing the motion within the atmosphere is theCorioliseffectcausedbytheEarth’srotation.TheEarthisrotatingarounditsaxis,whichstretchesfromtheNorthtotheSouthPole.Itcausestheeffectthatanobjectattheequatormovesatabout100milesanhour(160kilometersperhour)eachday,whileanobjectattheNorthPole stands still.TheCorioliseffect isadeflectionofamovingobject,whenobserved in a rotating reference frame. It comes into effect in thegeostrophic flow, forexample when air moves north from the equator and gets deflected into a counter-clockwise rotational motion, or when it moves south and is deflected in a clockwisemotion.Thesemotionscanbeseeninlarge-scalewindsystemssuchashurricanes.Theyfollow a complex interaction of centrifugal forces and the forces caused by pressuregradientsduetotemperature(seeFigure2.11:TheCorioliseffect).

Urban areas create a boundary layer that ismore unstable than the rural atmospherebecause of the numerous obstacles and roughness factors.3 Temperature also plays asignificantroleasitincreasestowardsthecenterofanurbanarea;thusurbanareascreatetheirowninternalwindflowsandgustsaspartofurbanmicroclimates.4

Understanding the velocity and direction at the inlet of a window is thus morecomplicatedinanurbansituationthanitisinaruralsituation,wheretheairflowthroughabuildingisbasedonpressuredifferencescausedbywindorbuoyancyorboth.Inurbansurroundings,thenaturalforcesareinfluencedbyseveralfactors,including5:

Roughnessfactor

Topographicalfactor

Wakefactor

Theroughnesslayerextendsbeyondthetopsofsurfaceroughnesselementstoatleastonetothreetimestheirheightandspacingproportion.

Experimental and computational definitions of these factors and their computationalcoefficients are the subject of major international research projects, foremost theURBVENTproject6 fundedby theEuropeanCommunity.Further informationabout theurbanmicroclimateisprovidedinSection7.3.

4.2 TheScienceofAtmosphereandClimateTheEarth’sclimateisalargesystemofenergyandmassexchangesandcreatesabalancebetweenthesolarenergysystemandtheEarth’senergysystem.1

Thefirstlawofthermodynamics(conservationofenergy),whichdeterminesallenergybalances,statesthatenergycanneitherbecreatednorbedestroyed,onlyconvertedfromone form to another. Four different forms of energy exist in the Earth’s atmosphericsystem that are important toclimatology: radiant, thermal,kinetic, andpotential energy.Theexchangeofenergycanoccurinthreedifferentmodes:convection,conduction,andradiation. The interaction of these forms of energy and thesemodes of transfer createsweather,andonalargertimescaleclimate.

AccordingtoOke,7thegeneralsystembalancereadsEnergyInput=EnergyOutput.Inclimaticterms,thisequalitycanonlybevalidoveralongerperiodoftime.Overshorterperiods, the balance is not reached because of accumulation or depletion of system-inherent energy storage. Thus, the system balance should bemore precisely written asEnergy Input = Energy Output + Energy Storage Change. In the case of the Earth’sclimate, theEarth’ssurfaceactsasstorage.Storingorretractingofsolarradiationinthesoil results in the rising or falling of soil temperatures.Wind systems are generated byhorizontalthermaldifferencesintheboundarylayer.

Figure4.3

Thermodynamicsandclimate:thermalenergyisconstantlyexchangedbetweentheEarth’ssurfaceandtheatmospherebylong-waveradiation,whileshortwaveradiationfromthesunisabsorbedbytheEarth’ssurface.

Climate effects influencing natural ventilation strategies need to be evaluated ondifferentscales.

XXXL=Atmospheric boundary layer: the atmospheric boundary layermoves acrosstheroughandrigidsurfaceoftheEarth.

XXL=Macroclimate context: topography, solar geometry, lunar influence, landscapefeatures.

XL=Meso-regionalclimatecontext:thelargerextentofthesite.

L=Local climate context: the features of a building site, neighboringbuildings, andplants are related to the turbulent air layer that is in direct contact and interactionwiththem.

M=Buildingscale:thenearbuildingandinteriorbuildingclimateconditions.

4.3

4.4

S=Microclimate: thedirect interactionbetween thebuilding and theboundary layeraroundthebuilding(indoorairquality/climate).

TheLaminarBoundaryLayerThelaminarboundarylayeristhelayerofatmosphericairwithdirectcontacttotheEarth.ThisisthedefinitionfortheverythinlayerofairattachedtotheelementsontheEarth’ssurface, which is basically a calm layer unaffected by the turbulent surface layer. Thelaminarboundarylayerisonlyafewmillimetersthick.Itestablishesabufferbetweenthesurface and the more dynamic environmental condition above. The encyclopedia ofclimatesisbasedonthesescalesofairlayers.

Figure4.4

Laminarboundarylayer:veryclosetothesurfaceoftheEarththeflowislaminar.

EncyclopediaofClimatesBasedonthesimilarityoflong-termweatherpatterns,whicharegenerallycalledclimate,Koeppenclimateclassificationswerealreadydevelopedin1884bytheRussian-Germanclimatologist Wladimir Köppen (1846–1940).8 These widely used world climate zoneclassificationmapswerebasedonvegetation,temperature,andprecipitation.

Five main climate groups are identified in the system of the currently updatedKoeppen–Geigerclimatezonemap:8

GROUPA:Tropical/megathermalclimates

GROUPB:Dry(aridandsemiarid)climates

GROUPC:Mildtemperate/mesothermalclimates

GROUPD:Continental/microthermalclimates

GROUPE:Polarclimates

Figure4.5

Köppen–Geigermapofworldclimates:theseclimateclassificationsareusedworldwidetodeterminemajorclimatecharacteristicsofaregion.

Each group is further divided into many fine-grained subcategories, which relate toprecipitationandsummerconditionsversuswinterconditions.Severalmodificationsandclarificationshavebeenaddedandsuggestedsincethelatenineteenthcenturyinordertoimprove and fine-tune the system, and there are multiple suggestions for more fine-graineddifferentiations.

In theUSA, theDepartment ofEnergy’s climate zonemaps are basedonASHRAE9and are more fine-grained, based on county lines. These maps are also used forprescriptivethermalinsulationguidelinesintheenergyconservationcodes.

Understanding thebasicclimatezoneofabuildingsitecanprovidepreliminary inputfor the evaluation of ventilation strategy potentials. They can provide basic seasonalconsiderationsaboutventilationstrategiesandtemperaturedifferences.However,theydonotyettakelocalorregionalwindintoconsideration.

Climate scalewinds aredeterminedbywindpatterns in thenext layerof the climatescale.Manyonlinesourcesareavailabletotrackwindresources:current,forecasted,andrecorded.10Multiplepublicandprivateservicesofferwindmapsformostcountries.Thewind patterns can change significantly with the season as well as with local andmicroclimaticconditions.Inthecurrentageofinternetinformation,manyonlineresourcesdistributeclimateandspecificallywindinformation.11

4.5

Figure4.6

TheclimatemapsofASHRAE(AmericanSocietyforHeating,RefrigerationandAirConditioningEngineers)arebasedonheatingdegreedaysandusedtodetermineprescriptiveinsulationrequirements.

Large-scale topographical featuresaredirectlydetectableon theseclimatezonemaps.Thenorth–southdivideoftheRockyMountainsistheboundarybetweenhumidanddryclimates in the USA; analogously, the Alps in Europe represent the boundary betweentemperate (cool to warm summers) andMediterranean (warm to hot summers) climatezones.

WindasaResourceMultiple sources for wind information exist. Most resource sites address a specificaudience–forexample,thewindturbineindustry–butwindenthusiastssuchassurfersorsport sailors also use theWindfinder.12More information can be found in the resourcesectionattheendofthebook.Windmapsarepublishedonascaleaslargeasthewholeworld13oratcontinentalorregionalscales.

Wind maps for the United States are published by the National Renewable EnergyLaboratory(NREL)andaremainlygearedtowardsuseasresourcemapsforwindenergyproducers.10

4.6

Figure4.7

USwindresourcemapaspublishedbytheNationalRenewableEnergyLaboratory(NREL);darkerbluecolorsindicatehigherwindpowerandvelocityonanannualaverage.

ABriefHistoryofWindNotationsAccording toNova,14windshavebeennotated in a spherical roseof360degrees sinceantiquity,andtheearliestnotationsgobacktoPhilipofMedma(orOpunte),adiscipleofPlato andAristotle,whoapparentlydrewoneof the first diagrammaticnotationsof thewinds, noting their names, directions, and characteristic qualities. Later, Aristotle andThimostenesofRhodosusedthewordThesisAnemon(dispositionofwinds)forasimilargraphicdevice.Currentwindrosesstillusesimilarnotationforeachandeverylocationinamultilayerednotation.Windrosesarebasedonthecompassof360degrees,notingthefour cardinal directions and dividing the sphere into equal parts of quarters and thirds.Vitruviusalreadymentioned24distinctivewindsinthesecondpassageofhis“TreatiseonArchitecture.”15ThecurrentnamewindrosehasbeenusedonlysincetheRenaissance.Acircle indicating the horizon, with concentric rings indicating intensities, and radialdivisionfordirectionistheoriginofthewindrose.Itisstillusedtoday,forexampleintheweathervisualizationtoolClimateConsultantdevelopedbytheUniversityofCaliforniainLosAngeles.16

Figure4.8

AwindroseforChicago,IL,asderivedfromweb-basedClimateConsultantsoftwaretool.

Another important symbol for the meteorological indication of wind was introducedmuch later: the arrow in theweather forecastmaps.According toNova,17 this signifierdatesbacktotheearlydaysoftheRoyalSocietyinEngland.Measurementofairpressureusing a barometer to describe wind dates back to Robert Boyle in 166518 and RobertHooke(1635–1703).Intheirtreatise“MethodforMakingaHistoryoftheWeather”theysummarized the first comprehensive study of weather and introduced the idea to useobservation for forecasting.18 These early forecasting methods already included therecording of atmospheric data, including wind, but also temperature, dew point, cloudcover, andotherdata.TheRoyalSocietyprovideda center forgatheringandcollectingweather data, which led to the first international coordination of meteorologicalobservations and forecasting. Finally, in 1781 (according to Nova), the signature forweather conditions was noted: rain, snow, and storms all were assigned a symbol andnoted in the Ephemerides Societatis Meteorologicae Palatinae.19 After a sequence ofconsecutive maps of weather phenomena and climate observations, Heinrich WilhelmBrandesintroducedthearrowintotheweathermaps,20andthelittlearrowshavepersistedin depictions and predictions of wind ever since 1820. The American scientist EliasLoomis (1811–1889) later introduced the lengthof thearrow to indicate the strengthofwinds when studying hurricanes in the mid-nineteenth century.20 Finally, the EnglishadmiralFrancisBeaufort(1774–1857)developedascalein1806tomeasuretheforceofwindatsea,whichwasadaptedtometeorologyin1873andtothisdaycarrieshisname.

4.7

4.7.1

The Beaufort scale ranges from the light air designated by wind force 1 to hurricanesdesignatedbywindforce12.21

PersonificationofWindsPrior to the scientific understanding of how winds in the Earth’s atmosphere develop,mythologicalfiguresoccupiedtheEarthandrepresentedthewindphenomena.ThewindwasdepictedasGod,thebreathoflife,andNova22statesthat“theredoesnotseemtobeaculturethathasnotbeenprofoundlytouched”bythewind.FortheChinese,itisthe

spiritoftheworld…inJapanesemythology,itfillstheemptinessbetweenskyandearth…fornativeAmericans,itisaspecterthatlivesinthecloudsintheformofawildwhitecolt;thewindoftheHindureligionVayu…isthepersonificationofthecosmic spirit and theword. InancientPersia, thewindwas responsible for cosmicandethicalequilibrium.IntheIslamicworld,itindicatesthefourcompasspoints.

HefinallyquotesSaintFrancisasarepresentativeofearlyChristian,Europeanthought:“Allpraisebeyours,myLord,throughBrothersWindandAir,andfairandstormyalltheweather’smood,bywhichyoucherishallthatyouhavemade.”23

WindNamesandtheirCharactersAlthough wind representations and forecasting have a long established history, adescription of wind as an arrowwith a direction and a strength/velocity indicator wasintroducedonlyinthenineteenthcentury.Windsinantiquitywereassignedpersonalitiesandcharacters.InancientGreece,windsweregodsandhadspecificcharacteristics.Thoseeightwinddeitiesweredepicted in the towerofwinds inAthensandwerecarriedoverintotheancientRomancivilization.TheLatinmetaphorsandnamesofthewindscarriedinto contemporary life in Italy, where the major wind characters in the ancient city ofRome are still based on ancient names. The Levante and the Scirocco determine theenvironmental quality of the inner-city climate of Rome as it relates to the changingpatternsofwindstreamingupordowntheTiberRiverandswirlingaroundthesevenhills.

Homermentioned fourwinds in theOdyssey:Eurus,Notos, Zephyrus, andBoreas.24ThesenamesinGreekrelatedthewindstothedirectionstheycamefrom.Notos (south)came from beyond Egypt, while Boreas came from the Black Sea. Vitruvius thentranslated theGreek names intoLatin, and they appear again in theRenaissance in thearchitecturaltreatiseofScamozzi25andintheToweroftheWindsattheVatican.26

Thesometimesso-called‘dark’middleagesalsohadinterpretersofweatherandnaturalscience,forexampleHildegardofBingen,whowroteABookoftheEarths.27

D’ArcyWentworth Thompson28 provided an interesting analysis of theGreekwindsgoingbacktothewindroseofAristotle.Heclaimedthatthewindroseofantiquitymaynothavebeenequallydividedintoquarters,butintosectionsofthirdsandthushavebeenmoreconnectedtothesolarpathandthemovementofthesuninthevariousseasonsthantothecardinaldirections.

4.7.1.1

Figure4.9

WindrosedepictedbyVincenzoScamozzi25(1548–1616)inL’architetturaUniversale.

AeolusPriortoscientificevidencefortheoriginofweatherphenomena,anemoiandweathergodswerethoughttoliveinstrategicpositionstofacilitatethemostcommonweatherpatterns.InRomanmythology,Aeoluswas themaster god ofwinds. Large stormswere usuallyattributedtomoodsorfightsofgods,asinVergil’sAeneid,whereJuno,“sisterandwifetoJove”calleduponAeolustocallhisstormsinordertosinktheshipsofAeneas:

Seething,thegoddesscametostorminhabited

Aeolia,nativeregionofraginggales,

Foritishere,thatKingAeolusholdsinthrall

Therampantmoaningtempestsshackledimprisoned

Inacolossalcave.Inmuffledfury

Theychafeandrumbleinthemountain’sbowels

WhileAeolussits,scepterinhand,above

onhishighbattlementsoothingandcalming[thewinds].

Werehetofail,theywouldsweepawaylandandsea

Andeventhevaultofheavenitselfintothinair!29

4.7.1.2

4.7.1.3

Figure4.10

TheBirthofVenus(NascitadiVenere)bySandroBotticelli(1485/86),withapersonalizedwindgodblowingather.

AnemoiThe lower Greek and Roman wind gods were named according to their character andcardinaldirections.ThesecharactersarestilldominantintheRomanweatherforecastandthe Italian language. Boreas/Aquilo represented the vicious North, Notus/Auster camefrom the South, Eurus/Vulturnus came from the East, and Zephyr/Favonius were thefavorite westerly winds that brought food. They were brought to everlasting fame byRenaissance painter Sandro Botticelli (1445–1510) in his painting The Birth of VenusbringingflowersandinLaPrimaverabringingraintofertilizethegroundsandplants(intheUffizi,Florence).30

BoreasBoreaswas thenorthernwind that brought coldweather andwinter toRomeand Italy.Between 1578 and 1580 the Bolognese architect Ottaviano Mascherino (1536–1606)constructed theTorre deiVenti31 on top of theVatican library,which contained a largewind roseandananemometer in theceilingby IgnazioDanti (1536–1586)aswell asameridianthatwasusedtoinstallandverifytheGregoriancalendar.OneofthefrescoesbyNicolòCircignani (1517–1596)32 depictsBoreas, representing thenorthwinds,with theinscription“Aquilonepandeturomnemalum,”33indicatingthateverythingbadcamefromtheNorth:badweather,bad temper,andbadhabitsof intrudingalienforces(seeFigure10.4).Inthesixteenthcentury,scientificinvestigationshadalreadyfoundexplanationforthewindphenomenabeyond thegods:“inanAristoteliansenseas the resultofabattlebetween thewarm and the dry exhalations of the earth and their downwardmovement,afterwhichtheycooldownandcomeintocontactwiththehumidairoftheatmosphere.”Windasaresultofdifferentairdensitieswasalsoscientificallydiscussedinthesixteenth

4.7.2

4.7.2.1

4.7.2.2

centuryasnotedbyAlessandroNova.34

OtherMythologicalAiryCharacters

AngelsandSpiritsAngelsareusuallyinvisiblecreaturesoftheskyorthesacredheaven,whohelphumanscomprehendwhenrationalexplanationsfail.35AngelsareconsideredspiritualsymbolsofunexplainablephenomenaandmessengersofGod.Themostcommondepictionofangelsin Christian mythology is the archangel depicted in the Annunciation.37 Angels mostlikelyinheritedsomeofHermes’characteristics.InGreekmythology,Hermeswasthegodofmessengers; later he became theRomanMercuriowith similar attributes.He helpedtravelersatbordercrossings,butalsoheldhishandoverthievesandmerchants.Hermeswasdepictedusuallywithawingedhelmetandassuchwasconsideredafigureofair.ThewingedhelmetmusthavedevelopedintothewingsoftheangelsinChristianmythologyand depictions as in the basilica S.Giovanni in Laterano, Rome, byBorromini (1599–1667).

Figure4.11

SculptedangelwithruffledfeatheredwingsinS.GiovanniinLateranobyFrancescoBorromini(1599–1667),around1646.

ArielWicked and violent demons have found testimony in a particular great work of theElizabethan theater,WilliamShakespeare’sTheTempest,whereAriel, the spirit, sets inmotionthetempeststormasorderedbyProspero,thestrandedDukeofMilan.

Prospero:Hastthou,spirit,

perform’dtopointthetempestthatIbadethee?

4.8

4.9

Ariel:Toeveryarticle.

Iboardedtheking’sship;nowonthebeak,

Nowinthewaist,thedeck,ineverycabin,

Iflam’damazement:sometimeI’ddivide,

Andburninmanyplaces;onthetopmast,

Theyardsandboresprit,wouldIflamedistinctly,

Thenmeetandjoin.Jove’slightnings,theprecursors

O’th’dreadfulthunder-claps,moremomentary

Andsight-outrunningwerenot:thefireandcracks

OfsulphurousroaringthemostmightyNeptune

Seemtobesiege,andmakehisboldwavestremble,

Yea,hisdreadtridentshake.36

CondensationandCloudsHotaircanholdmoreabsolutehumiditythancoldair.Thisrelationshipisexemplifiedinthepsychrometricchart,inwhichtherelativehumiditylevelindicatesthecapacityofairatacertaintemperaturetoholdmoisture(seeFigure2.12).Whenthetemperatureofanairsample drops, for example when it contacts a cold glass surface, the water vaporcondensesoutof theairandcreatessmallairdropletsontheglasssurface.Thelevelofhumidity has a significant impact on human thermal comfort, especially at elevatedtemperatures, as noted in respective thermal comfort standards.37While dry air cannotabsorb solar radiation, the humidity in the air, the small dissolved water droplets, canabsorbsolarradiation.Thatisonereasonwhyhumidaircanwarmupdirectly,whiledryair in arid climates warms up by heat conduction from solid surfaces that have beenwarmedupbysolarradiation.Therefore,astonecangetwarmexposedtosuninwinter,whiletheairremainscold.Humidairinsummerdoesnotcooldownasmuchasdryaridair when nights get fairly cold in arid desert climates. Although the overall content ofhumidity inair isonlyapproximatelyonepercent, thissmall fractionofairhasamajoreffectonclimaticvariations.

ImpactonBuildingsandInteriorSpacesAll major characteristics of climate have a direct influence on the natural ventilationcapacitywithinabuilding:outsidetemperatureanditsdiurnalchanges,relativehumidity,andwind velocity and direction. Solar radiation plays an indirect role as it creates hotspots,whichenableorrestricttemperature-inducedairmovement.

Horizontaltemperaturevariationsintheearth-atmospheresystemgiverisetohorizontalpressure difference systems that result in airmotion (winds). Thermal energy from thesolar energy cycle is converted into the kinetic energy of the wind system.Within the

4.10

kineticsystem,theenergycascadesdowntheladderofatmosphericscalesuntilitreachesthemolecularscaleofsmaller-sizeeddiesandisfinallydissipatedasheatwhenitreturnstothethermalportionof thesolarenergycycle.Thebuildingsitsright in-betweenthesedifferent scales and thus connects small-scale eddies with large-scale weather patterns.Ideally, the building interior makes optimal use of these multi-scale processes. Thebuilding can act as an obstacle to or facilitator of flow and enhances flow around andwithinforvariousoutcomesforinterioroccupantthermalcomfortaswellasforpedestriancomfort outside of the building.How architects can impact these various flow patternswill be discussed in later sections of this book. The urbanmicroclimate and pedestriancomfort isverywell coveredbyErell,Pearlmutter andWilliamson in their2011UrbanMicroclimate.39

WindSystemsLarge-scalewindsystemssuchasjetstreamsandhurricanesarebasedoncontinentalscaletemperaturedifferencesbetweencoldandhotairmasses.

Prevailingwinds are very common climate features and need to be consideredwhendevelopingnatural ventilation strategies.They typically changewith the seasonorwithmajorshifts inweatherpatterns.Themistral intheMediterraneanisastrongwindfromthenorth, crossing the sea into thewest coast of Italy away from the southern coast ofFrance.ThejetstreamintheMidwestof theUSAblowsfromthesouthformostof thesummer,bringingwarmandhumidairfromtheGulfofMexico.Thenorthwesterlywindin thenorthofGermanyblowingfromtheNorthSeacoastusuallybrings rain fromtheAzorestotheshore.

Regional wind systems are based on topographical features and related temperaturedifference based on these changes in topographical height.Themost commonly knownregionalwind systems are sea-land breezes andmountain-valley breezes.38 In addition,there are also urban-rural breezes and forest-grassland breezes, which can significantlyinfluencewinddirectionandvelocityandthusshouldneverbeignored.

Every topographical change has an influence on thewind pattern.Moderate changescreatemoderate shifts in flow pattern and steep topographical changes create eddies oreventurbulence.

Table4.2Localthermalbreezes

Localwindsystems Systemcharacteristics,scaleofspeedandheightofthermallayer

Land-Sea(orlake)

Duringtheday,theseaorlakebreezemovesfromabovethewatertowardsthelandandreversesatnightflowingfromlandtosea/lake.Thedaytimecirculationhasalargerextensionthantheevening/nightcirculation.

Speed:2to5m/s(395to985f/m)

Heightofthethermallayer:1to2km(0.62to1.25miles)

Mountain-Valley

Valleysproducetheirownlocalwindsystems;horizontaltemperatureandpressuredifferencescauselocalbreezes.Byday,theairabovetheslopewarmsandcoolairsinksintothevalleycenter.

Speedofupliftalongslope:2to4m/s(395to787f/m)

Heightofthethermallayer:20to40m(65.6to131ft)

Urban-RuralWithweakregionalwinds,acitycangenerate‘countrybreezes’.Verticalinstabilityaidsthethree-dimensionalcirculation.Heatislandintensityisrelatedtothesizeofthecity.

4.11

Forest-Grassland Thermalcontrastbetweencoolsub-canopyforestinteriorbydayandunshadedsurroundingfieldsorgrassland.

Source:T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),pp.167–170,290

Figure4.12

Flowpatternaroundtopographicelementsandfeatures.

HowArchitectsCanInfluencetheImpactofWindontheBuildingVentilationPath

Inthecontextofatmosphericairflow,everybuildingcanbeconsideredanobstacletothelocalandregionalscaleof thewindsystem.Theairhas tomovearoundtheobstacleorthroughtheobstacle,andtheshapeofthebuildingaswellasitsorientationandpositioninfluences the flow pattern around and through the building. The building builds upresistanceagainsttheflow,andthisresistanceresultsinthenecessarypressuredifferentialtoforcetheflowofairthroughabuildingfollowingthedesignedflowpath.

Buildingscanalsobe sourcesof thermalenergy.Denseurbanmassescanchange thewind patterns and temperature scales of the open landscape around them by creatingdistinct urban climates. Large areas of urban agglomeration influence largerclimate/weather patterns. The most commonly known scenario of building-inducedweatheristheurbanheatisland(UHI)effect,whereasignificantdifferenceintemperaturebetween theurbanareaand thesurrounding ruralareacanbeexperiencedundercertainweather conditions.39 Developing pressure differentials in the urban context is morechallenging than in the open landscape, as the air flow patternswithin the urban street

4.12

4.12.1

4.12.2

4.12.3

1.

2.

3.

4.

5.

6.

7.

8.

4.12.4

canyonarelesspredictableandlessconstant(seeSection7.3).

InformationforArchitectstoStarttheDesignProcessInordertoutilizewindasaventilationdriver,thebuildingshapeneedstobedesignedtobuildupresistanceagainsttheflow,sothatapressuredifferentialcanbedevelopedacrossthedesigned internal flowpath.Openingsneed tobepositionedas inletsandoutletsoneithersideoftheflowpathbetweenhigh-pressurezonesandnegative/low-pressurezonesontheleewardside.Ifstackventilationisconsidered,theheightofthestackneedstobedevelopedinproportiontothetemperaturedifferencewithintheoutsideboundarylayer.

Macro-ScaleInformationUnderstandingprevailingwindpatterns(windrose)

RegionalScaleInformationUnderstandinganddeterminingterrain/topography/bodiesofwater

Micro-ScaleInformationUnderstandinganddetermining:

Sitetopographyandtrees,etc.

Heatislandsaroundthebuilding

‘Cool’landscapingaroundthebuilding

Shadingaroundthebuilding

Summer-winterdistinction/seasonalplanting

Groundtemperatureduetomateriality

Humiditycontentinair,soil,andwind

Positioningthebuildinginthestreamofthewind

FinalScale:TheBuildingScalePositioningtheaperturesinthestreamofthewind(orcreatingthepressuredifferencebypositioningtheopenings).

Amajorchallengeofallofthesescalesofsystemsinteractingwiththebuildingistheirdynamicandtransientstate.

Figure4.13

Urbanflowpatternaroundbuildings.

Figure4.14

Flowpatternaroundandthroughbuildings.

4.13

1

2

3

4

5

6

7

8

Figure4.15

Climatezonesfornaturalventilation:mapofmeanclimaticcoolingpotentialinKWhpernightbasedonMeteonormdataforEurope.

ClimatesforNaturalVentilationMappingprojectsinEurope40andtheUSA41havebeenundertakentodevelopindicatorsfor locationswith good climate context for implementation of natural ventilation. Theywill aid architects, engineers, and designers in determining the maximal potential fornatural ventilation given the climate conditions of their site.As an example, the abovemaphighlightsthepotentialfornighttimeventilationinEurope.42

NotesT.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),p.27.

Ibid.,p.57,Table2.2.

HelmutErichLandsberg,TheUrbanClimate(NewYork:AcademicPress,1981).

EvyatarErell,DavidPearlmutter,andT.J.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London;Washington,D.C.:Earthscan,2011).

FrancisSantamouris,M.Allard,andAlvarezServando,NaturalVentilationinBuildings:ADesignHandbook(London:James&James,1998).

Istworld,“NaturalVentilationinUrbanAreas–PotentialAssessmentandOptimalFaçadeDesign(URBVENT),”http://www.ist-world.org/ProjectDetails.aspx?ProjectId=857bad8bd0a3434f983d9faf1c6d2d86&SourceDatabaseId=9cd97ac2e51045e39c2ad6b86dce1ac2(accessed5/20/2014).

T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),p.7.

WorldMapsofKöppen-GeigerClimateClassification,http://koeppen-geiger.vu-wien.ac.at/(accessed5/20/2014).

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

ASHRAE,“ClimateDataCenter,”https://www.ashrae.org/resources–publications/bookstore/climate-data-center(accessed5/20/2014).

NationalRenewableEnergyLaboratory,WindEnergyResourceAtlasoftheUnitedStates,http://rredc.nrel.gov/wind/pubs/atlas/(accessed5/9/2014).

Intellicast,“CurrentWinds,”http://www.intellicast.com/Global/Wind/Current.aspx?region=europ(accessed5/8/2014).

Windfinder,http://www.windfinder.com(accessed5/8/2014).

Seehttp://earth.nullschool.net/#current/wind/surface/level/orthographic=-2.34,48.43,280(accessed5/8/2014).

AlessandroNova,TheBookoftheWind:TheRepresentationoftheInvisible(Montreal:Ithaca,2011).

Vitruvius,TheTenBooksonArchitecture(DeArchitectura),bookI,translationMorisHickyMorgan(NewYork:DoverPublications,1960),p.B.

“EnergyDesignTools,”http://www.energy-design-tools.aud.ucla.edu/(accessed5/8/2014).

Nova,TheBookoftheWind:TheRepresentationoftheInvisible(Montreal:Ithaca,2011).

Ibid.,p.186.

Ibid.,p.187.

Ibid.,p.191.

TheBeaufortWindScale,NOAA,http://www.spc.noaa.gov/faq/tornado/beaufort.html(accessed5/8/2014).

Nova,TheBookoftheWind:TheRepresentationoftheInvisible(Montreal:Ithaca,2011),p.197.

Ibid.

Ibid.

VincenzoScamozzi,L’ideaDellaArchitetturaUniversale,2vols.(Ridgewood,NJ:GreggPress,1964).

Seehttp://www.archiviosegretovaticano.va/en/archivio/ambienti/torre-dei-venti/(accessed5/8/2014).

See“TheBookofEarths:St.Hildegard’sUniverse,”http://www.sacred-texts.com/earth/boe/boe29.htm.

D’ArcyWentworthThompson,“TheGreekWinds,”ClassicalReview,32(3/4),1918,pp.49–56.

Vergil,TheAeneid(NewYork:SignetClassicsPenguin,2002),p.8.

Seehttp://www.polomuseale.firenze.it/(accessed5/8/2014).

Seehttp://asv.vatican.va/it/arch/torre.htm(accessed3/5/2011).

Seehttp://asv.vatican.va/en/visit/VR_affr/VR.htm(accessed3/5/2011).

Seehttp://asv.vatican.va/en/visit/VR_affr/s_mer.htm(accessed3/5/2011).

Nova,TheBookoftheWind:TheRepresentationoftheInvisible(Montreal:Ithaca,2011).

MichelSerres,Angels:AModernMyth(Paris;NewYork:Flammarion,1993).

WilliamShakespeare,TheTempest(London;NewYork:Arden,1954).

ANSI/ASHRAEStandard55–2013.

T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),pp.158–189.

EvyatarErell,DavidPearlmutter,andT.J.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings(London;Washington,D.C.:Earthscan,2011),Chapter3.

IvanOropeza-PerezandPoulAlbergØstergaard,“PotentialofNaturalVentilationinTemperateCountries:ACaseStudyofDenmark,”AppliedEnergy,114(0),2014.

J.W.AxleyandS.J.Emmerich,“AMethodtoAssesstheSuitabilityofaClimateforNaturalVentilationofCommercialBuildings,”in:ProceedingsofIndoorAir2002,Vol.2(Monterey,California),pp.854–859.

N.Artmann,H.Manz,andP.Heiselberg,“ClimaticPotentialforPassiveCoolingofBuildingsbyNight-TimeVentilationinEurope,”AppliedEnergy,84(2),2007.

5.1

Chapter5

InheritedSpatialArchetypesforNaturalVentilationArchitectural theory, history, and design have always asked about the origin of form,shape,andspace.Thischapterwill thereforeexplore thespatialarchetypescreatedovertime based on “generative concepts or mind models,” a term coined by Lewcock.1Presentedhere isagenealogyofarchetypesforspacescapableofmovingair.Therearemultipleways of looking at traditions in architecture.BernardRudofsky2 promoted theapproach that the vernacular is the other, beyond the artistic creative architect, thearchitecture without architects. Another approach investigates tradition as part of aninclusive architectural development and as archetypal base for architectural thinking ingeneral,asdiscussedbyAldoRossi inTheArchitectureof theCity.3This approachhasbeentracedtothewritingsofCarlG.JungonarchetypesinManandHisSymbols4andtoGaston Bachelard in The Poetics of Space5 and Air and Dreams: An Essay on theImaginationofMovement.6

These traditions were practiced prior to industrialization and prior to mechanicallyenhancedenvironmentalcontrols.Currently,theyenjoyarevivalandreinvestigationasasourceforclimate-responsivedesign,withnewpublicationsappearingandwithincreasedresearch interest addressing traditional building and construction types. This renewedinterestparallelstheattentionofarchitecturalhistoriographytotheglobalversusapurelyWesternapproachtoarchitecture.Forexample,inVernacularArchitectureintheTwenty-First Century Lewcock7 discusses “generative concepts” and analyzes vernaculararchitecture as mind models for architectural archetypes. He identifies the cave, thecovered and open courtyard, and the hearth. Further following Gottfried Semper,8 heidentifiestheplinthasameansagainstdampness,theroofagainstrain,andthescreenorwallagainstthewind.GastonBachelard’sThePoeticsofSpace9discussesarchetypesasbasis formemory. Fire and fire exhaust became integrated spatial components of thesearchetypalformations.

SharedIdeasasArchetypesEnvironmental characteristics have significant impact on the development of spatiallanguage, symbols, and icons, as culture is made manifest through atmospheric andclimaticproperties,and inscribed intoarchitectural space.Humidity,dryness,heat,cold,andlightintensityhavelefttheirmarkinthebuiltform,rooftype,surfaces,andopeningsofbuildings.Buildingsarepositionedinrelationtothedirectionofthesun,theprevailingwinds, and other influences. The need for vision, light, heating, and cooling is alwaysbased on the interrelation between the exterior climate and internal needs. Addressingthese challenges with limited material resources has led to refined archetypes across

5.2

variouscultures,climatezones,geographies,andcontinents.

In the past, anecdotal information based on travel reports10 often served as the onlyaccount of traditional architecture in distant locations. Both vernacular and indigenousarchitecture can be regarded as only one resource for the development of spatialtypological strategies for passive cooling and natural ventilation. However, recentlyresearch teams have picked up the challenge to reproduce the spatial environmentalstrategiesoftraditionalarchitecturethroughmeasurementsandsimulatedmodelsandhavedevelopedscientificevidenceoftheiractualoperations.

Thesestudieshaverevealedthattheadaptationofvernacularpassivenaturalventilationstrategies into contemporary architecture in current societies is often considered oldfashioned or obsolete, which poses a hurdle to a widespread implementation of thesestrategies. IsaacA.Meir and SusanC.Roaf have reported on this issue relating to theMiddleEast.11

TheImportanceofInheritedVernacularStrategiesforSustainableDesign

Recently, vernacular architecture has enjoyed new attention as an architectural conceptthatisbasedonthelocalclimateandterraincondition,nurturingtheneedsanddemandsof the user. Multiple recent research projects have pointed out that vernacular orindigenous architecture’s approach to passive design strategies is often highlighted as aprecedent for environmentally conscious architecture without scientifically quantifiedproof and without actual understanding of former comfort expectations and buildingperformance.Thiscanobviouslyleadtoseveremisunderstandings,ifatraditionalstrategyis evaluated against contemporary comfort and convenience expectations. In addition,traditional building strategies may require unusual control strategies, based on verydifferentparametersandagaindifferentcomfortacceptancelevels.12

Itisalsoimportanttonotethattraditionalbuildingsmayhaveincorporatedmorethanone strategy to respond to comfort needs of occupants and are not per se meetingcontemporaryuserexpectations.Thus, theexamplesof traditionalarchitecturepresentedherehavebeenselectedbasedonavailableliteratureandpersonalobservationandstudies,because theyhaveprovidedpassivecoolingpotential in thepastandmightstillprovidecooling today. However, caution is necessary, because an adaption of these strategiesmightnotbedirectlypossibleforcontemporaryenergy-efficientprojectsduetochangesinoccupancypatterns,lifestyle,andunderstandingofconvenienceaswellascomfort.13

Bernard Rudofsky14 directed attention to “architecture without architects” at a timewhenhighmodernarchitecturewasenteringatimeofcrisis.Hefindsmanywordsforthearchitecture hewould like to reveal: “vernacular, anonymous, spontaneous, indigenous,rural…”

There is much to learn from architecture before it became an expert’s art. Theuntutoredbuilders in spaceand time…demonstrate anadmirable talent for fitting

5.3

theirbuildingsintothenaturalsurroundings.Insteadoftryingto‘conquer’nature,aswedo,theywelcomevagariesofclimateandthechallengeoftopography.

Figure5.1

ReynerBanhamdescribestwotribesinhisArchitectureoftheWell-TemperedEnvironment,thosewhowouldusethefoundwoodtomakeafireandthosewhowouldbuildashelter.

Contrary to Rudofsky’s idea of an anonymous and spontaneousway of building is theinterpretationbyRonaldLewcockofvernaculararchitectureasanarchetype,andthisalsoneedstobeconsidered.

Inhisimportanthistoryofarchitectureandthedevelopmentofenvironmentalcontrols,ReynerBanham15introducesthefableoftwotribesencounteringastackofwood.Basedon their traditions, one tribewillmakea fire and thus staywarm,butwill need to findmorewoodthenextday,whiletheothertribewillbuildasheltertobeprotectedfromthewind.

Umberto Eco16 considers spatial types as a syntactic code within the variety ofarchitectural codes. The other codes he reveals are technical codes that have nocommunicativecontent(thecolumnjuststandsup)andsemanticcodes(theornamenthasa religious meaning). The syntax, the spatial type, is thus the conceptual logic whichrelatesthetechnicalcodestothecommunicativesemanticcontentofanarchitecturalformorelement.

SpaceTypes:Cave,Courtyard,Chimney,Passage/Arcade/Loggia,Basket

Ventilation in traditional architecture has often been a major provider of form, andfollowing these theories of archetypal generic concepts, five different inherited spatialconceptshavebeenidentifiedhere.

WhilethethreespacetypesintroducedinChapter1(bolted, incorporated,sliding)arebased on contemporary compositional principles, spaces can also be classifiedtypologically with respect to their relationship to air movement. Here we distinguishbetween caves, courtyards, passages/loggia, baskets and chimneys/wind catchers. Theycanbecombinedtoformcontemporaryspacetypes(Chapter8).

5.3.1

5.3.1.1

Figure5.2

Thesemajorinheritedspatialtypologiesareanalyzedwithrespecttopromotionofairmovement:caves,courtyards,passage/loggia,baskets,windcatchersandchimneys(lefttoright).

UtilizingTemperature-InducedPressureDifferentials:CavesThe cave is a recognized archetypal spatial configuration and has a significant place inGastonBachelard’sThePoeticsofSpaceastheultimatehouseandshelterandanimageofprotectedintimacy.

Oneoftheprimalwaystoshelterfromtheelementsistooccupyanexistingcaveortodigintothegroundtocreateacaveforshelter.Thecaveundergroundiswarmerinwinterandcoolerinsummerbecauseofthegreatthermalmassandtimelagofheattransfer.Thefirstmeans to utilize the force of airmovement for ventilationmaywell havebeen thechannelingofairthroughcavesfollowingpressuredifferentialsdevelopedbythethermalmass of the cavewalls, the difference to the outside temperature, and the height of thecave.

Usingcavesforcoolingorheatingcomfortandtochannelwindbythestackeffect ismost likely one of the oldest environmental control strategies. Cave dwellings are stillfairly common in hot and dry regions of the world, for example in southern Spain,southern Italy, southeastern Anatolia, Kapadokia of Turkey, France, and China. Somehistoricbuildingtypes,suchastheHarranHouses17 insoutheasternAnatolia,18madeofsquareroomswithcorbelleddomedroofstructures,mayhavefollowedacavedwelling.Cavedwellingstakeadvantageofthereasonablystabletemperatureofrocksorsoil intowhichthecaveiscarved.Afewexamplesthroughthecenturiesandacrosscontinentsarediscussedhere.

TheKivaoftheAnasaziPeopleInadditiontousingthegroundasaheatsink,somecavedwellershavedevelopedquitesophisticatedventilationmechanismstochannelairintoandthroughthecaves.Thenowunoccupied Anasazi Pueblos in southern Colorado most likely used ventilation shaftsbehind the fire place to provide space ventilation as well as to supply air for thecombustionofthefire.TheAnasazikiva,mostlikelyceremonialspaces,wereventilatedbyaseparatewind-catchingchimneythatwasconnectedtotheinhabitablecaveandalsoprovidedheatingtothekivacave.19

5.3.1.2

Figure5.3

Anasazicavedwellingsdemonstratedsophisticatedventilationstrategiesastheywereidentifiedtoutilizewindcatchingtechnologies.

AdilSharag-EldinandJamesDaltonfromKentState19 examinedapotential scenarioforanAnasazikiva.Their teammeasuredareconstructedkivainOverton,Nevada, thatdidnothaveaventilationshaftandthenmodeledacompletekivawithventilationshaftusingenergy-modelingsoftware.Theresultsindicatethattheround,below-groundspaces,whose function is still not completely understood by archaeologists,may have becomerather uncomfortable during heating and needed the ventilation chamber as ameans todrivethecoolingprocess.Comfortwasassessedbasedoncurrentcomfortunderstanding.However,thecomfortexpectations1,000yearsago,whenthekivaswereoccupied,mighthavebeenverydifferent.TheadjustmentsmadetothespatialcompositionwerebasedonarecordbyanthropologistWalterFewkesdatingbackto1908.20Thisarchaeologistwaspuzzledbyairshafts thatshowednosignsofsmoke,andcalled themchimney-like,butnotchimneys.Theshaftswerealsotoosmalltobeusedasentrances.Thus,thesimulationconducted by the Kent State team19 indeed provided a potential interpretation of thespatial layout. If that chimney-like shaftwas actually used to introduce fresh air at theleveloftheoccupantsabovethecavefloor,thespatialsystemmightactuallymakesenseasaventilationshaft.

TheCorbelledDomesoftheHarranHousesinSoutheastAnatolia,Turkey

Domedstructuresareverycommoninregionsinwhichverylittleconstructiontimberwasavailable for roof structures, such as in the high plateau desert regions of upperMesopotamia and the high desert plateau of central Iran. Instead of flat roof structuresconstructed of timber beams, these mostly residential structures of northern Syria andsoutheasternTurkeyhaveroofstructuresthatarenotvaulteddomes,butcorbelleddomes.Theyareconstructedofspiralinglayersofmudbrickswithacentralopeningatthetopoftherooftoexhaustsmoke,quitesimilartothetipitentinNorthAmerica.Thehousesarewellknown for theirpassive cooling strategies basedon their spatial geometries.ThesestrategiesareemployedintraditionalTurkishHarranhouses,locatedintheHarrandistrictof S¸anlıurfa province in the southeast part of Turkey. The houses date back multiplecenturies,andtheoriginofthetypologyisunclear.Domedandconicalroofsarecommon

and unique to traditional architecture in the Middle East as well as throughout theMediterraneanBasin.Theyemploycomplexconditioningandenergy-efficiencystrategiesforextremelyhot-aridclimateswithhighsolarinsolationsof~7kWh/m2×day.Conicalroofed Harran houses are rooted in the regional history and showcase significant low-energy adaptation to the climatic conditions. There is general agreement that Harranhousesarewarmerinwinterandcoolerinsummerthancontemporarymodernstructuresandaretypicallymoreenergyefficientthanflatroofedbuildings.

Multiple research teams investigated the relationship between internal climaticconditionsandtheroofgeometryaswellastherelationshipbetweentheexternalclimaticconditions and the roof geometry. However, few studies examine and tie internal andexternalconditionssimultaneouslytotherooftypeandspatialcomposition.

The characterizationof the interesting internal and external thermal conditions of theHarran houses has fascinated contemporary researchers. The impact of their spatialcomposition on energy consumption and their thermal performance is still underinvestigation.21

Figure5.4

TheHarranhousesinsoutheasternTurkeynearS¸anlıurfa.Multipleopeningsinthemudbrickwallsandthetopofthecorbelledroofchannelairinhomes,whichresemblecool‘caves.’

Pearlmutter22 compared the solar exposure of a semi-cylindrical and a flat roofexperimentally and found that thevaulted roofgeometry receives an increase inoverallsolar exposure ranging from10 percent in summer to 30 percent inwinter. Faghih and

Bahadori23 estimated the solar radiation on several domed roofs and determined thatdomedroofsreceivemoresolarradiationthantheflatroofsonanequalbasearea.Tangetal.24 investigated the heat flux through curved (domed and vaulted) roofs in an air-conditioned building compared to that in flat roofed structures to determine the energyefficiencyofbuildingtypeswithregardtocoolingload.Theresultsshowthattheheatfluxthrough curved roofs is always higher than through flat roofs when airconditioning isemployed.Tangetal.25investigatedtheeffectofvaultangleonsolarheatgaintoimprovecurved roof performance and found that a roof with a half dome angle of 90 degreesabsorbedapproximately30percentmore total radiationdaily thana flat roofduring thesummermonths.Gomesetal.26alsostudiedsolarincidencebasedonsolaraltitudeoverahemisphericalvaultroofandcomparedthesefindingstothoseforahorizontalroof.Theydeterminedthatwhenthesun’spositionnearsthezenith,thesummersolarperformanceofa dome is better than that of a flat roof of equivalent base area for northern latitudes.These investigations indicate that incident solar radiation cannot be the cause of theperceived superiority of a domed roof compared to a flat roof. Therefore, the internalthermal conditions related to heat flux and fluid dynamics (stratified air movement aspassive cooling strategy) are currently also evaluated in order to calculate, model, andpredicttheactualperformanceofvaultedanddomedroofs.27

ItisinterestingtonotethattheHarranHousesarecomposedofacellstructureformingacompoundthatusuallyconsistsofavarietyofcellsonafairlysmallfootprintofaboutfivebyfivemeters,whereeachcellistoppedbyitsownindividualcorbelleddomedroof.Thecorbelleddomesaresituatedon topof thesquarebase,which isaboutashighasaperson. Air is channeled into the space through small paired ventilation openings andwarmexhaustisexpelledthroughthetop.Thethermalmassofthestonesaswellasthegeometryoftheroofapparentlyplayamajorpartinthisspatialventilationstrategy.

The origin of these collective cell structures may be manifold and has yet to bedetermined.Mileto andVegas28 attribute the spread-out cell structure toBedouin tents.Thecellstructuresallowforawidevarietyofcombinations,rangingfromsingle-tomulti-dome structures that congregate around two or three sides of a courtyard, with theremaining side closed off by walls. In most cases, many of the daily functions areconductedoutside.

Thecompoundsareoftenorientedfromnorthtosouth,withthemaincourtyardfacingsouthtobesituatedwellwiththesolarradiation(highoverheadinsummerandlowerinwinter).

MiletoandVegas28presentacomprehensivemorphologicalstudybasedongeometry,scale, and complexity. Similarity to the cave archetype is seen in the lack of access tolight,with openings for ventilation air flow only, and the reliance on thermalmass fortemperaturemediation.

Themajor climatic benefit of the dome, beside the thermalmass and the ventilationeffect,istheangleatwhichthesolarradiationimpactsthesurfaceofthedome.Althoughthesurfaceofthedomeis largerthanthesurfaceofahorizontalroof, thesteepangleat

5.3.1.3

whichtheradiationhitsthesurfaceresultsinlowerheatconductionintothespace,whichbenefits the cooling effect of the thermal stratification. This benefit is also positive atnight,whenalargersurfacecanreradiatetheheatbackoutintotheclearnightsky.

Figure5.5

CorbelledroofsareaveryspecifictechnologyutilizedmainlyintheMiddleEastinsoutheastTurkey,Syria,andIranandshowavarietyofmorphologicaldiversitybasedongeometry,scale,andcomplexity.

TheAeolianVillasinCostozza,VenetoThermalmassplayedanimportantpartintheancientcitiesofRome,Vicenza,andNaples,andthetimelagofthermalconductionfacilitatesnotonlycomplexandelaboratecooling

strategies, but also air exchanges and ventilation in summer. It can be utilized to pulloutdoor air through a cool basement, such as in theVillaRotonda,VillaEmo, orVillaPoiana,byAndreaPalladio.ThephysicsofairhasbeenevenmoreelaboratelyexploitedinthecavesystemoftheVilladaSchiobuiltbyFrancescoTrentoinCostozzaduringthesixteenthcentury.Herethevillasareconnectedtocavesinthemountainbehindthegardenwherethecoldairofthecaves‘pushes’thewarmairoutoftheinhabitedspacesthroughanelaboratelatticeworkinthefloor.

Here, a very distinct, cave-related ventilation strategywas employed, where cold airwaschanneledintoresidentialandrepresentationalvillaspaces(allofwhichformedaringaroundalarge,central,fairlydimlylitopenhall)fromadjacent‘caves’throughso-called‘ventiducts,’whichwereprominentlymentionedbyAndreaPalladio (1508–1580) inhisfour books on architecture.29 Like many Palladian villas, the Villa da Schio uses theconstanttemperatureinabasementorcavetocoolthebuilding’sinterior.

Usedearlierasquarries,thesecaveswerepositionedinsidetheBericihillsbehindandabovethevillas,andthusconnectingthecavetothewarmerairoftheinteriorofthevillaled to the development of a pressure differential and caused the air tomove.Here, thegroundperformsasawindcatcher,orratheracatcherofcoolingenergy.

Figure5.6

Palladio’sVillaslikeVillaEmoshownhere,designedbyAndreaPalladioin1559,utilizesimilarventilationtechnologiesconnectingthelivingspaceswiththecoolairofthebasements.

Figure5.7

TheAeolianVillasinCostozzaVenetoareventilatedandcooledthroughconnectionwithcoolcaveairinsidetheBericiHills.

Figure5.8

Ventiductsdirectthecoolairfromthehillcavesdirectlyintothebasementofthevillafromwheretheairrisesupintothelivingquarters.

AEOLUSHICCLAUSOVENTORUMCARCEREREGNATAEOLIA(“AeolusrulesoverAeoliabywayofthisprisonofwinds”)30

These lines referring to Greek mythology are inscribed visibly within theGrotta andundoubtedly refer to the use of the cool air, with its constant temperature, which waschanneled from thequarry into theupper rooms toprovideair-conditioning.Thegrillesthroughwhichtheairflowedarestillvisibleinthemainroom.Outsidethevillino,ontheroof,standsafigureofAtlas,bowedby thestrainofholdingup theceilingof thegreatcave above him. According to the descriptions left by historical sources, this AtlasprobablyformedpartoftheoriginalsculpturaldecoroftheinterioroftheGrotta.30

Theyearningforsweetcoolrelief,intheblazingdogdaysofsummerintheVeneto,inspiredashrewdseventeenth-centuryabbot tohavepartofhisvilladideliziadugout of the rock of a hill. The better to complete the illusion, he had the wallsdecoratedwithwoodsandruinsandstatuesofairydivinities.30

Barbara Kenda’s compilation of essays31 from a symposium in the same Veneto villasprovides deep insight into pneumatology, a nearly forgotten concept in Renaissancearchitecture, which grounded humanwell-being in air and spiritual breath. This theoryprovidedthebackgroundofRenaissancevillaconcepts,asthepneumawasthevitalspirit,whichwas translated in the heart from the air breathed in through the lungs. Thus theRenaissance architects saw a direct relationship between air, ventilation, and a healthyenvironment.32

Inorderforthecoolingsystemtooperatecorrectly,thecavewithitscoldairmustbelocatedabovethevillaandthetemperatureoutsidehastobehigherthaninthecavestopushthecoldairdownintothebuilding.Windandtheunderstandingofphysicswereanintegralpartof thedevelopmentofcomfortablearchitectureandprominentlyfeaturedintreatisesbyPalladio,29Alberti,33andScamozzi.34

Wind channeling devices and orifices became very common in Renaissance andBaroquearchitecture, as seen inFigure5.10 in the openings ofBorromini’s S.Carlino,whichconnectthecryptatotheoutsideairandcreatelightandairentrances.Theywereutilizedforpleasureandcomfortpurposes.

Figure5.9

TheventilationopeninginthefloorofVillaTrentoaCostozzashowselaboratelatticework.

5.3.2

Figure5.10

VentilationopeninginthecryptaofBorromini’sS.CarloalleQuattroFontane(1638–1641).

Figure5.11

TheNordiccourtyard,recallingtheCarelianfarmstead,hasamuchlargerwidth-to-heightrelationshipandletsinsolarradiationwhileprotectingfromharshwinds,likehereinAlvarAalto’sExperimentalHouseinMuuratsalo(1952).

SimultaneouslyUtilizingTemperature-andWind-InducedPressureDifferentials:Courtyard

According toGottfried Semper,35 the archetype of spatial formation is the hearth. Thehearthisthecentralfocusofhisarchetypaldwelling.Itcreatesthebasisforthetwobasiccourtyardtypologies,themostlycoveredcourtyardasintheRomanatrium,andtheopencourtyardasderived fromtheHellenisticGreekperistyle.Bothwerecreatedaround thehearthtoexhaustthesmokeofthefireandtodeliverventilationandcombustionairtothehearth and surrounding living quarters. The courtyard is a building typology found inmanyclimatezones,bothhotandcold,asitcanaddressmultipleclimaticeffects.Botharestill verycommonspace types today,both inurbanand in rural contexts.AlvarAalto’sexperimentalhouseinMuuratsalo,Finland,designedandbuiltwithElissaAaltoin1952,focusesonanoutdoorcourtyardwithacentralfirepit.

5.3.2.1 CourtyardasClimateDevice36

Thetypologicalcourtyarddiscussionrelatesdirectlytobuildingclimateresearchprojectsthat investigated the tectonic importance of the courtyard for the internal climate.Courtyardsarealreadyknownin therespective literatureas implying“ingeniousnaturalcoolingstrategies.”37 VittorioGregotti states, for example, that “the enclosure not onlyestablishesaspecificrelationshipwithaspecificplacebutisaprinciplebywhichahumangroup states its very relationshipwith nature and the cosmos.”38 He also discusses thequestion whether the courtyard house is a universal archetype. However, there areopposing opinions about the environmental properties of courtyards. The essay“Courtyards:ABioclimaticForm?”37byRaydanetal. is important in thisdiscussion. ItcomparesthecourtyardhousetypologyinScandinaviaandtheArabicworldwithrespecttotheirclimaticperformance,takingthedifferenceincourtyardproportionintoaccount.This climatic study relies on research done by Mänty,39 who analyzed inheritedarchitecture throughout Sweden, Norway, and Switzerland and praised the use ofcourtyardsfortheirabilitytocreate“pocketsofsolargain,”39thusbalancingtheharshnessofcoldernorthernclimates.

Raydan,Ratti,andSteemers’40essaytriestoanswerthequestionwhetherthecourtyardisasunprotectororasuncollectorbycomparingitwithisolatedlow-andhigh-risebox-shaped blocks. They calculated a number of well-established environmental variables,takingtheparametersofthehot-aridclimateandthecoldScandinaviannorthernclimateintoaccount,whileabstractingthespatialparametersasthereisno“universallyoptimumgeometry.”41 To examine the impact of geometry, the analysis addressed the followingparameters:surface-to-volumeratio,shadowdensity,daylightdistribution,andskyview.Neither air flow nor themateriality or openingswere considered in the analysis. Theyconcludedthatthecourtyardimpliesa“coolisland”andthat“theclimaticadvantagesofthecourtyardformareapparent.”42Althoughincolderclimatestheimpactofthetypologyisnotasapparentbythetestedparameters,itisstilldetectable.

Thepotentialtoimprovetheenvironmentalperformancebyadoptingcourtformsincoldclimatesexists,althoughthisislargelydeterminedbyalowerHeighttoWidthratio than inhot-aridregions,which isnotsurprisingas the latitudeofScandinaviaimplies also a different sun altitude, therefore different proportions are commonsense.

Consideringnighttimecoolingbasedon spatial typology,43 theycome to theconclusionthat “the courtyard becomes a thermal sink that provides coolness to the surroundingrooms with less humidity and a suitable place for tropical plants to grow, creating apleasantambience”(seeSäynätsalobyAlvarAaltoinFigures1.25–1.30inChapter1).44

Theproportions in relationship to the prevailingwind and the generated air flow areimportant because the solar gain can be more beneficial when the wind is blocked.Therefore,theenclosedopenspaceexposedtotheexteriorregionalclimaticforceshastobe proportioned right in order to produce a microclimate favorable for the in-betweenspace.Ithastobeabletofiltertheclimaticconditionsandtoreducetheirharshimpacton

5.3.2.2

the interior climate. The key here is that the change of air flow through spatialcompositionworksinfavorofclimaticinteriorproperties.Amorerefinedstudyoftheairflowpatterns in relationshipwith theprevailingwindswouldbenecessary tounveil thesun-protecting quality of the northern courtyard for cool climates. The solar geometryanalysisofAalto’sSäynätsaloprovidesverificationofthetheoryraisedinMänty’sbook39onthevalueofthenortherncourtyard(seeChapter1).Hestatedthatthecourtyardactsasanextensionandelongationofthewarmoutdoorseasonintotheintermediateautumnandspring seasons.RalphErskine andBorisCuljat also point this out in their essayon thequalityandvalueofoutdooropenpublicspacesincoolerclimates.45

Consideringthelimitationsthattheclimateposesandtheundisputableimportanceofoutdoor activity and man’s relationship to the natural environment, it becomesnecessarytoexamineandunderstandthetwodifferenttypesofsocialspacethatexistintheurbansetting:theoutdoorandtheindoor.Theoutdoorspatialtypechosenhereis ‘the courtyard’, an urban element with a history as long as the history ofurbanizationinSweden.

Afterananalysisoftherelationshipofsocialspace,activities,climate,andthecourtyardtype,ErskineandCuljatconclude:“Theconclusionmustbe,thattheoutdoorsocialspacehastobelocated,designedandequippedtoextendtheoutdoorseason.”45Andtheyalsorefertothevernacularforreference:

ScandinavianFarmbuildingsusuallygroupsmall-roomedbuildingsaroundacentralcourtyardwithanopenfireplaceinthecentraldwellingspace,whichradiateswarmthtothesurroundinglivingspaces.Thecourtyardenclosureactsasadevicecreatingafavourable mirco-climate protected from exterior winds. For example in Finland,peopleandanimalslivetogetheronasidebysidebasisandinCareliaanimalsbelowandpeopleabovetherebybenefitingfromthereleaseofheat.

Theyconclude,“Wemustlearnnotonlytoacceptseasonalchangebutalsotoappreciateitsfundamentalbeauty.”46

TheCourtyardHouseinChinaInChina,courtyardhousingalsohasalong-standing,inheritedtradition;however,inthelatetwentiethandearlytwenty-firstcenturiesitsexistencehasbeenthreatened.Similartotrends in the Western world, contemporary approaches to courtyard dwellings haveemergedwithinhistoricalcities,forexampleinSuzhou.Basedonthephilosophyofyinandyangandfengshui,livingspacesareplacedaroundtheChinesecourtyard,whichisrather an agglomeration of compounds than a court carved out of a solid volume.Strategicallyplacedopeningssupporttheenvironmentalcontrolstrategies.DoniaZhang47goesintogreatdetailanalyzingthehistoricandcontemporarycourtyardhousetypologyinChina. She discovered a large array of compositional variation in the arrangement ofroomsaroundthecourtyard,allofthemusingthecourtyardasthemaincirculationspacenot just for air, but also for its inhabitants. Because of the large geographic spread ofChinesecivilization,thecourtyardtyperangesfromveryhotandhumidtocolderclimatezones.Zhangnoticedastrongandvery interestingcorrelationbetween theclimatezone

and the spatial proportion of the courtyard. Drawing from Knapp,48 she points to thedifference between the large scale of the courtyards in the northern Chinese climate,allowingthepenetrationofthesun’sradiationforpassivesolarheating,andtheextremelysmallcourtyardssituatedinthesouthernChineseclimates.

In order to manipulate the flow path and allow for variation of interior spatialcomposition, the Chinese courtyard house (similar to the Japanese house) incorporatedmultiple movable and sliding walls/doors to change, facilitate, or block the internalmovementoftheairdependingonclimatesituationandneeds.

AttentiontoventilationismoreprominentinsouthernChina’sSuzhouthaninBeijing,where the construction focusesmore on shielding from coldwinds and accessing solarradiation,muchliketheCarelianfarmhouseanalyzedbyAlvarAaltoinFinland.49

Figure5.12

Chinesecourtyardschangesignificantlyinproportionbetweensoutherntropicalandnortherncolderlocations,ashasbeenanalyzedbyKnappin2005.

5.3.2.3

Figure5.13

MuuratsaloExperimentalHouseseenfromtheoutside,whichhighlightstheproportionofthecourtyardspace.

Two-CourtyardsVentilationStrategyAnevenmorecomplexscenarioisutilizedinhotandaridclimateswiththecombinationofmultiplecourtyards forclimatecontrol.50Here,a largercourtyard isexposed tosolarradiationandheatedup,whileasecondsmallercourtyardisshaded,allowingairtomovefrom the cooler to the hotter courtyard, creating a slight breeze through the in-betweenspaces.

Hassan Fathy51 discusses in great detail convection-based air movement created bysolarradiationandtheutilizationofthisstrategywithinthecourtyardhousetypologyinthehotandaridclimateoftheMiddleEasterncity,wherewindingstreetsarefairlynarrowandshadedandcourtyardsare largerand thusexposed tosolar radiation throughout theday.

Invernaculararchitecture,thiseffect(thestackeffect)hasbeenexploitedtoproducesmallareaswithcoolbreezes,usingthegroundheatedbythesunastheheatsource.Aslongasalargevolumeofcoolerairisavailableandisunaffectedbyheatfromthesun,thehottersunheatstheground,thestrongerwillbethebreeze.

Fathyattributesthesemovementstotheradiationtotheclearskyatnightandtheresultingtemperaturedifferencebetweennightairandcourtyardair.Thecourtyardair,heatedupbythesunduringtheafternoon,risesintheearlyeveningintothecoolernightsky,whichinturndescendsintothesmallercourtyardsandseepsthroughintothelivingspaces,coolingthem.

Figure5.14

ThetheorythattwocourtyardsoperatetogetherhasbeenmadepopularbyHassanFathyandisnowvalidatedbymeasurementsofErnestandFordattheCasadePilatosinSevilla.

HassanFathyclaimspotentialtemperaturedropsof10to20°C(~18to36°F),citingDanielDunham,52anddeclaresthecourtyarda“reservoirforcoolness.”ErnestandFord53recentlysetouttoverifythismainlyanecdotalclaiminthedoublecourtyardoftheCasade Pilatos in Seville, Spain. They performed the necessary field measurements, whichverified the convective cooling potential of two connected courtyards in a hot and aridclimate.TheCasadePilatosisalavisharistocraticurbanpalace,incorporatingtwogardencourtyardsandtwointernalcourtyardsthatarevoidofanyplantings.

Theirconclusionissignificantfortheevaluationoftheimpactofmultipletransitionalspacesontheconditionofinhabitableinteriorspacewithnaturalenergies:

Freecoolingisavailablebecausetheenthalpyofairinthegardencourtyardismuchlower than indoor air. In addition adiabatic cooling by evaporation can beincorporatedthroughevaporativecoolingtolowertheindoortemperaturebycloseto20degreesCelsius.54

Allcourtyardsacrossthestudiedcultureshaveonemajorcommoncharacteristic:theyactas both social spaces and climatic spaces, and this cultural significance guaranteed thesurvivalandrevivalofthisbuildingtype.

5.3.3

Figure5.15

ThegardenoftheRealesAlcazaresdeSevillaisconnectedtosmallershadedcourtyardsintheinteriorofthepalace.

HorizontalWindCatchers:Passage,Arcade,LoggiaThe analysis of the courtyard typology has already highlighted the importance of in-between spaces – the spaces between inside and outside – in developing a comfortablelived-in spatial configuration and in protecting from some of the environmental forces,while allowing for other environmental forces to flourish by embracing outdoors andindoorsatthesametime.Anotherverydevelopedspatialtype,developedovercenturies,ifnotmillennia, is thepassageorcovered street, thearcadeorcoveredportico, and theloggiaasacoveredlivingroom.Allthreespatialtypeshaveincommonthatoneormoresidesoftheirspatialboundariesareopentotheoutdoors.Coveredstreetsorpassagesarecommon in many climates from Jerusalem to Brussels to Helsinki, shading from rain,snow, wind, or the sun. Arcades in Hamburg and Bologna provide covered spaces forpassage,butalsospacesfortradeandcommerce.Loggiasprovidedabreezyretreatfromthe heat of the sun from Rome to Cadiz all around the Mediterranean Sea, the mostprominentonesbyMichelangeloandBorrominidominating theviewofRomeover theTiberriver.

5.3.4

Figure5.16

TheBelvedere,athreebayloggiaonthetopofPalazzoFalconieri,wasaddedtothepalacebyFrancescoBorrominiin1646.

ThegreatnarratorofRomanarchitecturePlinytheYounger(61AD–112AD)describedhis coastal villa in great detail and certainly did not fail to mention the pleasureencountered in arcade spaces, whichwere able to catch the breeze and dilute stale air.“Insidethearcade,ofcourse,thereisleastsunshinewhenthesunisblazingdownontheroof, and as its open windows allow the western breezes to enter and circulate, theatmosphere is never heavy of stale air.”55 The current prominence of the double-skinfaçadescanberelatedbacktothearcadeasanin-betweenspace,mediatingbetweentheinsideandtheoutsideofabuilding.

Wind-InducedPressureDifferentials:WovenStoneBasketThe woven screen or wall is the second important architectural feature mentioned inGottfried Semper’s theoretical treatise on architecture.56 In very warm and humidclimates,whereprotectionagainstcoldorcoolweatherisnotdesired,andthewallsandroofs of a building only need to protect from rain and provide privacy, the wall canbecome a screen of woven fabric, sometimes of stone and sometimes of vegetativematerial.Thisapproachcreatedanarrayofvernaculararchitecturalprecedents.

One of themost important archetypes of this spatial strategy is the storage building,whichwas developed to expose asmuch as possible of the stored grain to thewind tofacilitate drying. This led to the development of a wind-permeable wall, while theforemost aimof the structurewas to keep the vital grain safe frompests and intruders.Their spatial structure led to a very interesting connection between these grain storagestructures–whichare still visible andutilized inLindoso inNorthernPortugal; similarstructures called Horreos exist in Galicia, Spain57 – and the Hellenistic Greek temple,which also exhibited a semi-open, permeable, yet very refined external wall structure.

Ventilated storage spaces as encountered in the corn cribs and granaries of the SpanishprovinceofGaliciacouldbeconsideredspatialpredecessorsoftemplearchetypes.Whiletheplacesfor thegranaries inLindosowerefoundinprivilegedhigherpositions to takeadvantageofthewindsforventilationanddrying,asRudofskypointsout,57thepositionof theAcropolisof course also followedceremonial strategies.Yet, theiroriginmaybesimilaraswelltotheoriginofwovenornaments,asSemper35pointedout.

Figure5.17

ThegrainstoragebuildingsinLindoso,northernPortugal,areraisedstone‘baskets’providingventilationaccesstothegrainwhileprotectingthegrainfromintruders.

GastonBachelard recalls the poetic dimension of thewind houses inThe Poetics ofSpace.5

Theimageofthesehousesthatintegratethewind,aspiretothelightnessofair,andbearonthetreeoftheirimpossiblegrowthanestallreadytoflyaway,mayperhapsberejectedbyapositive,realisticmind.…itistouchedbytheattractionofopposites,whichlendsdynamismtothegreatarchetypes.58

And…thewellrootedhouselikestohaveabranchthatissensitivetothewind,oranatticthatcanheartherustleofleaves.58

Thehouse,asIseeit,isasortofairystructurethatmovesaboutthebreathoftime.Itreallyisopentothewindofanothertime.59

HousesinBachelard’spoemsbreatheandacheandmove.Theyareairycreatures.HequotesGeorgeSpyridaki:“[a]housethatisdiaphanous,butitisnotofglass.Itismoreofthenatureofvapor.ItswallscontractandexpandasIdesire.”60Allthesedescriptionsmayhintatintersticesinthewallprovidingventilation.BachelardcontinuedhisinvestigationinacompletebookonAirandDreamswithafullchapterdedicatedtowindsandstorms

astheoriginofimagination.6

Reyner Banham points to the great California tradition of sleeping porches, whichresemblethehouseofair–thehousethatbreathes.Thegardenporcheshavepermeablewalls and aprotective roof, and following thedescriptionof the summer cottageof theGamblefamilybyGreeneandGreeneatPasadenain1908,“thewidelyprojectingroofsovermostgablesarejoinedbyanelaboratesystemofexternalroofedsleepinggalleriesontheupper floorand terracesat theground floor level.”61Theoutdoor spaces thuscoverabout the sameamountofareaas theenclosedspaces inorder to takeadvantageof thelight southernCalifornia breeze and to shelter thewalls from the direct solar radiation.Thishouse,likemostoftheGreeneandGreeneresidentialdesignprojects,wasdevelopedfrom exquisite timber members and appeared as if woven together just from linearelements as if directly following Gottfried Semper’s textile wall coverings in the“primitivehut.”35

“One may enter almost anywhere for doors and windows are nearly alike,” wroteCharles Greene in an article titled “On California Home Making”62 quoted by EstherMcCoy, and she continues: “There was no attempt to make the flow of interior andexteriorspaceasingleundefinedareaasisdonetoday”(sonotMiesian).Eachspacehaditsownidentityandwasrelatedtoallpartsofthesitedevelopmentaswellastheinterior.Theinteriorshadanintimate,sheltered,anddarkenedatmosphere,coolandcomfortablelikeacave,whichduringthedayprovidedanescapefromthehotburningraysofthesunandthedryair.Duringtheafternoonorevening,thedoorsandwindows–setinhorizontalbands–wereswungopentotakefulladvantageofthecoolbreeze.

Figure5.18

TheGambleHouseinPasadenadesignedbyGreeneandGreenein1908providesaniconicexampleoftheCaliforniagardensleepingporches,raisedtimber‘baskets’opentotheventilationbreezes.

5.3.5 Wind-InducedPressureDifferentials:WindCatcherThe Iranian and Middle Eastern wind catcher is probably the most studied inheritednaturalventilationstrategy,andithasalsobeensuccessfullyintegratedintocontemporarybuiltprojects.63Thefascinationwithwindcatchersasclimatedevicesisalreadyapparentin Bernard Rudofsky’s Architecture without Architects,2 where he points to the windcatcherinHyderabadSind,Pakistan.SueRoafwithhergroundbreaking,butunfortunatelyunpublished,PhDwork64onIranianwindcatchershasbecomeaninspirationforatleastonegenerationofresearchers.InspiteofthefactthatIranhasbeenfairlydifficulttoreachforWesternresearchersduringthelast30years,therearecurrentoccupancysurveysandmeasurementsforwindcatchers,orbadgir,inIran65andinparticularinthecityofYazd.66

Windcatchersareessentiallyspatialdevicesthatchannelcoolerairfromhighersurfacelayersabove the roof,wherewindspeedsarehigher than theyarecloser to theground,downintotheoccupiedlivingquartersofthebuilding.

Windcatchersinthepasthavebeenpartofalargerstrategyofpassiveenvironmentalcontrol features and processes, one of which seems to have been daily and seasonalmigrationfromoneroomtoanother,asnotedbyRoaf.67

Recentnumericalandquantitativeresearchstudiesontherelationshipofwindcatchersto thermal comfort and comfort perception have revealed that the most comfortablesummer rooms in houses with wind catchers were actually in the basements.66 Thisinformationisanindicationoftheinterrelationshipofvariousimplementedenvironmentalstrategies,includingtheutilizationofthermalmassasaheatsinkforcoolingpurposes.

Windcatcherswere implementednotonly in traditionalbuildings in Iran,but also inotherpartsofthehotanddryaswellashotandhumidregionsoftheMiddleEast,suchasinDubai,Egypt,andSaudiArabia,aswellasinIraq.ButmostofthesetraditionalformscanactuallybeattributedtoIraniansmovingaboutthePersianGulfandsettlinginotherpartsoftheregionasmerchants,bringingtheirconstructiontraditionwiththem.

Thefirstandmajorcharacteristicofwindcatchersistheirstrongvisibilityintheurbancontext.ThephotoofHyderabadpublishedbyRudofsky68showsaforestofhundredsoftall,slenderstructurestoweringoverthecity,orientingtheirshieldstowardstheprevailingwinddirection.

Current insight into Iranianwind catchers goes back to a few sourceswhose authorswere actually still able to visit the location in the 1970s: SueRoaf’s unpublished PhDthesis in architecture from the late 1980s and the travel report of geographer MichaelBonine,publishedasafieldreportinthelate1970s.69Onlyrecently,withgreatermobilityinandoutofIran,haveresearchersbeenabletoconductoccupancysurveysaboutcomfortperceptioninwindcatcherventilatedbuildings.13SueRoaf’saccountonwindcatchers,orbadgir, published in “Livingwith theDesert,”67 is based on her fieldwork and revealsmanyimportantgeometricpropertiesandtheimmensevarietyofproportionalconditionssheencounteredinjustonecity.

Thetowersofvaryingheightareconstructedofmudbricksanddividedintoanumberof chamberswith vents opening in various combinations to the prevailingwinds.Windcatchershavebeenbuiltoverresidentialhomesofvariousscalesaswellascisternsandmore public buildings such as baths.Wind catchers are often connected to a complexsystemof roomsandcourtyards,andall those features togetherwereeffectivelyable tocreate thermal comfort.However, thismost likelydoesnotdescribe thermal comfort asconsidered desirable in today’s air-conditioned world, but an environment with highertemperatureswings thatoftenmayhave reliedonsweatingasacoolingstrategyfor thehumanbody,astrategythatisnolongerconsideredappropriatebycurrentoccupants.Butaccording to Sue Roaf’s report,70 comfort was created through convective evaporativeheatlossbasedonwindvelocityandthroughcoolingbyevaporatingsweatonoccupants’skin with the very dry air current. Still, many wind catchers are in use today and areconsideredcomfortablebymostofthebuildings’occupants.13

The operation of awind catcher is directly related to the fluid dynamics ofwind inrelationship to obstacles.When wind impacts the wind tower, positive pressure on thewindwardsideiscoupledwithnegativepressureontheopposite,leewardside.Avortexwillbecreatedontheleewardsideonthebackofthemassivetowerstructure.Theaironthepositivepressure side travels down the chamber shaft of the toweron that side andreachesthebase,whileairfrominsidetheroomgetspulledupbythenegativepressurecreatedontheleewardsideofthetower.“Theperformanceofawind-catcherisaffectedbyvariablessuchasheight,cross-sectionalplan,theorientationofthetowerandlocationofitsoutlets.”67

In Yazd, Roaf detected two major types of wind catchers: first, ordinary, functionalwind catchers for smaller homes and cisterns, and second, those built by wealthierhouseholdsandoverpublicbuildingssuchasmosquesandbathsorcaravanserais.Towersoverwealthierhomesalsofunctionedassignsanddecoration.Dependingon thesizeofthe house, multiple sections of the home may have had individual wind catchers ofdifferentheightsandfunctions.Thesmallerwindcatchersrangedfromabout1.2m(4ft)to3m(10ft)andwereusuallydividedintotwooreveneightshafts.Largerwindcatchersmayrisebetween2and22m(6and71ft)withornateanddetailedinletandoutletventsatthetop,sometimesonadiagonalplan,organizingmultiplesetsofinletandoutletshafts.Usuallywind-catcher openingswere oriented on all sides, so that inlet and outletmayactuallychange,butRoafalsosurveyedwindcatcherswithjustoneorientation.67

Withrespecttothefloorplan,theouteroutletoftheshaftwasusuallypositionedattheedgeorevencornerofaroom,sometimeswithoutletspositionedonmultiplefloorsallthewaydowntothebasement.

ItisimportanttonotethatintheYazdhousesacomplexinteractionofvariouspassivecoolingdevicesandarchitecturalfeaturesaswellasbehavioralroutinesandmaybeevenclothing options was at play. Iranian desert residences incorporate courtyards, waterfeatures,windcatchers,basementrooms,arcades,summerrooms,andwinterrooms.

According to Roaf,71 the Yazdi lifestyle was characterized by internal migration.

Insteadofmigratingtohighergroundsinthemountains,eventhesmallesthomesarelaidoutforseasonalmigration:theyhavesummerlivingroomsinthecenterconnectedtothewindcatchershaft,whilethewinterroomisclosertothesolar-exposedfaçade.Basementroomsinlargerbuildingshadthecommonfunctionofsummerdaytimeretreats,becausethey were the best locations owing to their thermal mass and constant temperaturebetween25and28°C(77and82.5°F).Windcatcherairintroducedtobasementroomsexhausted stale humid air, even when the introduced air was warmer than internal air.Thus,ventilationdoesnotalwayshaveacoolingfunctioninthesensethatitreducesairtemperature,butitremovesheatfromoccupants’bodiesandthuscoolsthebodiesdirectlyandnottheinternalair.

Figure5.19

ApairofwindcatchersinYazd,Iran.

Figure5.20

AhighlydecoratedpairofwindcatchersinYazd,Iran,showingtheroofareaasoccupiedspaceandindicatingtherelationshipofwindcatcherstothedemonstrationofwealthinYazd.

Figure5.21

ThiswindcatchershowstheproportionalvarietystillexistinginYazdtoday.

Figure5.22

5.3.6Thesewindcatchersshownfromtheroofshowlessdetailandfewerventilationopenings.

Temperature-InducedPressureDifferentials:ChimneyMostcommonlyachimneyactsasaspatialdevicetochannelairneededforcombustionintofiresusedinsidethebuildingforheatingorcookingandtoremovesmokedevelopedduring the process. Often, the air gets pulled into the combustion chamber throughopenings in the envelope of the building (such as vents, windows, or cracks). The hotcombustionairrisesandexhauststhroughthechimney,whichactsasaverticalflukeandoftenisadominantfeatureofthebuilding.

Otherexamplesofchimneysorventilationshaftsaremanifoldinbuildingtypes.Theymaybeusedtochannelwindthroughastoragespaceinordertodrygrainorhops,likeintheoasthousesinKent,England,whichwereusedtodryhopsforbeerbrewing.Theyhadasimilarshapetoachimneyandweretoppedwithawindcowlthatturnedwiththewindtoprovideforthebestpressuredifferentialbetweenthefrontandthebackoftheopeningto allow the warm air to escape.While the wind passes over the top of the chimney,warmerairrisesandthuscoolerairispulledfromalowerairsource.71

Chimneys have often contributed to the character and appearance of sophisticatedpalatial or casual rural inherited architecture. Sintra National Palace, for centuries theresidenceofthePortugueseroyalfamilyoutsideofLisbon,exposestwoenormousconicalkitchenchimneysthatarevisibleondrawingsofthepalaceasearlyas1509.72

Similar spatial objects can be found in the kitchen of the Cistercian monastery inAlcobaca, Portugal, founded in 1153. Two enormous chimneys constructed in theeighteenthcenturydominatethespace.

Traditional farmsteads in colderAlpine climateshave also integrated significantbuiltformsfortheirkitchenchimneys.InDavos,Switzerland,theyevenrelatedtotheatriumorcentralhallofthehomeandthuscanbecross-referencedtothecourtyardtypology.TheAlteSennhütteinDavos73wascomposedofmultiplestackedvolumes,leavingthecenterwith thehearthempty,butcovering thewholecompositionwithoneover-encompassinglargeroof.TheSennhüttethuscombinestheventilationstrategyofcoveredcourtyardandchimney. The Topkapi palace in Istanbul and its seraglio are also towered by largechimneys.Traditionalchimneysobviouslyserveaskeyprecedentsforallstackventilationusedincontemporarynaturalventilationcases.

Figure5.23

ThewindcowlsoftheoasthousesinKent,England,usedtodryhopsforbeerbrewing,areabletomovewiththechangingwinddirection.

Figure5.24

ThekitchenchimneysdominatetheappearanceofSintraNationalPalaceinSintra,Portugal,alreadyinthisearlysixteenth-centurydrawing.

Figure5.25

ThekitchenintheMonasteryofAlcobacaincorporatesanenormousfree-standingchimneyoverthecookingstation.

Figure5.26

TraditionalfarmhousesliketheSennhütteinDavoswerebuiltaroundacentralfurnaceandcooktop,whichresemblesanatrium.

5.4

Figure5.27

ChimneysalsodominatetheexteriorappearanceoftheSerailoftheTokapiPalaceinIstanbul.

InheritedBuildingTypesandClimateTheinheritedventilationtypologiesdescribedinthischaptercanberelatedtotheclimatezonesinwhichtheyarelocated.Anecdotally,theinhabitantsofdesertclimatesdevelopedthe largest variety of spatial ventilation types. Cultures in moderate climates wereobviouslymoreconcernedwithkeepingwarm,followedbytherequirementforfreshair,and thus the chimney-atriumcourtyard relationship is dominant in the Mediterraneanclimate,wherebothheatingandcoolingareobviousneeds.Strategiesinhumidclimatesseemed to induce a lot of wind directly as the major ventilation strategy so that thebuildingenveloperemainedjustavisualprivacybarrier.Formoreinformationonclimate-based design see Saldanha, Hausladen and Liedl’s recent publication.74 Table 5.1summarizestheprevailingstrategiesinthevariousclimatezones.

Table5.1Spatialtypologiesrelatedtomajorclimatezones

5.5 TraditionalVernacularandContemporaryModernArchitecture

A vigorous discourse prevailed all through the Modern Movement in a number ofcountries on how to relate Modern thought with inherited vernacular traditions. LeCorbusier’straveltotheOrient75andAlvarAalto’sreferencestotheKarelianfarmstead,76aswellasFrankLloydWright’scentralfocusonthehearthinhisprairiehomes,arejustafewindicatorsthatdirectlyrelateModerncompositiontospatialstrategiesenhancingairmovement.Whileclimate-responsivearchitecturewasnotofmajorconcernintheModernMovement, references to inherited traditions celebrate a revival as part of theenvironmental,sustainable,orgreenarchitecturedevelopment.Insteadofmerelyclaimingsuperior performance, many contemporary research teams are currently examiningperformance-basedevidencetoverifytheactualperformanceoftheseinheritedconceptsforcontemporaryapplications.

Moreresearchisnecessarytovalidatemanyclaimsaboutthevalidityoftheseinheritedconcepts in contemporary architecture. The European research project on downdraftcoolingsupportedbythesixthEuropeanUnion(EU)researchframeworkprogram63andcurrent projects funded by the US National Science Foundation within the EmergingFrontier in Research and Innovation (EFRI) program are examples of initial efforts toimprovethescienceforsustainablebuildings.77

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The evolving knowledge base can help to integrate typological knowledge into thedesign process and refine the place traditional architecture can take within thecontemporarydiscussiononglobalcultureandthedevelopmentofsustainablearchitectureforachangingclimate inawarmingworld.78However,what shouldbeclear already isthat spatial typologiesactas socialandclimatespace,but furtheranalysisof thespatialdistributionof heat through air flow in three-dimensional volumetric proportions is stillneeded.

NotesRonaldLewcock,“‘GenerativeConcepts’inVernacularArchitecture,”in:LindsayAsquithandMarcelVellinga(eds),VernacularArchitectureintheTwenty-FirstCentury:Theory,EducationandPractice(NewYork:Routledge,2005),p.199.

BernardRudofsky,ArchitecturewithoutArchitects:AnIntroductiontoNon-pedigreedArchitecture(NewYork:MuseumofModernArt;distributedbyDoubleday,GardenCity,NY,1964).

AldoRossi,TheArchitectureoftheCity,revisedfortheAmericaneditionbyAldoRossiandPeterEisenman,ed.PeterEisenman(Cambridge,MA:MITPress,1982).

C.G.Jung,ManandHisSymbols,ed.Marie-LuisevonFranz(GardenCity,NY:Doubleday,1964).

GastonBachelard,ThePoeticsofSpace,translatedfromtheFrenchbyMariaJolas,forewordbyÉtienneGilson,ed.GastonBachelard(Boston:BeaconPress,1969).

GastonBachelard,AirandDreams:AnEssayontheImaginationofMovement,BachelardTranslationSeries(Dallas:DallasInstitutePublications,DallasInstituteofHumanitiesandCulture,1988).

RonaldLewcock,“‘GenerativeConcepts’inVernacularArchitecture,”in:LindsayAsquith,VernacularArchitectureintheTwenty-FirstCentury:Theory,EducationandPractice(NewYork:Routledge,2005),p.203.

GottfriedSemper,TheFourElementsofArchitectureandOtherWritings,translatedbyHarryFrancisMallgraveandWolfgangHerrmann,introductionbyHarryFrancisMallgrave(Cambridge,England;NewYork,USA:CambridgeUniversityPress,1989).

GastonBachelard,ThePoeticsofSpace,translatedfromtheFrenchbyMariaJolas,forewordbyÉtienneGilson(Boston:BeaconPress,1969),pp.3–37.

MichaelE.Bonine,“AridityofIndigenousHousinginCentralIran,”in:KennethN.ClarkandPatriciaPaylore(eds),DesertHousing:BalancingExperienceandTechnologyforDwellinginHotAridZones(Tucson,AZ:UniversityofArizona,OfficeofAridLandsStudies,1980).

IsaacA.MeirandSusanC.Roaf,“TheFutureoftheVernacular:TowardsNewMethodologiesfortheUnderstandingandOptimizationofthePerformanceofVernacularBuildings,”in:LindsayAsquithandMarcelVellinga(eds),VernacularArchitectureintheTwenty-FirstCentury:Theory,EducationandPractice(NewYork:Routledge,2005),pp.215–230.

AhmadrezaForuzanmehrandMarcelVellinga,“VernacularArchitecture:QuestionsofComfortandPracticability,”BuildingResearch&Information,39(3),2011,pp.274–285.

AhmadrezaForuzanmehr,“TheWind-Catcher:Users’PerceptionofaVernacularPassiveCoolingSystem,”ArchitecturalScienceReview,55(4),2012,pp.250–258.

BernardRudofsky,ArchitecturewithoutArchitects:AnIntroductiontoNon-PedigreedArchitecture(Albuquerque:UniversityofNewMexicoPress,1964),preface.

ReynerBanham,TheArchitectureoftheWell-TemperedEnvironment(Chicago:UniversityofChicagoPress,1984).

UmbertoEco,“FunctionandSign:TheSemioticsofArchitecture,”in:GeoffreyBroadbent,RichardBunt,andCharlesJencks(eds),Signs,Symbols,andArchitecture(Chichester,England;NewYork:Wiley,1980),pp.38–39.

A.Bekleyen,I.A.Gönül,H.Gönül,H.Sarigül,T.Ilter,N.Dalkiliç,andM.Yildirim,“VernacularDomedHousesofHarran,Turkey,”HabitatInternational,22(4),1998,pp.477–485.

TahsinBasaran,“ThermalAnalysisoftheDomedVernacularHousesofHarran,Turkey,”IndoorandBuiltEnvironment,20(5),2011,pp.543–554.

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J.WalterFewkes,“VentilatorsinCeremonialRoomsofPrehistoricCliff-Dwellings,”AmericanAnthropologist,10(3),1908,pp.387–398.

Seehttp://nsf.gov/awardsearch/showAward?AWD_ID=1345381&HistoricalAwards=false(accessed5/11/2014).

D.Pearlmutter,“RoofGeometryasaDeterminantofThermalBehaviour:AComparativeStudyofVaultedandFlatSurfacesinaHot-AridZone,”ArchitecturalScienceReview,36(2),1993,pp.75–86.

AhmadrezaK.FaghihandMehdiN.Bahadori,“SolarRadiationonDomedRoofs,”EnergyandBuildings,41,2009,pp.1238–1245.

RunshengTang,I.A.Meir,andY.Etzion,“ThermalBehaviorofBuildingswithCurvedRoofsasComparedwithFlatRoofs,”SolarEnergy,74,2003,pp.273–286.

TangRunsheng,I.A.Meir,andY.Etzion,“AnAnalysisofAbsorbedRadiationbyDomedandVaultedRoofsasComparedwithFlatRoofs,”EnergyandBuildings,35,2003,pp.539–548.

VictorM.Gomez-Munoza,MiguelAngelPorta-Gandarab,andChristopherHeard,“SolarPerformanceofHemisphericalVaultRoofs,”BuildingandEnvironment,38,2003,pp.1431–1438.

LucasMutti,“NumericalModellingofaComprehensive1-DBuildingEnergyModelandConjugateHeatTransferAnalysisontheInternalFlowFieldattheHarranHousesinSouthernTurkeyforaBrickCorbelledInternalSurface”,GraduateThesesandDissertations,paper14049(2014).

LetiziaDipasquale,C.Mileto,andF.Vegas,“TheArchitecturalMorphologyofCorbelledDomeHouses,”in:EarthenDomesandHabitats:VillagesofNorthernSyria:AnArchitecturalTraditionSharedbyEastandWest(Pisa:EditioneETS,2009),pp.267–285.

AndreaPalladio,TheFourBooksofArchitecture,translatedfromtheoriginalItalianbyIsaacWare,ed.IsaacWareandAndreaPalladio(London:printedforR.Ware,attheBibleandSun,1738).

BarbaraKenda,“OntheRenaissanceArtofWell-Being:PneumainVillaEolia,”AnthropologyandAesthetics,34,1998,pp.101–117.

BarbaraKenda,AeolianWindsandtheSpiritinRenaissanceArchitecture:AcademiaEoliaRevisited(NewYork:Routledge,2006).

Ibid.,96

LeonBattistaAlberti,OntheArtofBuildinginTenBooks(Cambridge,MA:MITPress,1988).

VincenzoScamozzi,L’ideaDellaArchitetturaUniversale,2vols.(Ridgewood,NJ:GreggPress,1964).

GottfriedSemper,TheFourElementsofArchitectureandOtherWritings,translatedbyHarryFrancisMallgraveandWolfgangHerrmann,introductionbyHarryFrancisMallgrave(Cambridge,England;NewYork,USA:CambridgeUniversityPress,1989).

UlrikePasse,“SustainableBuildingTypologies:FreeFlowOpenSpaceasaClimateTechnology,”InternationalJournalofEnvironmental,Cultural,EconomicandSocialSustainability,3(4),2007,pp.15–28.

D.Raydan,C.Ratti,andK.Steemers,“Courtyards:ABioclimaticForm?”in:BrianEdwards,MagdaSibley,MohamadHakmi,andPeterLand(eds),CourtyardHousing:Past,PresentandFuture(NewYork:Taylor&Francis,2006).

AtilioPetruccioli,“TheCourtyardHouse:TypologicalVariationsoverSpaceandTime,”in:BrianEdwards,MagdaSibley,MohamadHakmi,andPeterLand(eds),CourtyardHousing:Past,PresentandFuture(NewYork:Taylor&Francis,2006).

JormaMantyandNormanPressman,CitiesDesignedforWinter(Helsinki:BuildingBook,1988),p.13.

D.Raydan,C.Ratti,andK.Steemers,“Courtyards:ABioclimaticForm?”in:BrianEdwards,MagdaSibley,MohamadHakmi,andPeterLand(eds),CourtyardHousing:Past,PresentandFuture(NewYork:Taylor&Francis,2006).

Ibid.,p.135.

Ibid.,p.144.

KhalidA.MegrenAl-SaudandNasserA.M.Al-Hemiddi,“TheThermalPerformanceoftheInternalCourtyardintheHot-DryEnvironmentinSaudiArabia,”in:BrianEdwards,MagdaSibley,MohamadHakmi,andPeterLand

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(eds),CourtyardHousing:Past,PresentandFuture(NewYork:Taylor&Francis,2006),pp.163ff.

Ibid.,p.170.

BorisCuljatandRalphErskine,“AScandinavianPerspective,”in:JormaMäntyandNormanPressman(eds),CitiesDesignedforWinter(Helsinki:BuildingBook,1988).

NormanPressman,“Introduction:ANeedforaNewApproach,”in:JormaMäntyandNormanPressman(eds),CitiesDesignedforWinter(Helsinki:BuildingBook,1988),pp.25–30.

DoniaZhang,CourtyardHousingandCulturalSustainability:Theory,Practice,andProduct(Farnham,Surrey;Burlington,VT:Ashgate,2013).

RonaldG.Knapp,ChineseHouses:TheArchitecturalHeritageofaNation(Singapore:Tuttle,2005),p.25.

AlvarAalto,“KarelianArchitecture”(1941),in:GoranSchildt(ed.),AlvarAaltoinHisOwnWords(NewYork:Rizzoli,1998),p.118.

RahaErnestandBrianFord,“TheRoleofMultipleCourtyardsinthePromotionofConvectiveCooling,”ArchitecturalScienceReview,55(4),2012.

HassanFathy,“TheSunFactor,”in:WalterShearerandAbd-El-RahmanAhmedSultan(eds),NaturalEnergyandVernacularArchitecture:PrinciplesandExampleswithReferencetoHotAridClimates(Chicago:publishedfortheUnitedNationsUniversitybytheUniversityofChicagoPress,1986),pp.62–70.

DanielDunham,“TheCourtyardHouseasaTemperatureRegulator,”NewScientist,1960,pp.659–666(asquotedbyFathy,“TheSunFactor,”p.63).

RahaErnestandBrianFord,“TheRoleofMultipleCourtyardsinthePromotionofConvectiveCooling,”ArchitecturalScienceReview,55(4),2012.

Ibid.,p.248.

PlinytheYounger,TheLettersoftheYounger,BookII(NewYork:PenguinClassics,1969),p.78.

GottfriedSemper,TheFourElementsofArchitectureandOtherWritings,translatedbyHarryFrancisMallgraveandWolfgangHerrmann,introductionbyHarryFrancisMallgrave(Cambridge,England;NewYork,USA:CambridgeUniversityPress,1989).

BernardRudofsky,ArchitecturewithoutArchitects:AnIntroductiontoNon-PedigreedArchitecture(NewYork:MuseumofModernArt;distributedbyDoubleday,GardenCity,NY,1964),pp.90–94.

GastonBachelard,ThePoeticsofSpace,translatedfromtheFrenchbyMariaJolas,forewordbyÉtienneGilson(Boston:BeaconPress,1969),p.52.

Ibid.,p.54.

Ibid.,p.51.

ReynerBanham,TheArchitectureoftheWell-TemperedEnvironment,2nded.(Chicago:UniversityofChicagoPress,1984),p.102.

CharlesGreene,“OnCaliforniaHomeMaking,”in:EstherMcCoy,FiveCaliforniaArchitects(NewYork:Reinhold,1960),p.109.

BrianFord,RosaSchiano-Phan,ElizabethFrancis,ServandoAlvarez,andPaulThomas,TheArchitectureandEngineeringofDowndraughtCooling:ADesignSourcebook(London:PHDCPress,2010).

PersonalconversationwithSueRoaf(2011).

AhmadrezaForuzanmehrandMarcelVellinga,“VernacularArchitecture:QuestionsofComfortandPracticability,”BuildingResearch&Information,39(3),2011,pp.274–285,doi:10.1080/09613218.2011.562368.

AhmadrezaForuzanmehr,“TheWind-Catcher:Users’PerceptionofaVernacularPassiveCoolingSystem,”ArchitecturalScienceReview,55(4),2012,pp.250–258.

ElisabethBeazleyandMichaelHarverson,LivingwiththeDesert:WorkingBuildingsoftheIranianPlateau(Warminster,UK:Aris&Phillips,1982).

BernardRudofsky,ArchitecturewithoutArchitects:AnIntroductiontoNon-pedigreedArchitecture(NewYork:MuseumofModernArt;distributedbyDoubleday,GardenCity,NY,1964),pp.113–115.

KennethN.ClarkandPatriciaPaylore(eds),DesertHousing:BalancingExperienceandTechnologyforDwellinginHotAridZones(Tucson,AZ:UniversityofArizona,OfficeofAridLandsStudies,1980).

70

71

72

73

74

75

76

77

78

SueRoaf,“TheTraditionalTechnologyTrap(2):MoreLessonsfromtheWindcatchersofYazd,”in:PLEA2008Proceedingsofthe25thConferenceonPassiveandLowEnergyArchitecture(Dublin,10/22/2008to10/24/2008).

See“HoppingDowninKent,”http://www.hoppingdowninkent.org.uk/oasthouse_interactive.php(accessed5/11/2014).

See“File:Sintra-DuarteArmas.jpg,”LibrodasFortalezas(early16thcentury),Wikipedia,http://en.wikipedia.org/wiki/File:Sintra-DuarteArmas.jpg.

A.Giedion,DieArchitekturderDavoserAlphütten:ErnstLudwigKirchners“AlteSennhütte”undihrVorbild(Zürich:Scheidegger&Spiess,2003).

GerhardSaldanhaMichaeldeHausladenandPetraLiedl,BuildingtoSuittheClimate:AHandbook(Basel:Birkhäuser,2012).

LeCorbusier,JourneytotheEast,translationanded.IvanŽaknićincollaborationwithNicolePertuiset(Cambridge,MA:MITPress,1987).Frenchoriginal:LeCorbusier,LeVoyaged’Orient(Paris:ForcesVives,1966).

AlvarAalto,“KarelianArchitecture,”in:GöranSchildt(ed.),AlvarAaltoinHisOwnWords(Helsinki:OtavaPub.Co.,1997),pp.116–119.

See“ENG/EFRIFY2010AwardsAnnouncement,”NationalScienceFoundation,http://www.nsf.gov/eng/efri/fy10awards_SEED.jsp(accessed5/11/2014).

ColinPorteousandKerrMacGregor,SolarArchitectureinCoolClimates(London:Earthscan,2005).

Chapter6

NaturalVentilationandThermalComfortBuildingsaredesignedandconstructedtobesheltersthatprotectfromuncomfortableorevendangerousclimaticandenvironmentalconditionssuchasrainandsnow,highwinds,heat and cold, and strong solar radiation. The classical ‘primitive hut’, a roof on fourpillars, appears inLaugier’s famousandoften citeddrawing1 as a startingpoint for thebasic necessity of shelter. The hearth as a center for buildings appears in GottfriedSemper’sarchitecturaltheory2andhasbeentracedasavitalarchitecturalfeature,relatingmonumentality and comfort. Butwhen shelter from the elements is required, designershavetoalsoallowforairtoenterthebuildingideallyinacontrolledmannerforthermalcomfort andof courseairquality (asnoted inChapter3).This chapterwill address themajor concepts related to thermal comfort in naturally ventilated and hybrid ormixedmodebuildings.

Before the advent of mechanical cooling systems, cooling was achieved only byutilizing the storage capacity of latent heat in water or ice through evaporation andconvection. Wind moving air over the body resulted in a cooling sensation throughevaporation.Evaporativecoolingdirectlyfacilitatestheremovalofheatfromthehumanbody.Bothstrategiesneededspecificspatialdesignstrategiesinordertomakebestuseoftheexistingenvironmentalforces,ashasbeendiscussedinthepreviouschapter.

Thermalcomfortasadesigncriterion,especiallyduringsummer,isstillafairlyrecentdesignparameter andhasonly fullydevelopedwith the introductionof air-conditioningand mechanical ventilation into the heating, ventilation, and air-conditioning (HVAC)systems of larger buildings. Unfortunately, matching thermal comfort with low energyconsumptionisoftenverylittleconsideredandunderstoodasaparameterforpreliminarydesign. The results are buildings with energy-consuming, deep plans that come with atighttemperaturecontrolsetpointandthatofferneithertheopportunityforacontinuousflowpaththroughthebuildingnoranoptiontoopenawindow.

6.1

Figure6.1

TherustichutasenvisionedbyMarcAntoineLaugierinhisEssayonArchitecture,writtenasanarchitecturalrulebookin1753,indicatestheprimaryneedforarchitecture:shelter.

StandardizingComfortThermalcomfortconsiderationsintheUSAareguidedbyASHRAEstandard55,3intheUKbyCIBSE,4andinGermanybytheISOstandardENISO7730.5Othernationalandinternationalstandardbodiesarealsorelevant.

Although ventilation standards and thermal comfort standards are related, they aredeterminedseparately.Thesameapplies to illuminationstandards,whichmaynotbeascloselyrelated,buttheyhaveajointsource:thesun.Inaddition,airtemperatureisnottheonlycriteriondeterminingthequalityofthermalcomfort,althoughitisoneofthemajor

6.2

6.3

influences.

Thermalcomfortstandardsandcomfortexpectationsoverthepast50to80yearshavechanged significantly, and the responsibility toprovide indoor environmental conditionsthatmeettherequiredcomfortstandardshasgenerallybeenpassedfromthearchitectstothebuildingserviceengineers,with theresult that therequirementsaremostlymetwithactive mechanical HVAC systems and not necessarily through spatial design. Thermalcomfortisrarelytaughtinthedesignstudio,butisaddressedintheenvironmentalforcesand systems classes and thus is often considereddetached from spatial or visual designconceptsandconsiderations.

Thermalcomfort is theconditionofmind that expresses satisfactionwith the thermalenvironment, and it is assessedby subjective evaluation (ANSI/ASHRAEStandard55–2013).3

Table6.1TheadaptivecomfortstandardaccordingtoASHRAE55–2013FIGURE5.4.2:Acceptableoperativetemperature(to)rangesfornaturallyconditionedspaces

Source:ASHRAE55–2013withpermission

Air-ConditioningAir-conditioning, or artificial weather, was basically invented byWillis Carrier (1876–1950)6intheearlytwentiethcentury.Itwasdesignedasameanstocontrolairhumiditycontentandasacoolingdevice,initiallyfordepartmentstores,theaters,andcinemasandlaterforthepost-warAmericandreamhome.7Air-conditioningisseeminglycontrollable,while natural air movement is seemingly not. Air-conditioning has led to a totaldetachmentofoccupantsfromtheoutdoorenvironmentanditsconditionsandcontributedtremendouslytothesoaringenergyconsumptionintheUnitedStatesandotherdevelopedanddevelopingnations.

ComfortResearch

6.4

6.5

Major steps towards the definition of thermal comfort parameters were conducted inclimatechambersinthe1960sand1970sbyOleFanger’sresearchteam.Theydeterminedthe predicted mean vote or predicted percent dissatisfied (PMV/PPD) model8 throughstudiesconductedintightlycontrolledclimatechambers.Furtherresearch9conductedbydeDearandBragerintheUSAaswellasNicolandHumphreyintheUKindicatedthatthis model was not suitable enough for thermal comfort understanding in naturalventilation spaces. The PMV/PPD model is not dynamic enough for the environmentcreated innaturallyventilatedbuildingsas itdefinesa toonarrowbandof temperaturesconsideredcomfortablebyusers.

ThermalComfortParameterThermalcomfortisamulti-facetedexperience,whichisgovernedbyfourvariablesofthethermal environment: air temperature, relative humidity, mean radiant temperature (thetemperatureofthesurroundingsurfaces),andairvelocity.Clothingaswellasactivityandthe metabolic rate of occupants are personal conditions, which also influence comfortperception. In addition, temperature stratification and temperature difference betweenheadandtoesmatter.Itwillbenearlyimpossibletocreateanenvironmentthatsatisfiesalloccupants.Therefore,thestandardrequiresonlyacertainpercentageofoccupantstohavea comfortable sensation in order to consider a situation to meet the definition of‘comfortable.’

Surface temperatureof adjacentwalls is as important, ifnotmore important, thanairtemperature for an occupant to express thermal comfort. Cooling the air around theoccupant is thus only one of multiple means to develop a comfortable thermalenvironment. Chapter 10 will highlight the relationship between controls, comfort, andnaturalventilation.

AdaptiveComfortStandardforNaturalVentilatedBuildings

Gail Brager, Richard de Dear, Fergus Nicol and many of their colleagues10 in theirsignificant body of work defined the thermal comfort sensation in natural ventilatedbuildings.Rather thanconductingclimatechamber investigations, theyconductedmanyfieldstudiesofactualbuildingsandtheiroccupants.ThesemultiplestudiesresultedinalongdebatewithinASHRAE’s standardcommittee, resulting in ageneral agreementonwhatisnowcalledtheadaptivethermalcomfortmodel.10Thismodeldoesnotaimforaperfect thermal comfort number, but acknowledges adaptability, changeability, usercontrol,andintuitionaswellasresponsestoseasonsandweather.11

Theadaptivecomfortmodel,asithasnowbeenincludedintheASHRAEstandard55–2013,3 is defined as “a model that relates indoor design temperatures or acceptabletemperaturerangestooutdoormeteorologicalorclimatologicalparameters.”10

Changingcomfort levels inrelationtotheexteriorclimateisanewinsight inthermalcomfortresearch,anditisofhighvalueandinterestwithrespecttonaturalventilationand

6.6

passivecoolingconcepts.Thenotionthatpeopleneedthesametemperaturelevelallyearround,takingneitherseasonsnortheexteriorclimatenorweatherconditionsintoaccount,hasproventobetoonarrowaconcept.12

ThermalDelightLisa Heschong’s Thermal Delight in Architecture13 is an exception in this discoursebecause it addresses the delight of diverse thermal experiences. While an intuitiveapproachaddressesthedesignofspaceeitherasageometricalcompositionorassensualphenomena,acombinationofbothisnecessary.“Thermalqualities–warm,cool,humid,airy,radiant,cozy–areimportantpartsofourexperienceofspace;theynotonlyinfluencewhatwechoosetodotherebutalsohowwefeelaboutthespace.”14

LisaHeschongalsoremindsherreadersthatthermaldelightcaninfluencethecreationofsocialcommunities.13Acommunityiscreatedbysittingaroundthefireplaceandtellingeach other stories over a cup of hot tea, or by hanging out on the porch swing andproducingalightbreezetofeelcomfortableintheheatoftheafternoon.Hangingoutontheporchalsoconnectedtheneighborsinastreet,allowedforsupervisionofkidsplayingin the front yards, and made the near-home urban environment most likely safer.Unfortunately, the porch as a communal space in the midwestern and southern UShouseholddisappearedwithair-conditioning.“Thewordsweusetodescribesuchplaces[suchasinglenooksandgazebos]–snugandcozyorairyandrefreshing–allimplythattheseplacesofferusasenseofthermalwell-being.”15

Heschong continues that we usually remember these childhood places fondly. Theygaveusjoyanddidnotleaveusasoccupantsneutral.Thefocusonthermalneutralityhaseliminated the care for thermal delight she already considered in 1979. Many of herexamples relate toheatingandwarmth, like theFinnishsauna,butshealsodrawscloseattention to the Islamic garden for cooling. “Other than the hearth, perhaps the richestexampleofa thermalplacewithaprofoundrole in itsculture is theIslamicgarden, thecooloasisthatisthetraditionalcenteroftheIslamichouse.”16(SeeFigure5.15.)

Figure6.2

FireplaceinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

Figure6.3

InglenookinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

Figure6.4

GazeboinHvitträsk,Kirkkonumi,Finland,designedbyHermanGesellius,ArmasLindgren,andElielSaarinenbetween1901and1903.

6.7

Figure6.5

UrbancourtyardinŞanlıurfa,Turkey,highlightsshade,water,andopeningsforventilation.

RelationshipofAirVelocityandComfortThe development of the adaptive comfort model was essential to generate a morestandardizedmodelfornaturallyventilatedbuildings,especiallyinwarmerclimatezoneswithhigherhumiditylevels.

TherearetwoparametersthatdistinguishtheadaptivecomfortstandardfromthePMVvote.Firstofall,elevatedairspeedincreasestheacceptanceofhighertemperatures.Thisisofcoursehighlyimportantfornaturalventilationinbuildings,astheyusuallyemployhigherairvelocities,butalsohighertemperatures.Air-conditionedbuildingsaredesignedtoshowhardlyanyperceivableairvelocity.Thustheadaptivecomfortstandardintegratesscenarioswhenindeedtheoccupantsopenawindow.

Second, the adaptive comfortmodel, unlike thePMVmodel, accepts the relationshipbetweenoutdoor climate and temperatures anddesired indoor conditions as dynamic oradaptive and acknowledges that people dress differently depending on whether theweather is niceornot.Thisprovides themodelwith theopportunity to raise indoor airtemperatureinsummerwithrisingoutdoortemperatures.

6.8

Thismodelappliesinparticulartooccupant-controlled,naturallyconditionedspaces,inwhichtheoutdoorclimatecanactuallyaffecttheindoorconditionsandthusthecomfortzone. In fact, studies by de Dear and Brager17 showed that occupants in naturallyventilatedbuildingsweremoretolerantofawiderrangeoftemperaturesthanthoseinair-conditionedbuildings.18Asavariablestandard,theadaptivecomfortstandardrequiresthechangeofindoorcomfortconditionswithoutdoorclimate.

Table6.2Comfortventilationw/higherairspeedaccordingtoASHRAE55–2013FIGURE5.3.3A:Acceptablerangesofoperativetemperature(to)andaverageairspeed(Va)forthe1.0and0.5clocomfortzonepresentedinFigure5.3.1.1,athumidityratio0.010

Source:ASHRAE55–2013withpermission

Thedownsideofatightlycontrolledindoorenvironmentalcondition,forexample72°F(22 °C) and 50 percent relative humidity, is the energy it takes to keep an indoorenvironment at such levels, in particular when the outside conditions change rapidly.Adjusting to these changes can consume a significant amount of energy because ofvariable dynamic and transient outdoor conditions. Adaptation results in a change inbehaviorbasedonareachedthresholdortolerancelevel.

Adaptation is a process over time that adjusts behavior to a condition of dynamiccontext.Adaptationalsorequiresactivecontrolopportunitiesfortheoccupants.Buildingswith adaptive comfort control operate under the “adaptive principle.” When a changeoccursthatrenderstheconditionuncomfortable,peoplegenerallyreactinwaysthattendtorestoretheircomfort.Theadaptivecomfortconceptisbuiltonsurveysconductedinthefieldandnotbasedonlaboratoryexperiments.

ThermalComfortandMetabolismThermalcomfortisdirectlyrelatedtothehumanmetabolismandtheneedofthehumanbody to keep a close to constant internal temperature of 37 °C (98.6 °F),which is thestable core body temperature, independent of the activity level of the person.

6.8.1

‘Thermoregulation’19 is the process directed towards maintaining this stable coretemperature.Mostbodyactivitiesrequireenergyandproduceexcessheat,eventhinking.Overtime,theheatproducedmustequaltheheatlosttotheenvironmentthroughourskin,otherwisewewilldevelopafeverorsufferfromaheatstroke.Wethusdonotdevelopafeverwhenweworkoutandincreaseourheartbeatrate.

In order to increase heat loss, more blood flows towards the skin to lower thetemperature; tominimizeheat loss, blood iswithdrawn fromhandsand feet inorder toreduce their temperature and to thus reduce heat lost through the skin. That is why inextremecoldconditions,toes,fingers,andearsfreezefirst,becausethebodytriestokeepthe vital functions of the body active. The body just refuses to circulate blood throughthoseouterlimbs,andintheworstcaseletsthemdie.

EnergyofMetabolicRateThemetabolicrateofoccupantsindicatesthemajoractivityundertakenbytheoccupantsandtheenergyproducedandreleasedbythatactivity.Thisenergyisimportantasenergyloadforthecoolingenergyneeded,butitisalsoanindicationoftherateatwhichheatisdissipatedfromthebodyandinfluencestheairtemperatureatwhichoccupantsexperiencecomfortdependingontheiractivity.Themetabolicequivalentoftask(MET)istheratioofmetabolicratewhenworkingtothemetabolicratewhenresting.

OneMET is defined as 58.2W/m2 (18.5BTUH/ft2) and provides a measure of theenergy(heat)releasedbyanaveragepersonseatedatrest.The‘standard’personexpendsenergy over a surface area of 1.8 m2 (19.5 ft2), so at rest approximately 100 W(341BTU/h)arereleasedtothesurroundings.AstandardlistofmetabolicratesisgiveninISO8996(2004).20These rateshavebeen recordedforasteady-statesituation,whereaseated person always sits and won’t get up.10 In real-world scenarios, people tend tochange their activity and that change also has an impact on their comfort perception,whichisdifficulttoaccountforandhasnotyetfoundawayintothestandards,becauseitwouldneeddynamiccontrolsettings,whicharedifficulttoachieve,aswillbediscussedinChapter10.Peopleinagymgiveoffaboutfivetimesasmuchthermalenergyasaseatedperson,whichhasadirectinfluenceontheirthermalcomfort.Tofeelcomfortable,theairtemperaturehas tobe lower thanforaseatedperson.Thiscomfortsettinginagymcanalsobeachievedbyturningonafanoropeningawindowandthusincreasingairvelocityandtheremovalofheatbyevaporationfromtheskin.

6.9

6.10

Figure6.6

Metabolicrate:thehumanbodyconstantlyexchangesthermalenergywithitsenvironment.

BehaviorandComfortPeoplehavecertaintolerancelevelsuntiltheyinterrupttheiractivityandcreateachangetotheircomfortconditionsbyputtingonasweater(changingclo–clothing–factor;1cloisequalto0.155m2K/Wor0.88°Fft2h/Btu),3bymovingaroundinthespace(changingmetabolic rate), bymoving into a different room, bymoving between different thermalenvironments,byopeningorclosingawindow,orlastbutnotleastbyturninguptheheatoractivecooling.

ClothingandComfortThe role of clothing is significant in maintaining thermal comfort. Clothes act likeinsulationfortheheatleavingthebodyaswellasaninsulatingbarrierbetweentheoutsideconditionandthebody.Airlayerswithintheclothesareasimportantasthematerialofthetextilesthatmakeuptheclothing.Theopportunitytotraphumidityinadryaridclimateissimilarly important, as is the opportunity for the skin to breathe and thus for sweat toevaporate.Therelationshipbetweenvarioustextilesandfabricsandthermoregulationandhuman thermal comfort was studied as early as 1873 by the German public healthresearcherMax von Pettenkofer in his notable lecturesThe Relations of the Air to theClothesWeWear,theHouseWeLivein,andtheSoilWeDwellon.21

Itisalsocommonknowledgethatpeopledressdifferentlywiththeseasons.Theywearlighter clothes in summer andheavier,warmer clothes inwinter.Dependingon culturalandbehavioral norms, people adjust their clothingwith the seasonsor on aday-by-daybasis.BasicPMVcomfortstandardsarebasedonofficeattirefortheconventionalofficeenvironment.3

Theactualequationgoverningtheheatbalanceofthehumanbodyisquitecomplexandconsidersallpotentialchangesnecessarytokeepthebodyinsteadystate.Thedeterminingfactors for the thermal heat balance of the human body are themetabolic rate and themechanicalworkdone.Here,theconvective,evaporative,andradiativeheatlostfromtheclothedbodyaswellastheconvectiveandevaporativeheatlostbyrespirationneedtobeconsidered.Asignificantportionofthemetabolicheatratewillalsobestoredwithinthebody tissue. All heat flows are determined by temperature differences as well as bysurfaceareaof thebodyandmultipleother factors related to thequalityof theclothingandtospecificpropertiesofclothingandthebody.Similarrelationshipsandfactorsexistforconvectiveheattransferandevaporativeheattransfer.

Table6.3CLOfactor(thermalinsulationofclothing)

Workingclothing CLO m2K/W

Underpants,shirt,trouser,socks,shoes 0.75 0.115

Underwearwithshortsleevesandlegs,shirt,trousers,jacket,socks,shoes 1.0 0.1555

Underwearwithshortsleevesandlegs,shirt,trousers,jacket,thermojacket,socks,shoes 1.25 0.19

Underwearwithshortsleevesandlegs,shirt,trousers,jacket,thermojacketandtrousers,socks,shoes 1.55 0.225

Underwearwithshortsleeves,trousers,jacket,heavyquiltedouterjacketandoveralls,socks,shoes,cap,gloves 2 0.31

Underwearwithlongsleevesandlegs,thermojacketandtrousers,parkawithheavyquilting,overallswithheavyquilting,socks,shoes,cap,gloves 2.55 0.395

Dailywearclothing

Panties,T-shirt,shorts,lightsocks,sandals 0.3 0.05

Underpants,shirtwithshortsleeves,lighttrousers,lightsocks,shoes 0.5 0.08

Underwear,shirt,trousers,sock,shoes 0.7 0.11

Panties,petticoat,stockings,dress,shoes 0.7 0.105

Panties,shirt,trousers,jacket,socks,shoes 1 0.155

Panties,stockings,blouse,longskirt,jacket,shoes 1.1 0.17

Underwearwithshortsleevesandlegs,shirt,trousers,vest,jacket,coat,socks,shoes 1.5 0.23

Source:Adapted fromF.Humphreys,MichaelA.Nicol,andSusanRoaf,AdaptiveThermalComfort:PrinciplesandPractice(London:NewYork,2012),p.101,Table8.1

Theadaptivecomfortmodelisbasedonfieldsurveysandpost-occupancyevaluationsand thusondirectanswersofoccupants toquestionsofcomfort. Ifanadaptivecomfortmodelisappliedtothedesignofabuilding,itisexpectedthattheoccupantsadapttheirclothingandbehaviortotheclimateoutside.10

Thus, thecomfort temperature isdirectly related to theclothesoccupantswear insidebuildings aswell as to their activities. Therefore a strategy such as the Japanese “Cool

6.11

Biz” campaign22 that allows office workers to dress less formally in summer, togetherwith setting the thermostat slightly higher, provides a laudable reduction in energyconsumption.AccordingtopressreleasesfromtheJapaneseministryofenvironment,thecampaign was a success and it was reinstituted as “Super Cool Biz”22 during theelectricity shortageafter the2011earthquakeand tsunami,which shutdownallnuclearpowerplantsinJapanandcausedamajorenvironmentaldisaster.

Table6.4MetabolicRatesfortypicaltasksaccordingtoASHRAE55–2013Table5.2.1.2

Activity MetabolicRate

MetUnit W/m2 BTU/hft2

Resting

Sleeping 0.7 40 13

Seated,quiet 1.0 60 18

Standing,relaxed 1.2 70 22

Walking(onlevelsurface)

0.9m/s,3.2km/h,2.0mph 2.0 115 37

1.8m/s,6.8km/h,4.2mph 3.8 220 70

OfficeActivities

Reading,seated 1.0 55 18

Typing 1.1 65 20

Lifting/packing 2.1 120 39

Misc.OccupationalActivity

Cooking 1.6–2.0 95–115 29–37

Lightmachinework 2.0–2.4 115–140 37–44

Handling50kgbags 4.0 235 74

Misc.LeisureActivity

Dancing,social 2.4–4.4 140–255 44–81

Exercise 3.0–4.0 175–235 55–74

Wrestling,competitive 7.0–8.7 410–505 130–160

Source:ASHRAE55–2013withpermission

OutdoorComfortandWindWhen a body is warm, a cool breeze will provide relief, but when a body is alreadyworking hard to keep warm, a cool breeze will feel chilly. The opposite is also valid:warm winds can be wonderful when one needs to warm up, but can create anuncomfortablesituationwhenonewouldrathercooldown.Thusoutdoorcomfortandthedesignofcomfortthroughthedevelopmentofmicroclimateenvironmentsshouldreceivemore attention in the future in order to provide improved comfortable outdoorenvironments. Therefore, increasing attention is focused on outdoor comfort, which isparticularly important inurbanareaswithhotclimates,butalso incolderenvironments,whereasunnywindlessspotcanbecomeahaven,thesamewayashadyspotcanbecome

6.12

anoasisinahoturbanenvironmentexposedtodirectsolarradiation.

This means that outdoor thermal comfort perception is as multi-layered as interiorcomfortperception.Intheoutdoors,radiationandconvectionareevenmoreimportantforcomfortsensationthantemperatureandhumidityalone.Thisrelatestoexposuretodirectorreflectedsolarradiation,wind,andtheabsorptionofheatfromthehumanbodythroughwind.Thisabsorptionisfacilitatedbysweatingandheattransferbyevaporation.Clothingisthemajormeanstocounterexternalradiationaswellasconvection.

Thebodysurfacetemperaturecanaverageatapproximately35°C(95°F).Inordertosimplifycalculations,thebodyinspaceisoftenestimatedasacylindricalrotationalbodyofadiameterofabout20cm(0.70ft).Forthisbody,Erell,PearlmutterandWilliamsonstateaheattransfercoefficient,whichmaybeestimatedbytheempiricalrelationof8.3×velocity0.6withanenergyheatfluxexpressedinW/m2.23Iftheairtemperatureisabovethe body’s surface temperature, the air is adding heat to the body, which can bedetrimentalforthemetabolismunlesssweatingsetsinandheattransferbyevaporationisutilized.MoreinformationaboutthisenergybalanceofahumanbeinginanurbanspacecanbefoundinUrbanMicroclimatebyErell,PearlmutterandWilliamson.23

A sweating person is under thermal stress, which can be expressed by the so-calledindexofthermalstress(ITS)whenevaluatingtheenergybalanceofaperson.AccordingtoErell, Pearlmutter andWilliamson, this termwas developed byBaruchGivoni23 andexpresses the overall thermal exchange between the body and its surroundings underwarmconditions.

TheITSisameasureoftherateatwhichthehumanbodymustgiveupmoisturetothe environment in order to maintain thermal equilibrium through severalmechanisms of evaporative cooling, particularly through the production of sweat.[…]Thus the value of the ITS is given in termsof equivalent latent heat (in totalwatts) also considering the cooling efficiency of sweating. For this measure it isimportanttounderstandtherelativehumidityoftheairandtheevaporativecapacityof the air given by thewind speed, vapor pressure and clothing. Sweating is thusmosteffectiveindryandhotclimateswithalightbreeze.24

OperativeTemperatureandComfortAccording to the adaptive comfort standard as it is currently understood,10 the meancomforttemperaturecanbederivedfromtherespectiveoutdoortemperature.Thisdirectnumerical relationship has been developed inmultiple comparative field studies and issummarizedinthelineargraph:

The implementation of adaptive comfort conditions might need significant complexcontrol algorithms to operate effectively. More about control strategies is covered inChapter10.

Table6.5GraphicComfortZoneMethod:Acceptablerangeofoperativetemperature(to)

6.13

andhumidityforspacesthatmeetthecriteriaspecifiedinSection5.3.1(1.0≤met<1.3;0.5<clo<1.0)–(a)I-Pand(b)SIaccordingtoASHRAE55–2013FIGURE5.3.1.ASHRAE55–2013withpermission.

VentilationandHumidityTheinfluenceofhumidityonhumancomfortisnotclearlydefinedandinsomerespectsnotevenclearlyknown.Itisobviousthatthepotentialforthermalcomfortinveryhotandhumidairconditionsissignificantlyreducedbecauseofthelowerrateofevaporativeheattransfer via sweating. Sweating in many cultures, especially in the Western world, ishighlydislikedandsometimesevenconsideredataboo.Althoughitmaycreatecomfort,itsuffers from low acceptance rates as a cooling strategy. The requirement to preventsweating in summer is not ametabolic concern, but a cultural concern.Sweating is themostfeasiblemeansofthehumanbodytoprovidecoolcomforttopeople.

Inhotanddryclimates,layeredlonggarmentsareworntopreventdehydrationduring

6.14

6.15

6.16

the hot day. Higher air velocity can expel higher air humidity, both in summer and inwinter,butinwintercaremustbetakentoprotectthestructuralintegrityofthebuildinginorder to prevent condensation on walls and colder surfaces. Condensation may causeissuessuchasmoldgrowththathavedetrimentaleffectsonairqualityandhumanhealthandshouldbepreventedatallcosts.Still,themolditselfisnottheoriginoftheproblem,but merely a symptom of lack of ventilation, while thorough misunderstandings ofcondensationatthedewpointwithinthebuildingassemblyleadstomoldgrowth.

TheConceptof‘Coolness’asaSocialRatherthanaHealthConcern

TheUnitedStatesisthemainuserofair-conditioning,partlybecausetheclimateinpartsof the country is not conducive to human comfort as perceived today. Summertemperatures exceeding 100 °F or 38 °C are not perceived as comfortable, evenwith acoolbreeze–inparticularinbuildingswithoutanymeansofpropellingairmovementorkeepingcoolinamorecontrolledmanner.Mechanicalcoolingturnedintoasocialstatussymbolandair-conditioningbecameawayoflifeandnotmerelyanecessity,asanalyzedbyMarshaAckermaninhercomprehensivebookCoolComfort:America’sRomancewithAir Conditioning.7 HenryMiller’s The Air Conditioned Nightmare25 repeats the notionthatAmerican lifestyle has detached itself fromnature.Miller also complained that thecomplacency created by comfort and convenience was an issue of the new Americanmiddle class and their dream of life. This relates directly to issues of productivity andefficiency raised on the North American continent related to the detrimental summerclimate as compared toEurope.Betterwork ethicswere related to cool climates,whileheat supposedly led to laziness and lackofproductivity.LewisMumford inTechniquesandCivilization,26 as quotedbyAckerman, found comfort tobemodernman’sgreatestachievement,butitputs“disproportionateemphasisonthephysicalmeansofliving.”27

ThermalLimitsinaNaturallyVentilatedBuildingWith rising concerns regarding energy consumption, climate change, and resourcedepletion,amongotherthings,thequestionis:Howwarmcanweallowittobecomeinanaturallyventilatedbuildingandhowoftenshouldorcanweallowit tobewarmerandstill feel comfortable in order to be less harmful to the environment?This reverses thedebaterecordedinAckerman’sthesisabouttheonsetofair-conditioning:Howcooldoesit need to be? Ackerman quotes Huntington, the author of the controversial bookCivilizationandClimate, as stating that “the uniformity of conditions promised by air-conditioning seriously impaired human achievements.”28 The answer is continuedresearch.

ThermalPleasureVersusThermalBoredom:TheConceptofAlliesthesia

There isnoagreement in thermalcomfort researchabout theneed for,usefulnessof,or

6.17

evendesireforincreasedairmovementinsideindoorenvironments.Whilethemechanicalventilationindustryaimsatminimizingperceivedairmovementinsideafullyconditionedbuilding, natural ventilation of course requires perceivable air velocity. In addition, thetoleranceforhighertemperaturesincreaseswithairmovement.RicharddeDear29goesasfar as to question the whole notion of thermal comfort as a neutral case. He and hisresearch teamaskwhywe shouldaim for thermalneutrality inside abuildingwhenwecouldpursuethermalpleasureoralliesthesia,ashenamesit.

The third andmost recent shift proposes a new approach to indoor environmentalquality, going beyond thermal comfort and reaching for thermal pleasure.Thermalcomfort is defined as the state of mind that expresses satisfaction with thesurroundingenvironment(ASHRAEstandard55–2010).Theemergentapplicationofthermalalliesthesia to the thermalcomfortexploredbydeDear (2010) investigatessituations in which a peripheral thermal sensation can assume either positive ornegativehedonic tone,dependingon the stateofcore temperature in relation to itsthermo-neutralset-point.29

TheconceptofalliesthesiacoinedbyCabanac(1971)impliesthepresenceofinternalsignalsmodifying the conscious sensations aroused from peripheral receptors. Forinstanceaccelerations inair speedonskinsurface triggerdynamicdischarges fromthe skin’s cold thermoreceptors. So, in the warm adaptive comfort zone theseturbulence-induced dynamic discharges from exposed skin’s cold thermoreceptorselicitsmallburstsofpositivealliesthesia.29

Beyondthephysiologicalissuesofskintemperatureandsensorialtriggers,itmaybeevenmore important that natural ventilation and movement of fresh air also have a strongpsychologicalcomponent,whichcouldbeexplainedassimplythejoyofandconnectionwiththeoutdoorsornotbeingenclosedinsideabuilding.Thisfeelingmaygoalongwiththesmellofearthorflowers,butofcoursenotwiththesmellofautomobileexhaustsoridling delivery trucks. Nevertheless, designing for thermal pleasure again becomes achallengeforthearchitectratherthantheissueofthermalcomfort,whichwaspushedintothecornerofthebuildingservicesengineersasitwasstuckbehindsuspendedceilingsandininvisiblecornersofthebuildingandwasnotpartofthearchitecture,thedesignofthespace.

EvaluatingThermalComfortConditions:TheThermalComfortCalculator

Air-conditioning and the advent of comfort standards seem to have gone hand in hand.The set point for air temperature seems to have guided the understanding of thermalcomfortforthelastfivedecadesofthetwentiethcentury.Theadaptivecomfortmodelontheotherhandacknowledgestheeffectofmanymoreinteractingvariablesatplayaroundthehumanbody,includingthestateofthehumanbodyitself.Thereforenewtoolshavetobeimplementedinordertounderstandwhichconditionsarenecessarytoprovidethermalcomfortorevenpleasuretooccupants.OneofthesetoolshasbeendevelopedbyRichardde Dear at the University of Sydney and can be found at the following link:

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http://web.arch.usyd.edu.au/~rdedear/.30 It provides output values for a variety ofinterdependentenvironmentalandbodyvariables.Thecomplexityof thisapproachmaymakeitlooktedious,buttheoutcomeofitsapplicationmayleadtoimprovedarchitecturalexperienceandimprovedcomfort.AsecondtoolhasjustbeenreleasedbytheCenterfortheBuiltEnvironment(CBE),Berkeley,andcanbefoundhere:

http://www.cbe.berkeley.edu/research/thermal-tool.htm.31

NotesMarc-AntoineLaugier,AnEssayonArchitecture,DocumentsandSourcesinArchitecture(LosAngeles:Hennessey&Ingalls,1977).

GottfriedSemper,TheFourElementsofArchitectureandOtherWritings,translationHarryFrancisMallgraveandWolfgangHerrmann(Cambridge,UK;NewYork:CambridgeUniversityPress,1989).

ANSI/ASHRAEStandard55–2013:ThermalEnvironmentalConditionsforHumanOccupancy(Atlanta,GA:AmericanSocietyofHeating,RefrigeratingandAir-ConditioningEngineers,2013).

CIBSEGuideA,Section1.3,http://www.arca53.dsl.pipex.com/index_files/thermco2.htm(accessed5/12/2014).

ISO7730:ErgonomicsoftheThermalEnvironment–AnalyticalDeterminationandInterpretationofThermalComfortUsingCalculationofthePMVandPPDIndicesandLocalThermalComfortCriteria(2005).

SeeWillisCarrier,http://www.williscarrier.com/(accessed5/12/2014).

MarshaAckermann,CoolComfort:America’sRomancewithAir-Conditioning(Washington:SmithsonianInstitutionPress,2002).

P.O.Fanger,ThermalComfort:AnalysisandApplicationsinEnvironmentalEngineering(NewYork:McGraw-Hill,1972).

RicharddeDearandG.S.Brager,DevelopinganAdaptiveModelofThermalComfortandPreference,FinalReportASHRAERP-884,MacquarieUniversity,Sidney,Australia,CenterfortheBuiltEnvironmentDesignResearch,UniversityofCalifornia,Berkeley,1997.

FergusNicol,MichaelHumphreys,andSusanRoaf,AdaptiveThermalComfort:PrinciplesandPractice(London;NewYork:Routledge,2012).

FergusNicol,“ThermalComfort:ANeedforaNewApproach,”in:M.Santamouris(ed.),SolarThermalTechnologiesforBuildings(London:James&James,2003).

R.J.deDear,“AdaptiveThermalComfortinBuildingManagementandPerformance,”in:E.deOliveiraFernandes,M.GaeirodaSilva,andJ.RosadoPinto(eds),ProceedingsoftheHealthyBuildingsConference,Vol.I(Lisbon:2006),p.31.

LisaHeschong,ThermalDelightinArchitecture(Cambridge,MA:MITPress,1979).

Ibid.,p.vii.

Ibid.,p.34.

Ibid.,p.ix.

R.deDearandG.S.Brager,“DevelopinganAdaptiveModelofThermalComfortandPreference,”ASHRAETransaction,104(1a),1998,pp.145–167.

NickBakerandMarkStandeven,“ThermalComfortforFree-RunningBuildings,”EnergyandBuildings,23(3),1996,pp.175–182.

“Thermoregulation”(definition),FreeMerriam-WebsterDictionary,http://www.merriam-webster.com/dictionary/thermoregulation(accessed5/12/2014).

ISO8996:ErgonomicsoftheThermalEnvironment:DeterminationofMetabolicRate(Geneva,Switzerland:ISO,2004).

M.vonPettenkoferandA.Hess,TheRelationsoftheAirtotheClothesWeWear,theHousesWeLivein,andtheSoilWeDwellon:ThreePopularLectures(London:N.Trübner&Company,1873).

22

23

24

25

26

27

28

29

30

31

“CoolBizCampaign,”Wikipedia,http://en.wikipedia.org/wiki/Cool_Biz_campaign(accessed5/12/2014).

EvyatarErell,DavidPearlmutter,andTerryJ.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London:Earthscan,2011).

Ibid.,p.120.

HenryMiller,TheAir-ConditionedNightmare(NewYork:NewDirections,1961).

LewisMumfordandL.Winner,TechnicsandCivilization(Chicago:UniversityofChicagoPress,1934).

MarshaAckermann,CoolComfort:America’sRomancewithAir-Conditioning(Washington:SmithsonianInstitutionPress,2002),p.143.

MarshaAckermann,CoolComfort:America’sRomancewithAir-Conditioning(Washington:SmithsonianInstitutionPress,2002),pp.8–26.

ChristinaCandidoandRicharddeDear,“FromThermalBoredomtoThermalPleasure:ABriefLiteratureReview,”AmbienteConstruído(PortoAlegre),12(1),2012,pp.81–90.

“HumanHeatBalance,”http://web.arch.usyd.edu.au/~rdedear/(accessed5/12/2014).

“CenterfortheBuiltEnvironment:CBEThermalComfortTool,”http://www.cbe.berkeley.edu/research/thermal-tool.htm(accessed5/12/2014).

Part2 Parameters

7.17.1.1

Chapter7

PressureasIndicatorGenerally, air is set in motion by temperature and wind, causing pressure differencesbetween the inside and outside of the building. The pressure is needed to overcomeresistance at the inlet opening and all other openings on the air flow path through thegeometry of the building. The difference in pressure will cause the flow of air.Temperature-inducedpressuredifferenceswillbediscussedfirstinSection7.1,andwind-inducedpressuredifferenceswillbe introduced inSection7.2.Eachventilationstrategyhasanimpactonthespatialconfigurationandcomposition,andthisimpactwillbeevenmorecomplexwhen the twostrategiesarecombined.Therefore,beforediscussing theircombined influence, temperature and wind-driven natural ventilation will be discussedseparately. For all natural ventilation strategies it is also important to take the externalconditionsofthedrivingforcesintoconsideration.Wewillthereforepayspecialattentiontourbancontextswheretheoutsidedrivingforcesaresignificantlydifferentthaninruralenvironments,asaddressedinSection7.3.

Temperature-InducedAirMovementStackVentilationorThermalBuoyancyVentilation

Hotairrises,expands,andbecomeslighter(seeFigures2.9and2.10).Buttowhatdegreedoes this affect natural ventilation and what conditions are required for buoyancy tofacilitatenaturalventilation?

It is important to understand the effect of temperature differences on air movement.Firstofall,temperaturedifferenceleadstopressuredifference.Thepressuredifferenceisaresultofthetemperaturedifferencebetweenthecolumnofwarmairinsidethebuildingandtheambienttemperatureoutsideofthebuildingaswellasoftheheightofthecolumnof warm air. According to the 1994 Building Research Establishment digest,1 for eachdegree of temperature difference between inside and outside, a pressure difference ofapproximately0.04pascalspermeterofbuildingheightiscreated.Thehigherthepressuredifference is at the top of the air column, the higher the induced air movement at thebottomof the column and inside the space.This phenomenonof airmoving out of thebuildingatthetopofthecolumnandmovinginatthebottomleadstothedevelopmentofaneutralplane,wherethepressuredifferenceswitches.

The ultimate goal of ventilation is to achieve the required air change rate (ACH) involume(cubic feetorcubicmeters)per timestep(hourorminute),whichrequiresveryspecificspatialproportionsanddesigndevelopmentsinordertopreventoldstaleairfromremaining in the occupied zone and to allow fresh air to enter the occupied zones of abuilding.

Important for the determination of the flow direction inside a building designed toutilizestackeffectventilationisthepositionoftheneutralpressurelevel.Freshairflows

inwardsbelowtheneutralplaneandstaleairflowsoutwardsabovetheneutralplane.Theposition isdefinedby the ratioof thedistancebetween theneutralplaneand thecenterlineofthebottomopeningtothetopopeningwithrespecttotheratioofthetemperaturedifferencemultipliedbythefractionoftheareasquared.Thepositionoftheneutralplaneshiftstowardsthelargeropeningproportionaltotheareaoftheopening,ascanbeseeninFigure7.1.2

Figure7.1

Definitionofneutralplane:theneutralplanedefinestheplaneintheheightofaventilationstack,whereinwardpullingairmovementforceschangetooutwardmovingforces.

There are two different strategies to achieve stack ventilation. The first one assumeshomogenoustemperatureswithinthebuildingandrequirestheinteriortemperaturetobehigherthantheoutsidetemperature.Thesecondstrategykeepstheoccupiedzoneswithinthebuildingbelowtheoutsidetemperature,forexamplethroughnighttimeventilation,andreliessolelyonthebuoyancyeffect.

Thus the spatialdimensionshave tobe setup specifically tocreateawarmair spacewithasignificantheightabovetheoccupiedzoneofabuildingsothatthestaleairflowsoutwards above occupied spaces and not through occupied spaces. Inlets for fresh airshould be positioned below the neutral plane and at a location in the building whereoutsideairisideallythecoolest.Theoutletontheotherhandshouldbepositionedabovethe neutral plan at the top of thewarm air column,where the space is thewarmest.Adesignershouldalsomakesurethattheoutletiswellabovetheneutralplaneandthatthewarm air will notmove through occupied areas, whichwould render them too hot foroccupation.

Figure7.2

Solarchimney:increasingthetemperatureatthetopofthestackincreasesthepressuredifferentialandthustheairchangeratebystackventilation.

A space that is exposed to solar radiation in order to facilitate the warming up and

7.1.2

consequently the risingofhotair iscalleda solarchimney.Sucha spaceshouldnotbeused for occupancy, exceptwhenused for a transitional space such as a staircase.Heatlossthroughtheenvelopeofthesolarchimneyrequirescautiousattention.Anatriumcanalsoactasa solarchimney, if the topof theatriumextendsbeyond the roof lineof thebuildingandprovidesadditionalsolarexposure.

Figure7.3

Thepressuredifferentialactiveattheinlethastobestrongenoughtoovercomethefrictionofairmovingagainstthematerialsandgeometryattheventilationinletopeningarea.

Buoyancyaffectsallairmovement,as there isalwaysacertaincombinationofwind-inducedventilationandbuoyancyventilation;forsimplicity,thestrategiesareintroducedseparatelyfirst.

User-operated windows can be designed as inlets and outlets for stack ventilation;however, especially at the topof abuilding, automatedvents and louversmaybemoreappropriatebecausethereistypicallyonlylimitedaccesstotheselocations.

Beforestartingtodesignfornaturalventilationbystackeffect,designersmustensurethat they have reduced heat gain as much as possible, utilizing shading, low-energy-consuming equipment, and lighting aswell as daylighting.Heat that does not enter thebuildingdoesnotneedtoberemoved.Thepressuredifferentialhastobestrongenoughtoovercomethefrictionworkingagainsttheflowinthetwoopenings.

PositionofNeutralPressureLevelItisimportanttounderstandthepositionoftheneutralpressurelevel(NPL)inthestackspace.BelowtheNPL,coolerairwillflowinwardstowardsthewarmerstackofrisingairandabovetheNPLwarmairwillflowoutwardstowardsthecooleroutsideair.Thesumof all inflow air volumehas to balance the sumof all outflow air volume.The drivingforceisgreatestattheopeningfurthestawayfromtheNPL.Withequalsizeopenings,theNPLispositionedhalfwaybetweenthetwoopeningsandwillshiftwithchangingopeningsizeandthedistancetotheneutralpressurelevel.Theheightoftheneutralplanecanbedeterminedbytheratioofthedistancebetweentheinletandoutletandthepressureatthe

inletandoutletarea.3Airdensitydependsupontemperature.

For each increase of temperature with height, there is a corresponding decrease inpressure.Windvelocityandpressuredropacrossanopeningdeterminetheairflowrateacross that opening. Stack pressure equals the pressure losses. Driving stack pressurevarieswithbuildingheightandthetemperaturedifferencebetweenindoorsandoutdoors.

Duringsummer,whenoutdoorairtemperatureiswarmandclosetoindoortemperature,thestackpressuredifferencesaregoingtoberathersmall,unlessthebuildingisverytall,andwillbemuchlowerthanwind-inducedpressuredifferences.Thus,summerventilationbased on stack ventilation can only be utilized if the upper stack gets really hot, forexamplethroughexposuretosolarradiation.

For a three-story building with a height of approximately ten meters, the differencebetween indoorandoutdoor temperature shouldbeabout23°Cor10Pa.Foraneight-story building, it should be approximately 10 °C. These temperature differences rarelyoccur in summer and thus most stack ventilation strategies are combined with windpressureinordertooperateattherequiredairexchangerate.4

Otherrulesofthumb5requirethatthestackoutletbeatleasthalfofonestoryabovetheceilinglevelofthetopfloor.

A stack terminal device can be added for a wind-buoyancy combined strategy. Thisdevice, combinedwith the air outlet on top of the stack, can respond to the prevailingwinddirectionandmaximizethenegativewind-inducedpressure.Theoutletonthetopofthestackshouldthereforealwaysbepositionedontheleewardsideofthewindinordertoenhancetheflowthroughwindinducedpressuredifference.

Figure7.4

Theheightrequirementofthestackisdeterminedbythetemperaturedifference,whichcanbeexpectedbetweenallinletscombinedandtheoutlet.

Buoyancy-drivennaturalventilationsystemsarethecommonchoiceforsystemsinthe

urbancontextbecauseoftheoftenreducedwindspeedintheurbanstreetcanyon.Inthissituation,solarassistedbuoyancycanalsobeanoption.

As with all controlled ventilation strategies, it is important that air infiltration bereducedsothatleaksdonotobstructtheairflowpath.

Figure7.5

Stackterminaldevicescanbedesignedjustasoutletsorasacombinedsystemofwindcatcherandstackexhaust.

TheAffleckHousewassimulated(furtherdetailsinChapter12)toexaminehowwindentersthroughtheventinthefloor(purpleregioninFigure7.6)andconvectsthroughthehousebeforeexitingthroughopenwindowsanddoors.

Figure7.6

SimulationoftheAffleckHouseshowingtemperatureandstreamlines.Enlargedviewsemphasizethewind

7.1.3

7.2

drawnintothefloorventandexitingthroughthewindowsanddoors.

ClassificationofStackVentilationStrategiesStackventilation lends itselfmore todeep-planspacesandcan thusengagemoreof thefull, three-dimensionally composed building than cross-ventilation.6 An active group ofresearchers in theUK aroundKevin Lomas developed fourmain spatial characteristicsthatdistinguish the spatialplacementof the inlet andoutletby theirpositionwithin thefloorplanofthebuilding.

Figure7.7

Thespatialplacementforstackventilationinletandoutletcanfollowavarietyofcombinations,asdescribedbyLomasetal.:Edgein–centerout/Edgein–edgeout/Centerin–centerout/Centerin–edgeout.

Wind-InducedVentilationInsidethearcade,ofcourse,thereisleastsunshinewhenthesunisblazingdownontheroof,andasitsopenwindowsallowthewesternbreezestoenterandcirculate,theatmosphereisneverheavyofstaleair.7

Pressuredifference iscreatedbywind impingingonabuildingfromacertaindirection.Positive pressure is created on the windward side, and negative pressure on the wind-opposing side. Wind-driven air flow over a building induces positive (inward-acting)pressures on windward surfaces and negative (outward-acting) pressures on leewardsurfaces; thus the building creates a pressure difference across the section that drivescross-ventilation.

Figure7.8

Windpressuredistributionaroundastand-alonebuildingshowsthepositivepressureonthewindwardsideandthenegativepressureontheleewardsideandonsurfacesperpendiculartothewind.

Windpressureonthebuildingdependsonthewinddirection,itsspeed,andtheshapeof thebuilding.According to the1994BuildingResearchEstablishment (BRE)digest,8the total wind pressure acting across a building is roughly equal to the wind velocitypressure.Windvelocityincreaseswiththeheightofthebuildingandisreducedinbuilt-upareasbecauseof theurbancanyoneffect.Onlyisolatedareasallowfortheutilizationofthefullmeteorologicalwindspeedmeasuredatanairportweatherstation.Airentersthebuildingononeside,sweepstheindoorspace,andleavesthebuildingontheotherside.Theidealwind-drivenpressuredifferenceforcross-ventilationis10Pa,butwinddirectionandintensitycharacteristicsareunsteadyandcanchange.9

7.2.1

Figure7.9

Anexampleforawindcoefficientdatamaponbuildingsurfacesdependingonheightandwidthofthebuilding.Thisinformationisavailableatavarietyofresources(CIBSE,p.54).

In order for wind-driven ventilation to work effectively, the pull from the negativepressure needs to be able to engage the air inside the full depth of the space to beventilated;thereforenaturallyventilatedspacesthatrelyonwindcanonlyhaveacertaindepth.Abasicruleofthumbrelatesthedepthofthespacetotheheightofthespacetobeventilated.Mostsourcessuggestaratiooffivetimestheheightforthedepthofthespace.Thus, increasing the height of the ceiling is of great value to the natural ventilationscheme.Inaddition, therealsoshouldbenooronlylimitedobstructionsinthespace.Ifobstructions exist, theyneed to haveopenings that resemble the size of the inlet (see amoredetaileddescriptionofopeningsizinginChapter9).

Figure7.10

Cross-ventilationisoftencombinedwithastackventilatedatriumtoincreasebuildingdepthandcoordinatewithdaylightingandcirculationstrategies.

Windasaresourceisneversteady,eitherinmagnitudeorindirection.Asaresult,thepressurefieldoverthebuildingvariesconstantlyandexactairchangeratesatalltimesforwind-inducednaturalventilationstrategiesarehardtopredict.

Cross-VentilationCross-ventilationoccurswheninletandoutletarepositionedonoppositeexternalwallsofthebuildingorspace,withaclearflowpathdesignedbetweenthem.Wind-inducedcross-ventilation can also be combinedwith a local stack component.Withmoderate to highinternalheatgain,thedepthofaventilationpathhastobelimitedtoaboutfivetimestheheightoftheroom.

The relationship between air velocity, inlet opening (e.g. the window), and depth ofspacecanresultindifferentmixingcharacteristics.AstheCFDsimulationsindicate(seeFigures 7.11 and 7.12), a larger opening creates larger mixing capabilities andrecirculation regions above and below the opening, independent of wind velocity.However, for a smaller opening, the wind is directed toward the end of the room and

7.2.1.1

largerrecirculationregionsformwhereusedairisnotreadilyexchangedbyfreshair.

Flow paths for cross-ventilation strategies need to be properly designed as a spatialcontinuum.Thesmallestopeningalongthepathdeterminestheairchangerate.

Cross-ventilationcanbeintroducedatahigherlevelanddistributedovermultipleinletsinto a variety of floors. Double-skin façades can also be used to even out pressuredifferentials across the façade, as will be further discussed in Chapter 8 using theKreditanstaltfürWiederaufbau(KfW)casestudyproject.

Cross-ventilation disproportionally mixes incoming air with current room air. Thismeansthattheairattheinletisfresherandcoolerthantheairclosertothecenterofthespace because air picks up heat and pollutants fromoccupants and equipment along itspath.Thisisanothermajorreasontorestrictthedepthofaroom.

Anatriumorcourtyarddesignedforstackventilationcanactasaventilationoutletandthusextendthedepthofthebuildingwhilestillprovidingaflowpathforcross-ventilation.A stack in an atrium can act as the negative pressure generator that creates a pressuredifferenceacrosstheventilatedspace.Thus,bothsidesalonganatriummaybeasdeepasfivetimestheheightofthespaceandstillcreateproperventilationandallowindaylight,aslongastheatriumisproperlydesignedtopromotestackventilation.

Flow rateswill varywith the seasons, and thus strategieshave tobe evaluated for atleast three major scenarios (winter, spring/fall, summer). Designing wind-inducedventilation strategies starts by incorporating wind as a resource to force air flow. Thisimplies anunderstandingof howwindvelocity extendspressuredifferentials across thefaçade. It is also important to take the influence of geometry and wind pressure intoconsideration,especiallyattherooflevel.

BasicProportionsandStrategiesforWind-InducedCross-VentilationTheair change rate forwind-inducedventilationcanbe fairlyeasily foundutilizing thecomputationalrelationshipthattheairchangerateequalstheflowratewithrespecttotheoverallvolumeofthespacewithrespecttotherequiredtimestepofonehour.Theflowrateiscomputedbasedontheairvelocityattheinletandtheareaoftheopening.

With the volumetric flow rate and the flow velocity into the room, the basic spatialproportionalruleofthumbforcross-ventilationcanbemodeledandsimulated,wherethedepthoftheroomequalsfivetimestheheightoftheroom.Oncesteadystateisreached,thevolumetricflowrateattheoutletwillbeequaltotheflowrateattheinlet.Toverifythatthetime-dependentsimulationshavereachedsteadystateconditions,theoutletflowrate is calculated tomake sure it is equal to that at the inlet. Three rooms of the samedimensionswithdifferentinlet-to-outletratiosweresimulatedtotesttheinfluenceofinlet-to-outlet ratio on air flow rate. The time-dependent computations were conducted forwind-drivenscenarioswithbothlowwindvelocity(V=0.5m/s)andhighwindvelocity(V=5m/s).ThevaluesfortheairchangeratearelistedinTable7.1.

Results are shown inFigures7.11and7.12 for thedifferent roomconfigurations andwind speeds. Velocity vectors and streamlines are used to help identify the air flow

patterns.ThesteadystatesolutionsforRoom1–1(smallinlet,largeoutlet)andRoom1–3(smallinlet,smalloutlet)areverysimilarbecausetheinletwindowsofthesetworoomshave the same size. Although the results for Room 1–1 are not shown here (but areincluded inDetaranto’s2014 thesis10), the streamlinesandvelocityvectorsarevirtuallyundistinguishable. There are minor differences at the outlet due to the different outletopeningsize.OfcoursetheACHisidenticalbecausetheinletareaisthesamesize.Thestreamlinesandlocationsofeddiesthroughoutthetworoomsareverysimilarinsizeandlocationandtendtofollowregionswithatemperaturegradient.ThesamepatterncanbeseeninRoom1–2(largeinlet,smalloutlet).Obviouslythemostimportantfactorsarethewindvelocity and the area of the inlet.With the sameopening size, a ten times highervelocityleadstoafivetimeslargerairchangeratebasedonafivetimeslargervolumetricflowrate.Table7.1alsoshowsthatboththeairchangerateandthevolumetricflowrateincreasewithincreasinginletarea.

Table7.1Airchangeratesforcross-ventilationdependingonwindvelocity,volume,inletarea

Figure7.11

Wind-drivenflowforcross-ventilationinRoom1–2for(top)lowvelocity(V=0.5m/s)and(bottom)highvelocity(V=5m/s).

7.2.2

Figure7.12

Wind-drivenflowforcross-ventilationinRoom1–3for(top)lowvelocity(V=0.5m/s)and(bottom)highvelocity(V=5m/s).

Single-SidedVentilationSingle-sidedventilationdescribesasituationwhenwindentersandleavesthroughalargeopening or through two openings spaced apart on the same side of the building/space.Single-sided ventilation is the most de-central natural ventilation strategy and it canoperate independently in different parts of the building. Air exchange occurs by windturbulence, resulting in air alternating pushing in and exhausting out of the space,dependingonthechangingpressuredifferenceacrosstheopeningandbetweeninsideandoutsideofthespace.Thiswillresultinafluctuatingpressureandthuspressureandflowdirection will be constantly reversing, thus mixing and displacing the exhaust air withfresh, incomingair.Outwardopeningscanenhancesingle-sidedventilationbyengagingtheexternalairstream,whichcanbefurtherenhancedbya localstackeffectwithin thespace.Single-sidedventilationcanproviderequiredairchangeratesforuptoadepthoftwoandahalftimestheheightaslongasthespaceandtheopeningportionofthewindowareaequalapproximately1/20thofthefloorarea.Single-sidedventilationismostsuitablefor cellular room environments, such as offices,while cross-ventilation requires a flowpath that spatiallyconnects twosidesof thebuilding.Cross-ventilation ismore suitablewhenanopen-planenvironmentisplanned.

Single-sidedventilationusuallyresultsinlowerventilationratesthancross-ventilation,anditcanpenetrateonlyashorterdistanceintothespace.

Withinternalheat loads,single-sidedventilationisalsoachievedbyacombinationofwind-andbuoyancy-drivenventilation.Whenopeningsareprovidedatdifferentheightsaboveeachotheronthesamesideofthefaçade(onemoretowardsthetopofthespaceandonemoretowardsthebottom),wind-driventurbulencecombineswithtemperature-orbuoyancy-drivenforcesinordertoexchangeair,slightlyexpandingthedepthtowhichairwillbemixed.

Figure 7.13 shows steady-state simulations of velocity vectors and streamlines for

7.37.3.1

wind-drivenflowwherethespacingbetweentheopeningsistheonlydifference.Room2–1hasalargerverticaldistancebetweentheopeningsthanRoom2–2.Awindspeedof1m/swasused in the simulations.TheACHshown inTable7.3 is identical because therooms have the same volume flow rate. However, Room 2–2 shows that the airrecirculatedinaregionabovetheupperopeninganddoesnotreadilymixwiththerestoftheairintheroom.Thebettermixingstrategywouldbetohavetheopeningsseparatedbyalargerdistance,suchasinRoom2–1.

Figure7.13

Wind-drivenflow(V=1.0m/s)forsingle-sidedventilationin(top)Room2–1and(bottom)Room2–2.

Bothcross-andsingle-sidedventilationstrategiesarediscussedfurtherinChapter12inrelationtomodelingtechniquesandtheeffectsofwindversusbuoyancydominatedflows.

Table7.2Airchangeratesforsingle-sidedventilationbasedonwindvelocityforRooms2.1and2.2

Parameters Rooms2–1and2–2

WindvelocityV(m/s) 1.0

Volume(m3) 760

Inletarea(m2) 0.6

Outletarea(m2) 0.6

Volumetricflowrate(m3/hr) 2160

ACH 31

WindPatternsintheUrbanClimateContextPopulationinUrbanAreas

According to the United Nations, “the world is undergoing the largest wave of urbangrowth in history.”11 In 2013, more than half of the world’s population lived in urbanareas.Urbanareasaredefinedbyaheightened levelofpopulationandbuildingdensity,

7.3.2

whichaffects the innerurbanclimateaswellashumanindoorandoutdoorcomfortandwell-being.Thusthepotentialfornaturalventilationneedstobespecificallyexploredindensecities.

Figure7.14

AerialviewofaverydenseurbanenvironmentinaresidentialquarterofMumbai,India.

The influences are manifold and there is a continuous feedback loop between theinteriorandexteriorclimaticconditions.Thespatialproportionoftheopentothebuilt-upspacestronglydeterminesthewindpatternanditsstrengthinsidethecity.Mostbuildingsact asanobstacle to themajorwind flowpatterns,notonly reducing thepossibility fornatural ventilation in the urban context, but also increasing the temperature differencebetween inside and outside conditions, causing the so-called urban heat island (UHI)effect. Buildings are thus both sources and consumers of thermal energy in the urbanlandscape.

UrbanPatternsandtheModernMovementThelayoutofthecitywasthesubjectofamajorarchitecturaldebateintheearlytwentiethcentury. The dense urban working-class neighborhoods of the industrialized latenineteenth-centurymetropolitan cities had created environmentsmoreor less unsuitableandseverelyunhealthyforhumanoccupation.Tuberculosisandotherrespiratorydiseasesweremajor issues and the outcry for a new urban environment was born: theModernMovement,dasNeueBauen,orModernism.MainlyEuropeaninorigin,theproponentsofCIAM(CongrèsInternationauxd’ArchitectureModerne)metbetween1928and1959to

discuss and spread the major architecture principles of the Modern Movement. Thecongress was initiated by Le Corbusier. Its most influential manifesto was The AthensCharter,12developedin1933andmainlyaddressingurbanandsocialissues.TheAthensCharterledtoconceptsandnewurbanplansforcitieswithlesstightlyspacedbuildingsand more open and green areas. The report of the third CIAM congress says: “Theinhuman character of large cities was evident to all from the outset and the need totransformtheirstructureentirelyagreedupon.”

ThemottoLichtLuftSonne(“Light,Air,Sun”)wasalreadycoinedinthelateeighteenthcenturybytheearlygroupofsocialutopiansincludingtheFrenchCharlesFourier,13 theBritish Robert Owen,14 and the German Franz Heinrich Ziegenhagen.15 They allconnectedthedevelopmentofutopiansocialorsocialisticidealswithanewwayoflivingandanewurbancitylayout.Ziegenhagen16inparticularrelatedsocialandhumanhealthtoareconnectionofcitydwellerstonatureandthenaturalelements.Heconsideredaccessto sunlight and pure air as the basis for good living conditions. This parameter led tovariousarchitectural formsof lowerdensityon thegroundand improvedaccess to sun,light,andair.

The relationshipbetweenurban layoutand freshairwasalsopartof theGardenCitymovement, which originated in England as a response to the dense working-classneighborhoodsofEnglishmill towns suchasManchesterwherehealth issueswerealsomajor concerns. Ebenezer Howard’s “Garden City” proposal17 is known for its iconicthreemagnets:town,country,andtownandcountry.Thethirdmagnet,townandcountry,istheidealgardencityforHoward.Itwouldtakethebestfromthecountry(pureair)andthebestfromthetown(socialopportunity),whileavoidingtheworstofthetown(foulair)and theworstof thecountry(lackofpublicspirit),andcombine themintoanewurbanfabric:thegardencity.

ButCIAMrealizedthatthesinglefamilyorthesemi-detachedhousesproposedbytheEnglishGardenCitymovementwerenottheanswertotheissuesofurbansettlementsonthewhole,becausetheywouldspreadoutthecitytoofar.High-risedwellingsneededtobestudiedinordertodeterminetheirimpactondwellingandwhethertheywouldbeabletodeliver“notthedisseminationoftheelementsofthecity,butrather…theaerationofthe city.”Therefore, the immeublevilla18was conceived byLeCorbusier in 1922, in acoupleofspeculativedrawings,whichliftedthesinglefamilyhouseupintotheair.19

Figure7.15

EbenezerHoward(1850–1928)describedthebenefitsoftheGardenCityinthisdiagramofthreemagnets,wheretheGardenCityprovidesthebestofbothworlds:freshairandsocialopportunity.

LeCorbusier’sLaVilleRadieuse,orRadiantCity,20becameoneofthemostprominentexamplesofthenewideal,andthe1957HansaviertelinBerlinmaybeoneofitsbestbuiltexamples.He again proclaimed that air, sound, and lightwere the elements of the newcity,theRadiantCity.21TheAthensChartermournedthedisappearanceof“urbanlungs”and related high population densities to a permanent state of disease and discomfort(Observation9).WhileZiegenhagenstillappliedoperablewindowstohisutopiancolonyresidential quarters, Le Corbusier’s answer to “doctors and the fitters of heating andcooling systems “unfortunately was: “exact air prepared in thermal power stations,disinfected,dustfree,givenasuitabledegreeofhumidity,pureandready.”22Observation12oftheAthensCharterpostulatedthat“theair,whosequalityisassuredbythepresenceofvegetation,shouldbepureandfreefromboth inertdustparticlesandnoxiousgases”anddeclaredsun,vegetation,andspaceasthethreerawmaterialsofurbanism.

CIAMalsonoted inObservations13and14 that themostdenselypopulateddistrictswere located in the least favored zones, while the well-to-do lived in the areas withabundant sunshine and pleasing views, sheltered from hostile winds. Observation 16promoted the separation from traffic and habitation to avoid the noxious gases in theexhausts.

Requirement23stated:

Wemustseeksimultaneouslythefinestviews,themosthealthfulair(takingaccountofwinds and fogs), themost favorable slopes, and,wemustmake use of existing

7.3.3

verdantareasanddetermineamaximumpopulationdensity.Tointroducethesunisthenewandmostimperativedutyofthearchitect.

CIAM thus promoted a radically differentway of designing, zoning, and operating theurbanenvironmentaftertheriseofvehiculartrafficandtheoverpopulationofcitiesduringthesecondhalfof thenineteenthand the first twodecadesof the twentiethcenturyhadalreadycauseddetrimentalchaoticurbanconditions.

Figure7.16

LeCorbusier’siconicmodelfortheRadiantCity(VilleRadieuse)incorporatestheobservationsofCIAM’sCharterofAthensandreducestheurbandensitywhileproposinghigherbuildings.

Yet,themassivereconstructionoftheEuropeancitiesandarisingsocialissuesledtoaseriousbacklashagainst thenewurbanmodels inthe1960s.Inthe1970s, theEuropeancity was reinvented conceptually, for example during the reconstruction of Berlin after1990, namedCritical Reconstruction.23 Still, inmost developing nations, urban densitywas a necessity rather than a choice. In the developing world, density and high-risedevelopmentseemtohavebecomeeconomicnecessities.Urbandensityisthuscrucialnotonly to understand wind patterns but also to develop solutions for sustainable citysolutions.

UrbanMeteorologyThissectioncoverstheaerodynamiccharactersofcitiesasdescribedinmultiplescientificsourceswithinthefieldofurbanmeteorologyandurbanmorphometry.24

Windingeneralisahighlyvariableandirregularphysicalphenomenon,evenmoresoin theurban context,wherewind is generally reduced compared towindover theopenlandscape,andthedirectionofwindcanbesignificantlyaltered.Inaddition,windpatternsspecificonlytourbanareashavetobeconsidered.Everyurbanspatialplanningprocessshapesthewindandenergyflowswithinthearea,asinturnitisshapedandinfluencedbytheseflows.

Urbanclimaticconditionsarecomplexandsubjecttoscientificresearchallacrossthe

7.3.4

globe. For example, the urban heat island (UHI),25 analyzed as early as the 1940s byHelmut Landsberg, affects surface temperature depending on material, color, andreflectivity and vice versa. Beyond temperature, the urban wind patterns are crucial topedestriancomfortaswellasbuildingventilation,airquality,andenergyuse.

The layer of air in which the effects of the solid surface can be felt is called theboundarylayer.26

UrbanTypologyInordertounderstandthebasicrelationshipbetweenurbanspacesandtheirpotentialfornaturalventilation,thespaceshavetobeevaluatedbasedontheirstreetcanyonproportionand the relationship to wind direction and other climate aspects, such as diurnaltemperatureswings,whichareimportantfornighttimeventilation.Erell,Pearlmutter,andWilliamson27developedimpressivedatabasesforstreetcanyonproportionsandresultingwindpatterns.Inordertovisualizetheseproportionalrelationships,Figures7.17 to7.19show the major street canyon proportions of select cities to correlate the findings byGrimmond and Oke as well as Erell, Pearlmutter, and Williamson with actual urbanlandscapes.

Figure7.17

BasedonGrimmondandOke’surbanmorphometry,weanalyzedtheurbanproportionofeightglobalcities(Ames,Iowa,Tokyo,London,CapeTown,Berlin,Chicago,Barcelona,SaoPaolo,andGenoa)andfoundthatallofthemhadaverysimilarstreetcanyonproportioninspiteofdiverseheightandwidthofblocks.

Figure7.18

7.3.5

UrbanCanyonsectionaldiagramshighlightingthediversityofsection.

Figure7.19

UrbanCanyonfiguregroundcomparisonandplandimensions.

Table7.3Calculatedurbanmorphometryratiosforvariouscities(basedonGrimmondandOke24)

WindandtheUrbanStreetCanyonThemajorparameteroftheurbanclimateisthespatialdistributionofbuildings,indicatedby the spatial proportions between height,width, and length of the so-called height-to-widthaspect ratioof the street canyon. In addition, thedistributionofopengreenareasandofbodiesofwaterwithintheurbanfabricneedtobeevaluated.AsCIAM’sAthens’sCharter28alreadynoted,greenareasactasthelungofthecityandimprovethehealthofcitydwellers.

Theurbanboundarylayerisdefinedastheportionofairthatshowstheeffectsofthesolidsurfacesoverwhichtheairflows.Althoughwindflowcausedbypressuredifferenceusuallyprogresseshorizontally,withintheurbanboundarylayerthispatternchanges.Theflowchangesrelativetothepropertyofthesurfaceandisaffectedbyobstructiveobjectsinitsway.Sharp-edgeobstacles,suchasrectilinearbuildings,causeaseparationoftheairflow,whilerounderobjectsallowtheairtoadheretothesurface.

7.3.6

The approach direction of air movement is only partially of importance wheninvestigatingtheflowaroundanisolatedobjectorbuilding.Thepatternwillstillbeverysimilar; only thevelocityof air impingingon the surfacewill changedependingon theangleatwhichthebuildingisimpingedbythewind.

Onceseveralbluffbodiesaremovedclosetogether,theurbanareaisformed,andthusthethreedistinctairflowzonesidentifiedearlierwillbegintooverlapandmerge,creatingthe specific urban street canyonwith air flow patterns very different from those in theopenfield.Inthisscenario,theairflowwithinthestreetcanyonrelatesmainlytotheflowdirectionofthewindabovetheurbancanopylayer.AccordingtoErellandPearlmutter,27three wind regimes have been identified as flow patterns across urban canyons:perpendiculartothestreetcanyon,paralleltothestreetcanyon,andatanoddangletothestreetcanyon.All threearecharacterizedbyspecificsecondaryflowswithin thecanyonand thecomplexityofair flowineach ischaracterized in termsofspeed,direction,andturbulence.

The most complex scenario related to building ventilation is the flow pattern thatdevelopswhen thewind blows perpendicular to the street canyon. In this case, the airwithinthestreetcanyondevelopsvorticessimilartocorkscrewsandtheseflowpatternsconstantlyalternatetheinletandoutletfunctionofventilationopeningswithinthestreetfaçade.Thestrengthandextentofthevortexinthecanyondependsonwinddirectionandstreetproportions.

ObstaclestoFlow/FlowAroundBuildingTheflowofairaroundanobstacleisdefinedbytheshapeoftheobject.Thelaminarflowofair is separatedby sharp-edgedobjects, the so-calledbluffbodies,while theair flowadheres to rounder objects such as valleys and hills. Most urban construction can beconsideredbluffbodies.Generallyspeaking,theflowisseparatedbytheobject,andthreedifferent zonesaround thebuildingcanbe identified: thedisplacement zone, thecavity,and thewake.Veryclose to thebuilding the flowwill reverseand turnaroundon itselfintosmallcircularpatternsofairmovement,alsocallededdies.29

Figure7.20

Schematicsectionoftheurbanatmosphere,differentiatingbetweentheurbanboundarylayer(UBL)andtheurbancanopylayer(UCL)withroughnesssub-layerandmixedlayerastransitionzonesinbetween.

Figure7.21

Thedistinctzonesdevelopedbyairflowingaroundanobstacle:thedisplacementzone,thecavityzone,andthewake.

Whenairflowsparalleltothegroundandhitsanobject,fourzonesarecreated:thefirstzoneisthezonewheretheairapproachesthebuilding(onthesidefacingthewind),thesecondisthezoneabovetheroof,andthethirdisthezonecalledthe‘wake,’whichisa

zone downwind. The in-between zone forms the cavity zone. The height above thebuildingatwhichtheairflowremainsundisturbedisroughlyestimatedtobethreetimesthe height of the building. If urban elements are spacedwide apart, each buildingwillcreate these zones, aswill large trees.Within the closer vicinity of a building, smallerscaleflowpatternswillform,whichcancreateratherhighwindspeeds.

Turbulence structures will form behind the building, where the pressure differencebetweenthelowpressurewakezone(aroundleewardandsidefaces)andthegeneralflowis strongest.Turbulencewill also form in frontof thebuilding,where the flowstarts toseparate. Large masses of buildings can thus have a strong influence on the air flowaroundtheiredges,impactingoutdoorcomfort,butalsoonventilationinlets,whichmightbepositionedatthoseedgeswithturbulentflows.

These flow patterns overlap when buildings are closer together and thus createdistinctly different sets of flows that can be identified by their character and roughlydeterminedbythestreetcanyonaspectratio.Consideringwindintheurbancanyon,onecan distinguish the difference between wind flow parallel with the street canyon orperpendicularwiththecanyon.

When thewind flowsparallel to the street canyon, thewind inside the street canyondevelops in the same direction. When wind approaches perpendicular to the streetdirection, the air starts to develop a variety of vorticeswithin the canyon that interfacewiththeupperlayerflowonlyatcertainmoments.

Figure7.22

Flowaroundsharpedgeobjectscreatesturbulence.

7.3.6.1

7.3.6.2

7.3.6.3

Figure7.23

Urbansurfaceenergybalanceandexchangeofheatbetweenurbanzoneandtheatmosphericsurfacelayerabove.

Figure7.24

Streetcanyonwindpatternschangesignificantlywiththegeometricrelationshipofprimarywindflowtostreetdirection.

IsolatedRoughnessFlowWhenthespacingbetweenbuildingsisrelativelylarge,thatis,theH/Wratioislessthan0.3–0.5, the flowfieldsofconsecutivebuildingsdonot interact.Thus theseurbanareascanbeconsideredasisolatedbuildings.27

Figure7.25

Isolatedroughnessflowoccursinurbanareaswithbuildingsspacedfarapart(H/Wratiolessthan0.3–0.5).

WakeInterferenceintheUrbanCanyonWhenbuildingsareclosertogether,forexamplewithanaspectratiobetween0.5and0.65,secondaryflowsaregeneratedwithinthecanyonspace,wherethedownwardflowofthecavityeddyisreinforcedbythedeflectiondownthewindwardfaceof thenextbuildingdownstream.27 Thus, the bolster and lee eddy work together to increase turbulence.Despitethemoreturbulentcirculation,averagewindspeedsaregenerallylowerthanwhenbuildingsarespacedfurtherapart.

SkimmingFlowRegimeWhensuccessivebuildingblocksare tightlyspaced, forexamplewhen theH/Wratio isgreaterthan0.65,thecanyonmaybeconsideredshelteredfromthedirectimpactofwindsperpendiculartoitsaxis.27

Urbanmicroclimateisstronglyinfluencedbytheinnerurbanproportionalrelationshipbetween built-up areas and open areas such as lakes and parks. These flows aredeterminedbyinnerurbanbreezesinducedbylocaltemperaturedifferences.

7.3.6.4

7.3.7

Figure7.26

Wakeinterferenceflowintheurbancanyonoccurswithaspectratiosbetween0.5and0.65wherethezonebehindthebuildinginterfereswiththezoneinfrontofthenextbuildingtocreatefairlyturbulentmixingsituations.

Innercanyonairflowisalsoinfluencedbysolarradiation,whichreachesintothestreetcanyonandheatsitup.Thesepatternsoverlapwithwind-inducedpatternsand influenceairmovementrelevantforventilationaswellasurbanairquality.

Figure7.27

Skimmingflowregimeoccurswhenthebuildingsareclosertogetherandtheprimarywindflowskimsacrossthecanyonandthebulkofthefreshairflowdoesnotenterthestreetcanyon.

Urbanflowpattern ismainlycharacterizedby turbulencearoundbuildings,and inletsand outlets will change their function depending on the specific flow regime. Anotherissueinfluencingthecapacitytonaturallyventilateisthefactthatairspeedsaregenerallylowerwithintheurbanareathanovertheopenlandscape.

FlowFieldsabovetheCityTheurbanfabricalsoinfluencestheflowfieldandthetemperaturedistributionabovethecity.30Themost obvious and commonlyknownphenomenon is related tohot air risingandthebubbleofhazed,warmerairhoveringaboveeachmajorurbanagglomeration.

InfluenceofUrbanClimatologyonUrbanPlanningandArchitecturalDesign

A variety of wind velocity profiles can be identified over various distinct terrainconditions and in particular over urban conditions. Ideally, for urban sites site-specific

7.3.7.1

•

•

•

7.3.7.2

7.3.7.3

7.3.7.4

climatedatashouldbeused,andtheseareoftenhardtoobtainowingtotheuncertaintyoftheinnercanyonturbulence,unlessthesitehasitsownweatherstation.

Forexample,becauseoftheshiftingpatternsofairmovementinsidethestreetcanyons,theventsintheurbancontextneedtobedesignedbothasinletsandasoutletsinordertoaccountfordifferentwinddirectionsandthereversaloftheflowinthecanyon.

ClimaticCoolingPotential(CCP)Major parameters in the urban environment influencing the potential for naturalventilationare

Reducedwindspeed

Increasedtemperature

Variabilityanduncertaintyofairflowpatternsanddirections.

This is of particular importance for nighttime ventilation inwarm or hot climateswithincreased night temperatures in the urban context. For this scenario, Erell, Pearlmutter,andWilliamson developed a calculation methodology to evaluate the cooling potentialcalledclimaticcoolingpotential(CCP).31

ThermalInfluenceonUrbanAirFlowIfonesideofthestreetcanyonisexposedtosolarradiationandwindisweak,buoyancyforcesinterferewiththewind-inducedstreetcanyonvortexandmostwilllikelysplitthevortex. If strong solar heating on the canyon walls or floors warms the canyon in thedirectionofthewind,thevortexinthestreetcanyonwillseparateandtwooutwardflowsoneithercanyonwallwillbecreated.Ontheotherhand,solarheatingoftheleewardwallwillreinforcethecorkscrew-likestreetvortex.Theeffectofthermalbuoyancycausedbysolarradiationdiminisheswithstrongerwindacrossthestreetcanyon.31

InteractionofAirFlowintheUrbanBoundaryLayer(TheCity)withotherFactors

Wind speed in the Earth’s atmospheric (or planetary) boundary layer usually increaseswithheightabovesurface.Withanurbanroughnesslayer,thestartingpointoftheverticalprofile is moved upwards away from grade level, because the surface of the groundprovidesafrictionaldragowingto theroughnessof thesurface.Smoothsurfacescreatelessfrictionthanroughersurfaces,similartoothermovements,forexamplethoseofcars.Theurbansurfaceisrougher thananyothersurfaceontheplanetEarth,exceptforhighmountainranges,whichindeedalsocreatetheirownspecificclimate.

BoundaryLayerRoughnessLengthAerodynamic resistance plays an important role in this overall evaluation of the urbanboundary layer. Velocity and turbulence thus relate directly to the roughness of theboundary layer over which the air is flowing. Francis Allard32 defines the roughnessheightasan

aerodynamic characteristic of the ground surface. For an identical geostrophic(velocity) and an identical height above the ground, the average velocity willdecrease foran increasing roughnessof theground.The roughnessheight is thusafunctionofthenatureofthegroundandthegeometryofexistingobstacles.

Figure7.28

Solarradiationenteringthestreetcanyonsignificantlyimpactsthecanyonflow.Top:solarradiationhitstheleewardside;middle:solarradiationhitsthewindwardside;bottom:solarradiationhitsthefloorofthecanyon.

Table7.4Roughnesslengthofvarioussurfacetypes

Typeofsurface Roughnesslength(orheight)(inm) Roughnessclass

Sea,loosesand,snow 0.0002(U-dependent) I

Concrete,flatdesert,tidalflat 0.0002–0.0005 I

Flatsnowfield 0.0001–0.0007

7.3.7.5

Roughicefield 0.001–0.012

Fallowground 0.001–0.004 II

Shortgrassandmoss 0.008–0.03 III

Longgrassandheather 0.02–0.06 IV

Lowmatureagriculturalcrops 0.04–0.09 IV

Highmaturecrops(grains) 0.12–0.18 V

Continuousbushland 0.35–0.45 V

Maturepineforest 0.8–1.6 VII

Denselowbuildings(suburb) 0.4–0.7 VII

Regularlybuiltlargetown 0.7–1.5 VIII

Tropicalforest 1.7–2.3 IX

Highrise(fromAllard,p.62) 4.00 IX

Source: Adapted from JonWieringa, “Representative Roughness Parameters for Homogeneous Terrain,” Boundary-LayerMeteorology,63(4),1993,p.348,TableVIII;andChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005),p.62

Intheurbancontext,pollutiondistributionandnoiseattenuationarealsoinfluencedbytheroughnessheightoftheurbancontext.

In general, thewind speed increaseswith distance from the ground and so does theboundary layer influencedby the roughnessclass.Thezero-planedisplacementdependsontheroughnesslengthoftheboundarylayer.

Figure7.29

Dependingontheroughnessoftheurbanenvironment,theverticalprofileofwindvelocityaboveterrainisshiftedupwardssignificantly,reducingthewindvelocityavailabletourbanventilationstrategies.

Zero-PlaneDisplacementThezero-planethusshiftsupwardswiththedensityoftheurbanenvironmentbasedontheroughness length. This is called zero-plane displacement,33 which in many cases isapproximatelyequaltotwo-thirdsoftheaverageheightofroughnesselements.Thezero-planedisplacementliterallyindicatestheshiftofwindspeedcurveupwardsrelativetotheopen field.Thus, there isanoverlaybetween theair flowpattern in thecanyonand theflowfieldabovetheurbanarea,whichinfluencestheupperthirdofthestreetcanyon.

Various sources provide experimental data for this shift and the various patterns, butalmost all go back to the Davenport roughness classification tables,34 which were lastupdatedbyWieringain1991and1993.35

Table7.5Terraincategoriesandhomogenousfetchrequirements

7.3.7.6

7.3.8

7.3.9

TerrainCategory Proportion Description

Smoothturbulentflow Occursoverflatsurfaceswithoutanyobstacleswhichareprominentenoughtoproduceanywakes

Semi-smoothturbulentflow x/H>15 Occursoversurfaceswithisolatedobstacleswhicharesufficientlyfarapartthattheindividualwakesdissipateintheinterspaces

betweentheobstacles

Wakeinterferenceflow x/H~10 Occurswhenobstacleinterspacesareequaltoorslightlylessthantypicalwakelength(5to15obstacleheights)

Skimmingflow x/H<5 Occurswhenthesurfaceissocloselycoveredwithobstaclesthattheflowintheinterspacebetweentheobstacleshasaflowregimequiteseparatefromthebulkflowabove(D<orequal3H)

Source: Adapted from JonWieringa, “Representative Roughness Parameters for Homogeneous Terrain,” Boundary-LayerMeteorology,63(4),1993,p.327,

UrbanPollutantsMajor research onwind in the urban context has recently focused on the dispersion ofpollutants created mainly by vehicular traffic, but also by industrial operations.Understandingthedispersionofpollutantscanbeextremelyvaluablewithrespecttothepositionof air inlets andoutlets.Unfortunately, the current stateof research is far fromreliablypredictingspecificdistributionpatternsofairpollutants.36

UrbanGeometryUrbangeometryalsohasaneffectonroughness, inparticularwhentheurbansurfaceisheterogeneous. Ingeneral,densityandspacingofurbanobjectsare themajor factors indeterminingtherelationshipoftheseobjectstoexternalwindforces.

Thebuildingheightisthemajorparameterrequiredtodeterminehowthewindmightflowinanurbanarea.Otherimportantparametersarefrontalareadensitiesandplanareadensity.Aconvenientandoftenusedruleofthumbsaysthattheverticaldisplacementofwindintensitymaybeapproximatedasone-tenthofthecanopyheightasapproximatelytwo-thirdsoftheheightofthebuilding.

UrbanMorphometry

The term‘urbanmorphometry’canbe tracedback toGrimmondandOke.24Roughnesselementsintheurbancontextcanbebuildingsaswellastrees.Withdecreasingheightofbuildings, theinfluenceoftreesbecomeslarger,andwithincreasingbuildingheight, theinfluenceoftreesonurbanwinddecreases.

Table7.6Typicalroughnessandotheraerodynamicpropertiesofhomogenouszonesinurbanareas,orderedbyheightanddensity.ThecolumnsshowzHaselementheight(inmeters),zdaszeroplanedisplacementplane(inmeters),z0assurfaceroughnesslength(inmeters),gaMasaerodynamicconductance(inmm/s),andCDasdragcoefficient(×10-2)

7.3.10

Source: Adapted from C. S. B. Grimmond and T. R. Oke, “Aerodynamic Properties of Urban Areas Derived fromAnalysisofSurfaceForm,”JournalofAppliedMeteorology,38(9),1999,Table6,p.1281,Figure7andFigure8

Roughnessincreaseswithdensitysothatwindvelocityinthestreetcanyondecreases,while its patterns become more volatile and turbulent. Depending on the researchreference and research group and depending on whether the researchmight have beenconductedbyfieldexperimentorcomputationalmodels,threeorfourcategoriesofurbanflowaredetected.

AirportWindDataandEnergyModelingToolsWinddataobtainedfromairportweatherstationsoftenprovidethebasisforclimatefiles,which are inserted into building energy modeling software tools, and may very wellprovide an unrealistic context for ventilation design within the denser urban context.Reducedwindvelocitywillusuallyleadtolargerventilationopeningstoensurethesameamount of volume flow rate in the urban context. Some tools, like MIT Coolvent(http://coolvent.mit.edu/), already address the different environments for naturalventilation.

Table7.7Typicalnon-dimensionalroughnesspropertiesofhomogenouszonesinurbanareas,orderedbyurbandensityandflowregime

7.3.11

1

2

3

4

5

6

Table7.8Availableurbanenergymodels

Model Description Date

CanyonAirTemperatureModel(CAT)

CATisaparametricmodelthatpredictssite-specificairtemperatureinanurbanstreetcanyonforextendedperiodsonthebasisofdatafromareferencestationintheregion.Inadditiontoarudimentarydescriptionofthetwosites,itrequiresonlytime-seriesofmeteorologicalparametersmeasuredatstandardstationsasinput,whichserveasdescriptorsoftheconstantlyevolvingmeso-scaleweather.

2006

TownEnergyBudget(TEB)Model37

Anurbansurfaceschemeforatmosphericmeso-scalemodelsispresented.Ageneralizationoflocalcanyongeometryisdefinedinsteadoftheusualbaresoilformulationcurrentlyusedtorepresentcitiesinatmosphericmodels.Thisallowsrefinementoftheradiativebudgetsaswellasmomentum,turbulentheat,andgroundfluxes.Theschemeisaimedtobeasgeneralaspossibleinordertorepresentanycityintheworld,foranytimeorweathercondition(heatislandcoolingbynight,urbanwake,waterevaporationafterrainfallandsnoweffects).

2000

Ali-ToudertDortmund38

ThismethodcombinestheurbancanyonmodelTEBwiththethermalenergymodellingsoftwareTRNSYS16.1toevaluatetheinteractionbetweeninteriorandexteriorurbanclimates. 2010

ModelingtheUrbanEnergyBalanceModelingtheurbanenergybalanceandtheeffectoftheurbanformonwindandnaturalventilationiscomplex,andvariouscomputationalmodelshavebeendeveloped,eachwithitsownadvantagesanddisadvantages.

NotesGarston,Watford,BREdigest,Vol.399(BuildingResearchEstablishment,DepartmentoftheEnvironment,1994).

Claude-AlainRoulet,VentilationandAirflowinBuildings:MethodsforDiagnosisandEvaluation(London;Sterling,VA:Earthscan,2008).

FrancisAllard,“TheoryforNaturalVentilation,”in:FrancisAllard,MattSantamouris,andServandoAlvarez,NaturalVentilationinBuildings:ADesignHandbook(London:James&James,1998).

MattSantamourisandPeterWouters,BuildingVentilation:TheStateoftheArt(Sterling,VA:Earthscan,2006),p.10.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005).

K.J.Lomas,“ArchitecturalDesignofanAdvancedNaturallyVentilatedBuildingForm,”EnergyandBuildings,39(2),2007,pp.166–181.

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26

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33

34

PlinytheYounger,TheLettersoftheYounger,BookII(NewYork:PenguinClassics,1969),p.78.

Garston,Watford,BREdigest(BuildingResearchEstablishment,DepartmentoftheEnvironment,1994).

ChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005).

M.Detaranto,“CFDAnalysisofAirflowPatternsandHeatTransferinSmall,Medium,andLargeStructures,”M.S.thesis(VirginiaTech,Blacksburg,VA,2014).

“Urbanization:AMajorityinCities,”UNFPA,https://www.unfpa.org/pds/urbanization.htm(accessed5/13/2014).

LeCorbusier,TheAthensCharter,translationAnthonyEardley(NewYork:GrossmanPublishers,1973).

CharlesFourier,DesignforUtopia:SelectedWritingsofCharlesFourier,StudiesintheLibertarianandUtopianTradition(NewYork:SchockenBooks,1971).

RobertOwen,ANewViewofSocietyandOtherWritings(London;Toronto:J.M.Dent&Sons;NewYork:E.P.Dutton&Co,1927).

GerhardSteiner,FranzHeinrichZiegenhagenUndSeineVerhältnislehre;EinBeitragZurGeschichteDesUtopischenSozialismusinDeutschland(Berlin:Akademie-Verlag,1962).

FranzHeinrichZiegenhagen,WolfgangAmadeusMozart,andDanielChodowiecki,LehreVomRichtigenVerhältnissZuDenSchöpfungswerkenUndDieDurchÖffentlicheEinführungDerselbenAlleinZuBewürkendeAllgemeineMenschenbeglückung(Hamburg:1792),pp.15,192–195.

EbenezerHoward,GardenCitiesofTo-Morrow,ed.FredericJamesOsborn(Cambridge,MA:MITPress,1965).

“Immeubles-Villas,”FondationLeCorbusier,http://www.fondationlecorbusier.fr/corbuweb/morpheus.aspx?sysId=13&IrisObjectId=5879&sysLanguage=fr-fr&itemPos=78&itemSort=fr-fr_sort_string1%20&itemCount=217&sysParentName=&sysParentId=65(accessed5/13/2014).

LeCorbusier,TheCityofTomorrowandItsPlanning,translatedfromthe8thFrencheditionofUrbanisme(NewYork:Dover,1987),p.224.

LeCorbusier,TheRadiantCity:ElementsofaDoctrineofUrbanismtoBeUsedastheBasisofOurMachine-AgeCivilization(NewYork:OrionPress,1967),p.141.

Ibid.,p.47.

LeCorbusier,TheRadiantCity:ElementsofaDoctrineofUrbanismtoBeUsedastheBasisofOurMachine-AgeCivilization(NewYork:OrionPress,1967),pp.48–49.

JosefPaulKleihuesandHeinrichKlotz,InternationalBuildingExhibitionBerlin1987:ExamplesofNewArchitecture(NewYork:Rizzoli,1986).

C.S.B.GrimmondandT.R.Oke,“AerodynamicPropertiesofUrbanAreasDerivedfromAnalysisofSurfaceForm,”JournalofAppliedMeteorology,38(9),1999.

HelmutErichLandsberg,TheUrbanClimate(NewYork:AcademicPress,1981).

T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987).

EvyatarErell,DavidPearlmutter,andT.J.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London;Washington,D.C.:Earthscan,2011).

LeCorbusier,TheAthensCharter,introductionbyJeanGiraudoux,translatedfromtheFrenchbyAnthonyEardley(NewYork:GrossmanPublishers,1973).

T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),p.288.

T.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),p.274.

EvyatarErell,DavidPearlmutter,andT.J.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London;Washington,D.C.:Earthscan,2011),p.221.

ChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment:AssessmentandDesign(London;Sterling,VA:Earthscan,2005).

EvyatarErell,DavidPearlmutter,andT.J.Williamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London;Washington,D.C.:Earthscan,2011),p.96.

A.G.Davenport,“RationaleforDeterminingDesignWindVelocities,”in:ProceedingsoftheAmericanSocietyof

35

36

37

38

CivilEngineers:StructuralDivision,Vol.86,pp.39–63.

JonWieringa,“RepresentativeRoughnessParametersforHomogeneousTerrain,”Boundary-LayerMeteorology,63(4),1993.

EvyatarErell,“J4C.4:TheEffectofStabilityonEstimatedVariationsofAdvectedMoistureintheCanyonAirTemperature(Cat)Model,”19thSymposiumonBoundaryLayersandTurbulence(2010),https://ams.confex.com/ams/19Ag19BLT9Urban/techprogram/paper_172717.htm.

ValéryMasson,“APhysically-BasedSchemefortheUrbanEnergyBudgetinAtmosphericModels,”Boundary-LayerMeteorology94,no.3(2000).

FaziaAli-Toudert,“KombinierteStadtklima-undGebäudeenergiemodellierungzurBestimmungdesEnergiebedarfesvonUrbanenGebäude,”inBauSim2010,German–Austrianconference.

8.1

Chapter8

SpatialStrategies/Space-InducedAirMovement

DevelopingtheFlowPathNatural ventilation needs a carefully crafted flow path through the building, whichdevelops thecorrectpressuredifferential across thebuildingbetween inlet andoutlet inorder to removeexhaustairandventilateat therequiredrate forairqualityandcoolingpurposes.TheCIBSEApplicationsManualAM10(2005),1oneofthemostcomprehensiveguidelines todateonnatural ventilation, confirms that the first design consideration fornaturalventilation is toplan the flowpath through thebuildinganddesign for the flowpattern and strategy. The CIBSE manual states necessary design considerations:understanding heat gain, narrow plan or courtyards, noise and pollution level outdoors,occupancyadaptationtoweatherconditionswithchoiceofclothing,andtighttemperatureandhumiditycontrol.2

Unfortunately,drawingafewarrowsontoasectionaldiagramisnotsufficient.

Firstofall, the formof thebuildinghas tomatch the strategy.Theorientationof thebuildingaswellasthedepthofthefloorplateandthesectionallayoutallhavetobalancethe outside forces and the internal needs. For cross-ventilation, the orientation of thewindwardfaçadehasasignificantimpactontheflowdirectionwithinthebuildingandthedegree of mixing with fresh air, which is the major requirement for wind-drivenventilationstrategies.

The collaborative engineering and architecture design team needs to ensure that thestrategychosencanprovidetheneededairflowratesatthenaturallyprovidedpressures.Because of the dynamic nature of the outside conditions, the design teamwill have toconsider a variety of conditions and scenarios to develop a flow path and a ventilationstrategy.Theteamshouldlookatahighcoolingsummermode,heatingwintermode,andmost likely also a spring and fall mode, as wind direction and temperatures cansignificantlyvaryintheseshoulderseasons.The2005CIBSEmanual1furthernotesthat

themagnitudeandpatternofnaturalairmovementdependsonstrengthanddirectionofthenaturaldrivingforcesandtheresistanceoftheflowpath,thusthedesignteamhastodevelopadynamicinteractionbetweenflowpath(space)andforce(pressuredifferential).

Hightemperaturedifferencesandstrongerwindswillmakeforstrongerdrivingforcesinwinterwhen thecoolingcapacityofnaturalventilation isonlyneeded inbuildingswithvery high internal gains. Thus, in most cases fresh air intake can be reduced to theminimumneeded for indoor air quality. Spring and fall are the best seasons for naturalventilationbecauseweatherconditions forcoolingareverygood,but thedriving forces

8.1.1

will often be reduced because the temperature difference between inside and outside issignificantly lower.Wind speed is alsomuch lower inmost locations. In peak summersituations,theoutsideconditionsmayreachhighertemperaturesthanindoorsconditions,whichwouldbedetrimental forwind-andtemperature-drivenventilationstrategies.Thestackeffectmayevengetreversedandintroduceairattemperaturesthatexceedcomfortlevel.Thiswouldwarmuptheinternalspacesinsteadofcoolingthem.Insuchlocations,onlyhybridormixed-modesystemswillbeabletoachievethermalcomfort,forexamplein combination with chilled beams or radiant cooled surfaces. Similar to the winterscenario, air supply in hot summers should be reduced to the minimum air qualityrequirementsinordertobalanceadditionalenergyuseanduncomfortablesituations.

Thefollowingcasestudyprojectshighlightspecificdesignstrategiesandtheircontextandparameters.Itshouldalsobenotedthatnaturalventilationstrategiescanbecombinedanddifferentpartsofabuildingcanbeventilatedusingdifferentstrategies.Somelargerprojectscanalso incorporatehybridventilationstrategies,whichallowforventilation tobeswitchedseasonallytomechanicalventilation.

Ventilationneedstobedesignedinsectionandplancombined,ideallyasavolumetriccomposition,becauseair isnotanobjectmovinginspace,butisspaceitself,expandingandcontracting,mixinganddisplacing.

Path1:Cross-VentilationCross-ventilation is the typical flowpathstrategy forofficeorapartmentbuildingswithshallow plans, where floors are separated vertically, and where a flow path can beestablishedhorizontallybetweenthewindwardandtheleewardsideofthebuilding.Thisdemandonthebuildingformhasadirectrelationshiptothesituationofthebuildinginitsurbanorlandscapecontext.Thebuildingformandorientationneedtosupportthecreationofapressuredifferentialandresistanceagainst theflow.Inaddition, therequirementoncross-ventilation strategies to develop a spatial continuum can lead tolimitations/restrictions of the spatial layout for the building circulation and location ofapartment and office buildings. This often leads to open floor plans in order to avoidobstructionoftheflowpathandprovidetherequiredflowrate.Moreover,economicsofspace are also in effect, as most often the cross-ventilation flow path calls for twoapartments to flankastaircase inorder toopen thecrosspathonbothsidesof thestairspace.Inordertoaddathirdorevenfourthunittotheonestaircase,theventilationpathhas tocross thecirculationpath.Multiplearchitectsduring theModernMovementhavedeveloped spatial strategies to overcome this dilemma. Themost prominent case is thesectional layout of the Unité d’Habitation inMarseille by Le Corbusier, built in 1945,whichusedonlythreestairtowersfor337apartmentson12floors,andonlyonecentralcirculation corridor on every third floor. The so-called split level section enables acombined cross-stack ventilation path across the central corridor. A similar system hadalready been used almost 20 years earlier by Hans Scharoun in Breslau (1929) in theLedigenheim (Bachelorhostel).Manyvariationsof this spatial strategy followedduringthe 1950s and 1960s, one ofwhich is theBakema tower3 at theHansaviertel inBerlin(1957).

8.1.1.1

Figure8.1

LeCorbusier’sUnitéd’Habitationdevelopedthemosticonicsectionaldiagramforasplit-levelapartmentcirculationlayoutoverlappingwithacirculationcorridor.

Figure8.2

HansScharoun’sLedigenheim(homeforsingles)developedanevenmorecompactsectionallayoutforacross-ventilationpathoverlappingwithacirculationcorridor.

This spatiallycomplex layoutalsosupportsadaylight scheme for theapartmentsandimprovesoverallenvironmentalquality.Yettheseprojectswerestructurallycomplexandin some jurisdictions, such as Berlin, Germany, alterations were required to meet fireegressrequirements.

The two selected case studies highlighted in the following section approach therequirement todevelopacontinuous flowpathwith spatialdesign innovationaspartofthesamepioneeringdevelopment.Theyaimedtoovercomeissuesofbuildingdepthandfaçadeaccessforinletsoroutletsinaninnovativeway.

CasaadAppartamentiGiulianiFrigerio,Como,byGiuseppeTerragni(1939–1940)

This apartment building is Giuseppe Terragni’s last built project in Como4 before heenlistedinthemilitaryduringWorldWarIIanddiedatayoungagein1943.5Thecentralstaircaseservesthreeapartmentsinasplitlevelconfigurationonfourfloors,whichallowsthecentralapartmenttobecross-ventilatedabovethecorridor,whichleadstooneofthecornerapartments.Thisconfigurationdevelopedacomplexinterlockingandoverlapping

of volumes and frames, which has been thoroughly analyzed as an architecturalcompositionbyPeterEisenman.6,7Forexample,thefaçadecompositiononthesoutheastdoesnotnecessarilyrevealthesplitlevelconfigurationbecauseoftheclevercompositionandlayoutofwindowsinbathroomsandkitchens.Yet,theactualperformancebenefitofthe split level configuration revealed itself during a site visit in 2012. The split levelallowsthreeapartmentstobeaccessedfromonestairwell,whileallthreereceivenaturalcross-ventilation.

Figure8.3

CasaGiulianiinComobyGiuseppeTerragni:southernstreetfaçadeasthebuildingappearsin2012.

Whenthebuildingwasconstructedin1939to1940,thebuildingappearedtohavebeenstanding fairly remotely in the vicinity of Lago di Como. This site situation has beenalteredand tocontemporaryvisitors thebuildinghardly reveals itself,because it isnowmostlysurroundedbyverycloseneighborsandembeddedinatighturbangrid.Thisnewcontext obviously also changed the ventilation context and most likely reduced theventilationpotential.

Figure8.4

CasaGiulianiinComobyGiuseppeTerragni:interiorviewofthecorridorbeneaththeventilationwindow,2012.

Figure8.5

CasaGiulianiinComobyGiuseppeTerragni:easternstreetfaçadewiththewindowsofthecorridorvisiblebeneaththekitchenventilationwindow,2012.

CasestudydesigndataDesignintention:

Thedesignrevealsefficientspaceplanningtoachieveaneconomicapartmentlayoutwhile providing daylight and cross-ventilation to all spaces in each apartment,includingbathroomsandkitchens.Thetrade-off is that theelevatorissituatedat themidway point between the three apartments and thus none of the apartments iswheelchairaccessible.

Ventilationstrategy:

Natural ventilation strategy and mechanical integration: cross-ventilation combinedwithradiantheatinginwinterSpatialdesignstrategy(flowpath)plan/sectionanalysis:splitlevelcompositionFaçadestrategies(apertures):operablewindows

Projectdata:

Yearofcompletion:1940

Height/buildingtype:Apartmentbuilding(15m/49’11”)

Stories:Four

Function:Housing

Structure:Reinforcedconcreteframeswithinfillmasonrybrick

Plandepth:Approx.18m/59’,whichisapproximatelyfivetimesthefloortoceilingheight

Climaticdata:

Location:VialeFratelliRosselli24,Como,Italy

Geographicposition:45.8167°N,9.0833°E

Elevation:300m/985ft

Figure8.6

WindroseforComo,Italy,showingtheprevailingwinddirectionsthroughouttheyear(inm/s).

Climate classification: Temperate climate of northern Italy, Koeppen Geiger (KG)climate classification: Cfb (warm temperate, fully humid, warm summers).Lugano/Agnohasamild,humid, temperateclimatewithwarmsummersandnodry

season.

Prevailingwinddirection:Thewindtypicallyblowseitherfromthenorthorfromthesouth,whichhasa significant influenceon thevalleyofLagodiComo,which runsnorthtosouthintotheAlps;Comoislocatedatthesoutherntipofthelake.

Averagewindspeed:5mph(8km/h)yearround

Mean daytime temperature during summer: The warm season lasts from June 7 toSeptember6withanaveragedailyhightemperatureabove75°F/24°C.ThehottestdayoftheyearisJuly30,withanaveragehighof83°F/28.5°Candlowof63°F/17°C.

Meandaytimetemperatureduringwinter:ThecoldseasonlastsfromNovember19toFebruary 28 with an average daily high temperature below 51 °F / 10.5 °C. ThecoldestdayoftheyearisJanuary7,withanaveragelowof31°F/0.5°Candhighof44°F/6.5°C.Heatingdegreedays65°F/18°C:84804/2700Coolingdegreedays78°F/25°C:9114/45

Day-nightdifferenceduringhottestmonths:approximately20°F/7°C

Meanannualprecipitation:Warmseasonrainoccursmostlyduring thunderstormsatthefootoftheAlps,whilecoldseasonprecipitationoccursasmoderaterainorsnow.Average relativehumidity:Dewpointsvarywithhighest about65 °F /18.5 °Candthusjustslightlyonthemuggyside,mostoftheyearcomfortableanddryinwinter.

Highestrelativehumidityandlengthofhumidseason:N/A

Energydata:N/A

Time of year natural ventilation can be utilized: Year round, heating-dominatedclimate.Forefficiencyinwinter,preheatingofventilationairwouldbeideal,butisnotutilized.

Savedheatingandcoolingenergy:N/A

Typicalannualenergyconsumption:N/A

Considerations, obstacles, issues, etc.: Heating-dominated climate, site context haschanged.

Projectteam:

GiuseppeTerragni(1939–1940)

Figure8.7

SectionthroughthecentralapartmentofCasaGiulianishowingthelocationofthekitchenwindowabovethecorridor.

Figure8.8

SpatialcompositionofapartmentsatCasaGiulianidevelopingtheflowpath.

8.1.1.2

Figure8.9

VolumetriccompositioncreatingtheflowpathwithinCasaGiuliani.

Figure8.10

CFDsimulationsofflowpaththroughthecentralapartmentseenfrominletside(ambienttemperature24°C,windspeed5mph).

KanchanjungaApartmentBuildingbyCharlesCorrea(1970–1983)Mumbai,India,islocatedonapeninsulawithalargecurvingbayopeningtotheArabianSeaonthewestside.ThesiteoftheKanchanjungaApartmentBuildinghasaviewofthebayonthewestaswellastotheharborontheeastside.

InMumbai, abuildinghas tobeorientedeast-west to catchprevailing seabreezesandtoopenupthebestviewsofthecity.Unfortunately,thesearealsothedirectionsof the hot sun and the heavy monsoon rains. The old bungalows solved theseproblemsbywrappingaprotective layerofverandasaround themain livingareas,

thusprovidingtheoccupantswithtwolinesofdefenseagainsttheelements.10

CasestudydesigndataDesignintention:

DrawingfromLeCorbusier’sUnitéscheme,CharlesCorreadevelopeddoubleheightgardenterraces,whichaidedthechannelingoflightandair,butalsoshieldedtheinnerspacesfromstrongsolarradiationanddrivingmonsoonrains.

Ventilationstrategy:

Naturalventilationstrategyandmechanicalintegration:Originalcross-ventilation,butACwindowunitsinstalledpostcompletioninselectedapartments.

Spatial design strategy (flow path) plan/section and analysis: Complex split levelcomposition with multiple space heights. The apartments always have one doubleheightterraceandalowersectionstackedoneontopoftheother.

Façadestrategies(apertures):Operablewindowsanddeeprecessedterraces

Projectdata:

Yearofcompletion:1970–1983

Height/buildingtype:84m/275ft,residentialhigh-risetower

Stories:32luxuryapartments,with3to6bedroomseach,on26stories

Function:Apartments

Structure: Reinforced concrete structure with a central core and 6.3 m / 20.6 ftcantileversfortheterraces

Plandepth:21m/69ftinbothdirections

Figure8.11

KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:viewofthetowerasitsitsinthecityscape.

Figure8.12

KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:differenttwo-storysplit-levelapartmentsarecomposedasinterlockingvolumesformingonecubictower.

Climaticdata:

Location:72PeddarRoad,Tadeo,Mumbai,India

Geographicposition:Latitude:19°11’8.124”N;longitude:72°51’0.3514”E

Climate classification: Hot and humid tropical. Tropical savannah climate with drywinters,Aw(equatorial,wintersdry)

Prevailingwinddirection:Predominantlywesterlyandsouthwesterlywinds

Averagewindspeed:Highestaveragewindspeedis9mph(14.4km/h)inJuly;lowestaveragewind speed is 4mph (6.5 km/h) in winter; the highest wind speed can beexperiencedduringtherainyseason.

Mean daytime temperature summer: The warmest time in Mumbai is inOctober/November.

Mean daytime temperature winter: The coolest time of the year is from June toSeptember,monsoonseason.

Figure8.13

KanchanjungaApartmentBuildingbyCharlesCorreainMumbai,India:thecornersoftheapartmentsarelargedoubleheightloggiastomodulatetheincomingairflowfromthebreezeoftheArabicSea.

Heatingdegreedays65F/18C:0

Coolingdegreedays76F/24C:2294/1256

Day-nightdifferenceduringhottestmonths:ThewarmseasonlastsfromOctober13toNovember 26 with an average daily high temperature above 92 °F / 33.5 °C. ThehottestdayoftheyearisOctober31,withanaveragehighof93°F/34°Candlowof76°F/24°C.

The cold season lasts from June 25 to September 17 with an average daily hightemperaturebelow87°F/30.5°F.ThecoldestdayoftheyearisJanuary30,withanaveragelowof66°F/19°Candhighof87°F/30.5°C.11

Meanannualprecipitation:Februaryhastheleastclouds,whileJune,July,andAugusthavearound80percent to90percentofcloudcover. July isalso the rainiestmonthwithprecipitationon89percentofthedays.

Averagerelativehumidity:N/A

Highestrelativehumidityandlengthofhumidseason:Thehighestrelativehumidityoccurs in Julywith95percent.Thehumidmonsoonseason lasts fromJune throughSeptember. Highest dew points will be around 79 °F / 26 °C, which feels ratheruncomfortableandmuggy.

Figure8.14

WindroseforMumbai,India,showingtheprevailingwinddirectionsovertheyear(inm/s)overlaidwiththesiteplanoftheKanchanjungaApartmentBuilding.

Energydata:

N/A.Energydataisnotavailableduetothetimeofconstruction.Thebuildingisalsonotmonitored.

Time of year natural ventilation can be utilized: The building was constructed fornaturalventilationallyearround,butconsideringthehighhumiditylevelinsummer,June through September should probably be excluded from natural ventilationconsiderationsinthisclimate.

Savedheatingandcoolingenergy:N/A

Typicalannualenergyconsumption:N/A

Considerations,obstacles,issues,etc.:Summerheat,highrelativehumiditycombinedwithhightemperaturesandheavymonsoonrain.

Projectteam:

CharlesCorreaAssociates,Mumbai,India

Figure8.15

Volumetriccompositioncreatingtheflowpathforcross-ventilationatKanchanjungaApartmentBuilding.

8.1.2

8.1.2.1

Figure8.16

SpatialcompositionofKanchanjungaApartmentBuildingdevelopingtheflowpath.

Path2:Single-Sided(Comfort)VentilationSingle-sided ventilation is less effective than cross-ventilation in comparable situationsand only serves a fairly narrow zone close to the façade. Single-sided ventilation oftencombineswind-andtemperature-inducedairflowandusesthesameopeningastheinletandoutlet.Moreeffectivecombinedstackventilationutilizestwoopeningsononesideofthe space (a high and a low opening) in order to facilitate the stack in the space. Thislocally limited strategy can be combined with other strategies. The Anglo-Saxon sashwindow(seeFigure9.3)provides thepotential to combine anupper and loweropeningbeautifully. But single-sided ventilation serves far less space as it is only effective inbuildingzonesclosetotheinlet/outletopeningunlessitisconnectedtoother,largerscalestrategies, for example an atrium stackor cross-ventilation, as in the case studyprojecthighlightedhere.

CommerzbankbySirNormanFosterTheCommerzbankbuildinginFrankfurt,Germany,byNormanFoster’sdesignteamwasoneof the firsthigh-riseoffice towers to relyheavilyonnaturalventilation inamixed-modesituation.ItisconsideredEurope’sfirstecologicalofficetower,movingawayfromthehomogenousglassbox.ThetowerrisesfromaplinthwhichisintegratedintotheblockstructureofthehistoricalFrankfurtcitygrid.Thetowerisnotcompletelysurroundedbyothertowersofsimilarheight,butisratherasingularentityinacontextoflowerblocks.Thedesignintentionforthetowerisbasedoninterconnected‘WinterGardens’linkedtoacentralatrium,whichspiralsupthetowertobecomethevisualandsocialfocusforfour-storyclustersofoffices.Thetowerissetbackfromthestreetandisbasedonatriangularplanwith a central atrium connecting all tower floors.A glass ceiling above the lobbyvisuallyconnectsthetowertotheentrance.Skygardensandofficespacesarecomposedin a spiraling configuration. Thus, two office segments always face one sky garden.Outward-facing offices are naturally ventilated through a double-skin façade,while theinward-facing offices are ventilated driven by the stack flow inside the atrium and outthrough the sky garden. Four sections are separated vertically by a diaphragm glassceiling,whichmanagesthestackflowandkeepsitfrombecominga‘storm.’Inaddition,itprovidessmokecontainmentandrestrictsthespreadoffireincaseofanemergency.Thestructuralsystemsupportsthesemajorspatialcompositionswithsixmega-columnsinthecornersofthebuildingandthreeatriumcolumnssupportingeight-storyvierendeelgirders,whichsupporttheofficesections.

Figure8.17

CommerzbankTowerasitappearsabovethestreetcanyonofFrankfurt/Main.

Figure8.18

ViewuptheinteriorcourtyardofCommerzbankTowershowingoneofthehorizontalglassscreens,whichcreatetheboundarybetweenthemultipleskygardens.

Figure8.19

Close-upviewoftheCommerzbankfaçadeshowingthedouble-skinfaçadeandtherecessedvolumeoftheskygarden.

CasestudydesigndataDesignintention:

The natural ventilation strategy engages a macro- and a micro-level. The centralatrium and sky gardens combine large-scale stack and cross-ventilation in threestacked12-floor‘villages,’andbecauseofthespiralingcomposition,thelayoutallowsfor ventilation with all major wind directions, as there is always a windward skygarden. Depending on the direction, stack ventilation can also be reversed to wind

flowpushingdownthroughtheatriumandoutthroughthelowerfloorskygarden.12

Theoveralllengthofflowpathacrosstheatriumandskygardenisapproximately48m/157.5ft,andtheindividualofficedepthandheightforsingle-sidedventilationis16.5m/54ft.ThisreinforcestheruleofthumbgiveninSection7.2.

Ventilationstrategy:

Natural ventilation strategy andmechanical integration:Natural ventilation chimneycreatesnegativepressuretopullairthroughandupthebuildingandtheskygardens.In addition, the building can be ventilated and cooled with a complementarychangeover system that switches between natural and mechanical ventilation on aseasonal or even daily basis to combat high summer temperatures and coldtemperatures inwinter,and tooperate thebuilding incaseof toohighwinds,whichwouldcausediscomfortintheatrium/skygardens.

Spatialdesignstrategy(flowpath)plan/sectionandanalysis:Triangularinplan,three‘petals’ and one ‘stem.’ Façade strategies (apertures): Every office has operablewindowsandreliesonnaturaldaylighting.

Projectdata:

Yearofcompletion:1997

Height/building type:Top:298m(978 ft);main tower:259m (850 ft); commercialbuilding

Stories:56

Function:Commercialofficetower;120,736m2/85,500m2inthetower(1.3mioft2/920,315ft2).

Structure:Reinforcedconcrete,steelframe

Plandepth:16.5m/54ft

Climaticdata:

Location:Frankfurt,Germany

Geographicposition:50.1106°N;8.6742°E

KGclimateclassification:Oceanicclimate,Cfb/warmtemperate,fullyhumid,warmsummers

Prevailingwinddirection:SSW

Averagewindspeed:8mph/12.85km/h

Meandaytimetemperaturesummer:18.3°C/65°F

Meandaytimetemperaturewinter:1.83°C/35°F

Heatingdegreedays:fiveyearaverage,15.5°C/60°Fbase:2232/4050

Day-nightdifferenceduringhottestmonths:17.73°C/64°F

Meanannualprecipitation:621mm/24.4inAveragerelativehumidity:50.9percent

Highestrelativehumidityandlengthofhumidseason:July16,75percent

Energydata:

The building is powered completely by renewable energy as of January 1, 2008.Referenceenergydatawasmeasuredin2008.

Timeofyearnaturalventilationcanbeutilized:85percentofyear(vs.60percenttimeofyearanticipation).

Figure8.20

WindrosediagramforFrankfurt/Main(inm/s)showinghowthevolumeoftheCommerzbanktowersitswithintheprevailingwinds.

Figure8.21

SectionthroughtheCommerzbanktowershowingthediagonallyconnectedinterlockingcompositionoftheskygardensconnectingtheinnerflowpathofthebuilding.

Figure8.22

Volumetriccompositionofofficesectionandskygardens,whichfacilitatetheoverallventilationpath,whileeachofficeindividuallyisconnectedtotheflowpaththroughsingle-sidedventilationstrategy.

Saved heating and cooling energy: 63 percent compared to a fully air-conditionedGermanofficebuilding(measured)and38percentcomparedtoafullyair-conditionedoffice building built to EnEV 2007, the German Energy Conservation Ordinance(measured)13

Typical annual energy consumption: Approximately 50 percent of traditional officebuildings

Considerations, obstacles, issues, etc.: High winds can lead to switch-over tomechanical ventilation. Fire and smoke prevention lead to horizontal glass barriers,butthesealsoaidintheventilationstrategy

Projectteam:

Structuralengineer:OveArupandPartners/KrebsandKiefer

Quantitysurveyor:DavisLangdonandEverest

8.1.3

M+E engineer: Roger Preston & Partners/RP&K Sozietat GmbH/Perrerson andAhrens

Landscapearchitect:Sommerland&Partners

Lightingengineer:Lichtdesign14

Path3:StackEffectVentilationOtherthanthefirst twoflowpathstrategies,stackventilationmostoftenusesthewholebuilding to develop the flow path in order to achieve the high temperature differentialnecessarytodevelopthestackdrivingforcefortheairexchangerate.Flowpathsareoftendesignedascentralcommunalspaces,suchasatriaorstaircases,inordertointegrateandenhancethestack.Forappropriatestackdesignitisimportantforarchitectstounderstandtheconceptoftheneutralplane.Belowtheneutralplane,theairflowsinwards,andabovethe neutral plane, the air flows outwards. This can become problematicwhen occupiedspaces are situated above the neutral plane andwarmer air flows out through openingsabove the neutral plane, passing through occupied spaces.This is an often encounteredmistakeindesigningstackeffectventilation.15

Thissituationrequiresthatcloseattentionbegiventotheroofandthetopofthestackshaftduringthedesignphase.Mostidealarespatialstrategieswherethetopofthestackexpands over the roof of the building to provide additional height in order to lift theneutralplaneabovetheoccupiedspaces.Strictlytemperature-inducedventilationisrare.Itismostlikelythatwindwillworkinconjunctionwiththestackeffectattheinletaswellasattheoutlet.Infact,therearemultiplecaseswheretheexhaustofthestalewarmairatthe top of the stack is assisted by the negative pressure produced by awind-enhancingdevice,usingtheVenturieffectormerelybyopeningtheexhausttowardstheleewardsideofthestack.

Multiple iconic contemporary buildings utilize stack effect ventilation and oftencombine the stackwith the public and/or circulation space. One of themost publishedbuildingsusingandpromotingstackventilationistheEastgateshoppingcenterinHarare,Zimbabwe,byMickPearceArchitects.16Inthepublisheddescription,MickPearcereferstothetermitemoundasinspiration.Accordingtohisdescription,thetermitesuseaveryrefined systemof stack vents to provide a constant temperature inside their nest and toexhaust stale and warmer air, which rises through the vents. The Eastgate center, heclaims, operates using a similar strategy of concrete stack vents that pull air up andventilatedconcretefloorstopullfreshairintotheofficespaces.17

Figure8.23

WindrosediagramforHarare,Zimbabwe,showinghowthevolumeoftheEastgateshoppingcentersitsperpendiculartotheprevailingwinds(inm/s).

Figure8.24

VolumetricspatialcompositionofEastgateshoppingcenter.

8.1.3.1

Figure8.25

SectionthroughEastgateshoppingcenterinHarare,Zimbabwe,showingthetwocentralventilationstacksaswellasthecourtyard,whichreducestheflowpathdepthandaddsdaylightingcapacitytoeachfloor.

JudsonUniversityinElgin,Illinois,nearChicagoTheHarmA.WeberAcademicCenteratJudsonUniversity,byAlanShortandAssociates,isamongthefirstcontemporarylarge-scalebuildingsintheAmericanMidwesttoexploitnaturalventilation in the extremesof theMidwesternclimate.Thebuildingexploits theuseofstackventilationthroughspecificallydesignedshafts,whichterminateinmultipletowers above the building. The building is composed as an assemblage of three verydistinct formaland functionalparts.Themajorvolume is thecubeof the library/studio,whichcenters itselfonaday-lit atrium,whichalsoprovidesoneof the stacks for stackventilation. The bowtie contains classroom spaces, which are typically mechanicallyventilated,andtheofficeslabisventilatedbythestackspacesleftbetweenthebowtieandtheslabaswellasshaftsthatareintegratedintothefaçadelayer.Libraryandstudiospacesaswellasofficesincorporateoperablewindowsinadditiontostack-inducedairflow.

Beneficial for thebuildingstrategywas theoverlappingapproachofday-lightingandventilationstrategies,whichalso resulted inwellday-lit spacesandprovidedsignificantelectricitysavings.

Figure8.26

SouthfaçadeoftheHarmA.WeberAcademicCenteratJudsonUniversityinElgin,Illinois,highlightingthephotovoltaicarrayonthetopoftheventilationstackswarmingtheupperlevelofthestacktoincreasethepressuredifferencebetweeninletandoutlet.

Figure8.27

InteriorcourtyardoftheHarmA.WeberCenteratJudsonUniversitydoublingupasventilationflowpathanddaylightingdevice.

Figure8.28

VentilationexhaustdeviceontheroofofHarmA.WeberCenteratJudsonUniversity,addinganiconicfeaturebehindthephotovoltaicarray.

CasestudydataDesignintention:

Thedesignteam,AlanShortandAssociatesfromtheUK,aimedtodevelopanaturalventilationstrategyforadeepplanbuildinginthecontinentalwarmhumidclimateoftheAmericanMidwest.Thegoalwastooperatethebuildingwithnaturalventilationforasignificantperiodoftheyear.

Ventilationstrategy:

Naturalventilationstrategyandmechanical integration: Integratingstackventilation,cross-ventilation,andmechanicalventilationintoahybridsystem

Spatialdesignstrategy(flowpath)plan/sectionandanalysis:Multiple:narrowplanforcross-ventilation, shafts and atrium for stack ventilation, exhaust towers exposedaboveroof

Façadestrategies(apertures):LargeinletventatthebackofthebuildingforIEQandcooling,operableventilationforpersonalcomfort,roofexhaustsforstackventilation

Projectdata:

Yearofcompletion:2007

Buildingtype/height:Academicbuilding/21m/69ft

Stories:Four

Function:Mixed-useeducationalbuildingwithoffices,classrooms,libraryanddesignstudios

Structure:Mainstructuralmaterialisconcreteinwalls,floors,andceilingsforthermalmass as amajor component for the natural ventilation strategy.The exteriorwall ismadeof stick frame extensions to include the vent stacks and the daylighting splaywindowsaswellasshadingofthewindowglass.

Plandepth:Overall:32m/105ftwitha7m/33ftatriuminthecenter

Climaticdata:

Location:Elgin,Illinois,USA

Geographicposition:42°2’N;88°17’W

Climateclassification:Climate/context:climatezoneKöppenDfa(snow,fullyhumid,hotsummers).18Humidcontinentalclimate (KöppenclimateclassificationDfa)withhot,humidsummersandcooltocoldwinters.

Prevailing wind direction: South/southwest and all other westerly directions; leastprobablearewindsfromtheeast.Between8and14mph/12.85and22.5km/h.

Averagewindspeed:Windspeedishighestinwinterwithanaverageofabout12mph/19.5km/handlowestinthewarmestmonthofJulywith8mph/12.85km/h.Thisisone reason why stack ventilation was used as the major driver for the naturalventilationflowpath.

Meandaytimehightemperaturesummer:Between73and84°F/22.75°C;maximum91°F/32.75°C

Meandaytimetemperaturewinter:Between15and24°F/-9.4and-4.4°C

The warm season lasts fromMay 25 to September 21 with an average daily hightemperatureabove73°F /22.75°C.Thehottestdayof theyear is July24,withanaveragehighof84°F/29°Candlowof65°F/18.3°C.ThecoldseasonlastsfromDecember1toMarch3withanaveragedailyhightemperaturebelow40°F/4.4°C.ThecoldestdayoftheyearisJanuary20,withanaveragelowof15°F/-9.4°Candhighof29°F/-1.5°C.

Figure8.29

WindrosediagramforElgin,Illinois,showinghowthevolumeoftheHarmA.WeberCentersitsperpendiculartoaprettydiversedistributionofprevailingwindsforbothsummerandwinter(inm/s).

Heatingdegreedays65F/18C:7480/4138

Coolingdegreedays78F/25C:360/182

Day-nightdifferenceduringhottestmonths:20°F/12°Cmaximum

Meanannualprecipitation:Mainlythunderstormsinsummerandlightsnowinwinter

Averagerelativehumidity:Between47percentand95percentinsummer

Highestrelativehumidityandlengthofhumidseason:JulyandAugustcanbehumidandmuggy

Energydata:

Timeofyearnaturalventilationcanbeutilized:Shoulderseasonsofspringandfall,mildsummerandmildwinterdays

Savedheatingandcoolingenergy:18.3percentsavingsoverbasecode42.6percentnaturalgas

Typicalannualenergyconsumption:7423.3MBtu/2175MWh19

Considerations,obstacles,issues,etc.:WindowscreensareneededfortheMidwesttoprotectagainstbugsandmosquitoes,whichdoublestheinletsize.

Projectteam:

Architect:Short&AssociatesArchitect

Architectofrecord:BurnidgeCassell&Associates

Landscapearchitect:SlaineCampbell

Energyconsultant:InstituteofEnergy&SustainableDevelopment

Mechanical,electrical&sructuralengineer:KJWWEngineers,DesMoines,Iowa20

8.1.4

Figure8.30

Flowpathdiagramofthelibrarybuildingshowingthespatialcompositionalrelationshipbetweenthestackventsinsidethedouble-skinfaçadeandtheinternalcoveredatriumattheHarmA.WeberCenterofJudsonUniversity.

Figure8.31

SectionthroughtheHarmA.WeberCenterhighlightingtheverticalstackspacesinbetweentheactualvolumesofthebuildingcomposition.

Path4:SolarChimneysSolar chimneys are a specific variation of the stack effect employed by conventionalchimneysandutilizedforcenturiestoexhaustcombustionairandsmokefromfireplaces.Inthecaseofthesolarchimney,thetopofthestackisadditionallyheatedthroughglassorsheetmetalbythesun’sradiationinordertoincreasetheairtemperatureonthetopofthestacktoraisethedifferentialbetweentheinletandtheoutletofthestacktemperatureandthusthepressuredifferential.Paradoxically,thisisparticularlyusefulinwarmorevenhotclimatesbecausestackventilationonlyworkswhentheinnertemperatureatthetopofthestackisabovetheoutdoortemperature.Otherwise,theoutsidewarmairwouldflowintothebuilding.Theairinthesolarchimneyalwayshastobewarmerthantheoutsideair.

OneknowncaseofsolarchimneyenhancedstackventilationistheBuildingResearch

8.1.4.1

Establishment’s (BRE) Environmental Building in Garston, Watford, UK, designed byFeildenCleggArchitectsandArup’sasengineers.21 In thisproject,glazedfaçadeshaftsextendabovetherooftoformmetalcladchimneys,whicharetoppedbya‘hat’toassistwind enhancement of the flow.The glass façade of the ventilation shafts and the shinymetalchimneyscreateaniconicelevationwitharhythmofstackchimneysateveryaxisofthebuilding.

Solar-enhancedventilationhasalsobeenintroducedintotheSidwellFriendsSchoolbyKieranTimberlake22asameanstofacilitatenaturalventilationintheirclassroomsincasethewind-inducedcross-ventilationisnotsufficientforproperairchangerates.

Toensureadequateventilationonveryhotandstilldays,fan-assistedventilationmaybeconsidered.

Stackventilationfollowsthesamerulesofthumbascross-ventilation;thusthedistancebetweentheinletandoutletshouldnotbemorethanfivetimesthefloortoceilingheight.Thestackoutletneedstobeatleasthalfofonestorylevelabovethelastceilingofthetopfloor.23 If possible, the exhaust outlet should be placed onto the leeward or negativepressure side of the chimney away from the side on which the wind impinges on thechimney.

In comparative research studies24 the effectiveness of solar versus nonsolar chimneyventilationhasbeenstudied,andAlfonsoandOliveirareportanincreaseinefficiencyof10 to 22 percent. The efficiency is higher in warmer months and generally in warmerclimates.Solarchimneysshouldalsobeinsulatedthesamewayaspassivesolarcollectingspacesinordertodirectallgatheredsolarenergytowarmuptheairandnotconductbackoutintotheatmosphereorintotheinteriorspace.Theyalsostudiedthedesignparametersofthechimneysectionandchimneyheightandcametotheconclusionthat“forsatisfyingtheneededaverageflowrate:theaverageflowratechangeslinearlywithchimneysection;foragivensolarcollectionarea,itisbettertohavealargerchimneywidthandasmallerheight.”25

The influenceofwindon solar stackventilation is randomand inmost cases canbeignoredinordertocomputetheappropriateairchangerates.26

TheCharlesdeGaulleSchoolTheCharlesdeGaulleSchool,completedin2007/08inDamascus,Syria,bytheFrenchteamLionArchitects,isaveryrecentexampleofsolarchimneyventilationinahotanddryclimate.EngineeringwasconductedbyTranssolarKlimaEngineering,fromGermany.The building itself is a cluster of two- to three-story classroom buildings, with a solarchimneyextendingaboutonefloorupintotheskyabovetheupperclassroomceiling.Assolar chimneysdonot serveanyother function thanventilation, their areacanbe fairlysmall and only needs to fulfill the outlet area and height requirements to increase thestack.Importanttonoteisthecarefuldesignofthebuildingsectionandtheintegrationofavegetationmicroclimatedesigninthecourtyard,whichenablesthecoolingofthefreshintakeairoverthefloorofthecourtyardbeforeitentersontheshadedsideofthebuilding.

The proportions of the building follow exactly the rules of thumb for cross- and stackventilationwithevenlessthanfivetimesthefloortoceilingheightasspacedepthandastack that extends about one floor high over the top of the roof. The overall site planrevealsaveryintricateintegrationofinsideandoutsideclassroomsandbreakspacesforthisairyschoolbuilding.

Figure8.32

LycéeCharlesdeGaulleinDamascus,Syria:overviewofthecompositionofbuildingandcourtyardspaces.

Figure8.33

LycéeCharlesdeGaulleinDamascus,Syria:detailofsolarchimney.

Figure8.34

LycéeCharlesdeGaulleinDamascus,Syria:courtyardwithtrees.

CasestudydataDesignintention:

UtilizestackventilationinhotandaridclimateofDamascus,Syria

Ventilationstrategy:

Solarchimney.

Naturalventilationstrategyandmechanicalintegration:Noactivecooling

Spatialdesignstrategy(flowpath)plan/sectionandanalysis:Chimneyheightisequaltoonefloor

Façade strategies (apertures): Ventilation inlets are situated in cool, vegetation-enhancedcourtyard

Projectdata:

Design:2006

Yearofcompletion:2007/08

Height/buildingtype:Schoolbuilding

Stories:Two,withoneadditionalstoryforthesolarchimney

Function:School,classroombuildings

Structure:Thewalls aredouble-block for their thermalproperties: solidconcreteontheinsideandconcretebreeze-blocksontheoutside,separatedbyanairpocket

Plandepth:15m/49ftapproximately

Site size: Ground floor area: 4,995 m2 / 53,766 ft2 – Total site area: 10,000 m2 /

107,640ft2

Climaticdata:27

Location:Damascus,Syria(WestAsia)Geographicposition:33°30’47”N;36°17’31”E

Elevation:680m/2231ft

KGclimate classification:BWhhot arid desert;winters aremildwith precipitation,sometimessnow.

Prevailingwinddirection:Thewindismostoftenoutofthesouthwest(24percentofthetime),south(13percentofthetime),andwest(11percentofthetime).

Averagewindspeed:Between10and20mph(16and32km/h)

Meandaytimetemperaturesummer:26°C/79°F;averagehighinJuly/Augustis36°C/97°F;recordhigh45°C/113°F.

Meandaytimetemperaturewinter:6to12°C/43to53.6°F

Heatingdegreedays65F/18C:2769/1520

Coolingdegreedays:825/440

Day-nightdifferenceduringhottestmonths:20°C/40°F

Meanannualprecipitation:25mm/1inchinwinter;noneinJuly/August

Averagerelativehumidity:Canrangebetween15percentand90percent inAugust,withdewpointsbetween41and65°F/5and18°C.

Highestrelativehumidityandlengthofhumidseason:Varied

Figure8.35

WindroseforDamascus(Beirut,Lebanon)showingtheprevailingwesterlywindsoftheregion(inm/s).

Projectteam:

8.1.5

8.1.5.1

Architect:AteliersLionAssociés,DagherHanna&Partners,Paris,France

Climateengineer:TranssolarKlimaEngineering

Client:FrenchMinistryofForeignAffairs

Figure8.36

VolumetricdiagramhighlightingtheflowpathandspatialcompositionofLycéeCharlesdeGaulleinDamascus.

Path5:WindTowers–PassiveandHybridDowndraftCoolingWindtowerssimilartothosedevelopedcenturiesagoinIran/PersiaandtheMiddleEastarerecentlyexperiencingastrongrevival.Researchandinnovationismainlydrivenbyagroup of innovative architects and engineers from Italy and theUK led byBrianFord,whostartedtoexplorethisstrategyinthe1990sasanalternativetoair-conditioneddeep-planbuildings andwho createddesigndata basedon a largeEuropean researchproject(PassiveandHybridDowndraftCooling,PHDC).26

HabitatResearchandDevelopmentCenter(HRDC)byNinaMaritzArchitects,Katatura,Windhoek,Namibia

NinaMaritz designed the HRDCwith the ambition “to be the centre of excellence inhousing research and development by applying newmethods and ideas of science andtechnology for the sustainable development of theNamibian housing sector,”27 and thecenterwasdevelopedwiththemission“topromotetheuseoflocal,indigenousbuildingmaterialsanddesigns, toengagemulti-disciplinaryteamsinbasicresearch,andtoadaptexistingknowledgeandappliedresearchtoachieveaholisticapproachtoproblemsolvinginthefieldofhousingandrelatedissues.”28

The center has been developed with a holistic profile and architecture concept.Whenever possible reclaimed material was used, for example reclaimed pavers and

cementblockataboutathirdofthepriceofnewones.Thebuildingisspreadoutoverthesiteforthevariousprogramparts,andeachsectionistoweredbyawindcatcher,sixalltogether,topullinairfromthewindflowabovethebuildingintothelowersectionsofthebuilding.Ifpossible,requirementsforcross-ventilationspacedimensionsaskforoperablewindows.

CasestudydataDesignintent:

This building is located in the southern hemisphere and therefore the main solarorientation is to the north. To mitigate the prevailing wind direction and the solarexposure, the building’smain axis is oriented about 25 degrees east of north. Thisorientation shelters thebuilding from the low-angleDecember (summer) sunon thesoutheastandsouthwestsideofthebuilding.Thewindcatchersaresupplementedbyoccupant-controlled lower-leveloperablewindowsaswellasclerestorywindowsfordaylighting.

Ventilationsstrategy:

Naturalventilationstrategyandmechanicalintegration:Windcatchertowersonlyforcooling

Spatial design strategy (flow path) plan/section and analysis: Open plan combinedwithwindcatchers

Façade strategies (apertures): Wind catchers for cooling combined with operablewindowsforcomfortventilation

Figure8.37

HabitatResearchandDevelopmentCenter(HRDC)inWindhoek,Namibia:thecenterwithitswindtowersinthelandscape.Stackventilationwindowsarealsovisibleatthetopofthebuilding.

Figure8.38

HRDCinWindhoek,Namibia:oneofthewindtowersasseenfromtheexteriorpassageways.

Figure8.39

HRDCinWindhoek,Namibia:thetopofthewindtoweriscoveredbyasheetmetalroof,whichhelpstoinducetheVenturieffectandincreasestheairvelocityatthetopofthetower.

Projectdata:

Yearofcompletion:2004

Height/buildingtype:5mforthebuildingplusadditional3m/9.84ftforthetower;mixeduse

Stories:Twotothree

Function:Researchcenter,offices,publicspaces

Structure:Recycledandfoundmaterialssuchasstones,sheetmetal,steelbeams,usedcartires,brick,andwillows

Plandepth:Between11and19m/36and62ft

Buildingsize:2196m2/23,640ft2

Climaticdata:

Location:Kataturatownship,Windhoek,Namibia

Geographicposition:22.5231°S,17.0603°E

Climateclassification:Windhoek is situated ina semi-aridclimatic region (Köppen:BSh).

Prevailing wind direction: Northwest (May through September), east/northeast(February, March April, November) and south (October/January), depending onseason

Averagewindspeed:Veryconstantwindspeedaround8/9mph/12.85–14.5km/h

Meandaytimetemperaturesummer:Maximum32to34°C/90to93°F

Meandaytimetemperaturewinter:4to6°C/39to43°F

Heatingdegreedays65°F/18°C:926/496

Coolingdegreedays78°F/25°C:633/334

Day-nightdifferenceduringhottestmonths:Dailytemperatureswings20°C/36°F

Meanannualprecipitation:Medianrainfall12to14in/305–356mm

Averagerelativehumidity:Humidityaverage10to20percent

Highestrelativehumidityandlengthofhumidseason:None

Energydata:

Timeofyearnaturalventilationcanbeutilized:Yearround

Savedheatingandcoolingenergy:N/A

Typicalannualenergyconsumption:N/A

Considerations,obstacles,issues,etc.:None

Figure8.40

WindroseforWindhoek,Namibia,showingtheprevailingwindsinthelocation(inm/s).

Projectteam:

NinaMaritzArchitects

Figure8.41

SectionthroughthemainspaceoftheHRDCshowingtheinteractionofcross-ventilationandwindcatcherventilation.

Figure8.42

AxonometricviewoftheoverallspatialcompositionoftheHRDC.

8.1.6

8.1.6.1

Figure8.43

Volumetricflowpathdiagramsshowingthespatialcompositionofthewindtowers,whichareintegratedintothemainspatialvolumeasanedgein–edgeoutflowpathcomposition(seeFigure7.7).

Path6:CombinedStrategiesMostoftennaturalventilation strategies in larger scalebuildingscombinemultiple flowpathstrategiesandmostoftenalsomultipleventilationstrategies.Oftencombinationsarebasedondifferentidentifiedzonesinthebuilding.

FreieUniversitätBerlinLibraryTheFreeUniversityBerlinwasfoundedin1948intheWesternsectorofBerlin,Germany.Twenty years later, a newbuildingwas designed in the suburb ofDahlembyCandilis,Josic,Woods, and Schiedhelm based on their winning competition entry of 1963. Thebuildingwasnotconstructeduntil1967,andwas finallycompleted in1973.The iconicyetconfusingclusteredlayoutofstreetsandcourtyardscarriedthesocialoptimismofthetime. However, the materials, assemblies and construction techniques were prone todilapidationandfailureandthusamajoroverhaulhadtotakeplaceinthe1990s,whichalsoincludedtheinsertionofanewmajorlibrarycomplexintooneofthecourtyards.AllofthisworkwasconductedbySirNormanFosterandPartnersbetween1997and2004.Thenewphilologicallibrary,alsocalled‘TheBrain,’consistsofmultiplelevelsofreadingareasandshelvescoveredbyalarge,free-carryingroofmadeofsteeltrussesandcoveredbyinnerandouterlayersofskin,whichfacilitateheating,naturalventilation,andcoolingoftheinner,open-planlibraryspace.29

CasestudydataDesignintention:

Hybridsystemwheretheouterskinactsasbufferandventilationduct;thermalmassisusedtobalancethetemperatureswings.

Ventilationstrategy:

Naturalventilationstrategyandmechanicalintegration:Cross-ventilationonlyforthelibrarysectionthroughventilationskin

Spatialdesignstrategy(flowpath)plan/sectionandanalysis:Openplan

Façadestrategies(apertures):Multipleoperablewindows.

Projectdata:

Yearofcompletion:2005

Height/buildingtype:19m/62ft

Stories:Fourfloorsenclosedinabubble-like,free-standingstructure

Function:Library

Structure: A covering shell of white fiberglass fabric panels and translucent ETFE(Ethylenetetrafluoroethylene)elementsspans64×55×19m(210×180×62ft).Itisa double-layered skin with a MERO28 wide-span steel structure painted in brightyellow.29

Plandepth:6290m2/67,705ft2

Figure8.44

PhilologicallibraryoftheFreieUniversitätBerlin:interiorviewofthebuildingskin.

Figure8.45

PhilologicallibraryoftheFreieUniversitätBerlin:interiorviewoftheventilationopeningsinthebuildingskin.

Figure8.46

PhilologicallibraryoftheFreieUniversitätBerlin:exteriorviewoftheall-encompassingbuildingskin.

Figure8.47

WindroseforBerlin,Germany,showingtheprevailingwesterlywindofthelocation(inm/s).

Figure8.48

VolumetricdiagramhighlightingtheflowpathandspatialcompositionofthePhilologicallibraryattheFreieUniversitätBerlin.

Figure8.49

SectionaldiagramofthePhilologicallibraryattheFreieUniversitätBerlinshowingtherelationshipofskin,core,andventilationflowpathinbetween.

Climaticdata:

Location:Berlin,Germany

Geographicposition:Latitude:52°28’N;longitude:13°18’E

KGclimateclassification:BerlinliesontheedgebetweenthetemperateOceanicCfbclimate of Western Europe and the humid continental climate Dfb of Poland andWesternRussia.

Prevailing wind direction: The wind is most often out of the west (28 percent),southwest (12 percent), east (11 percent), south (11 percent), and northwest (10percent).

Averagewindspeed:7to10mph/11.25to16km/h

Meandaytimetemperaturesummer:19°C/66°F

8.28.2.1

Meandaytimetemperaturewinter:2°C/35.6°F

Heatingdegreedays65F/18C:6261/3438

Coolingdegreedays78F/25C:44/6(basicallynocoolingneeded)

Day-nightdifferenceduringhottestmonths:16°F/10°C

Meanannualprecipitation:20mm/0.86in

Averagerelativehumidity:N/A

Highestrelativehumidityandlengthofhumidseason:N/A

Energydata:

Timeofyearnaturalventilationcanbeutilized:Yearround

Savedheatingandcoolingenergy:N/A

Typicalannualenergyconsumption:N/A

Considerations,obstacles,issues,etc.:Securityisamajorconcernforlibraries.Berlinhas a heating-dominated climate, therefore preheating the ventilation air and heatexchangewasessentialfortheventilationstrategy.

Projectteam:

Architect:FosterandPartners

Structuralengineer:PichlerIngenieure

M+Eengineer:SchmidtReuterPartners/PINIngenieure

ConnectingtheInnerFlowPathtotheOuterConditionKfWWestarkade,Frankfurt,Germany,bySauerbruchHutton

CasestudydataDesignintention:

Kreditanstalt fürWiederaufbau (KfW)Westarkade30 adds a tower on a plinth to anexistingagglomerationofbankofficebuildingsofvariousheights.Aringofdouble-skinfaçadesurroundsasingleringofoffices,whichcirclearoundthecirculationandinfrastructurecore.Corridorsmeetthefaçadeatthreepointstoenablenighttimecross-ventilation and core activation.Wind is used as the driving force to provide freshventilationair,whilestackpressuredifferenceisutilizedtoexhaustthestaleandwarmair through shafts in the core of the building. The double-skin façade is closed offbetween the floors in order to prevent an unwanted stack effect in the double-skinfaçade.Thedouble-skinfaçademerelysupportsthedistributionofpressurearoundthewhole ringofoffices, so that allouterofficewindowsact asventilation inlets.Thisfacilitates consistent fresh air input across all offices and makes the offices

independent from each other within the ventilation regime. The saw-tooth façadehighlights the difference between light-admitting surfaces,which are fixed, and air-admitting openings, which are colored and alternate with acoustic panels. The airintakepanelsaremuchmoreslenderthanthedaylightwindows.

Ventilationstrategy:

Natural ventilation strategy and mechanical integration: Mixed-mode/complementary/concurrent;wind-drivencross-ventilationcombinedwithstack-drivenshaftventilationSpatialdesignstrategy(flowpath)plan/sectionandanalysis:The streamlined, drop-shaped tower sits on a three- to four-story plinth and isintegratedintoanassemblageofotherbuildingsofvariousheights.

Façade strategies (apertures): Double-skin façade with operable windows in bothlayers to enable multiple opening combinations to facilitate a variety of flow pathstrategies

Projectdata:31

Yearofcompletion:2010

Height/buildingtype:56m/184ft,office

Stories:14

Function:Officestotal22,300m2/240,035ft2

Structure:Composite/glassfaçade

Plandepth:6.3m/20.6ftfromcoreand26m/85.3fttotal

Figure8.50

KfWWestarkadeFrankfurt,Germany:exteriorviewofthetowerfromthewest.

Figure8.51

KfWWestarkadeFrankfurt,Germany:viewupthetoweredgewithventilationwingsopen.

Figure8.52

KfWWestarkadeFrankfurt,Germany:detailedviewofthebuildingenvelopewithventilationwindowsopen.

Figure8.53

WindroseforFrankfurt,Germany,showinghowtheshapeofthetowerislocatedwithintheprevailingwesterlywindofthelocation(inm/s).

Figure8.54

VolumetricdiagramhighlightingtheflowpathandspatialcompositionoftheKfWWestarkadebuildinginFrankfurt.

Figure8.55

SectiondiagramhighlightingtheseasonallychangingflowpathfornaturalventilationintheKfWWestarkadeFrankfurt.

Climaticdata:

Location:Frankfurt,Germany

Geographicposition:latitude:50°7’N;longitude:8°41’E

KGclimateclassification:Warmtemperatewithfairlymildweatherandgoodnaturalventilation potential. Oceanic climate, Cfb/warm temperate, fully humid, warmsummers.

Prevailingwinddirection:SSW

Averagewindspeed:8mph/12.85km/h

Meandaytimetemperaturesummer:18.3°C/65°F

Meandaytimetemperaturewinter:1.83°C/35°F

Heatingdegreedays:Five-yearaverage,60°F/15.5°Cbase:4050/2232

Day-nightdifferenceduringhottestmonths:17.73°C/32°F

Meanannualprecipitation:621mm/24.4in

Averagerelativehumidity:53percent

Highestrelativehumidityandlengthofhumidseason:July16,75percent

Energydata:

Timeofyearnaturalventilationcanbeutilized:Eightmonthsoftheyear

Saved heating and cooling energy: 84 percent compared to fully air-conditionedGermanofficebuildings

Typicalannualenergyconsumption:Estimatedat50kWh/m2/15,850BTU/ft2

Considerations,obstacles, issues,etc.:Continuousspacesarealways inconflictwithfire protection measures. Therefore the continuous cavity ring of the double-skinfaçadecanbesubdividedintothreezonesinsynchwiththethreefireprotectionzonesinsidethebuilding.

8.2.2

Projectteam:

Architect:SauerbruchHutton

Associatearchitect:architektenTheissPlanungsgesellschaftmbH

Structuralengineer:WernerSobekGroup

Energyconcept:TranssolarKlimaEngineering

MEPengineer:ReuterRührgartnerGmhB:Zibell,Willner&Partner

Maincontractor:ARGEZüblin,Bögl

SanFranciscoFederalBuildingbyMorphosis

CasestudydataDesignintention:

SanFranciscoprovidesperfectconditionsfornaturalventilationbecauseofitsfairlymild temperatures and constant ocean breezes. The Federal Building combines anelongated towerwitha slender floorplanandabaseplaza.Theplanprovidesgoodconditions for floor-by-floor cross-ventilation utilizing operable, out-swinging, top-hungwindowscombinedwithamulti-layeredshadingsystemnecessarybecauseofitsorientation. The positioning of the tower into the prevailingwind coming from thenorthwestconflictsherewiththelow-anglesolarradiation.Thisleadstotheexposureof the elongated west and east façades to the low-anglemorning and evening sun,which can cause significant solar heat gain, which does not facilitate low energyventilation.Duetofederalsecurityconcerns, thebottomfivefloorsarenotdesignedwith operablewindows and are thus fully air-conditioned. This zoning requirementwas then supplemented by the programming for the building. The base contains aconference center, fitness center, and daycare center. The narrow floor plan iscomplementedby anopen floor planwith intersectionsof closedvolumes formoreenclosedspacessuchasbathroomsandmeetingrooms.Agapofhalfameterabovethese volumes permits air to flow across the spaces.Ceilings are exposed concrete,cast with a wavy underside to enhance daylighting through reflection, but also toexposealargerareaofmasstotheventilationairfornighttimecooling.

Ventilationstrategy:

Naturalventilationstrategyandmechanicalintegration:Mixed-modebasedonzones.Mechanical ventilation is used inparts of thebuilding that arenot connected to theperimeter open plan. In addition, mechanical ventilation can be supplemented andtrickle vents are added above baseboard heaters to warm incoming ventilation airduringthecoldseason.

Spatial design strategy (flow path) plan/section and analysis: Open plan combinedwithenclosedvolumes;bottomfivefloorssealedforsecurityreasons

Façade strategies (apertures):Operable, top-hungwindowswith shading screen and

additionaltrickleventsforcoolerseasons

Figure8.56

FederalBuildingSanFrancisco,California,USA:exteriorviewofthetowerfromthenortheast.

Figure8.57

FederalBuildingSanFrancisco,California,USA:exteriorviewofthetowerslabfromthesoutheastshowingthesolarshadingscreen.

Figure8.58

FederalBuildingSanFrancisco,California,USA:detailedviewofthebuildingenvelopefromthenorthwest.

Figure8.59

WindroseforSanFrancisco,California,USA,showinghowtheshapeofthetowerislocatedwithintheprevailingwesterlywindofthelocation(inm/s)

Figure8.60

VolumetricdiagramhighlightingtheflowpathandspatialcompositionoftheFederalBuildinginSanFrancisco,California.

Figure8.61

SectionhighlightingtheflowpathofthenaturalventilationflowoftheFederalBuildingSanFrancisco,California.

Projectdata:32

Yearofcompletion:2007

Height/buildingtype:71m/233ft/federaladministration

Stories:18

Function:Officesandconferencespaces

Structure:Concrete

Plandepth:19m/62.3ftbetweenfaçades

Climaticdata:

Location:SanFrancisco,NorthernCalifornia,USA

Geographicposition:Latitude:37°47’N;longitude122°26’W

Climateclassification:Temperate

Prevailingwinddirection:West

Averagewindspeed:9.5mph/15.5km/h

Meandaytimetemperaturesummer(July,August,September):23°C/73.4°F

Meandaytimetemperaturewinter(December,January,February):14°C/57.2°F

Heatingdegreedays65F/18C:2719/1510

Coolingdegreedays:31/17(basicallynocoolingneeded)

Day-nightdifferenceduringhottestmonths:10°C/18°F

Meanannualprecipitation:500mm/19.68in

Averagerelativehumidity:60percentduringhottestandcoldestmonth

Highest relative humidity and length of humid season: Maximum 75 percent inFebruaryduringcoldseason

Energydata:

Timeof year natural ventilation can be utilized: 21 percent of the building’s usableareaisnaturallyventilated100percentofthetime.

Saved heating and cooling energy: 55 percent compared to a conventional air-conditionedbuildingof the same size and typology (estimate) andabout15percentcomparedtoCaliforniaTitle24EnergyCode.29

Typicalannualenergyconsumption:Unpublished

Considerations, obstacles, issues, etc.:Additional heat gaindue to orientationmightnotalwaysbeoffsetbynaturalventilation.

Projectteam:

Owner/developer:USGeneralServicesAdministration

Designarchitect:Morphosis

Associatearchitect:SmithGroup

Structuralengineer:Arup

MEPengineer:Arup

Projectmanager:HuntConstructionGroup

Maincontractor:DickCorporation;MorgantiGeneralContractors

Other consultants: Lawrence Berkeley National Laboratory (Natural VentilationModeling);curtainwall:Design&Consulting,Inc.

Notes

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005),pp.8–10.

Ibid.

See“DasBakema-VanDenBroek-Punkthochhaus,”http://www.acamedia.info/arts/architecture/bartning7.htm(accessed5/13/2014).

Seehttp://www.architetturadelmoderno.it/scheda_nodo.php?id=72&lang=_eng(accessed5/13/2014).

BrunoZeviandGiuseppeTerragni,GiuseppeTerragni,1sted.,SerieDiArchitettura(Bologna:Zanichelli,1980).

PeterD.Eisenman,“FromObjecttoRelationshipII:GiuseppeTerragni,CasaGiulianiFrigerio,”Perspecta(YaleUniversity),13/14,1971,pp.36–65.

PeterTerragni,GiuseppeEisenman,andManfredoTafuri,GiuseppeTerragni:Transformations,Decompositions,Critiques(NewYork:MonacelliPress,2003).

Heatingdegreedays(HDD)aredefinedasameasurementtoreflectthedemandforheatingenergyagainstabaselineindoortemperatureforaspecificlocationandaveragedailyoutsidetemperature.TenHDDreflectanaveragetemperaturedifferenceof10°For10Kbetweenadesiredindoortemperatureof18°C/65°Fandtheoutdoortemperatureofaparticularday.AddingallHDDforayearprovidesameasurementfortheseverityofwinter.

Coolingdegreedays(CDD)aredefinedasameasurementtoreflectthedemandforcoolingenergyagainstabaselineindoortemperatureforaspecificlocationandaveragedailyoutsidetemperature.TenCDDreflectanaveragetemperaturedifferenceof10°For10Kbetweenadesiredindoortemperatureof25°C/78°Fandtheoutdoortemperatureofaparticularday.AddingallCDDforayearprovidesameasurementfortheseverityofwinter.

See“CharlesCorreaAssociates,”http://www.charlescorrea.net/(accessed5/13/2014).

Seehttp://weatherspark.com/averages/33910/Mumbai-Bombay-Maharashtra-India(accessed5/13/2014).

AntonySalibandRubaWood,NaturalVentilationinHigh-RiseOfficeBuildings,CTBUHTechnicalGuides(NewYork:Routledge,2013),pp.33–41.

Variouswebsourceswereconsultedforthiscasestudyproject(allaccessed5/13/2014):http://www.fosterandpartners.com/projects/commerzbank-headquarters/,http://www.degreedays.net/#generate,http://sustainability2009.commerzbank.com/reports/commerzbank/annual/2009/nb/English/703025/co_sub_2_sub_-accounting-energy-use.html.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005),pp.11–13.

Seehttp://www.mickpearce.com/about/pressmedia/(accessed5/13/2014).

Seehttp://www.mickpearce.com/works/office-public-buildings/eastgate-development-harare/(accessed5/13/2014).

M.Kottek,J.Grieser,C.Beck,B.Rudolf,andF.Rubel,“WorldMapoftheKöppen-GeigerClimateClassificationUpdated,”Meteorol.Z.,15,2006,pp.259–263,doi:10.1127/0941-2948/2006/0130.

KeelanP.Kaiser,DavidM.Ogoli,andMalcolmCook,“HarmA.WeberAcademicCenter,Post-occupancyBuildingPerformanceandComfortPerceptions,”ARCCJournalofArchitecturalResearch,6(2),2009.

“TheEnvironmentalBuilding”(BRE),http://projects.bre.co.uk/envbuild/.

“GreenBuilding”(SidwellFriendsSchool),http://www.sidwell.edu/middle_school/ms-green-building/index.aspx.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005),p.17.

ClitoAfonsoandA.Oliveira,“SolarChimneys:SimulationandExperiment,”EnergyandBuildings,32(1),2000,pp.71–79.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005).

Seehttp://weatherspark.com/averages/32874/8/Damascus-Rif-Dimashq-Governorate-Syria(accessed5/13/2014).

BrianSchiano-Phan,RosaFrancis,andElizabethFord,TheArchitecture&EngineeringofDowndraughtCooling:ADesignSourcebook(PHDCPress,2010).

26

27

28

29

30

31

32

“HabitatDevelopmentandResearchCenter,”cndstudio2012.files.wordpress.com/2012/10/hrdc.pdf.

Foster+Partners,http://www.fosterandpartners.com/projects/free-university/(accessed5/13/2014).

“MeroConstructionsystems”,MeroStructures,http://www.mero-structures.com/construction-systems-2.html(accessed05/18/2014).

“TheFreeUniversityStillEmbodiestheSocialandArchitecturalDynamicofthe1960s,”Architects’Journal,9/15/2005.

AntonyWoodandRubaSalib,GuidetoNaturalVentilationinHigh-RiseOfficeBuildings(NewYork:Routledge,2012).

Ibid.,pp.122–123.

AntonyWoodandRubaSalib,GuidetoNaturalVentilationinHigh-RiseOfficeBuildings(NewYork:Routledge,2012),pp.104–111.

9.1

Chapter9

FaçadeasFilter:FromWindowstoCurtainWallstoAdaptiveandSmartSkinsThebuilding envelope is the crucial filter andmembrane for ventilation, supplying andexhaustingair throughitsopenings.Inordertodevelopafunctioningnaturalventilationstrategy, these inlets and outlets have to be properly placed and sized to provide therequiredventilation rate,while the remainingpartsof the façadeshould ideallybe fullysealed inorder to control the flowand toprevent infiltrationnegatively influencing theflowrate.

The building envelope also plays a significant role in controlling the exchange ofthermalenergybetweeninsidecomfortandoutsideclimaticconditions.Thisexchangecanonlybepreventedbyvacuuminsulation,whichisstillaverycostlyendeavor.Thus, theconstructionandsealingofthebuildingenvelopehastobeconductedwithutmostcaretoprevent the creation of thermal bridges. Air infiltration may result in uncontrolled airexchange rates, which can lead to reduced pressure differences elsewhere. Hightemperature differences inside the building envelope assembly can also lead to harmfuland destructive condensation. This in turn can lead to mold growth and thus healthhazards.

Inletsandoutletsfornaturalventilation,whichconnecttheventilationflowpathtotheexternal environmental forces, are a crucial factor in the design of spaces for naturalventilation.Themostcommonelementordevicetoenablethisconnectionistheoperablewindow.Theverticalwindowismainlyneededforwind-drivenventilationflows,whilethe window opening in the roof can also work together with buoyancy effects forventilation.

WindowVentilationinDifferentRegionsandClimatesThe Old English word for window ‘vindauga’ means wind-eye, fromOld Norse vindr‘wind’+auga ‘eye,’ the eye for thewind,whichcombines the twomajor functions foropenings inbuildings: letting in lightandairandallowing theview toventureout.Theword,alongwithmanyothers,waspresumablyintroducedtotheAnglo-SaxonlanguagebyDanishsettlersmainlyintheninth,tenth,andeleventhcenturies.ThemodernDanishword for ‘window’ is vindue, pronounced not very differently from its Englishcounterpart.1

Verydifferentstylesofwindowsdevelopedindifferentpartsoftheworld,dependingonclimate,availablematerials,customs,andotherrequirementssuchasculturalnormsandprivacy requests. Often the aspects of physics were intuitively integrated based onphysicalneedsforviewandairchangeratesversusheatandsecurity.

9.1.1

Figure9.1

Differentopeningstylesforwindowsdirectlyinfluencetheventilationinletflowdirectionoftheflowpathinsidethebuilding.Fromlefttoright:horizontalpivot,verticalpivot,tophung,sidehung,tiltandturn,verticalsliding,horizontalsliding,louvers.

Operable windows can be user controlled or automated (see Chapter 10). Overcenturies,differentopeningmechanismhavebeendeveloped,whichlendthemselvestoadifferentclimateanddifferentventilationstrategies.

FrenchDoorsSide-hungcasementwindowsare traditional inFrance,where theyopen inwardsas twopanes (French windows/doors). In the Netherlands or Northern Germany they openoutwards,whichisoftenexplainedbythefactthattheycanbeclosedbythewindandthewind presses them tight to the frame. These windows often provide better protectionagainstdrivingrainastheyclosetightlyagainstthedirectionoftherain.

Figure9.2a

Frenchwindows,asseenherefromtheexteriorofatypicalhouseintheParisregion,reachfromclosetothefloortoclosetotheceiling,aresplitinthemiddle,andaresidehungandusuallyopeninward.

9.1.2

Figure9.2b

AninteriorviewofaFrenchwindow.

EnglishSashWindowsEnglish sashwindows slide in a vertical direction; usually two frames, sometimes eventhree frames, slideover eachother to createopeningsofmultiple scaleson the top andbottom. Sash windows can allow for small and large air flow rates, but are prone toinfiltrationastheyaredifficulttomanufactureairtight,similarlytootherslidingwindows.The advantage of sash windows is that they do not protrude out into the space whenopened.

9.1.3

Figure9.3

Englishsashwindowsaredoublehung,horizontallysplitandslideupanddown,allowinggradualchangesintheopeningsize,anddonotprotrudeintotheoccupiedspace;thustheydonotredirecttheflow.

HopperWindowsHopper windows often combine an operable window frame with a closed sealed glasspane.This isacommonpractice in theNordiccountriesandhighlights thedistinctivelydifferentsizingrequirementfordaylighting,solargain,andnaturalventilation.

9.1.4

Figure9.4

Hopperwindowsaresmallwindowflapsopeningoutwards,ashereintheIowaInterlockHouse.

NorthernEuropeanBoxWindowsNorthern European box windows basically combine two layers of side-hung windows,whichtrapanairspacebetweenthemforimprovedinsulationinwinter.Thesetwolayersofglassalsogreatlyimprovetheacousticseparationofinsideandoutside.

Figure9.5

NorthernEuropeanboxwindowscanopeninwardsoroutwardsandarecomposedoftwosetsoffourwindows,whichencloseanairspaceinbetween(phototakeninTallinn,Estonia).

9.1.5

Figure9.6

ThisRomanwindowatPalazzoCenci,theISUCollegeofDesignstudioinPiazzadelleCinqueScole,Rome,Italy,includesthreelayers:anouterlayer,whichactsasashadingdevice,butalsoasaventilationlouver,theactualwindowwithglass,andaninnerlayer,whichcansecludethewindowfromtheinsidefortotalprivacy.

MultifunctionalRomanWindowsMultifunctionalRomanwindowsareanevenmorecomplexdevelopment.Theycombinetwoside-hungframeswithglasscombinedontheinteriorwithtwosolidwoodenshuttersthatcreatecompletedarknessandprivacyandanexternallayermadeofasetoflouveredshutters,whichcanprovideshadingof theglass from theexterioraswellasventilationinletswhentheglasspanesareopened.

9.1.6

9.1.7

Figure9.7

TheventilationopeninginAlvarAalto’sownhousewindow,whichhedesignedwithhisfirstwifeandpartnerAinoAalto,separatestheventilationfunctionclearlyfromtheviewwindow.

VentilationWindowsWhenventilationrequirementsandrequirementsforviewwindowsareevenfurtherapart,suchasintheNordiccountries,theverticalventilationopeningissosmallthatitdoesnotevencontainglass.AnexampleisseenintheventilationopeningsinAalto’sownhouseinHelsinki,Finland.Thisdesign removes the infiltration issuesbyusinggasketsandsealswithinthelargeviewwindow,whilestillprovidingampledaylightthroughthelargepaneof glass. The view window is sealed shut, and the assembly only contains one smallverticalventilationflap.

LaueferliinDavosAnother strategy to separate the ventwindow from the viewwindowwasdeveloped intraditional farmhousesof theDavosAlps inSwitzerland,where justone smallpaneof

9.1.8

glassismovable,whiletheothersarestationaryandsealed.

PivotWindowsPivotwindowsarehungat thecenteraxisof theoperable frame.Theyhavebeenfairlycommon in industrial applications, factory buildings, and greenhouses, and have beenmade famous by the Bauhaus building inDessau, 1925–26, byWalterGropius (1883–1969).

Figure9.8

Theso-calledLaeuferliinDavosdescribesafairlysmallventilationslider,whichisintegratedinalargercomposition,whichwasbroughttoattentionbyAndresGiedion7inhisbookontheDavosAlphuette.

9.1.9

9.1.10

Figure9.9

WalterGropius’famousglassfaçadeattheBauhausbuildinginGermanyfrom1926connectsaseriesofpivotwindowsthroughamechanicalopeningmechanism.

WingWallsThe prevailingwind directionmay notmatch the orientation requirements forwindowsand/orfortheentirebuilding.Wingwallscanhelptochanneltherequiredairflowintotheopening. The opening frame of a window and/or its shutters can act as wing walls.Carefullyplacedfaçadeelementscanserveasimilarfunction.

VentilationHoles

InChinesetraditionalresidentialarchitecture,emblemsappliedtothebuildingaspartofthe structural features of the housewere common.Good fortune, longevity, andwealthand privilege were some of the wishes embedded in the building fabric. A ventilationopening captured byKnapp inMeixian, Guangdong, for example takes the shape of abottle gourd. The bottle gourd represents longevity and magic. The origin of thisrelationship is not clear, but it might lead back to the ‘Li Tiegui,’ one of the eightimmortalsoftheDaoistlifephilosophy,whoseemblemisagourd,themagicvaporsfromwhich are said to be capable of trapping evil, according to Knapp’s comprehensiveanalysisofChinesehousetypologies.2

Figure9.10

Wingwallscandirecttheairflowpatternsandinfluencethewayfreshairmixeswithstaleairininteriorspace.

9.2

Figure9.11

VentilationholefromMeixian,China,shapedlikeagourd.

Figure9.12

Thesizeofopeningdirectlyinfluencestheairflowrateinrelationtowindvelocity.

ProportionalRulesforWindowOpeningsandDistribution

Manyparametersareusedtodeterminethepositioningofventilationopeningsintheformofinletsandoutletsinthebuildingenvelope.Themostimportantofallarethegeometryofthebuildingandthepositionofthebuildingonthesiteorwithinthestreetcanyon.Theproportionofthestreetcanyondeterminestheforceoftheventilationairatairinletsandoutlets. These parameters also determine the quality of air at this important boundarycondition.Thepositionofthewindowintheheightoftheroomandheightabovegroundaswellasitsorientationareasimportantastheoperationmechanismofthewindowitself

and the direction inwhich they open. Inmost cases, the scalability of the opening sizeprovides control opportunities to manipulate the incoming air change rate and the airvelocity.

Theorientationofwindowsinthewinddirectiondirectlydeterminestheflowdirectionoftheairmovementinsidethespaceandthusthemixingcapacityoftheairstream.

Itisoftenoverlookedthatprecisepredictionforairchangeratescanonlybeobtainedforfairlyflatfaçades.Elementsattachedtotheoutsideofthefaçadecansignificantlyaltertheairflowpatternaswellastheairvelocityattheinletandoutlet.Suchobstaclesalongthe façade influencing the ventilation rate inside a building include solar shading,overhangs, balconies, bay windows, and other elements, such as awnings as shadingdevices,orbugscreens.Thesedevicescreatemorecomplexandturbulentwindpatternsattheinlet(aswellastheoutlet)andmaketheevaluationofaventilationstrategyevenmorechallenging.

ThereportfortheEuropeanUrbVent(2005)project3thusstatedthaturbanfaçadesaretoo complex to allow for a precise predictionof ventilation rates andmay even requirestudies in wind tunnels. Only simple geometries are predictable enough to developgeneralizedrecommendedguidelinesforopeningsizes.

In general, research has shown that multiple small openings can create a morehomogenousairflowregimethanasinglelocalopening,evenifthesizeoftheonelargeopeningequalsthesumofthesmallsizedopenings.4Ifdesignedcorrectly,balconiesandoverhangscaninsomecasesevenincreaseairflowrates.5Butoverhangscantrapwarmairinfrontofthewindow,whichmeansthatairwarmerthandesiredandnecessarymaypenetratetheinletandcounteractcoolingefforts.Inaddition,windowscreensandlouverssignificantlyreduceairflowratesandingeneralrequireadoublingoftheinletarea.

All of these additions to the building exterior jeopardize the precision at which thepressure coefficient and thus the rate and direction of wind entering the inlet can bepredicted.Butsomerulescanstillbeestablished.

Requiredventilationopeningscanberoughlysizedbyestimatingtheheatthatneedstobe removedand the temperaturedifferencebetweensupplyairand thedesired roomair(delta T). This information will provide the required air flow rate. Air flow raterequirements and available wind speed can then be used to size the required opening.First, the uncertainty of wind distribution over the ventilation inlet/outlet has to beconsidered. In general, inlets should have the same size as outlets in order to allow ahomogenousflowrateacrossthebuilding.

There are various scaling rules of thumb for the different air flow requirements andstrategies,buttheyallshareabasicrequirementforacontinuousflowrate:allopeningsalongtheflowpathshouldbedesignedatroughlythesamesizeandthesmallestopeningdeterminestheoverallflowrate.

Figure9.13

Overhangstraphotandhumidairinfrontofventilationopeningsandshouldbeavoidedinhotandhumidclimates.Movableshadingdeviceswillbemorebeneficial.

9.3

Figure9.14

Thesmallestopeningdeterminestheoverallairflowrate.

FaçadeProportionsandWindowVentilationStrategiesFrom an architectural perspective, the window is the most prominent compositionalelement in the building façade. Over the centuries it has developed multiple culturalvaluesandfunctions.LouisKahn(1901–1974)builtahomeforMrs.EsherickinChestnutHill,Philadelphia,Pennsylvaniain1961(alreadydiscussedinChapter1).IntheEsherickHousethewindowsareincorporatedinaspatialstrategywhichcombinescross-andstackventilation. When a connecting double height space is incorporated in an all-encompassingvolume,spatialcontinuityisachievedinacompactverticalandhorizontalvolumetriccomposition.Warmairrisesbyconvection,enablingthestackeffectowingtothehighspatialvolume.Thehigherthespaces,thefurtherawaytheexhaustairisallowedtomovefromthecomfortspaceoftheinhabitants,anditgathersattheceiling,whereitcanbeexhausted.Windcanassistthestackeffect.

This compositional strategy of ordering space and air is intentionally designed fornatural ventilation, and the façade includeswooden shutters tomodify the flow. Theseshuttersalsocontributetothecompositionalcomplexityofthefaçade,astheyaresetbackinthevolumetricsurface.Thusthevolumeof thewallshadesthesurfaceof theshutter,whileatthesametimeairvelocityisincreasedbythebottleneckeffectoftheinletpoints.Toreduceheatgain,thesealedglasssurfacesareshadedwithexteriorblinds.

Kahn’s architecture has often been described as a spatial composition of volumesdivided between server and served spaces. This analytical view indicates a distinctionbetween the spaces with a controlled environment and those helping to enhance andcontrol thisenvironment. In theEsherickHouse, thesedistinctboundariesarenotvalid.Server and served space are one and the same, because the spaces of the house are

designedtoenhancenaturalventilation.Thespatialcompositionexplorestheconnectionoftwosinglespacesandonedoubleheightspaceincorporatedwithinacompactvolume,which in itself is subject to a complex geometric composition. In this house, structure,space, light, and vents are intertwined in the same volumetric composition, enhancingimmaterial movements of air and light. The spatial envelope in the Esherick Housemediates the flow of light and air in a very distinct way by changing the relationshipbetweeninsideandoutside.

Figure9.15

EsherickHousefaçadewithhighlightedventilationshutters.

Figure9.16

ThespatialcompositionoftheEsherickHousejuxtaposesadoubleheightspacewithtwosinglestories.

This examplehighlights the relationshipbetweenair flowandgeometricproportions.Elementsneedtobedeterminedbyvolumetricproportions,notbyplanarcompositionandnumbersalone.Thus,forananalysisofairflowintheEsherickHousetheunderstandingof space needs to go beyond the obvious, established reading of the geometriccompositionofthehouseextensivelydescribedascomplexplanargeometry.Rykwert6forexamplenoted that thebuilding isdesignedasacubicvolumetriccompositionof9×9(+1)moduleswithverticalproportionsof1×2×1and2×2modules.

Anotherarchitectural featureutilized tomanipulateairmovement in space is the sizeandplacementofopenings.Achangeinrelationshipbetweeninletandoutletopeningshasa tremendous impact on the velocity of air, allowing the manipulation of flow. In theEsherickHouse, openings for air and openings for light are designed not as one but asseparate entities, which also enhances the changing relationship between interior andexterior, as shown in a related computational fluid dynamics (CFD) analysis of flowpatternsinsidethebuilding.7

AsButtiker8noted,closing thewoodenshutters thatactasventilationopeningshidestheviewtothegardenandleadstoawithdrawalintoaninnerworld.Inthisscenario,onlythe clerestory window high up provides daylight and views to the sky. Opening theventilationdoor relates theoccupant back to the exterior view, offering theviewof thegarden, theweather, and the changing seasons. This situation enables the interior to bepart of the greater flow of air. The house can thus be seen as a physical obstacle thatdistortsthelaminarflowintounpredictableturbulenceandeddiesthroughandaroundthebuilding.

Figure9.17

TheCFDanalysisoftheEsherickHousehighlightstheimportanceoftheheightofthespaceforcoolingpurposes.

Figure9.18

CFDanalysisoftheEsherickHouse:fourtimestepsofcoolingcase.

9.4 BenefitsofDouble-SkinFaçadesintheContextofNaturalVentilation

Double-skinfaçadesensurenoiseinsulationandsecurityaswellasreducedexternalwindvelocityattheinlet.Thisstrategybenefitshigh-risebuildingsorbuildingsinthevicinityofwindycoastlines,forexampleinaportlocationsuchasthecurrentdevelopmentintheHafenCity,Hamburg.9Double-skinfaçadesarebestsuitedforurbanenvironments,high-risebuildings,andcoastallocationsandcanalsobeusedasaretrofit.Shadingdevicescanbe integratedwithoutdangerofdamage,because theycanbe introduced into thecavitybetweenthetwofaçadelayers.

Whendesigningdouble-skinfaçades,thestackheightwithinthefaçaderequirescarefulconsiderationtodeterminewhetheritcanorcannotcontributetotheventilationstrategy.

9.5

Figure9.19

Double-skinfaçadeintheUnileverBuildinginHafenCityHamburg,Germany,wherethesingleouterlayerofplasticfilmclearlyservesthepurposeofslowingdownthewindvelocityatthiswindylocationinthemiddleoftheportattheElberiver.

Oneofthefirstdouble-skinfaçadesdesignedinthetwentiethcenturyismostlikelythedouble-glasswindow inAlvarAalto’s Paimio sanatorium inFinland.The two panes ofglassactedasventilationinletinordertoreducethevelocityofairandtopre-warmtheair,andavoiddraught for theoccupant in thecustom-designedpatient room(seeFigure3.5,Chapter3).

Figure9.20

ThedoubleglassfaçadeoftheGSWbuildinginBerlinfacilitatesthecross-ventilationbyprovidingastack.

Innovations:AdaptiveandSmartSkinsforAirandLight

Adjustability,interactivity,andadaptabilitytochangingdemandsandconditionsaroundaventilation opening has been a goal both in recent high-tech and in historical low-techapproaches.Insomeexamples,eventhedirectioninwhichtheventilationwindowopensmatters.Theair flowpatternchangesdependingonwhether thewindowopens towardsthe interior or towards the exterior. Thus, it is only a short step to consider thewholefaçade as a potential ventilation opening, offering flexible variations to let air in or toblock it, and to even channel or modify the air flow direction and its speed. Currentresearch and development directions are manifold. For example, research teams are

examining materials that can react to environmental changes in order to alter thecompositionofthefaçade,suchasbi-metalstripfaçadesthatcanreacttosolarradiation,temperature,and/orwind.Yet,contemporarydevelopmentsareoftenrepresentationalandartistic representations rather than functional, showcasing the turbulence of the windacross the façade instead of utilizing them. Kinetic architecture often uses wind as amotor,motivator,or actuator for avisual representationofwind,but thesedevicesveryrarelyactasventilationelementsatinletoroutletlocations.

The ‘Tower of theWind’ by Toyo Ito in Tokyo is a sculpture visualizing wind andsoundcarriedbywind,andmostairbubbles,suchasthewaterpavilionbytheDutchfirmNOX,arearchitecturemadeofair,butusuallynotnaturallyventilatedspaces.

Innovative research in this area is conducted by, for example, CASE, theCenter forArchitectureScienceandEcology,ajointresearchprogrambytheRensselaerPolytechnicInstitute(RPI)andthearchitecturefirmSkidmoreOwingsMerrill(SOM).10

Latest CFD simulation research on façade design and composition draws fromexperiencesofkineticmovementofmarinemammalssuchaswhales.Counterintuitivelytocommonthought,roughedgesontheirflippersseemtoreduceturbulencearoundthemand increase the animals’ ability to speed up inwater. According to simulations at theTechnicalUniversity (TU)Delft,11manipulation of the surface roughness of the façadethrough kinetic adaptation enhances the air flow related characteristics of the building.High-risebuildingscouldchangepressuredifferentials in the façade to influence theairvelocitythroughthebuilding.Thistheoreticalprojectwaspresentedinaresearchpaper,whichstated,“roughnesselementslocatedonthebuildingenvelopeare(considered)abletomodify the velocity field close to the façade; thismodification has an effect on thenaturalventilationand,primarily,ontheheatexchangeduetothewindconvection.”11

Mostdiscussionson the relationshipbetweenabuildingand its air flowenvironmentconsideredthelarge-scalelevelofthebuildingitself,wheretheformandpositionofthebuilding divides the flow and creates a pressure differential around the building. Thisnovel adaptive concept, presented in a theoretical aerodynamics research project,suggested the manipulation of the building’s surface roughness at the level of theopenings,suchaswithbalconies,overhangs,recesses,orevenatthelevelofthematerialandthesurfacetexture.

AsLingnaroloandhisteamwrite:

External roughness elements, which are able to change orientation, can stronglymodify the velocity field, for example, bymaking amore uniform pattern on thefacade or canalizing the airflow and moving it in different zones. These externalelementsshouldbeabletomoveandadjustthemselvesassumingdifferentaperturesand directions in different areas of the building façade according to the windcharacteristicandthecurrentneeds(e.g.coolingenergydemand).11

Theycontinuethat

the aerodynamic and hydrodynamic characteristics of a smooth body are not

necessarily better than the ones of a rough body, as it could be naturally expectedbasedonnormallyanticipatedphysicalphenomenon.Surfaceroughnessdoesindeedincreasethefrictionbetweentheflowandbody,butithasalsoapositiveinfluenceonotherphenomena.11

Figure9.21

Thetextureofagolfballfacilitatesitsmovementthroughairbyreducingtheresistanceofairagainstitsflow.

Thereareotherexamplesofroughsurfacesincreasingspeedinsomeobjects,suchasgolfballs.

Thedimplesonthesurfaceofagolfballcausetheairflowontheupstreamsideoftheballtotransitfromlaminartoturbulent.Theturbulentboundarylayerisabletoremainattachedtothesurfaceoftheballmuchlongerthanalaminarboundaryandsocreatesanarrower,lowpressure,wakeandhencelesspressuredrag.Thereductioninpressuredragcausestheballtotravelfurther.11

Thechangeinroughnessonabuilding’ssurfacecanreducedragaroundthebuildingandreduce the flow velocity around high-rise buildings, which may create significantadvantagesinnaturalventilationforhigh-risebuildings.

Balconies, forexample, reduce thewindpressureacross the flowpath,as reported intheTUDelft project,11which investigated the application of the concept to a high-risestructure. Usually, the upper floors experience too highwind velocities for any naturalventilation strategy, which is often counteracted with a double façade. In this case,horizontalbalcony-type façadeelementsaswellashigh fin-typeelementswere studied,and although the pressure field did not decrease significantly, the velocity field diddecrease, which would have a significant impact on the capacity to conduct naturalventilationbyopeningwindows.

9.6

Figure9.22

Balconiesorotherelementsontheoutsideofthefaçadeactasroughnesselementsandcansignificantlyaltertheairvelocityaroundabuilding.

RoofVentilators,Coils,andWindCatchersChimneysareaverycommonfeatureinhistoricalbuildingsandsometimeseventakeoverthecompleteformalappearanceofthebuilding,asinSintraPalace(seeFigure5.24).Themost important parameters for roof-integrated ventilation elements are their height andshape, which should be designed to enhance and even increase the flow rate over orthrough the device. The shape variety of historical wind catchers has been thoroughlystudiedbySueRoaf,12whorevealedalargearrayofoptionsthatalsorelateandshowcasesocialstatusandculturalvalues(seeChapter5).

9.7

Figure9.23

ThiswindcowlatNottinghamJubileeCampusisagoodexampleofpurposelydesigneddevicesenhancingnaturalventilation.

ContemporaryguidancecanbefoundinthedowndraughtcoolingsourcebookbyBrianFordetal.13 In order to keep elements small, internal and external heat gain should bekeptaslowaspossible.

RoofElementstoEnhanceAirFlowbytheVenturiEffect

High over the skyline of Berlin towers the signature roofline of the GSW building bySauerbruch andHutton, headquarter of a communal housing associationwith awingedrooftoenhancethestackventilationinthedouble-skinfaçadeonthewesternsideofthehigh-risebuilding.14

9.8

9.9

Figure9.24

TheroofwingonthetopoftheGSWbuildinginBerlin,Germany,increasestheairvelocityabovethebuildingandthusfacilitatestheventilationdriveinthestackfaçadeonthewest.

LouversLouvers for natural ventilation do not differ much in their exterior appearance fromlouversusedasair intakesinactiveventilationsystems.Theycanbeveryusefulfaçadeventilation elements when large air change rates are required, for example for nightventilation. They also offer protection against rain and intruders, can integrate screensagainstallkindsofinsects,andcanevenincludefiltersagainstpollen.

TrickleVentilationandVentilationSkinsTrickleventsarepurposefullydesigneddevices thatallowforconstantairchange rates,andavarietyofsystemsisavailableonthemarket.Theyclosewhenitrains, theyfilteragainstdust,andtheycanalsoattenuatenoise.

Figure9.25

Atrickleventactslikethisfinemeshedshadingscreen,whichletsinairataconstantrate,butaverylowvelocity.

Figure9.26

WindowpanesinhistoricalpalacesandvillasinGoa,India,madefromoystershellsfilterlightaswellasair.

SuchabreathingskincanbeseeninthepalacesofGoa,madefromtranslucenthand-size oyster shells with gaps between the shells for air penetration. They represent aspecific typology of trickle vents for a climate, in which temperatures never requireheating.Here,glassaddsunwantedheatgainandisnotanecessitysothatotherformsofclosureandclosingmechanismsshouldbereinvented.InthesehistoricresidencesofGoa,India,theoystershellswereusedtofiltertheharshdaylightandprovidecontinuoustrickleventilation.

PietrodellaValle,aseventeenth-centuryItaliantravelertoGoa,thePortuguesecolonyontheIndiansubcontinent,describes

thebuildingsof thecity [ofGoa]aregood, largeandconvenient, contriv’d for themostpartforthebenefitofthewindandfreshAir,whichisverynecessaryinregardof thegreatheats, andalso for receptionof thegreatRainsof the threemonthsofPansecal,whichareJune,JulyandAugust.15

Otherarchitecturalfeaturesof thesebuildingswerehighsteeproofs,verandas,galleries,andporches,whichalsocontributedtotheventilationandcoolingfortheinterior.

The historical precedent given by the Goa palaces and the colonial architecture ofMumbai with its façades of movable and permeable elements were revived by StudioMumbai in the Palmyra House andUtsavHouse (architects: StudioMumbai; location:Satirje, Maharashtra, India; principal architect: Bijoy Jain; project team: Roy Katz,Jeevaram Suthar, Pandurang Malekar, Mangesh Mhatre; structural engineer: Dwijen

Bhatt).16StudioMumbaiisacooperativeofarchitectsandcraftspeoplefoundedbyBijoyJaininMumbai.Thisteamcombinesdesignandcraftofmostofthecomponentsthatgointo their projects. This process allows for the designers to bring back traditionalknowledgeandtypologiesandavoidtheuseofmass-producedwindowproductsthatarenot well suited for the Indian climate. Both projects also show the traditional spatialcompositionneededforprotectionagainstrainandforairtoflowthroughtheverylightlyconstructedbuilding.

Figure9.27

ThisstreetfaçadeinMumbai,India,completelymadeupofventilationopeningsfilterslightaswellasair.

1

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5

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8

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11

12

13

Figure9.28

AMashrabiaisascreenwhichdoesnotallowaviewintotheinteriorofthebuilding,butpermitsfilteredlightandairinside,asseeninthisstreetfaçadeinMumbai,India.

Notes“WhatIstheOriginoftheWordWindow?”TheFreeDictionary,http://www.thefreedictionary.com/window(accessed5/14/2014).

RonaldG.Knapp,ChineseHouses:TheArchitecturalHeritageofaNation(Singapore:Tuttle,2005),p.89.

C.Ghiaus,F.Allard,M.Santamouris,C.Georgakis,andF.Nicol,“UrbanEnvironmentInfluenceonNaturalVentilationPotential,”BuildingandEnvironment,41(4),2006,pp.395–406.

M.SantamourisandPeterWouters,BuildingVentilation:TheStateoftheArt(Sterling,VA:Routledge,2006).

Ibid.,p.224.

JosephRykwert,LouisKahn(NewYork:HarryN.Abrams,2001),pp.53–54.

U.Passe,P.Stoakes,andF.Battaglia,“InterdisciplinaryResearchintotheFluidDynamicsofNaturalVentilationFlows,”in:HealthyBuildings2009:Proceedingsofthe9thInternationalHealthyBuildingsConferenceandExhibition(Syracuse,NY,USA),paperno.226.

UrsButiker,LouisI.Kahn:LightandSpace(NewYork:Birkhaeuser,1994),pp.90–95.

HafencityHamburg,http://www.hafencity.com/en/home.html(accessed5/14/2014).

CenterforArchitecturalScienceandEcology,http://www.arch.rpi.edu/2012/05/case/.

LorenzoLignarolo,CharlotteLelieveld,andPatrickTeuffel.“ShapeMorphingWind-ResponsiveFacadeSystemsRealizedwithSmartMaterials,”in:AdaptiveArchitectureConference(2011),pp.3–5.

ElisabethBeazleyandMichaelHarverson,LivingwiththeDesert:WorkingBuildingsoftheIranianPlateau(Warminster,UK:ArisandPhillips,1982).

BrianSchiano-Phan,RosaFrancis,andElizabethFord,TheArchitecture&EngineeringofDowndraughtCooling:

14

15

16

ADesignSourcebook(PHDCPress,2010).

AntonySalibandRubaWood,NaturalVentilationinHigh-RiseOfficeBuildings,CTBUHTechnicalGuides(NewYork:Routledge,2013),p.64.

PietroHavers,G.DellaValle,andEdwardGrey,TheTravelsofPietroDellaValleinIndia:FromtheOldEnglishTranslationof1664,translationG.Havers,2Vols(London:PrintedfortheHakluytSociety,1892).

StudioMumbai,http://www.studiomumbai.com/(accessed01/17/2015).

10.1

Chapter10

ControlofNaturalVentilationSenses,Sensors,andtheirControls

Wind chimes aremobile structures that indicatewind direction and airmotion on frontporchesandbackyardsarecommonvernacularobjectsinmanycultures.TheAmericanartistAlexanderCalder(1898–1976)raisedsuspended,air-drivenobjectstoadelicateartform.JeanPaulSartrecommentedonCalder’smobilesculpturesin19471:“Theyfeedonair,theybreathe,theyborrowlifefromthevaguelifeofatmosphere.”

Sensingwindasairmovement iscloselyconnected to the forecastingofweatherandhasalong-standingtraditioninmeteorologyandatmosphericscience.

Figure10.1

AlexanderCalder(1898–1976):VerticalFoliage.1941.Sheetmetal,wire,andpaint,157.5×167.6×142.2cm.

The termweatherlessnessbuildingwas coinedbyH.G.Wells inhis1933novelTheShapeofThingstoCome.ThesharpanalysisbyAckermann2 inherthesisindicatedthatUtopiahadahomogenous,neverchanging,indifferentclimatethatwouldcounteracttheeffectsofweatheronsocialmovementsofpeople,onbehaviorandclothinghabits.Shealso analyzed the American fairs of the 1930s and 1940s as exhibitions for the heroicfuture of America, which advertised a new American society relieved of its weatherconstraints.3

This attitude and desire changed the building fabric in the USA to this day. Air-conditioning demanded closed windows, and because the only control was the humanoccupant, the windows were sealed. In the current twenty-first century, sensors for allimpulsesandsensesareavailableandbuildingcontrolsystemscanbemorereceptivetoswitchesbetweenactivemechanicalsystemsandnaturalventilation.Inaddition,adebateisneededaboutwhoshouldbeinchargeoftheclimatecontrolsinsideabuilding.Theusercantakemorecontrol.

10.1.1

10.1.2

SensingAirMovementAirismovingconstantly,evenifweashumanscannotalwaysdetectitsmovementwithourmostsensitivesensor, theskin.Themajorstimulusforsensationofairmotionis itstemperatureaswellasthevelocityofitsmotion.

Themostcommonwaytosenseairmotionandthedirectioninwhichairismovingisknownbyeverychild.Youtakeyourfingerandwetitwithyourtongueandholditintotheair.Thedirectionofthewindcanbefeltonthesideofthefinger,whichisnowcooledbyevaporation.Thisexperiment(asalreadynotedbyPettenkofer4)doesnotworkaswellinmoistandhumidairasitdoesindrierweatherconditions.

Pettenkoferalsoalreadytooknoteofthethresholdofsensitivityofthehumanbodytothesensationofairmovement.5

The air in this room appears still, and yet it is in thousand-fold movement andceaseless restlessness; but happily our nerves are not aware of this, just as ashortsighted person may deny the existence of some object, till his eyes get theassistanceofaglass.Whoeverofyouwouldbeabletofeelorseeallthemovementsof air in this room,would probably not be able to stand it.A correct ideamaybeformedaboutitbytheactionofsmellingsubstances.If,forinstance,anescapeofgaswere to takeplace ina remotecornerof this room,youwouldbecomeawareof italmostimmediatelyallovertheroom.Ournervesarehappilysoorganized,thattheybegintofeelthemotionoftheaironlywhenitamountsto31/4feetpersecond.

SensorsforAirMotionThewinddirectionhasbeendetermined since antiquityusingawindvane, a techniquestillinusetoday.

Anemometersaretheinstrumentstomeasurewindandairmovements.Windvelocityisusuallymeasuredbyacupanemometer,rotatingcupsmountedonacross,firstdesignedby Leon Battista Alberti (1404–1472). These rotating cups measure the wind speedaccordingtothespeedofrotation.

Measuringlowspeedairvelocityanddirectionisaveryawkwardtask,andbecauseofthewind’svolatility,reliabledataaredifficulttoobtain.Someinstrumentsmeasureactualairspeed,othersmeasurepressure,butasthetwoarerelated,onepieceofinformationcanbeobtainedfromtheother.Hotwireanemometersuseaverythinhotwiretodetect thevelocityof air.Wind flowingover thehotwirehas a cooling effect, andbecause everymetal has a resistance related to its temperature, this information can be converted intowind speed.Hotwireanemometers are extremely sensitiveandcanbeused tomeasurecomplexturbulentflows.

Unfortunately, the simultaneous measurement of air direction and velocity is verycomplicatedanddemandscostlyultrasonicsensorsthatmeasurethetimeofsonicpulsesbetweentwotransducers.

10.1.2.1

Figure10.2

ThewindvaneandcupanemometeraspartoftheweatherstationatIowaStateUniversity’senergyefficiencyresearchlaboratory:theInterlockHouse.

TheToweroftheWinds,VaticanWhiletheancientGreekToweroftheWindsinAthensdidnotactuallymeasurewind,buttime,asdescribedbyVitruvius,6 theTorredeiVenti in theVaticanprovided theVaticanwithoneof thefirstsophisticatedweatherstations tomeasurewinddirection.OttavianoMascherino(1536–1606)constructedtheTorredeiVentiontopoftheVaticanlibrary.Itcontained a large wind rose and anemometer in the ceiling designed by Ignazio Danti(1536–1586) as well as the meridian that was used to install the Gregorian calendar.7Through a complex mechanical mechanism, the movement of the weather vane wastranslatedontoarotatinghandthatmovedacrossapaintedwindrosecreatedbyNicoloCircignani (c. 1517/1524–after 1596)with the allegoriesof the four seasons connectingtimeandwind.Thewholeceilingwas takenupby thisgiganticwindclock,whichwasconnectedtothewindvanebycoggedgears.8

10.1.2.2

Figure10.3

Ahotwireanemometerdetectswindvelocityanddirections.

AgeofAirIdeally the flowpath for the fresh, incomingair shouldbedirected so that the freshairreachestheheadsoftheoccupantsfirstbeforebeingdilutedwiththe‘older’roomair,andexhaust air should leave the room as directly as possible before it is mixed with theincomingfreshair.Inordertoextracttoxicpollutantsinresearchlabs,exhausthoodsareplacedrightatthesource.Thesamestrategyismostoftenusedinkitchenslargeandsmallto exhaust fumes when cooking. One measurement to control the functioning of aventilationstrategyistheevaluationofthe‘ageofair.’Ideally,theairenteringtheroomreachesalloccupantsat thesametime,whichisusuallynotpossible, forexamplewhenonepersonsitsnext to thewindowandanothercloser to the interiorof thebuilding. Inordertomeasuretheageofair,thatis,thetimeittakesfortheairinsideaspacetochangewiththerequiredairchangerate,theairenteringaroomcanbemarkedwithatracergas,whichallowsmeasuringtheconcentrationanddistributionofthisgasincertainlocations.The time it takes from the insertion of the tracer gas into the air to the measurementlocationisdefinedastheageoftheair.Themeasurementoftheageofairisimportanttodetermine thecapabilityof theventilationstrategy in termsofmixingand/ordilutingordisplacingtheroomairwithfresh,incomingair.

Figure10.4

ThewindvaneintheSalaMeridianaoftheTorredeiVentisituatedonthetopoftheSecretArchiveoftheVaticanconnectstoaceilingfrescoandaninteriorwinddial.

Atermusedbyairqualityexpertstoevaluateastrategyisthe‘airchangeefficiency.’This term indicates the time it takes to replaceair ina room.According toRoulet,9 theefficiency tellsushow the freshair isdistributed inagiven space.Fordisplacementorpiston-typeventilation,wheretheroomairisdisplacedfrombelowwith100percentfreshair, the efficiency is equal to one. In otherwords, all fresh air entering a spacemovesthroughthespacetotheoutletatthesametime.Withfullmixing,theefficiencywillbe50percent, andwhendeadzones remain, inwhich theair isallowed toage, theefficiencywillbeevenmorereduced.Inefficientairflowpathscreateshortcuts,whichmeansthatthefreshairintakeandexhaustaretooclosetogethersothatfreshaircanleaverightawaywithoutaffectingexchange, thus ‘wasting’ theair.Twenty-fivepercentefficiencywouldthenbeconsideredapoorperformance,becausethatwouldindicatethattenpercentoftheairattheexhaustisolderthanthreetimesthetimeittooktheearliestairtoexit.

Smoketestsareusedtoqualitatively(visually)determinethedirectionfromwhichairentersorleavesaspace.

10.1.3

Figure10.5

Winddirectioncanbedetectedwithasmokepen,asshownhereduringanexperimentattheIowaNSFEPSCoRcommunitylab,theInterlockHouse,originallyconstructedasIowaStateUniversity’s2009entryfortheU.S.DOESolarDecathloncompetition.

Howcandesignersevaluatetheageofairintheirdesignstrategywhendecidingonaflowpathandopeningstrategy?

ActuatorsAnactuatoriscomparabletoamotorthatsetsadeviceinmotion.Theycanbeoperatedby electrical energyor byhydraulic or pneumatic pressure and convert that energy intomotion, driving the opening element.Windows and vents operate on hinges, push-pullpistons, chains, gears, motors, hydraulics, levers, and multiple other means.10 Controlstrategiesneedtoconsidertheactivationmechanismaswellastheweightofthewindoworvent.Push,pull,flip,androtationarethemajormovements.Operationofactuatorsisautomated by a control algorithm, which can be challenging to program. Ideally, anactuatorshouldserveonlyoneventorwindow,butoftenmultiplewindowsarelinkedandcontrolledjointlybyoneactuator.

10.1.4

Figure10.6

ThewindowsintheBauhauslinedupinabandarealloperatedbyonejointactuator.

ControlsBecause of the dynamic nature of the external resources for natural ventilation, controlmechanisms are necessary in most cases. They can range frommanual control, whichusually means that the occupant gets up and opens or closes the window, to completeautomatedcontrols,andeverystageofoverrideinbetween.Oftencontrolsalsoneedtobeinstalled to enable other functions of the building: inlets and outlets need to be closedwhendrivingrain isexpected,whenwindsaresohighthatbuildingcomponentscanbeharmed,andwhenitgetstoocoldortoohot.Controlstrategiesfornaturalventilationalsoinclude the operation of elements that reduce or increase heat gain depending on theseason.Solarblindsneedtobepulledordrawntoreduceheatgain.Manyresearchstudiesshow the importance of proper and complex controls,whilemost thermostats only usetemperatureasanindicator.11But temperaturemaynotalwaysbeenoughtoaccountforallvariables.Occupancycontrol throughmotionsensororCO2 levelsonlyprovidesoneindicator(increaseinoccupancy).Itdoesnotnecessarilytellanythingabouttheactualairquality.

The interactionofoperationchoiceswithexternal forcessuchasrain,hail,snow,andhighwindshastobeprogrammed.

Control strategies are complex scenarios even if, at this point, most systems only

10.1.4.1

operateinanon/offmode,whichmeansthattheactuatorsareprogrammedtoeitheropenorclosetheventindividuallyortoopenorcloseabankofventsatthesametime.

The placement of the sensors that control the actuators is another highly importantdecisiontobemade.Asensordrivingaventilationsystemshouldneverbeplacedintoahot spotordirect sunlight. If nogoodplacement for a sensor canbe found, the controlstrategycanalsorelyonascheduleoranoccupancysensortoactivatethevents.

Figure10.7

Thecontrolalgorithmsforsummerandwinterventilationneedadjustmentfordifferentopeningsizes.

Currently,mostcontrolsareconnectedtomoreorlessautomatedbuildingmanagementsystems (BMS), which can operate vents and dampers. Downdraughts in vent stacks,whichindicateareversalofthestackflow,canbeidentifiedbytemperaturesensorswithinthestackoratrium.

OccupantsandControlsBuildings that open or close vents or blinds without input from occupants can be anightmarefortheusers.UsersinbuildingswithautomatedcontrolsmayfeellikeCharlieChaplininModernTimesorJacquesTati inPlaytime,wheremachinesorbuildings takeoverthecontrolsfromtheoccupants.The‘uncontrollable’controlsystemcanbetheworstannoyanceforoccupantsandarchitectsalike.Achievingusabilityofbuildingsystemsisrarely a successful endeavor. However, neither can the completely manually operatedbuilding fulfill all needs.Today, usually compromises in the formof automated controlsystems that can alwaysbeoverriddenbyoccupants are thebest systems available, butmany issues stillneed tobeaddressed to improve thebalancebetweenoccupantdesire,tolerance,andairqualityandenergyuseontheotherhand.

Occupantshave a certain levelof tolerance todiscomfort andoften ‘goodenough’ issatisfactorybefore a change is requested, either bygettingup andopeningor closing awindow or by changing a thermostat setting, or even by calling maintenance, whichobviously demands higher discomfort and is connected to real perceived dissatisfactionwiththegivensituation.Usually,occupantschoosetheeasiestpathtoaddressdiscomfort:they will choose the simplest, most convenient, and most accessible solution to theirdiscomfort, as noted in the CIBSE manual.12 In hybrid mode, the user will switch toautomated mode when the operable window is too far away and very rarely will anoccupantact inanticipationofachange in theirenvironmentalcondition; thus theywillonlyclosethewindowonceitalreadyhasbecomecold.

10.1.4.2

Automated control strategies, which are often perceived as capricious, can makeoccupantsangry,asnotedbytheCIBSEmanual,12mainlybecauseoftheinterruptiontheactioncauses in theirdaily routineandoftenbecausemovingparts forventsandblindstendtobenoisyandinterruptthecurrentongoingactivity.Researchhasalsoshownthatoccupantswillmake changes to reducediscomfort, butwill not turn things back again,oncethediscomforthasdiscontinued,whichwillleavewindowsopen,lightson,orblindsdownforlongerthannecessary,nottomentionothermishaps.

PredictiveControlsThefamoushockeyplayerWayneGretskyoncesaid,“Iskatetowherethepuckisgoingto be, not where it has been.”13 In order to best balance human thermal comfort andenergy efficiency, it can be beneficial to skate towhere the puck is going to be,whichmeans that the control strategy for a building should anticipate future changes. The setpoints for the heating and cooling of a building are determined by several factors,includingnaturalandengineeredfactors.Anticipationofthesign,magnitude,andfuturetrendofnaturalheatingandcoolingwouldprovidesomeclueaboutwhere, left to itself,the “puck is going to be.” This information, along with interior data, can be used tosuggestadjustmentstoaidinpassiveheatingorcooling.

Mathematicallywecandescribetheindoorheatingrateofabuildinginasimplisticwayby:

where is therateofchangeof indoorair temperaturewith time,H is theengineered

rateofheatapplied(orextracted), istherateofchangeofoutsidetemperature, is

the rate of change of external radiative heating, and is the rate of change of windspeed.α,β,andγareconstantsrelatingtotheresponsetime(thermalmass)ofthebuildingtochanges,inoutsideairtemperature,radiativeheatlossorgain,andwind-drivenchangeofbuildingheatlossorgain.Theseconstantscanbedeterminedexperimentally.

Inasimplecontrolscenario,wewanttokeeptheindoortemperatureconstant: .This leads to an expression for the rate of heat that needs to be applied to keep thetemperatureconstant.

Inreactivemode,theengineeredresponseaddsortakesawayheatinreactiontochangesinTi.Inanticipatorymode,TiwillremainconstantbecauseHwillmatchtheanticipated(forecasted)changesinTo,R,andW.Inprinciple,thisleadstobetterregulationofindoortemperature(presumablygreatercomfort),andinsomecaseswillpreventovershootingoftheengineeredresponsetochangingindoortemperaturewhenexternalfactorswereaboutto reverse thenaturalheating rates. Implementing this strategy requiresmeasurementof

10.1.4.3

theunknownconstantsandaccesstoaforecastofoutsidetemperature,radiantheat,andwindspeedoverthetimehorizondictatedbythemeasuredconstants.

Noveldevelopmentsincomputationalgorithmsgiverisetonewcontrolopportunities,called model predictive controls (MPC), which can base their control strategies onoccupancyschedulesandweatherforecastandthuscananticipateaneededchange.Theydrive the controls of a building’s thermal condition based not only on temperature setpoints,butalsoonanticipateddynamicchanges;forexample,theircontrolstrategiesaredrivenbasedonweatheroroccupancyforecastssothatchangesdonotoccuronlywhenthe trigger has been reached, but occur prior to this point so that the uncomfortablesituation isactuallyavoidedcompletely.14MPCstrategies takeuncertaintyanddynamicconditionsintoaccountandcan“evaluateatradeoffbetweenenergysavingsandthermalcomfort.”15Unfortunately,thesearedecisionsthatusersoftencannotmakeforthemselveswithoutadditional informationwhichalsohasaneffect, suchasutilitycostsorweatherforecast.

In natural ventilation cases, MPC works well when coupled with thermal mass; forexample, when a really hot day is expected the next day, the air change rate for nightventilation can be increased to cool down themass of the buildingmore than usual inordertocreateanevenlargerheatsinkforthedaytimeheatgain.MPCwillalsopreventtheactivecoolingfromkickinginattheendofahotdayforjustanhourorso,whenthenightconditionswillallowforheatremovalwithoutadditionalenergyconsumption.

AirtightnessandInfiltrationThecreationofanairtightbuildingenvelope isanoftenunderestimatedcontributor toagoodnaturalventilationstrategy.Buildingswithhighinfiltrationratescanoftennotbuildupthepressuredifferentialneededforthedemandedexchangerate.Inaddition,theycandivertairawayfromthedesignedflowpath.Highlevelsof infiltrationmayalso leadtohigher energy consumption in order to condition the cool orwarm air seeping into theoccupied spaces. Infiltration can also cause draught, condensation, and mold growthwithinthebuildingenvelope,whichinturnaffectsairquality.

10.1.4.4

Figure10.8

AcommerciallyavailableblowerdoortestkitwasusedtotesttheairtightnessoftheIowaNSFEPSCoRInterlockHouse.

Acommonmethodtotesttheairtightnessofabuildingenvelopeanditssystemsistheso-calledblowerdoortest,whereoneopeninginthebuildingisequippedwithanexhaustfan that pulls out air at a certain pressure andmeasures the rate of replacement.Mostcommonly,theairchangeratethroughinfiltrationismeasuredataconstantpressureof50Paproducedbyanexhaustfan.Allotherwindowsneedtobeclosed.Insuchascenario,the air change can bemeasured and compared with the figures for other buildings forefficiency.IftheACHstaysunder0.6ACHat50Pa,PassivHausStandardisachieved.16

An airtight building is thus a construction-based control strategy to obtain well-performingnaturalventilationflowregimesandpreciseairchangerates.

UserInteractionandOverridingControlsAccording tomany research studies, user satisfaction is onemajor advantageofnaturalventilation because users are in control of most natural ventilation building controlstrategies,oratleastinmostcasesthereisanoverridestrategysothatuserscandirectlyreact toadraught,chill,oroverheating.Low-technaturalventilationsystems,especiallyintheresidentialcontext,areusuallyusercontrolled.Mostimportantforoccupant-drivencontrol is that theoccupants arewell informedabout the control strategiesnecessary tokeepthemcomfortable.Ifenergyefficiencyisacommongoal,occupantswillalsoneedtoknowhowtheiractionswillrelatetohigherenergybills.Ithasbeenrecordedinresearchcase studies17 that occupants are actually quite considerate with energy and operate

10.2

10.2.1

mechanicalsystemssparingly, if theyhavethechoice,especiallyif theyhavetopaythebills themselves.This interactionbecomesevenmorecritical inhybrid situations,whenuserscanalsointeractwiththeactivesystemforanadvancedhybridmodesituation.

Figure10.9

Advancedcontrolsystemsneedtoadjustfortheinteractionandfeedbackloopbetweencomplexparameters.

DistinctNaturalVentilationStrategiesReynerBanham’s18famousparableofthetwosavagetribesisanappropriateintroductiontothissection,whichwillcovernighttimeventilationandthermalmass(seeFigure5.1).Thetribesarriveat“anevening-campsiteandfinditwellsuppliedwithfallentimber.”Thetimbercouldeitherbeusedasawind-break,whichBanhamcallsthestructuralsolution,orburnedforafire,whichhecallsthepower-operatedsolution.“Anidealtribeofnoblerationalistswould consider the amount ofwood available andmake an estimate of theprobableweatherforthenight–wet,windy,orcold,anddisposeofitstimberresourcesaccordingly.”Mostrealtribeswoulddononeofthat,hesays,butwouldeitherbuildafireor build a structure, depending on the knowledge passed down from their ancestors.Becausemostpre-technologicalsocietieshadverylimitedcombustiblematerialsavailable(especially prior to the extraction of oil), their architecture was dominated by heavy,massive constructions to mitigate the external climate. The only civilization thatdevelopedbasedonthepower-operativemodeisthemodernNorthAmericancivilization,whichstillconstructsverylightweightstructurestothisdayandconditionsthemwiththesupportofabundantenergy.

CoolingtheStructure:NighttimeVentilationEnteringamassivestonebuildinginRomeduringthesummerwillbeamemoryforever;here, the thickstonewallsradiate thecool temperatureof thewinterandtheheatof thesummerneverpenetratesthefulldepthofthematerial.

•

•

•

•

10.2.1.1

Nighttimeventilationisaverycommonandsuccessfulnaturalcoolingstrategy,whichincludes the activation of thermalmass in a building.Cooling themass in the buildingdown to a temperature below comfort zone temperature during cool summer nightsprovides a heat sink for the thermal energy gathered during the day. Usually, naturalventilationisthedrivingforceandlargevolumesofairflushthebuildingthroughtwoormore largeopenings.Nighttimeventilation takesadvantageofhigh thermalmass insidethebuildingand lowoutsideair temperatures.During the timewhen thebuilding isnotoccupied at night, the cooler air is flushed into the interior and directed over themasssurfacetocoolitdown,sothatitbecomesaheatsinkduringtheday.Theadvantagesofnighttimeventilationarethat:

Thebuildingfabriciscoolerduringtheday,whichinfluencesthermalcomfortowingtothemeanradianttemperatureeffectontheoccupants’bodies.

Internalpeaktemperatureswillbereduced,becausefirst thefabricofthebuilding(itsthermalmass)willstorethethermalenergyofinternalgainsaswellaspotentialsolargains.

Peaktemperaturesareshiftedtothelatertimesofthedayandinternalpeaksareshiftedincomparisontoexternalpeaks.

Reducedinternalairtemperatureisachievedthroughouttheday,thusreducingoreveneliminatingtheneedforactivemechanicalcooling.

Figure10.10

Nightflushventilationcoolsdownthethermalmassofthebuildinginteriorwithcoolnightairanddemandstheclosureofwindowsduringtheday.

Thequantitativecalculationmethodisfairlysimple.Theheatcapacityofthethermalmassneedstobedeterminedaswellasthehourlytemperaturedifferenceinordertocalculatetheoverallthermalmassrequiredfornaturalventilation.19

Temperature swing and time lag of thermal energy storage are the key factors to beincludedinthequantificationofnighttimecooling.

NighttimeVentilationCaseStudy:ThePaulWunderlichHaus

In the PaulWunderlichHaus in Eberswalde,Germany, designed byGAP,20 one of themostsustainablebuildingscurrentlyexistinginGermany,nighttimeventilationisutilized.This building is a very good example of current best practice of energy-efficientconstruction. Themost important feature of the building is a highly insulated building

envelope,with a 40percentwindow towall ratio and triple-paneglazing reducingheatgainsinsummerandheatlossesinwinter.Thebuildingcombinesactiveventilationandthermal active surfaces with night flush ventilation for cooling, at a time when thebuilding is unoccupied. The energy concept is well integrated into the architecturalconceptandlayoutof thefourbuildingpartsonsite.Naturalventilationiscoupledwellwithdaylightingstrategiesintheofficesaswellasinthemajorconferenceroomforthecountycouncil.

The climate in Eberswalde is temperate and thus cool nights in summer are mostcommon.Humiditylevelsinsummerarealsomoderate.Thusnightaircanbeusedmostof the summer to cool large parts of the building to an agreeable daily comfort rangewithoutanyaddedmechanicalcooling.

Figure10.11

ThePaulWunderlichHausinEberswalde,Germany,asitsitsinsidetheprevailingwinddirection,utilizesoperablewindowsforcross-ventilationandnightflushcooling.(Inm/s.)

Figure10.12

SiteplanofthePaulWunderlichHausinEberswalde,Germany.

The building complex is composed of four separate parts, each with fairly similarlayoutsofofficesaroundacombinedzonesurroundingacourtyard.Theassemblyhallisday-lit from above. Every office has operable windows, and there is a controlled airchangeratewithcombinedheatrecoveryventilation.

Figure10.13

ThecourtyardbetweenthefourbuildingsconnectedtoformthePaulWunderlichHaus.

Oneinvisiblefeatureoftheconstructionis theextremeairtightbuildingenvelopeandexposedconcreteslabsfornightflushcooling.Phasechangematerialsarealsoaddedtostorelatentheat.

Groundcoupledheatpumpsareaddedthroughenergypilesinthegroundforsummercoolingandwinterheatingthroughheatexchange.

Thenightflushstrategycanbeidentifiedasdirectnightventilation,21wherethenaturalflowofaircoolsthemassofthebuilding.Thehighheatcapacityofthemassallowsthebuilding fabric to absorb theheatgainsduring theday,whichwill prevent the air fromwarming up. Air will only start warming once the mass has warmed. Three years ofmonitoringtheenergybalanceofthebuildingrevealedthatventilationprovidedcloseto50percentofthecoolingenergy.19

The long-term monitoring also revealed another interesting challenge that resonateswithotherresponsestonightcooledbuildings:themorningtemperaturesweresometimesconsideredtoochillybyoccupantsandthusthefullcoolingpotentialofthethermalmasswasnotutilized.

Cooling capacity beyond natural night flush cooling ismainly used for server roomsandhighoccupancyloads.

10.2.1.2

10.3

10.3.1

Limitationsfornightflushventilationcoolingstrategiesarewarmnightsasexperiencedin urban centers, because of the heat island effect and lower wind speed in the urbancanyon. Eberswalde on the other hand is a small townwith plenty of potential to cooldownatnight.Nighttimecooling-potentialmapsarebeingdeveloped(seeFigure4.15).

Figure10.14

TheentrancespacetothePaulWunderlichHaus.

MaterialsforThermalMassinNighttimeCoolingThemostcommonmaterialsusedasthermalmassobviouslyareheavyweightstructuralmaterialsinthebuildinginterior,whichhaveahighheatcapacityandstorealargeamountofthermalenergywithoutcreatingatemperatureincreaseinthevolumeofairintheroom.Exposedconcrete slabsandwallsare thusoftenencountered inbuildingsdesignedwithnighttime cooling concepts. A new development in recent years is the use of so-called‘phase changematerials’ (PCM) as temporary thermal energy storage integrated in thebuilding.

LimitationsofNaturalVentilationsLimitationstotheapplicationofnaturalventilationcanbegroupedinmultiplecategories.The first challengesarebasedon the lackofavailablenatural resources in theurbanorrural environment.Others are related to the interior requirements for natural ventilationandopenconnectiontotheoutdoors.

ClimaticLimitationsHigh summer temperatures above the adaptive comfort zone threshold can limit thecoolingeffectofoutsideairforcross-andsingle-sidedventilation.Inlocationswithhighoutdoor summer temperatures, nighttime ventilation may be the only option for wind-inducedairmovement. In sucha scenario,daytimeventilation shouldbe reduced to theminimumrequiredbyIEQstandards.

Lack of sufficient diurnal temperature swing can severely reduce the opportunity for

10.3.2

nightventilationusingthermalmass.Insomelocations,night temperaturesonlydropinthe earlymorning and thus the time to cool down thenecessarymassbefore occupantsarrivebackinthemorningmaybetooshort.Highhumiditylevelsareoftenconsideredanobstacle,buttheyonlyseemtobedetrimentalinclimatescenariosinwhichwindvelocityisverylow.

Extremecoldwintertemperaturesrequirepreheatingofventilationairinordertosaveheatingenergy,whichcanbeachievedpassivelythroughdoubleskinfaçades.ThisstrategyhasalreadybeenusedbyAlvarAaltoatPaimiosanatorium(seeChapter3) and isnowadaptedwith ventilated sunspaces, Trombewalls, or transpired heat collecting façades,whichhasbeentestedatthenewNationalRenewableEnergyLaboratory(NREL)officebuildinginGolden,Colorado.22Activepreheatingofventilationaircanbeaccomplishedwith air-to-air heat exchangers. Night ventilation in winter should be avoided, and thebuildingenvelopeshouldbeextremelyairtight.

Low external wind velocity cannot be increased inside of a building, and thusopportunities for cross-ventilation strategies in the dense urban context can be verylimited. Therefore, stack ventilation or wind catcher strategies have seen increasingapplicationsindenseurbancontexts.

Figure10.15

Thebioclimaticchartshowingtheclimaticlimitationsfornaturalventilationstrategies.19

AcousticChallengesThe second group of challenges for natural ventilation strategies is related to outsidethreats resulting from the much more intense interconnectivity between indoor andoutdoorair.Thosechallengescanderivefromoutsidedrivingrainorsnow,mosquitoesorotherinsects,andoutsidenoise.

10.3.3

Figure10.16

Acousticbufferingisnecessarywhentheventilationinletissituatedclosetostreetswithhightrafficorothersourcesofdisturbingnoise.

High levels of thermalmass in the formof open concrete ceilings or floors can alsolower the acoustic quality of a building. Acoustic attenuation should therefore be anintegral part of any natural ventilation strategy.This can come in the formofwall andceilingpanelsorfurniture.Acousticchallengesrelatedtotherequiredspaceconnectivityacrossthebuildingcanbecounteractedbythelayoutoffunctions,theplacementofinletsand outlets, heavy sound-proofedwindows, bufferingmaterials, and landscaping in thevicinityoftheairintakeandexhaust.

IssueswithNoiseandPollutionObviouslyoutsidenoiseandpollutionaremajorconcernsintheurbancontextaswellasin specific locations with detrimental outside conditions when integrating naturalventilationstrategiesintoabuilding.Thus,operablewindowsandventsshouldalwaysbeplaced strategically. But when occupants are afraid of intruders, they will not leavewindows open, so perceived security concerns can also lead to reduced ventilationeffectiveness.

Pollutionshouldbe reducedat thesource,which isofteneasier said thandone.Non-VOC paint and carpets, less glue, less formaldehyde, non-smoking policies, localizedexhaust strategies, and other strategies are policies to reduce interior-based pollution.Reduced car exhaust can be achieved through speed limits or the promotion of electriccars.Onalargerscale,urbanplanningandzoningstrategiescanlimitpollutingindustriestocertainareasofthecityordistributethemonthewind-oppositesideofthecity.

10.3.4

Figure10.17

TheventsattheJudsonUniversityHarmA.WeberAcademicCenteraredirectedtowardsthenorthsideandtheparkinglot.

Buildingzoningstrategiescanalsohelppreventlocalpollution.Forexample,aloadingdockshouldnotbelocatednext totheventilationinlets.Ventilationinletsshouldnotbelocated next to a parking lot. Unfortunately, louvers and vents are often consideredaestheticallyunattractiveandarethusbannedfromthe‘front’façade.

IssuesofRiskandLifeSafetyforOpen-PlanSpacesandStackAtriaOpen-plan architecture needed for a continuous flow path through a building can poseseveresafetyandfirerisksaswellastransportnoiseandsoundacrossbuildingsandthusimpairqualityoflife,safety,privacy,andenvironmentalquality.Verticalstacksaregreattopromoteairchangerates,buttheyalsopromotethespreadoffireandsmoke.Verticalfire and smoke spread in particular needs to be restricted, which poses a conflict inverticallyconnectedspacesneededforstackeffectventilation.Fireandsafetyrisksneedtobecarefullyevaluatedduringegressplanningandmodeling.Smokeexhaustsaswellasmovable fire blankets or walls are usually required. Atrium spaces will need to beseparatedincaseofafire.Thus,movablefirewallsarerequestedinmostlocationsbyfiremarshalsinordertopreventthespreadofsmokeandfirebeforegrantingbuildingpermitsfornaturallyventilatedbuildings.

Double-skin façades, which continue along the complete height of a building, posesimilar risks of fire and smoke spread, and many permit jurisdictions require sealabledampersbetweeneverylevel.Insomeinstances,glassorwindowsprinklersystemshavebeen installed to prevent fire spread without the inclusion of fire rated glass. Eachnaturally ventilated building, especially on a larger scale, thus requires a very carefulevaluationof theriskoffireandsmokespreadanddemandsaclosely integrateddesignstrategyoverseenbyventilationengineers,designers,andfiresafetyexpertsontheteam.

Figure10.18

Openatriumspaces,forexamplehereintheUnileverHouseHamburgbyBehnisch&Behnisch,requirespecificprotectiveelementsagainstfireandsmoke.

Operablewindowsonlowerfloorscertainlycreatesafetyandsometimesprivacyissuesand have not been allowed on the lower five floors of the San Francisco FederalAdministrationBuilding;however,theyhavebeenacceptableonupperlevels.

10.3.5

Figure10.19

TheFederalBuildinginSanFranciscobyMorphosisrequiresoperablewindowsandsolarprotectivescreens,butonlyonupperfloors.

Screens,Louvers,andShadesAnykindofscreenforinsects,security,orprivacywillautomaticallyincreasetheneedforoverallopeningsize.Insectscreensprovideaninterestingproblem,astheirinfluenceontheairchangeratechangeswiththedistancebetweenthescreenandtheventilationinlet.

A recent computational research study23 showed that insect screens have a stronginfluence on the air flow rate of windward inlet openings, while they have hardly anyinfluenceontheleewardoutflowrateandthustheopeningsize.

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Figure10.20

ThedistancebetweenmosquitoscreenandinletwindowasinaMidwesternporchisimportanttomediatethereducedairflowratethroughthescreen.

Theair intakesfortheJudsonCollegeHarmA.WeberLibraryBuildingareequippedwith large areas of insect screens and thus had to be sized significantly larger thannecessarywithoutscreens.24Insomeintakelocations,themeshisfoldedinazigzagshapeinordertoincreasetheintakearea.

NotesAlexanderS.C.Rower(ed.),AlexanderCalder:SculptorofAir(Milan:Motta,2009).

MarshaE.Ackermann,CoolComfort:America’sRomancewithAir-Conditioning(Washington,D.C.:SmithsonianInstitutionPress,2002),p.79.

Ibid.,pp.77–102.

M.vonPettenkoferandA.Hess,TheRelationsoftheAirtotheClothesWeWear,theHousesWeLivein,andtheSoilWeDwellon:ThreePopularLectures(N.Trübner&Company,1873).

Ibid.,p.10.

PollioVitruvius,TheArchitectureofM.VitruviusPollio:TranslatedfromtheOriginalLatinbyW.Newton,Architect(London,1791).

“TheTowerofWinds,”ArchivioSegretoVaticano,http://www.archiviosegretovaticano.va/en/archivio/ambienti/torre-dei-venti/(accessed5/20/2014).

AlessandroNova,TheBookoftheWind:TheRepresentationoftheInvisible(Montreal:Ithaca,2011).

Claude-AlainRoulet,VentilationandAirflowinBuildings:MethodsforDiagnosisandEvaluation(London;Sterling,VA:Earthscan,2008),pp.39–57.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005),pp.29–36.

IonHazyuk,ChristianGhiaus,andDavidPenhouet,“OptimalTemperatureControlofIntermittentlyHeatedBuildingsUsingModelPredictiveControl:PartII–ControlAlgorithm,”BuildingandEnvironment,51(0),2012.

CIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual(London:CIBSE,CarbonTrust,2005).

Seehttp://www.goodreads.com/author/quotes/240132.Wayne_Gretzky(accessed5/15/2014).

FrompersonalconversationswithEugeneTakle,ProfessorofAtmosphericSciencesandAgronomyatIowaStateUniversity.

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19

20

21

22

23

24

A.Fontanini,U.Vaidya,andB.Ganapathysubramanian,“AStochasticApproachtoModelingtheDynamicsofNaturalVentilationSystems,”EnergyandBuildings,63,2013,pp.87–97.

“WhatIsaPassiveHouse?”PassiveHouseInstituteUS,http://www.passivehouse.us/passiveHouse/PassiveHouseInfo.html(accessed5/15/2014).

WilliamJ.N.TurnerandIainS.Walker,“UsingaVentilationControllertoOptimiseResidentialPassiveVentilationforEnergyandIndoorAirQuality,”BuildingandEnvironment,70(0),2013.

ReynerBanham,TheArchitectureoftheWell-TemperedEnvironment(Chicago:UniversityofChicagoPress,1984),pp.18–28.

WalterT.Grondzik,AlisonG.Kwok,BenjaminStein,andJohnS.Reynolds,MechanicalandElectricalEquipmentforBuildings,11thedn(Hoboken,NJ:Wiley,2010).

See“ForschungFürEnergieoptimiertesBauen:Projekt:Dienstleistungs-UndVerwaltungszentrumBarnim,”http://www.enob.info/de/neubau/projekt/details/dienstleistungs-und-verwaltungszentrum-barnim/(accessed5/20/2014).

M.SantamourisandPeterWouters,BuildingVentilation:TheStateoftheArt(Sterling,VA:Earthscan,2006).

http://www.nrel.gov/sustainable_nrel/rsf.html.

AmanuelTecle,GirmaT.Bitsuamlak,andTeshomeE.Jiru,“Wind-DrivenNaturalVentilationinaLow-RiseBuilding:ABoundaryLayerWindTunnelStudy,”BuildingandEnvironment,59,2013,pp.275–289.

AlanShortandKevinJ.Lomas,“ExploitingaHybridEnvironmentalDesignStrategyinaUSContinentalClimate,”BuildingResearchandInformation,35(2),2007,pp.119–143.

Part3MakingAirVisible–ComplexScienceSummarizedforArchitectsandDesigners

11.1

Chapter11

OverviewofMethodsforCalculationandSimulationThe most common approaches to study ventilation include small- and full-scaleexperiments,empiricalmodels,analyticalmodels,multi-zonemodels,zonalmodels,andcomputationalfluiddynamics(CFD)models.Experimentsarethemostcostlyapproach,requiring specialized equipment and resources. Empirical models are developed usingconservation equations and experimental data to provide simple relations.On the otherhand,analyticalmodelsarederivedfromthesameconservationequationsbutassumptionsareusedtoobtainsimplifiedequations.Alternatively,computationalmodelscanbeusedto calculate velocity, pressure, and heat transfer within a building, as well as help usvisualize the air flow patterns. The computational approaches, in order of complexity,includemulti-zonemodels,zonalmodels,andCFD.

Eachoftheseapproachesandmethodshasitsmeritsandcanbeusedtoprovidefurtherinsight into the complex dynamics of air flow and thermal interactions for naturalventilationapplications.Theaimofthischapteristobrieflypresenttoolsthatareusedtoprovideamorecomprehensiveunderstandingofairmotion.Theintentionistohelpguidethearchitectanddesignerwithtoolsthatwillbestmeettheirneeds.

ExperimentsandWindTunnelResearchExperiments are a necessary tool to helpdetermine thephysics of air flowandprovidemeasurementsintermsofvelocityandpressure.Theeffectofwindonbuildingventilationis greatly influenced by the building geometry and layout, as discussed in Chapter 4.Ventilation is also influenced by the proximity of surrounding buildings, especially inheavily populated urban areas. Thus, experiments are constructed to determine thepressure differences that occur around a building. Thermocouples can also beinstrumentedtomeasuretemperaturechangesthatarecomplementarytothevelocityandpressuremeasurements.

Small-scale experiments are used to model full-scale buildings; these are moreeconomical and do not require large spaces to perform the experiments. The size ofmodelscanrangefromscalesof1/10thto1/100thofthefullbuilding,orevensmaller.Ingeneral,thedatacollectedislimitedtoasmallnumberofmeasurementsandissusceptibleto errors. One source of error is the use of probes or other intrusive devices that candisrupt the flow patterns. There is also error with the accuracy of the equipment andrepeatabilityofthemeasurements.Althoughtheremightnotbelotsofexperimentaldata,thevalueofthedatacanbeseenintheliteratureasitisusedtodevelopcorrelations.

Wind tunnel experiments are used to determine air flowwithin a naturally ventilatedbuilding.Theapproachistoplaceasmall-scalemodelofabuildinginawindtunnelandmeasure the air flow and pressure distributions around the building. Such tests can be

performed for a multitude of wind speeds and wind orientations to the building. Thedrawbackisthatthedynamicsoftheairflowwithinthebuildingisnotmeasured(andtheuseofCFDwillprovidesuchinsight;seeChapter12).Themeasurementscanbeusedinthedevelopmentandvalidationofothermodels,discussedinSections11.2and11.3.

Wind tunnel data have an important role in understanding wind loads on buildingventilation. The American Society of Civil Engineers has published standards andguidelinesthatprovidebestpracticestoconductandinterpretwindtunneltests.1Oneofthe difficulties with wind tunnel testing is creating a wind profile that represents theambient air flow along the terrain that captures the boundary layer. The wind velocityprofiles u can be written as a power law u = Ayn, and are a function of the verticaldirectionyfromasurface.2TheconstantsAandndependontheroughnessoftheterrain.Tocontrast thedifferencesbetween terrains, typicallyvaluesofn are0.16 for flat open(country) terrain,0.28forsuburbanorwoodedareas,and0.4forurbanareaswithhigh-risebuildings.RefertoSection7.3forurbanwindpatterns.

Thereisalsotheissueof turbulenceandreplicatingturbulentscalesinawindtunnel.The use of a mechanism to trip the air flow helps facilitate creating the appropriateturbulentstructures thatarepresent inatmospheric flows.Pressureprobesaffixed to thebuilding provide measurements that are related to the upstream air flow pressure todeterminepressurecoefficientsforasetofconditions(buildinggeometry,windspeed,andwindorientation).

Although full-scale experiments are not common, there are a few studies related tonatural ventilation that should be acknowledged. An excellent review of experimentaltechniqueswasprovidedbyHitchinandWilson.3Includedinthereviewisadiscussionoftracer gas techniques, citing advantages and disadvantages, anemometer techniques tomeasure air speed, and guidelines for scale-model measurements. One decade later,Cockroft and Robertson4 measured velocity for ventilation due to turbulent wind flowthrough a single opening anddeveloped a simple analyticalmodel to comparewith theexperiments. An almost full-scale study was performed by Lane-Serff et al.5 for stackflow in a single enclosure. The impressive study byKatayama et al.6 began with datacollectionofwindmeasurementsforcross-ventilationofanexistingfive-storyapartmentcomplexduringa three-weekperiod in thesummer.Theyfurther investigated thecross-ventilationusinga1/300thscaledmodelinawindtunnel.Whiletheydidfindconsistencybetween the on-site measurements and wind tunnel measurements, differences wereattributed to the turbulence of the actual wind-building conditions. Dascalaki et al.7performed an extensive set of experiments to correlate their single-sided ventilationmeasurements with existing models. They concluded that discrepancies between theexperiments and models were due to the importance of inertia forces relative togravitationalforcesandproposedacorrectionfactor.Morerecently,CareyandEtheridge8investigatedventilationratesusingdirectwindtunnelmodelingforthreeconditions:windonly,buoyancyonly,andacombinedwind-buoyancyflow.

Itisworthnotingthatwatertunneltestshavebeenusedtostudystackdrivenventilation.

Theuseofwaterinsteadofairistoensurethatbuoyancyeffectsareproperlycaptured.Aswill be discussed in Section 11.2, non-dimensional parameters are used to preserveconditionsbetweensmall-andfull-scaleflows,andthisisparticularlydifficultwithstackflow.ThewatertunnelexperimentsofLindenetal.9forasmall-scalemodelwereusedtocomparewithafull-scalebuilding.Theeffectsofwindwereignoredandthereforeresultsfromthewatertunnelexperimentscouldbedirectlyrelatedtothermallydrivenflows,thatis,buoyancy.Theexperimentsintroducedbrine(asaltsolution)intofreshwater;whenthetwofluidsinteracted,thedifferentfluiddensitiescreateagradientidenticaltoconvectioncurrents.AmajorresultwasthatLindenetal.demonstratedthat thermalstratificationisduetothesizeoftheventilationopeningsandthethermalsource.

Themeasurementsobtainedfromsmall-scaleexperimentscanberelated to theactual(large-scale)scenariosusingnon-dimensionalparametersthatpreservesimilaritybetweenthetwosystems.ParameterssuchasaReynoldsnumber(Re)oraGrashofnumber(Gr)canbeusedtorelatevelocityandheattransfereffectsbetweentwosystems;however,caremustbetakenwhenselectingvariablestonon-dimensionalize.Forexample,theReynoldsnumberisdefinedas

whereVisthemeanvelocity,ℓisalengthscaleandthefluidpropertiesaredensityρanddynamic(absolute)viscosityμ.10Theratioofthedynamicviscositytothedensityisthekinematic viscosity, v = μ/ρ. The velocity might characterize the wind speed (forcedconvection) or the mean flow velocity if buoyancy is dominant (free convection). Thelength scale could be the height of an opening or the length of a surface. Despite thechoice of characteristic parameters, the interpretation of theReynolds number is that itrelates the inertia forces to theviscous forces.TheReynoldsnumber also indicates if aflowislaminarorturbulent.Formanyflows,thecriticalReynoldsnumberfortransitionfromlaminartoturbulentflowisestimatedbetweenRe=2×105to3×106becausethetransition varies from one problem or geometry to the next.10 Similarly, the Grashofnumberis

whereg is gravity,β is the thermal expansion coefficient that accounts for density andtemperaturechanges(refertoSection11.3),andΔT isa temperaturedifferencebetweenanobject(orsurface)andambientconditions.11TheinterpretationoftheGrashofnumberis that itmeasures the ratio of buoyancy forces to viscous forces. The forced and freeconvectioneffects canbe compared, anda ruleof thumb is thatwhenGr/Re2 ison theorderofunity,botheffectsare important. IfGr/Re2<<1,buoyancyisnegligible,andifGr/Re2>>1,buoyancyisdominant.11Todetermineifafreeconvectionflowislaminarorturbulent, the Rayleigh number (Ra) is used by combining the Grashof number andPrandtlnumber,Pr=v/α

11.2

whereαisthethermaldiffusivityofthefluid.TheRayleighnumberhasasimilarmeaningtotheReynoldsnumber.Anestimateofwhenabuoyancy-drivenflowmightbeturbulentisguidedbyRa≈109.11

When comparing different systems, defining a consistent set of characteristicparameters is important. A technique known as Buckingham pi theorem12,13 helpsmaintainsimilitudeandprovidesaneloquentwaytodetermine thefunctionalityofeachvariable of interest, such as velocity, pressure, andgeometry.With a proper set of non-dimensional parameters, the full-scale system can provide insight into the sizerequirements of the small-scalemodel and the required flow conditions. It is importantthatsimilitudeismaintained,otherwisethesmall-scalemodelmaynotexhibittheproperflow physics, especially when thermal changes are of interest. Although full-scaleexperiments are possible, they can be costly and require a large, dedicated, controlledenvironmenttoreduceerrorandunwantedconditionsinthemeasurements.

Experiments are avaluable tool tohelpusunderstand thebehaviorof airmovement,andpressureandtemperaturechangesthatpersistinventilation.Thedataarealsousefulto help create reduced models that provide trends and simple estimates for ventilationprocesses. The next section provides a few examples of how experiments are used tocreatesimplermathematicalmodels.

EmpiricalandAnalyticalModelsBoth empirical and analytical models are qualitative tools to help the architect andengineerdetermineventilationperformancefordifferentbuildinggeometriesandthermalconditions.Thegoverningconservationequations formass andenergy (refer toSection11.3) are the basis for developing empirical and analyticalmodels. Thesemodels oftenappeartobethesameapproach,buttheprimarydifferenceisintheprocesstoreducethegoverningequationstosimplifiedforms.

Empiricalmodelshavefunctionalformsthat includeconstantsandexponentsspecificto a set of experiments.14The simplifiedmodels offer a general expression to correlatebulk conditions for velocity and temperature. Single-sided ventilation has receivedconsiderable attention, and the experimental work by de Gids and Phaff15 provides anempiricalrelationshipforaneffectivevelocitythroughasingleopeningthatincludesthevelocity associatedwith stack flow,wind, and turbulence. They noted that the velocityprofiledependsonthemoredominantforcedueeithertowindvelocityortotemperaturedifference. Using a full-scale outdoor experiment, de Gids and Phaff developed anexpression for mean velocityUm due to wind, stack, and turbulence effects based onpressuredifferences

andthepressurecontributionswererecastintoarelationshipoftheform

whereUwindisthevelocityfrommetrologicaldata,HistheheightoftheopeningandΔTisthetemperaturedifference.Theconstantsweredeterminedbyfittingdatafromdozensofexperiments,wherethewindconstantC1=0.001,thebuoyancyconstantC2=0.0035,andtheturbulenceconstantC3=0.01.Althoughthisstudyisfrequentlyreferencedintheliterature, the use of Equation 11.4 is limited because the constants are specific to theconditionsoftheexperimentandtheparticularurbanenvironment.Morerecently,Larsenand Heiselberg16 developed an empirical relationship that has a very similar form toEquation11.4.However,theyincludedtheincidentwindanglef(β)andanexplicittermforthemeasuredpressurecoefficients

whereΔCp,openisbasedonthepressuredifferenceattheopeningasafunctionofincidentwindangle.Forcaseswherewind-driveneffectsbecomedominant,Dascalakietal.7usedexperiments to develop a correction factor CF that is a function of the Grashof andReynoldsnumbers

whereHisthecharacteristiclengthcorrespondingtotheopeningheightandDistheroomdepth.Thus,thecharacteristiclengthsinEquations11.1and11.2arereplacedwithDandH,respectively.Itisnotwithinthescopeofthisbooktopresentthenumerouscorrelationsthat are in the literature, but there are many useful resources that providerecommendationsforbasiccorrelations.17

The development of analytical models incorporates assumptions that reduce thecomplicated forms of the partial differential governing equations (Section 11.3).Assumptionssuchassteadystateandsymmetryorone-dimensionalflowgreatlysimplifythe equations. An advantage of the analytical model is that it is not as restrictive asempirical models. In most cases, the solutions do not require significant computerresources.

OneexamplerelevanttonaturalventilationisthedevelopmentofananalyticalmodelusingBernoulli’stheoryforabuoyancy-drivenflow.18Therelationshipprovidesameansto calculate the volumetric flowrate V as a function of temperature and geometry forsingle-sidedventilationthroughtwoopenings:

whereΔTisthetemperaturedifferencebetweentheoutdoor(ambient)conditionsT∞andtheindoortemperature,HisthedistancebetweenthecenteroftheopeningsofequalareaA,andg isgravity.Equation11.7canbeapplied tosingle-sidedventilation throughoneopeningsuchasadoorwhereHisdefinedastheheightoftheopening.ThecontractioncoefficientCd (also known as the discharge coefficient) accounts for losses due to a

11.3

pressure drop as the flow travels through a constriction. The coefficient has beendetermined fromexperiments for different scenarios,18 and a value of 0.6 is often usedwhenmodelingflowthroughadoorway.

Another exampleof an analytical expression is the relationdevelopedbyAndersen19for cross-ventilation in a room that is presumed fully mixed with a uniform indoortemperatureTinandaheatsource.TherelationforvolumeflowratehasthesameformasEquation11.7butwithdifferentdefinitionsforAandH.Areducedformofconservationofenergyassumes thatconvectionheat transferQconv isdue toa temperaturedifferenceandthebulkfluidmotion11

wherecpistheconstantpressurespecificheat.Equations11.7and11.8arecombinedwithΔT = Tin − T∞ and the area A is dependent on the complex geometry of the cross-ventilationopenings.Thevolumeflowrateiswrittenas

whereHistheverticaldistancebetweentheventilationopeningsandB=Qconvg/(ρcpT∞isthebuoyancyflux.Equation11.9canthenberelatedtothevolumeflowrateofabuoyantplumeinaheateduniformroomdevelopedbyMortonetal.20

whereCisafunctionofdomainconditionsandzisthevariableforverticaldistanceabovetheheatsource.Li21providesacomparativeanalysisofanalyticalmodelsanddiscussestheapplicabilityoftheequations.

ComputationalModelsComputermodelsalsoprovidedetailsfortheperformanceofventilationstrategiesandairflow patterns. There are three basicmodels known as themulti-zonemodel, the zonalmodel,andcomputational fluiddynamics.Eachmodelwillbepresented insomedetail,withthelastmodelbeingthefocusofChapter12.

Multi-zonemodelsprovideaneffectivewaytopredictairexchangerates inbuildingswithandwithoutmechanicalsystemsforventilation.Theirpurposeextendstopredictionofventilationefficiencyandenergy requirements, and there aremodels that incorporatethe transport of species that represent pollution or smoke. The multi-zone models arebased on the conservation equations for mass and energy but presume that the air isquiescentandthereforemomentumeffectsareneglected.Themodelsalsoassumeuniformair temperature,which limits thepredictivecapabilitiesof thermalstratification.Thus,aroomcanbemodeledas ahomogenousenvironment andventilation throughabuildingcanbepredictedbyconnectingmultiplezones,thatis,rooms.

A few software tools have been developed by government offices such as the U.S.

Department of Energy (DOE) and the National Institute of Standards and Technology(NIST). The DOE tool EnergyPlus22 evaluates energy requirements, and heating andcooling loads necessary to achieve thermal comfort in whole buildings. It includesweather-basedinput,radiationandconvectioneffects,andmasstransfermodelstopredictmoisture. EnergyPlus is a standalone simulation program that strictly reads input andwritesoutputastextfilesanddoesnotofferagraphical-userinterface(GUI).TheNISTtool CONTAM23 is a multi-zone air flow and contaminant transport analysis programdesigned to determine indoor air quality andventilation. It provides details for air flowand pressure through multiple rooms, infiltration, exfiltration, buoyancy effects due totemperature differences internal and external to the building, and the transport ofcontaminants. CONTAM can be coupled to CFD codes to provide input for detailedsimulations of an internal zone.NIST has also developedLoopDA,24 a design tool fornaturalventilationthatcandeterminethesizeofnaturalventilationopeningstoprovideairflow rates that satisfy ventilation and cooling load requirements.Another example of amulti-zoneairflowmodelistheprogramConjunctionofMultizoneInfiltrationSpecialists(COMIS).25

Acomprehensiveoverviewofmulti-zonemodelingisofferedinRef.26althoughmanymulti-zonemodelsweredevelopedtopredictthetransportofcontaminants.27,28Arecentstudy presents a multi-zone model program for natural ventilation (MMPN) that canpredictwindandbuoyancyeffects.29WangandChen30evaluatedtheassumptionsusedinmulti-zonemodelsandreportedguidelinestomaintainaccuracy.

Forroomsorbuildingswherethermalstratificationisprevalent,zonalmodelsareused.Zonalmodelsdividetheroomintozonessothattemperaturedifferencescanbepredicted.Although zonal models tend to provide more detailed information, they require morecomputationaltimetosolvethanmultizonemodels.Alimitingfactorwithzonalmodelsistheirabilitytoaccuratelypredictwind-drivenflows.Areviewofzonalmodelsforindoorenvironments presents the latest developments.31 Thesemodels have incorporatedmorephysics,suchasmoistureandpollutanttransport.Withincreasedcomputerspeeds,zonalmodels can be solved formany zones and provide a solution that is similar to a loweraccuracyCFDcalculationthatusesaverycoarsegridresolution.

Whilealloftheseaforementionedmethodsareusedtocalculateventilationconditions,CFDoffersmorecompletedetailsrelatedtoairflow,pressure,andtemperaturevariations,aswell as ameans to visualize the conditions. InChapter2, the physics of air flow isdescribedforageneralaudience toexplain terms thatarecommonlyusedbyarchitects.Themathematicalprinciples formasetofpartialdifferentialequations thatdescribe thetransport of a fluid. CFD is the numerical approach that solves for the dependent fieldvariablesofvelocity,pressure,andtemperature.Thegoverningequationsandmodelsarepresentednextforthosereadersinterestedinthedetails.

The conservation equations are derived by considering a small volume of fluid andapplyingbasiclawsformass,momentum,andenergy.32Theequationforconservationofmassis

wheretistime,Visthevelocityvector,andρisthedensity.Thephysicalinterpretationofdensityisthemassperunitvolume.ThegradientΔisamathematicalsymboltorepresentthespatialpartialderivatives

where the gradient has been written in a Cartesian coordinate system. Equation 11.11representsthechangeoffluiddensityovertimeandspaceasitmoves.

Conservationofmomentumis

wherepisstaticpressure, isthefluidstresstensor,and isthegravitationalforce.ThefluidstresstensorforaNewtonianfluidis

whereμ is thefluiddynamicviscosity.The last termon therighthandsideofEquation11.12 represents the buoyancy force. The Boussinesq model is employed to solve forbuoyancy effects and assumes that density can be treated as a constant except in thebuoyancyforce term.Theapproximation isonlyvalidwhen temperaturedifferencesaresmall so that density variations are very small.33 Relating changes of density andtemperature,thethermalexpansioncoefficient,isdefinedas

and the subscript 0 represents the reference value. Rearranging Equation 11.13, theBoussinesqapproximationcanberepresentedas

Equation11.14isusedtosolveforρandsubstitutedintotheρ termofEquation11.12.The other density terms in Equations 11.11 and 11.12 are constant equal to ρ0.Conservationofenergyiswrittenas

whereEistotalenergyandkeffrepresentstheeffectiveconductivity,whichconsiderstheturbulentthermalconductivityinadditiontofluidthermalconductivity.Viscousheatingisalsoincluded,whichisthesecondtermontheright-handsideofEquation11.17.Thelasttermmodelsvolumetricheatsources,ifsuchconditionsexist(e.g.,heatloads).

Thefollowingchapterwilloutlinestepstomodelandpredictnaturalventilationusing

1

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3

4

5

6

7

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10

11

CFD.The flows are assumed incompressible and include buoyancy but neglect viscousheating.Theformofthetime-dependent,incompressibleconservationequationsare

FurtherdetailsrelatedtoturbulencemodelingwillbeexplainedinChapter12tocompletethesetofequations.

Computational fluid dynamics has been used to determine air flow patterns in andaround buildings, as well as to assist in the design of ventilation systems.34 ExcellentreviewshavebeenwrittenbyLiddament35andJonesandWhittle36relatedtoearlierworkasCFDbegan toadvanceasa tool.Today the literature is filledwithnumerous studiesrelated to theuseofCFD,appropriatemodeling techniques,validation,andapplicationsforventilation.Thegreatestadvancementwasrelatedtoturbulencemodeling,andChen37provides anoverview to complete thepicture adecade later.Therehasbeen significantresearchconductedusingnumericaltechniquestomodelairflowinandaroundasingle-roombuilding,38,39 but fewdetailed studiesofwholebuildings.40,41,42,43 The followingchapter will present examples to demonstrate successful modeling techniques formodelingventilationthroughlargebuildingsandrooms.

NotesAmericanSocietyofCivilEngineers,WindTunnelTestingforBuildingsandOtherStructures(Reston,VA:AmericanSocietyofCivilEngineers,2012).

S.Goldstein,ModernDevelopmentsinFluidDynamics(London:OxfordPress,1938).

E.R.HitchinandC.B.Wilson,“AReviewofExperimentalTechniquesfortheInvestigationofNaturalVentilationinBuildings,”BuildingScience,2(1),1967,pp.59–82.

J.P.CrockfortandP.Robertson,“VentilationofanEnclosureThroughaSingleOpening,”BuildingandEnvironment,11,1976,pp.29–35.

G.F.Lane-Serff,P.F.Linden,andJ.E.Simpson,“TransientFlowThroughDoorwaysProducedbyTemperatureDifferences,”in:ProceedingsofROOMVENT’87(Stockholm,Sweden,1987).

T.Katayama,J.Tsutsumi,andA.Ishii,“Full-ScaleMeasurementsandWindTunnelTestsonCross-Ventilation,”JournalofWindEngineeringandIndustrialAerodynamics,41–44,1992,pp.2553–2562.

E.Dascalaki,M.Santamouris,A.Argiriou,C.Helmis,D.Asimakopoulos,K.PapadopoulosandA.Soilemes,“PredictingSingleSidedNaturalVentilationRatesinBuildings,”SolarEnergy,55(5),1995,pp.327–341.

P.S.CareyandD.W.Etheridge,“DirectWindTunnelModellingofNaturalVentilationforDesignPurposes,”BuildingServicesEngineeringResearchandTechnology,20,1999,pp.131–140.

P.F.Linden,G.F.Lane-Serff,andD.A.Smeed,“EmptyingFillingSpaces:TheFluidMechanicsofNaturalVentilation,”JournalofFluidMechanics,212,1990,pp.300–335.

B.R.Munson,D.F.Young,andT.H.Okiishi,FundamentalsofFluidMechanics,6thed.(NewYork:JohnWileyandSons,2009).

F.P.Incropera,D.P.DeWitt,T.L.Bergman,andA.S.Lavine,FundamentalsofHeatandMassTransfer,6thed.

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24

25

26

27

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37

(NewYork:JohnWileyandSons,2007).

E.Buckingham,“OnPhysicallySimilarSystems:IllustrationsoftheUseofDimensionalEquations,”PhysicalReview,4(4),1914,pp.345–376.

E.Buckingham,“ThePrincipleofSimilitude,”Nature,96(2406),1915,pp.396–397.

E.Buckingham,“ModelExperimentsandtheFormsofEmpiricalEquations,”TransactionsoftheAmericanSocietyofMechanicalEngineers,37,1915,pp.263–296.

W.deGidsandH.Phaff,“VentilationRatesandEnergyConsumptionduetoOpenWindows:ABriefOverviewofResearchintheNetherlands,”ProceedingsoftheThirdIEAAirInfiltrationCenterConference,Vol.1(1982),pp.4–5.

T.LarsenandP.Heiselberg,“Single-SidedNaturalVentilationDrivenbyWindPressureandTemperatureDifference,”EnergyandBuildings,40,2008,pp.1031–1040.

F.Allard,NaturalVentilationinBuildings:ADesignHandbook(NewYork:Routledge,1998).

D.EtheridgeandM.Sandberg,BuildingVentilation:TheoryandMeasurement(WestSussex,England:JohnWileyandSons,1996).

K.T.Andersen,“TheoreticalConsiderationsonNaturalVentilationbyThermalBuoyancy,”ASHRAETransactions,101(2),1995,pp.1103–1117.

B.R.Morton,G.Taylor,andJ.S.Turner,“TurbulentGravitationalConvectionfromMaintainedandInstantaneousSources,”in:ProceedingsoftheRoyalSocietyLondonA,234(1956),pp.1–23.

Y.Li,“Buoyancy-DrivenNaturalVentilationinaThermallyStratifiedOne-ZoneBuilding,”BuildingandEnvironment,35,2000,pp.207–214.

U.S.DOE,EnergyPlus,http://apps1.eere.energy.gov/buildings/energyplus/

“CONTAM,”NistMultizoneModelingWebsite,2013,http://www.bfrl.nist.gov/IAQanalysis/CONTAM/index.htm.

“LoopDA,”NistMultizoneModelingWebsite,2012,http://www.bfrl.nist.gov/IAQanalysis/software/LOOPDAdesc.htm.

H.-E.FeustelandA.Raynor-Hoosen(eds),FundamentaloftheMultizoneAirFlowModelCOMIS,AIVCTechnicalNote29(Coventry:AirInfiltrationandVentilationCentre,1990).

J.Axley,“MultizoneAirflowModelinginBuildings:HistoryandTheory,”HVAC&RResearch,13(6),2007,pp.907–928.

R.Y.PelletretandW.P.Keilholz,“COMIS3.0:ANewSimulationEnvironmentforMulti-zoneAirFlowandPollutantTransportModeling,”BuildingSimulation’97,FifthInternationalIBPSAConference(Prague,1997).

W.Stuart,G.Walton,andK.Denton,CONTAMW1.0UserManual(Gaithersburg,MD:NIST,1997).

G.TanandL.R.Glicksman,“ApplicationofIntegratingMulti-zoneModelwithCFDSimulationtoNaturalVentilationPrediction,”EnergyandBuildings,37(10),2005,pp.1049–1057.

L.WangandQ.Chen,“EvaluationofSomeAssumptionsUsedinMultizoneAirflowNetworkModels,”EnergyandBuildings,43(10),2008,pp.1671–1677.

A.C.MegriandF.Haghighat,“ZonalModelingforSimulatingIndoorEnvironmentofBuildings:Review,RecentDevelopments,andApplications,”HVAC&RResearch,13(6),2007,pp.887–905.

J.C.Tannehill,D.A.Anderson,andR.H.Pletcher,ComputationalFluidMechanicsandHeatTransfer,2nded.(NewYork:Taylor&Francis,1997).

W.M.Kays,M.E.Crawford,andB.Weigand,ConvectiveHeatandMassTransfer(NewYork:McGraw-Hill,2005).

H.B.Awbi,“ApplicationofComputationalFluidDynamicsinaRoomVentilation,”BuildingandEnvironment,24,1989,pp.73–84.

M.W.Liddament,AReviewofBuildingAirflowSimulation,TechnicalNote33(AirInfiltrationandVentilationCentre,1991).

P.J.JonesandG.E.Whittle,“ComputationalFluidDynamicsforBuildingAirflowPrediction:CurrentStatusandCapabilities,”BuildingandEnvironment,27,1992,pp.321–338.

Q.Chen,“VentilationPerformancePredictionforBuildings:AMethodOverviewandRecentApplications,”

38

39

40

41

42

43

BuildingandEnvironment,44(4),2009,pp.848–858.

P.Heiselberg,Y.Li,A.Andersen,M.Bjerre,andZ.Chen,“ExperimentalandCFDEvidenceofMultipleSolutionsinaNaturallyVentilatedBuilding,”IndoorAir,14,2004,pp.43–54.

S.AsfourandM.Gadi,“UsingCFDtoInvestigateVentilationCharacteristicsofVaultsasWind-InducingDevicesinBuildings,”AppliedEnergy,85,2008,pp.1126–1140.

C.Allocca,Q.Chen,andL.R.Glicksman,“DesignAnalysisofSingle-SidedNaturalVentilation,”EnergyandBuildings,35(8),2003,pp.785–795.

P.Stoakes,U.Passe,andF.Battaglia,“PredictingNaturalVentilationFlowsinWholeBuildings.Part2:TheEsherickHouse,”BuildingSimulation,4(4),2011,pp.365–377.

P.Stoakes,U.Passe,andF.Battaglia,“PredictingNaturalVentilationFlowsinWholeBuildings.Part1:TheViipuriLibrary,”BuildingSimulation,4(3),2011,pp.263–276.

C.A.Rundle,M.F.Lightstone,P.Oosthuizen,P.Karava,andE.Mouriki,“ValidationofComputationalFluidDynamicsSimulationsforAtriaGeometries,”BuildingandEnvironment,46,2011,pp.1343–1353.

12.1

Chapter12

ComputationalFluidDynamicsComputational fluid dynamics is the numerical solution of partial differential equationsthat describe conservation of mass, momentum, and energy. The physics are furthercomplicateddue to the turbulentnatureof the flows; therefore, additional equations arerequiredtomodelturbulence.Chapter2describesthephysicsandmodels,andthesetofequations that are solved in CFD are discussed in Section 11.3. A CFD simulationprovides time-dependent flow fields for pressure, velocity, and temperature.Herein liestheadvantageofusingCFDtoanalyzeventilation:arichhistoryofdataisprovidedfortheentireroomorbuildingofinterest.Visualizationtoolscanplotthethree-dimensionaldata and provide a ‘window’ into themovement of air and corresponding heat transferpatterns.

Computationalfluiddynamicshasbeenusedduringthelastquartercenturytoprovideinsight into thecomplexphysicsofair flowandheat transfer insidebuildings.The firstCFDstudieswereperformeddecadesagoatatimewhencomputationalresourceswereintheirinfancy.Today,itispossibletosimulatefull-scalethree-dimensionalbuildingsonapersonalcomputerwithouttheneedforhigh-performancecomputing.

The goal of this chapter is to distill the basics of a well-posed CFD model forinformativepredictionsofnaturalventilation.Includedaretipstodeterminewhatmethodsarebestanddemonstratehowtovisualizetheresults.

NumericalModelingThere are a number of commercially available software packages that are capable ofmodeling a large variety of flows.Themore common codes include Fluent1 andCFX2

(bothareproductsbyANSYS)andOpenFOAM.3SomecommercialcodesareGUI-basedand guide a user through the variousmodels that can be selected. There are numerousmethods that canbe employed to solve the coupled set of partial differential equations,andsomemethodsaremorerobustthanothers.Thefollowingwilloutlinemodelchoicesthatareofferedincommercialsoftware.

The first step is to create a model of a building; if the building is complicated,computer-aided design (CAD) softwarewill provide themost capabilities tomodel anddrawdetailed rooms,windows,doors, staircases, and soon.Anexampleof an intricatebuilding is shown in Figure 12.1 of the Affleck House to demonstrate that each wallpartition,staircase,skylight,window,anddoorcanberepresented.TheCADdrawingcanthenbeimportedintoaCFDpackagethathasthecapabilitiestogenerateameshwithinthebuilding.Anintermediatestepistousegrid-generatingsoftware,whichmaybemoreuser-friendly, to create the complex mesh before importing into a CFD package. TheskeletonofthehouseisshowninFigure12.1(a),andFigure12.1(b)isameshedregioninthemainportionofthehousewhereventilationisstudied.Becausetheimageissmall,the

gridcellsappearasablackregion.Redcellshavebeenusedtoidentifythewindowsandbluecellsidentifythedoors.Theskylightisalsoshowninred.Whatisuniqueaboutthishouse,asdescribedinSection1.3.1,isthatthereisanopeninginthefloorwhereambientairentersthebuilding;thisregionofairentrainmentbelowthehouseisshownwithpurplecells. Issues related to grid resolution will be described in Section 12.2 and boundaryconditionswillbediscussedinSection12.3.

Figure12.1

(top)CADmodeloftheAffleckHouseand(bottom)themeshusedtomodelthemaininterior.

Mostventilationproblemsaredependenton time,butassumingsteadystatecanbeareasonableapproachdependingon thecomplexityof theproblemorbuilding. Ifa time-dependentsolutionisdesired,afirst-orderimplicitmethodisreasonabletouse.Asolutioncanbeinitiatedbyfirstassumingtheflowissteadyforafewiterationsbeforeturningonthetime-dependentformulation.

Tosolveforflowsthatmaybedrivenbywind,pressure,and/orbuoyancy,caremustbetakentoselectappropriatesolversthatcouplethepartialdifferentialequations.Ventilationflowsare considered tobe incompressible, and specialmethodsareused.Thepressure-basedmethodisthemostcommonmethodtonumericallysolveincompressiblefluid-flowproblems.4Themethodcouplesthedependentvariablesforpressureandvelocitysothatefficientcomputationaltechniquescanbeused.Analgorithmknownasthesemi-implicitmethodforpressure-linkedequations(SIMPLE)solvesthepressure-velocitycoupling.5Inthe SIMPLE algorithm, the momentum equations are initially solved with a guessedpressure field, which is then used to solve the velocity field. Further corrections tovelocityandpressurecontinueuntilthefinalvelocityfieldsatisfiesconservationofmass.Toaccommodatethebuoyancythatmaydevelopinventilationproblems,theBoussinesqmodelshouldbeusedsothatdensitychangescanbecalculatedinthebuoyancyforceterm

inthemomentumequation.CFDpackagesmayhavetheoptiontoturngravityonoroff,andtoproperlymodelbuoyancy,gravitymustbespecified.

Equations that describe the turbulent nature of the flow are also solved. The three-dimensionalconservationequationsaresolvedbyusingeitheranaveragingorafilteringapproachandarecoupledwithaturbulencemodel.TheformerapproachistheReynolds-averagedNavier-Stokes (RANS)equations,which solves for averaged flowvariables tocapture the bulk (large-scale) motion and models the turbulence.6 The latter approach,which has gained recent attention, is large eddy simulation (LES).7 TheNavier-Stokesequations are filtered to resolve the large-scale eddymotion andmore of the turbulentbehavior.Thefilteringremovesthesmall-scaleeddiesandthefiltersizeisgrid-dependent.Bothcomputationalapproachesrequireclosuremodelsthatwillpredicttheturbulentflow.

Themost common turbulence closuremodel is thek-εmodel, inwhich the turbulentkinetic energy, k, and turbulent dissipation rate, e, are modeled and solved using twotransport equations.8 There are three types of k-ε turbulence models: standard k-e,renormalization group theory (RNG), and realizable k-ε.9 The standard k-ε model isconsideredas thesimplest two-equation turbulencemodel.TheRNGmodel includesanadditional term to improve the accuracy in the e transport equation for rapidly strainedflows and for swirling flows. The transport equation for ε is also modified for therealizablek-εmodeltosatisfycertainmathematicalconstraintsontheReynoldsstresses.Recentcomputationalstudieshaveshownthatthetraditionalstandardk-εmodelpredictsairflowinbuildingswithgoodaccuracy.10,11,12,13Unfortunatelythereisnoconsensusonclosuremodels,14 so the usermay need to test a few to determine if the simulation issensitive to the turbulencemodel.TheLESapproachhas receivedsomeattention in theareaofbuildingventilation,15,16butwillnotbepresentedhere.

Thestandardk-εturbulencemodelassumesthattheflowisturbulentandtheeffectsofmolecular viscosity are negligible. The turbulent kinetic energy, k, and its rate ofdissipation,e, in the flowfieldarecalculated from twoadditional transportequations.17Thek-εtransportequationsare:

Intheseequations,GkandGbaretheproductionofturbulentkineticenergyduetomeanvelocitygradientsandbuoyancy,respectively;μt is the turbulentviscosity;C1ε,C2ε,andC3ε are constants; and σk and σe are turbulent Prandtl (Pr) numbers for k and εrespectively.TheconstantC3εdeterminesthedegreetowhichisaffectedbythebuoyancyand is calculated using a relationship between the velocity vector parallel andperpendicular to the gravitational vector. Most commercial codes use defaults for the

12.2

constantsthattheusercanchange.

Theequationsformomentum,energy,andturbulencecanbesolvedusingdiscretizationschemesthataresecond-orderaccurate,suchastheupwindscheme.Examplesofsecond-ordermethods to resolve thegradient terms include the leastsquarescellbased(LSCB)and Green-Gauss based methods. The PREssure STaggering Option (PRESTO!) is therecommendednumerical scheme to interpolate forpressure innatural convection flows.The discretization formulas can affect the performance of a simulation, and there areoptions for under-relaxation factors to help improve convergence.Care should be takenwhenchangingthedefaults,andtheusercanrefertotheliteratureforrecommendations.

GridResolutionandValidationThediscretizationofthepartialdifferentialequationsfacilitatesacomputationalsolutionusingagridormesh.Discretizationsimplymeanstakingalargevolumeandrepresentingitwithsmallervolumes,knownasgridcells.Agridiscomposedofhundredsofthousandsof cells that are the internal volumes (or elements) of the domain beingmodeled. Thepartial differential equations (Section 11.3) are solved for each grid cell to give thepressure,velocity, and temperature fields in avery smallvolume.Eachcellwill haveadifferentsolutionthatprovidesdetailsoftheoverallfluidmotionandheattransfer.

Two-dimensional problems can use a relatively simple mesh, where the domain isdividedintoequallyspacedcellsintheshapeofsquaresorrectangles.Three-dimensionalproblems pose greater challenges, especially if intricate details are beingmodeled in abuilding.Returningtothethree-dimensionalmodeloftheAffleckHouse(Figure12.1),aclose-upviewofthemeshontheoppositesideofthehouseisshowninFigure12.2.Gridcells fill the interior volume (rooms),windows, doors, and open space under the housewherewindentersthroughahorizontalventinthefloor(purplecells).Thewindows(red)anddoors(blue)identifyregionswhereboundaryconditionscanbeappliediftheyaretobe modeled open for ventilation. In addition, as the air flows within the house, theinfluence of the stairs (green) will be captured. The entire building is modeled using390,000gridcells,wheretheapproximatesizeofacellis10cm×10cm×10cm.Thesizeofeachrectangularcellmayvaryinordertoaccommodatethegeometry(suchasthestairs),sotheedgeofacellmayrangefrom7cmto14cm.

Thenumber of grid cells is important formodeling to ensure that the predicted flowfields canbe considered accurate.There areguidelines formeshingadomain, althoughdetailedcomputationalstudiesmayberequiredtoensurethatthesolutionisnotadverselyaffectedbythegridresolution.Commercialcodesmayhavethecapabilitytousestandardwallfunctionsfortheflowfieldnearsurfacestoproperlymodeltheturbulentnatureoftheflow.8Recommendationswouldbegiventoensurethatenoughgridcellsarepresentnearasurfacetocapturethefluid-wallinteraction.

Figure12.2

EnlargementofgridresolutionfortheAffleckHouseusingaviewrotated180°,asshowninFigure12.1.

For complicated building geometries, it is not always feasible to investigate ifappropriatecomputationalmodelshavebeenselectedfortheCFDsimulation.However,asmaller problem can be examined first to help determine that the models and gridresolutionaresatisfactory.Validatingamorewell-knownproblemcanprovideconfidencewithusingselectedmodelsandgridresolution.Thepublishedliteratureisagoodplacetoseek if there is an experiment forwhich data can be used for validating theCFD.OneexampleisthestackventilationexperimentperformedbyMahajan.18Figure12.3(left)isa representation of the roomwith a heater and the doorway throughwhich ambient airentered. The study provided temperature and velocity data at a doorway,which can beused to test CFDmodeling. Grid resolution can also be examined to determine that asufficientnumberofcellsarebeingusedtodiscretizethedomain.Validationofasimplerstudycanbeusedtojustifythemodelingtechniquesandmeshforafull-scalesimulationof a building. Figure 12.3 (right) compares the experiments ofMahajan with the CFDpredictions fromPark19 for three different cell sizes. Park showed that a grid cellwithedgelengthsof6cmwasacceptableforverygoodaccuracywithareasonablesizegridof326,000cellsforthethree-dimensionaldomain.

Figure12.3

12.3

(left)ComputationaldomainusedtomodeltheMahajanexperimentsand(right)gridresolutionvalidationstudycomparingvelocityprofileinthedoorway.

InitialandBoundaryConditionsInitial conditions in a CFD simulation provide a starting guess of the flow field. Themodeling techniquesdescribed inSection12.1 use the guess to determine if the partialdifferentialequationsaresatisfiedand,ifnot,refinetheansweruntilasolutionisreached.Theanswerforeachrefinementiscomparedtothepreviousanswerandthedifferenceisthen compared to aprescribed error tolerance, knownas the convergence criterion.Thecriterion prescribes that the differences between two solutions are small, for example,smaller than 0.00001. Thus, for the simulation to advance in time, there is an iterativeprocessuntiltheanswermeetsthecriterion.

Defining the timestep fora transient simulationcanbeestimatedusing theCourant–Friedrichs–Lewy (CFL)number.TheCFL relates a characteristic velocity and length todetermineanappropriatetimestep.TheCFLis

whereVisthemean(orcharacteristic)velocity(seeEquation11.1)andΔc is the typicalgridcellsize(usuallythesmallest length).Formost incompressibleflows, theCFL=1,andthetimestepΔtcanbeestimated.

Boundaryconditionsarerequiredforanywallandopening.Itisstandardtousetheno-slipboundaryconditionforwallstoensurethefluidvelocityiszeroatasurface.Ifheattransfer is also modeled, using an adiabatic wall condition eliminates solving forconduction through the wall and greatly simplifies the simulation. The adiabatic wallconditionensuresthattherearenotemperaturegradientswithinawall.Therearedifferentboundaryconditionsthatcanbeusedforanopening,dependingonthetypeofventilation.Wind can be prescribed through an opening using a velocity boundary condition and atemperaturecanbeprescribedifheattransferismodeled.Anopeningthroughwhichtheair velocity is not known is modeled by prescribing the outdoor ambient pressure andtemperature. Sections 12.3.1 to 12.3.3 will elaborate on the most common types ofventilationscenarios.

Inordertoincorporatetheexternalenvironmentofabuilding,itisimportanttoensurethattheboundariesofthecomputationaldomainprovidearealisticrepresentationofwindand other ambient conditions. Furthermore, modeling the environment surrounding abuildingincreasestheoveralldomainusedinasimulation.Forexample,Schaelinetal.20simulatedtheconditionsinaroomwithadoor(single-sidedventilation)andheater,wheretheroomdimensionswere4.2mlong×3mhigh×4mwide.Thesimulationswerebasedon theexperimentsofMahajan.18However,Schaelinetal.modeled the environment ofsize34m×25m×18.7m,which ismore than300m3 larger than thevolumeof theroom. Based on the computational resources in the late 1980s, the entire domain wasdiscretizedusingagridresolutionwhereeachgridcellwasapproximately1m3 (16,000

12.3.1

gridcells).Suchacoarsegridresolutionreallyonlyprovidesaqualitativeunderstandingof the air flow. Reducing the size of the domain that represents the surroundingenvironment allows for higher grid resolution (i.e., more grid cells) to resolve thecomputationaldomain,asshowninFigure12.3(right)byPark.19Theoutermostdomainboundariesusedambientpressuretomodeltheenvironmentalconditions.

Usinga smaller computationaldomain requirescareful considerationof theboundaryconditions. Care must be taken when specifying the wind velocity in the immediatevicinityofanopeningtoensurethatthevelocityisrealistic.Aswillbeshownnext,threetypesofflowshavebeenmodeledandsimulatedusingboundaryconditionsspecifictothetypeofflow.Recommendationswillbementionedtohelpguidethemodelingtechniqueswithbestpractices.

ThefinalconsiderationwhendefiningaproblemtobesolvedusingCFDisrelatedtothe boundary conditions and the infinite number of combinations for conditions. Forexample, the Affleck House hasmore than two dozen doors and windows that can beopen,partiallyopen,or closed.Then, there is the considerationofweather.What is thewind speed and temperature?Clearly it is not possible to simulate all scenarios, so thedesignermust try todefineafewkeyscenarios thatmayincludetheslowestandfastestwindspeedsandminimumandmaximumtemperatures.Afewwindowsanddoorscanbemodeledopen.Thus,aselectnumberofsimulationsmayprovidesufficientinformationtohelp the designer determine where there are problems with ventilation. The followingexampleshavefollowedthisphilosophy.

Wind-DrivenFlowsOneofthebenefitsofambientwindisthatitisanaturalsourceofenergythatcanbeusedtoventilateabuilding.Windservesasavehicleforforcedconvectionwhentemperaturegradients are present. As described in Section 7.2, cross-ventilation and single-sidedventilationarethetwomostcommonstrategiestoinduceairflowintoabuildingorroom.Modeling wind-driven flows requires knowledge of the wind conditions such as windvelocityand temperature,whichconstantlychange in timeandonanygivenday.Thus,onemodelingapproachistopresumespecificvaluesfortheenvironmentnearabuildingtoestimatetheeffectsofventilation.

Two wind velocity conditions were investigated for cross-ventilation in Room 1–2(Figure 7.11) andRoom 1–3 (Figure 7.12) byDetaranto.21 The roomwas modeled byspecifyingavelocityinletboundaryconditionintotheleftwindowandambientpressureat the rightwindowon theoppositesideof the room.Thesescenarios representpassivecooling,wheretheinitialroomtemperaturewas4°Chigherthantheambienttemperature.TheGrashofnumberfortheseflowsisGr=3.17×109(Figure7.11)andGr=0.39×109(Figure 7.12), using the window height as the characteristic length (refer to Equation11.2).

AscanbeseeninFigure7.11, thevelocityvectorsshowairmovementwiththesamepatternsandonlydifferinvelocitymagnitude.Thestreamlineselucidatetherecirculationregionsandshowhowtheflowcontinuously‘circles’ toformaspiralpattern.Thescale

12.3.2

for the velocity field is shown above each image. The high-velocity flow is ten timesgreater than the low-speed flow.Therefore, theReynoldsnumbers for the lowandhighvelocitiesare57,700and577,000,respectively(refertoEquation11.1).Theonlyobviousdifference for these wind-driven simulations is the recirculation zone in the upper-leftcorner.Thesizeoftherecirculationzoneisduetotheeffectsofbuoyancyasaresultofthedifferenceinwindtemperatureandinitialtemperatureoftheroom.Forthehighwindvelocity, the wind-driven flow dominates the buoyancy effects and creates upper andlowerrecirculationregionsofequalsize.Incontrast,thelowwindvelocitycompeteswithbuoyancy, resulting in a smaller recirculation zone above the window opening. Toemphasize the use of non-dimensional parameters in Section 11.1, the Reynolds andGrashof numbers indicate the importance of forced convection versus buoyancy.UsingGr/Re2,thevaluesare0.95and0.0095forthelow-andhigh-velocitycases.Avalueclosetooneindicatesbotheffectsareimportantandaverysmallvalueindicatesthattheflowisdominated by forced convection, as shown in Figure 7.11. Similar conclusions can bemadeforthesmalleropeningwindowofRoom1–3(Figure7.12),whereGr/Re2=0.5and0.005. It shouldbenoted that thecross-ventilationsimulationsdonot includeadditionalheatloadsduetopeople,electronicdevices,orheaters,whichwouldchangetheairflowpatterns.Thesesimulationshelptovisualizewhereintheroomtheairmaybecomestaleorwherepocketsofhot(orcold)airmayaccumulate.

Prescribing the boundaries for wind-driven flow is more challenging when a wholebuilding(orlargesection)ismodeledinCFD.ThedistinctfeatureoftheAffleckHouseistheventinthefirstfloor(Figures1.8and1.13),throughwhichambientwindisentrained.ThemodelshowninFigures12.1and12.2 identifies aboundaryusing thecolorpurplewherealowvelocityisspecifiedastheboundaryconditiontoreplicatethewindspeedasit moves under the house. In effect, the vertical boundary is merely a computationalboundarytorepresenttheoutdoorconditions,thusreducingtheneedtomodeltheentireambient environment surrounding the house. Figure 7.6 shows results for temperaturecontours and the streamlines of the air flow into the vent (refer to the lower pop-outimage).Thesame ideawasused tomodelCasaGiuliani, shown inFigure8.10.A low-speed flow was prescribed at the vertical domain edge above the balcony ledge tofacilitate thewind thatmovesbetween the congestedurbanbuildings.The advantage isthat the overall computational domain is contained to the immediate region around thebuildingand thereforeallowsmoregridcells tobeusedwithin thebuilding to improvecomputationalaccuracy.

Buoyancy-DrivenFlowsThe variation in temperature within a building or between the external and internalenvironmentcaninitiatebuoyancy-drivenflows.Thechangesintemperaturearecoupledtochangesindensityoftheair,whichinitiateairmovement.Warm,lighterairrisesandcold, heavier air sinks. Thus, buoyancy can contribute to ventilation without requiringforced convection. Of course, buoyancy-driven flow can be combined with wind, thuscouplingtheeffectsofairmixingandthermalchanges.

Referring to the study of cross-ventilation by Detaranto21 for Room 1–2 and 1–3,

12.3.3

buoyancy-drivenflowwassimulated todemonstrate theeffectbetweenawarmambientenvironment and the room. These scenarios represent passive heating,where the initialroom temperaturewas 4 °C less than the ambient temperature. Thewindow height forRoom1–2istwicethewindowheightforRoom1–3andcanbeusedasthecharacteristiclength tocalculate theReynoldsandGrashofnumbers.Thenon-dimensionalparametersforRoom1–2areRe=56,190andGr=2.96×109.TheparametersforRoom1–3areRe=28,090(one-halfthevalueforRoom1–2)andGr=3.7×108.

ImagesshowninFigure12.4present the temperaturechangesover time(every60s),andstreamlinesareusedtoshowthedirectionoftheairflow.Thecolorbandsrepresentcoolertemperaturesusingblueandwarmertemperaturesusingred.Whatismoststrikingis that the largewindowopeningmodeled inRoom1–2 shows significantlywarmerairflow throughout the entire room.Comparing the Grashof and Reynolds numbers usingGr/Re2,theratiois0.94forRoom1–2andis0.47forRoom1–3.Therefore,bothroomshavemixedconditionswherebuoyancyandtheairentrainedintotheroomsareimportanteffects.However,theeffectsduetobuoyancyinRoom1–2aremorepronounced.

Figure12.4

Buoyancy-drivenflowforwarmambientconditionscomparingtemperatureandstreamlinesforcross-ventilation:Room1–2andRoom1–3.

Pressure-DrivenFlowsPressure-driven flows are the simplest flows that demonstrate natural convection. Thethermal conditions contribute to the motion of the air, and thus a pressure differencedevelops between the room and ambient conditions. In a flow that is driven by bothbuoyancyandpressure,thechoiceofboundaryconditionbecomesimportant.Heiselberg22showedthatthesolutionofcombined-effectflowsisdependentontherelativemagnitudeoftheforcesduetobuoyancyandpressure.

Thecross-ventilationinRoom1–2wasmodeledbyspecifyingambientpressureatbothwindowopenings.21Theambientairtemperaturewas4°Clessthantheroomtemperatureto model a scenario for passive cooling. Figure 12.5 shows the time-dependent

temperaturechangesevery15minutes,withstreamlinestoidentifytheairflowpatterns.Unlikethewind-andbuoyancy-drivenflows,thepressure-drivenflowstakeaverylongtime to reachasteadystate.Theairvelocitiesaremuchslowerand thehotairnear theceilingstillpersistsevenafter45minutesofpassivecooling.Itisalsointerestingtonotethat thecoolerairentersneartheupperportionofthewindowandformsajet-likeflowthatimpingesthefloor,creatingalargerecirculationregioninthemiddleoftheroom.

Figure12.5

Pressure-drivenflowtimesequenceoftemperatureandstreamlinesforcross-ventilation:Room1–2.

UsingtheCFDresultstocalculatethevelocitythroughtheleftopening(Figure12.5),thecorrespondingReynoldsnumber is23,090.TheGrashofnumber isGr=3.17×109.The flow presented in Figure 12.5 corresponds to a buoyancy-dominated flow, whereGr/Re2=6,andconfirmsthattheflowvelocityisverylowintotheroom.Toquantifytheventilation,theairchangesperhour(ACH)isused.ACHisdefinedasthevolumeflowrate(m3/hr)pervolumeoftheroom(m3)andgivesavalueofhowoftentheairchangesperhour.TheACHforthisflowisestimatedtobe1.Whilethisisacceptableandexceedsthe minimum ASHRAE23 recommendation of 0.35, it is below the Royal Institute ofBritish Architects (RIBA)24 recommendation of 2 to 15 to remove heat for cross-ventilation.TheACHvaluesforcross-ventilationwereshowninTable7.2forthewind-drivenflows(Figure7.11).Thesevaluesrangedfrom12to240.Incontrast,thebuoyancy-drivenflows(Figure12.4)contributedtoanACHof1.

Although the pressure-driven flow does not presume a velocity at the openings, thesimulationcanpredictthevelocity.Inanotherexample,single-sidedventilationisusedtodemonstrate the steady state velocity field in Room 2–1 (Figure 7.13), where ambientconditionsare4°Clessthantheinitialroomtemperature.21ThediscussioninSection7.2presentedresultsforRoom2–1wherea1m/svelocitywasspecifiedattheloweropening.The corresponding ACH values for cross-ventilation were shown in Table 7.2 for thewinddriven flows. Here, a pressure-driven flow is modeled, where ambient pressure isspecified at the openings. Figure 12.6 (left) presents the results for the pressure-drivenflow,wherethevelocityvectorselucidatethatflowentersthroughtheupperwindowand

12.4

createsalargemixingregionwherebytheairleavestheroomthroughthelowerwindow.The simulationspredicted that the flowentered thewindowat 0.4m/s (Re=6,734).Asimilar scenario was modeled but the air velocity was specified as 1 m/s at the upperwindow (Re= 19,240). The results for the pressure-driven andwind-driven flows lookalmostidentical,exceptthatthelatterhasavelocityfieldwithamagnitudealmostthreetimes as large. The Grashof number for these flows is 1.47 × 107. These simulationsdemonstrate that for the single-sided ventilation with windows far apart, the flow isdominated by bulk motion of air and buoyancy is not significant. The ACH for thepressure-drivenflowinRoom2–1isapproximately3,whichmeetsrecommendations.

Figure12.6

(left)Pressure-drivenflowand(right)wind-drivenflowcomparingvelocityfieldandstreamlinesforsingle-sidedventilation:Room2–1.

The placement of the openings has a far greater impact for pressure-driven flow. Asimulationforsingle-sidedventilationwithopeningsclosetogether(Room2–2)isshowninFigure12.7.Thenaturaltendencyforthispassivecoolingstrategyisfortheairtoenterthroughtheupperopening,incontrasttothewind-drivenflowsimulations(Figure7.13).However, thereare tworecirculationregions thatdivide theroomandpreventsufficientventilation. The ACH for this room is below 1 and is not acceptable according toventilation recommendations by ASHRAE and RIBA. It is worth noting that for thisscenario,Re=2886,Gr=1.47×107 (same temperaturedifferenceandwindowsizeasRoom2–1),andtheratioGr/Re2=1.76.Therefore,buoyancyisresponsibleforreducingthetemperaturegradientsastheroomcools.

VisualizingtheDrivingDynamicsofVentilationTheplethoraofdatageneratedusingCFDisarichsourceofinformationthatincludesthetemporal and spatial relationship between pressure, velocity, and temperature. A three-dimensionalsimulationcanbevisualizedbycreatingmoviesthatadvanceintimetoshowthedirectionoftheairmovementandthecoolingorheatingofabuilding.Whilemoviesmaybeanidealwaytovisualizeflow,weareoftenleftwith‘two-dimensional’meansforvisualization. In other words, we use static images to convey the motion. Pressure,velocity,andtemperaturefieldsareofprimaryinterest,andtwoofthesevariablescanbeshown simultaneously to provide amore complete picture.For example, superimposingvelocity vectors over pressure contours demonstrates where pressure is low or highrelative to large motions of the flow. Another issue is visualizing the time-dependenttransition and the air flow changes. The following will present natural ventilationscenarios of complex three-dimensional buildings to demonstrate different presentation

techniquesthatcanbeusedforvisualization.

Figure12.7

Pressure-drivenvelocityflowfieldandstreamlinesforsingle-sidedventilation:Room2–2.

Astudy related to natural ventilation byPark19 presented the stack effect for a roomwithadoorway(single-sidedventilation),aradiator,andfurnitureandheat loadsduetoelectricalequipment,shownintheschematicofFigure12.8(topleft).Thecomplicatedairflowpatternsoftenmakeitdifficulttodiscernthethree-dimensionalmotion.Toappreciatethe complexity of the flow, three-dimensional views for warm and cold ambient airconditions are shown in Figures12.8 (top right) and 12.8 (bottom), respectively. Theseviews are called instantaneousbecause they are for a particular instant in time, such aswhentenminuteshaselapsed.Temperaturecontoursprovideknowledgeofwhereregionsintheroomarewarmerorcooler.Blueidentifiesthecoolestregions(nolowerthan10°C)and red thewarmest regions (nogreater than40°C).Thecolorbands inbetweenshowwhere the air has mixed to intermediate temperatures. Streamlines, created from thevelocityfield,areusedtoidentifythepathoftheflow.Theseflowpatternsarerandomatsomeinstantintime,anditisdifficulttodiscerniftherearepocketsorregionswheretheair flow isnot significant.Whilea three-dimensionalviewprovidesa ‘bigpicture,’ it isdifficult to interpret temperaturegradients.Asproperventilation is theprimaryconcern,thedesignerwantstoensurethebestairexchangepossibleforagivengeometryandsetofambientconditions.

Referring to the discussions related to Figures12.4 and 12.5,multiple images of thesameviewareshown,whereeachimageisadifferentmomentintime.Thearrangementofthefiguresprovidesachronologicalprogressionofthechangesintemperatureandairflowpatterns.Consider the temperature inRoom1–2 (Figure12.4). There is initially alargeregionjustdownstreamofthewindowwherethetemperaturesarelowbutgraduallyincreasewithtime.However,forRoom1–3,theairremainsmorestratifiedandacoolerregionpersists near the floorover time.Figure12.5 shows that initially,warmair exitsclosetotheupperpartofthewindowontheleft,whilecoldairentersthewindowthroughthe lower portion. Examining the right window at t = 1min and 15min, there is onestreamlinethatshowsthatairentersandmovestotheleft,eventuallyexitingthroughtheleft window. Once 15 minutes have elapsed, the cooler air enters through the entirewindowareaandexits throughtherightwindow.After45minutes, thereisstillawarmregionofairneartheceiling,buttheairispassingthroughtheroomwithanACH=1.

Visualization can be improved by examining cross-sectional planes at differentlocationswithin the full domain.Two suchplanes are shown inFigure12.9,where thetemperatureandvelocityvectorsareshownatay-zplaneatthedoorway(x=0m)anda

y-xplaneatz=0mthatintersectsthecenteroftheroomthroughthedoorway.TheimagesinFigure12.9(top)areforwarmambientairconditionsandforFigure12.9(bottom)arecoldambientair.Thetwo-dimensionalviewsprovidemorequantitativedetailsrelatedtothemagnitudeanddirectionoftheflowusingvelocityvectors.Superimposingthevectorswiththetemperaturefieldelucidateswheretheairiswarmerandcoolerandthedirectionairmoves tocreate these temperaturegradients.Heat transfers fromhot to cold regionsand buoyancy induces motion so that hot air ascends and cold air descends. The coldambientairentersclosertothefloorandwarmairexitsthroughtheupperhalfofthedoor,demonstrating the stack effect. Also noticeable is the heat that is dissipated from thecomputermonitor (see Figure 12.8), causingwarm air to rise. Using a combination ofstreamlines and temperature helps to further visualize where the flow recirculates, orwheremixingofairisreduced,whichcansometimesleadtostratification.

Figure12.8

Three-dimensionalviewof(topleft)roomlayoutandtemperaturecontoursimposedwithstreamlinesfor(topright)warmambienttemperatureand(bottom)coldambienttemperature.

Figure12.9

Two-dimensionalviewsoftemperaturecontourssuperimposedwithvectorsandstreamlinesfor(top)warmambienttemperatureand(bottom)coldambienttemperature.

Additional CFD simulations were presented in Chapter 8 for the Casa Giulianiapartmentshowingthree-dimensionalviews(Figure8.9).Inaddition,Figure8.10isusedto show how the air exits through the vent. Two planes were identified to show bothtemperature and streamlines. The streamlines begin from the balcony,which is open toentrainambientair.Forthesectionoftheapartmentwiththeopenvent(planeclosesttothe right side), the streamlines showmovement through the doorway (located halfwaythroughtheapartment)andexitthroughthevent.However,theotherplaneindicatesthatthe air does not leave the apartment, and the streamlines persist in a circular motionknownasarecirculationzone.Infact,theairisverywarmtowardstheupperhalfoftheroombecause it isnotexhausted through thevent.Figure8.10 isanotherway inwhichthree-dimensionalflowcanbevisualizedusingthevolumeofthebuildingandidentifyingspecificplanes.

To bring the work full circle that started the collaboration between the authors onnaturalventilationusingpassivetechniques,Figure12.10showstheCADdrawingoftheViipuriLibrary(viewfromtherearofthebuilding).Priortotherestorationeffortsofthelibrary,25 ventilationwas achieved by opening the front doors aswell as a side door toinduceapressuredifferencethroughthebuilding.PasseandBattagliawantedtoexploreventilation strategies using CFD, and thus the architect and engineer began theircollaboration,whichculminatedinthisbook.26,27SimulationsperformedbyStoakes28areshown in Figure 12.10 using the full three-dimensional building volume (rotated 180degreesfromtheCADviewabove).Aswasshownthroughoutthisbook,mostbuildingshavemanywindowsanddoors;thus,therearealargenumberofcombinationsforwhich

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doorsorwindowsarefullyorpartiallyopen,toinduceventilation.TheimagesshowninFigure12.10modeledthefrontdoorsasfullyopenaswellasthesidedoor;however,theoffice windows along the front of the building were presumed closed. The simulationbegan with warm stagnant air in the library. Presuming that the library is open mid-morning,thesimulationusedaprescribedvelocityatthelibrarydoorstomodelthewindat a lower ambient temperature.As timeelapses, it is obvious that thegreat hall of thelibrarybeginstocoolandstreamlinesshowthattheairflowiscirculatingtocreateamorecomfortable internal environment.The figureselucidate thatopening someof theofficewindowswould help with the air flow and remove the warm stratified air through theofficesandcorridor.It issimulationslikethesethatcanhelpthearchitect,designer,andengineer make better choices for ventilation strategies. We hope that this book hasstimulated your interest in using natural ventilation and encourages architects andengineerstoworkmorecloselytogethertodesignenergy-efficientstructures.

Figure12.10

CADmodeloftheViipuriLibraryandtwoimagesoftemperatureandstreamlinesastimeelapsestodemonstratepassivecooling.

NotesSeehttp://www.ansys.com/Products/Simulation+Technology/Fluid+Dynamics/Fluid+Dynamics+Products/ANSYS+Fluent

Seehttp://www.ansys.com/Products/Simulation+Technology/Fluid+Dynamics/Fluid+Dynamics+Products/ANSYS+CFX

Seehttp://www.openfoam.org/.

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AuthorbiographiesUlrikePasseisAssociateProfessorofArchitectureatIowaStateUniversity,USA,wheresheteachesarchitecturaldesignandenvironmentaltechnologies.ShejoinedthefacultyatISUin2006andistheDirectoroftheCenterforBuildingEnergyResearch.ShereceivedherDiplom-Ingenieurdegree(equivalenttoanM.S.inArchitecture)inArchitecturefromthe Technical University in Berlin, Germany, in 1990. She is a licensed architect inGermany,wasamemberof theBundDeutscherArchitekten (BDA) from2005 to2010andisnowanInternationalAssociateoftheAmericanInstituteofArchitects(AIA).Herwork experience includes more than 15 years of professional practice in architecturespecializing in energy-efficient buildings and six years teaching and researching inarchitectural design and building technology at the Technical University in Berlin. HerfirmPasseKaelberArchitektenwonthe1998BDA(BundDeutscherArchitekten)YoungArchitect’sAwardinBerlin,Germany.

Ulrike Passe was the Principal Investigator and Faculty Advisor to the ISU SolarDecathlon Team to build an entirely solar-powered house on the National Mall inWashington, D.C., in fall 2009. The project involved interdisciplinary research intoenergy-efficientbuildingenvelopes,passiveandactivesolartechnologies,passivecoolingstrategies and natural ventilation, green design and technologies, thermal comfort, andbio-compositematerials.

Furtherfundedresearchincludes“TheFluid-DynamicsofAir-FlowinFree-FlowOpenSpace:AnArchitecturalApproach toEnergyEfficientBuilding,” fundedby theBostonSocietyofArchitectsResearchAward2007andconductedincollaborationwithco-authorDr.FrancineBattaglia,ProfessorofMechanicalEngineeringatVirginiaTech,andanNSFEFRI EAGER grant “Multi-Scale Material and Dynamic Thermo-fluid ComputationalModels and Controls for Sustainable Buildings Using Efficient Energy HarvestingMaterials.” Passe is also an investigator in the IowaNSFEPSCoRproject “HarnessingEnergyintheBiospheretoBuildSustainableEnergySystems,”wheresheleadsthestate-wide building science plank. Passe’s interest expands into the history of environmentaltechnologiesanditspositioninthearchitecturalcurriculum.Passeis therecipientof the2010 ImpactAward from the ISUAlumniAssociation and the 2009College ofDesignaward for extraordinary performance as well as two ISU Live Green Awards for hercollaborativeworkwithstudents.Shehasfrequentlybeeninvitedtospeakatinternationalengineeringandarchitectureconferences.

Francine Battaglia, Professor of Mechanical Engineering at the Virginia PolytechnicInstitute and State University, joined the faculty in 2007 and is the Director of theComputational Research for Energy Systems and Transport (CREST) Laboratory. Shereceived her B.S. degree (1991) inMechanical Engineering andM.S. degree (1992) inAerospaceEngineeringfromtheStateUniversityofNewYorkatBuffalo,andherPh.D.(1997)inMechanicalEngineeringfromthePennsylvaniaStateUniversity.From1997to1999,shewasaNationalResearchCouncilPostdoctoralFellowat theNationalInstituteof Standards and Technology in the Building and Fire Research Laboratory. Prior to

joiningtheVirginiaTechfaculty,Dr.Battagliawasonthemechanicalengineeringfacultyat Iowa State University from 1999 to 2007. Dr. Battaglia served as director of IowaState’s Center for Building Energy Research from 2004 to 2007, and developed amultidisciplinary center that emphasized research for efficient and renewable energytechnology related to buildings. Dr. Battaglia’s research endeavors to include usingcomputational fluid dynamics and developing computational models to explore issuesrelatedtothefluidandthermalsciences.Hercurrentresearchinterestsincludemultiphaseturbulent and reacting flows for applications in coal and biomass gasification, syngasproduction,andbuildingenergyutilization.Dr.BattagliaisinWho’sWhoinAmerica,isamember of the American Institute of Aeronautics and Astronautics (AIAA), AmericanPhysicalSociety(APS),AmericanSocietyofEngineeringEducation(ASEE),andSigmaXi,andisaFellowoftheAmericanSocietyofMechanicalEngineers(ASME).

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p.37,Fig.26.

0.2 ©UlrikePasse

0.3 ©PasseKaelberArchitektenBerlin

0.4 U.S.DepartmentofEnergy,publicdomain

0.5 U.S.DepartmentofEnergy,publicdomain

0.6 ©FrancineBattaglia/PrestonStoakes

0.7 ©NavazEbrahim

0.8 ©PasseKaelberArchitektenBerlin

0.9 ©PasseKaelberArchitektenBerlin

1.1 ©UlrikePasse

1.2 ©UlrikePasse

1.3 ©UlrikePasse

1.4 ©UlrikePasse,drawingbySuncicaJasarovic

1.5 ©UlrikePasse,adaptedfromRobinEvans,TranslationfromDrawingtoBuildingandOtherEssays(London:ArchitecturalAssociation,1997)

1.6 Publicdomain,fromLewisW.Leeds,LecturesonVentilation:BeingaCourseDeliveredintheFranklinInstituteofPhiladelphia(NewYork:Wiley&Sons,1868)

1.7 ©UlrikePasse

1.8 ©UlrikePasse

1.9 ©UlrikePasse

1.10 ©UlrikePasse,drawingbySuncicaJasarovic

1.11 ©UlrikePasse,drawingbySuncicaJasarovic

1.12 ©UlrikePasse,drawingbySuncicaJasarovic

1.13 ©UlrikePasse

1.14 ©R.M.Schindlerpapers,ArchitectureandDesignCollection,Art,Design&ArchitectureMuseum,UCSantaBarbara.JamesE.HowHouse,LosAngeles,CA,ViroqueBaker(photographer),ca.1925

1.15 ©UlrikePasse,drawingbyBlakeFisher

1.16 ©UlrikePasse

1.17 ©UlrikePasse

1.18 ©Commons.Wikimedia.org,Smallbones/WikiCommons

1.19 ©UlrikePasse

1.20 ©Commons.Wikimedia.org,Smallbones/WikiCommons

1.21 ©UlrikePasse

1.22 ©UlrikePasse

1.23 ©UlrikePasse,ownphoto

1.24 ©UlrikePasse

1.25 ©UlrikePasse

1.26 ©UlrikePasse

1.27 ©UlrikePasse

1.28 ©UlrikePasse,drawingbyJessicaBruck

1.29 ©UlrikePasse,drawingbyJessicaBruck

1.30 ©UlrikePasse

2.1 ©UlrikePasse,drawingbyShuaibuKenchi

2.2 ©UlrikePasse,drawingbyShuaibuKenchi

2.3 ©UlrikePasse,drawingbyShuaibuKenchi,adaptedfromNationalScienceFoundationvideobyJohnL.Lumley(seehttp://www.youtube.com/watch?v=Xg6L-dnUZ8c)

2.4 ©UlrikePasse,drawingbyShuaibuKenchi

2.5 ©UlrikePasse,drawingbyShuaibuKenchi

2.6 ©UlrikePasse,drawingbyShuaibuKenchi

2.7 ©UlrikePasse,drawingbyShuaibuKenchi

2.8 ©UlrikePasse,drawingbyShuaibuKenchi

2.9 ©UlrikePasse,drawingbyShuaibuKenchi

2.10 ©UlrikePasse,drawingbyShuaibuKenchi

2.11 ©UlrikePasse,drawingbyShuaibuKenchi

2.12 ©UlrikePasse,drawingbyShuaibuKenchi,adaptedfromMEEB

3.1 Publicdomain,fromLewisW.Leeds,LecturesonVentilationBeingaCourseDeliveredintheFranklinInstituteofPhiladelphia,p.29,Fig.6,scan

3.2 Publicdomain

3.3 ©NationalGalleryLondon.JosephWrightofDerby,AnExperimentonaBirdintheAirPump(1768).

3.4 ©AaltoMuseum.AlvarAalto,PaimioSanatorium,1929–1932,windowinthepatients’room.Photo:AlvarAaltoMuseum,drawingcollection.

3.5 ©AaltoMuseum.AlvarAalto,PaimioSanatorium1929–1932,solariumterrace.Photo:GustafWelin,AlvarAaltoMuseum,1932.

4.1 AdaptedfromT.R.Oke,BoundaryLayerClimates(London;NewYork:Methuen,1987),pp.4,5,Fig1.1,1.2

4.2 Adaptedfromhttp://www.weatherquestions.com/(accessed5/17/2014)

4.3 AdaptedfromT.R.Oke,BoundaryLayerClimates(1987),p.26,Fig.1.11

4.4 Redrawn;adaptedfromT.R.Oke,BoundaryLayerClimates(1987),p.39,Fig.2.3

4.5 ©MarcusKottek,J.Grieser,C.Beck,B.Rudolf,andF.Rubel,“WorldMapoftheKöppen-GeigerClimateClassificationUpdated,”Meteorol.Z.,15,2006,pp.259–263,doi:10.1127/0941-2948/2006/0130

4.6 ©ASHRAE,www.ashrae.org,ASHRAEStandard:169(2013)

4.7 ©NREL/publicdomain.Source:http://rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html.

4.8 CreatedusingClimateConsultant.Source:http://www.energy-design-tools.aud.ucla.edu/.ClimateConsultantiscopyrighted2014bytheRegentsoftheUniversityofCaliforniaanddevelopedbytheUCLAEnergyDesignToolsGroup.

4.9 Publicdomain.Source:VincenzoScamozzi,L’ideaDellaArchitetturaUniversale[inItalian],2Vols(Ridgewood,NJ:GreggPress,1964).

4.10 ©PoloMusealedellaCitta’diFirenze,S.S.P.S.A.EeperilPoloMusealedellacittàdiFirenze–GabinettoFotografico

4.11 ©UlrikePasse

4.12 AdaptedfromT.R.Oke,BoundaryLayerClimates(1987),pp.183,185,Fig.5.15,5.16

4.13 ©UlrikePasse,adaptedfromT.R.Oke,BoundaryLayerClimates(1987),p.243,Fig.7.6

4.14 ©UlrikePasse,adaptedfromArthurBowen,“ClassificationofAirMovementSystemsandPatterns,”in:PassiveCooling:InternationalPassiveandHybridCoolingConference(1981),pp.745–751,Fig.6a,6b,16,18,19,20,22,42,43,45

4.15 ©ScienceDirect,reprintedfromN.Artmann,H.Manz,andP.Heiselberg,“ClimaticPotentialforPassiveCoolingofBuildingsbyNight-TimeVentilationinEurope,”AppliedEnergy,84(2),2007,pp.187–201,withpermissionfromElsevier(2014)

5.1 ©ArchitecturalPress,butcurrentcopyrightownercannotbefound.AdaptedfromReynerBanham,TheArchitectureoftheWell-TemperedEnvironment(ArchitecturalPress,1964)

5.2 ©UlrikePasse

5.3AdaptedfromAdilSharag-EldinandJamesDalton,“DisplacementNaturalVentilationSchemeofanAnasaziTwo-ZoneUndergroundKiva,”SolarConference(Denver,July2006),p.2,Fig.1,3

5.4 ©UlrikePasse

5.5AdaptedfromLetiziaDipasquale,C.Mileto,andF.Vegas,“TheArchitecturalMorphologyofCorbelledDomeHouses,”in:EarthenDomesandHabitats:VillagesofNorthernSyria:AnArchitecturalTraditionSharedbyEastandWest(Pisa:EditioneETS,2009),p.5,Fig.9,10;p.11,Fig.20,21;p.13,Fig.25,26;p.15,Fig.30,31;p.17,Fig.35,36;p.18,Fig.38,39

5.6 ©UlrikePasse

5.7 AdaptedfromAldoFanchiotti,“TheCovoli:ANaturalCoolingSysteminPalladianVillas,”SpazioeSocietà,19,1982

5.8 AdaptedfromAldoFanchiotti,“TheCovoli,”1982

5.9 ©UlrikePasse,withgreatthanksforthegreattourtoContedaSchioofCostozzadiLongare

5.10 ©UlrikePasse

5.11 ©UlrikePasse

5.12 ©UlrikePasse,adaptedfromRonaldG.Knapp,ChineseHouses:TheArchitecturalHeritageofaNation[inEnglish](Singapore:Tuttle,2005),p.25

5.13 ©UlrikePasse

5.14 ©UlrikePasse,adaptedfromRahaErnestandBrianFord,“TheRoleofMultipleCourtyardsinthePromotionofConvectiveCooling,”ArchitecturalScienceReview,55(4),2012,pp.241–249

5.15 ©UlrikePasse

5.16 ©MattDarmour-Paul

5.17 ©Commons.Wikimedia.org.Photocredit:Lindosograinsilos,photographbyCTHOE,releasedonCommons.Wikimedia.orgforreuse.

5.18 ©InterphotoOgnenBorissov

5.19 ©NavazEbrahim

5.20 ©NavazEbrahim

5.21 ©NavazEbrahim

5.22 ©NavazEbrahim

5.23 ©Commons.wikimedia.org,OastHouseArchive,releasedonCommons.Wikimedia.orgforreuse

5.24 PublicDomain.SintraRoyalPalacedrawingfromDuarteD’Armas–LivrodasFortalezasfrom1509fromCommons.Wikimedia.org.

5.25 ©Commons.wikimedia.org.MosteirodeAlcobacaCozinha,photographbySchwarzeEngel,releasedonCommons.Wikimedia.orgforreuse.

5.26 ©UlrikePasse,adaptedfromA.Giedion,DieArchitekturderDavoserAlphütten:ErnstLudwigKirchners“AlteSennhütte”undihrVorbild(Zürich:Scheidegger&Spiess,2003)

5.27 ©UlrikePasse

6.1 ©Hennessey&Ingalls,withpermissionfromHennesseyandIngalls

6.2 ©UlrikePasse

6.3 ©UlrikePasse

6.4 ©UlrikePasse

6.5 ©UlrikePasse

6.6 ©UlrikePasse,drawingbyShuaibuKenchi

7.1 ©UlrikePasse,adaptedfromCIBSE,NaturalVentilationinNon-domesticBuildings,CIBSEApplicationsManual10(London:CIBSE,CarbonTrust,2005),p.12,Fig.2.12,2.13(a),2.13(b)

7.2 ©UlrikePasse,adaptedfromCIBSEApplicationsManual(2005),p.16,Fig.2.24

7.3 ©UlrikePasse,drawingbySuncicaJasarovicandShuaibuKenchi

7.4 ©UlrikePasse,adaptedfromCISBEApplicationsManual(2005),p.13,Fig.2.14

7.5 ©UlrikePasse,adaptedfromCISBEApplicationsManual(2005),p.16,Fig.2.22

7.6 ©FrancineBattagliaandMichaelDetaranto

7.7 ©SuncicaJasarovic,adaptedfromKevinJ.Lomas,“ArchitecturalDesignofanAdvancedNaturallyVentilatedBuildingForm,”EnergyandBuildings,39(2),2007,p.3,Fig.2

7.8 ©SuncicaJasarovic,adaptedfromCISBEApplicationsManual(2005),p.13,Fig.2.15

7.9 ©SuncicaJasarovic,adaptedfromCISBEApplicationsManual(2005),p.54,Fig.4.19

7.10 ©SuncicaJasarovic,adaptedfromCISBEApplicationsManual(2005),p.18,Fig.2.25

7.11 ©FrancineBattagliaandMichaelDetaranto

7.12 ©FrancineBattagliaandMichaelDetaranto

7.13 ©FrancineBattagliaandMichaelDetaranto

7.14 ©UlrikePasse

7.15 Publicdomain

7.16 ©F.L.C./ADAGP,Paris/ArtistsRightsSociety(ARS)NewYork2015,(fromLeCorbusier,LaVilleRadieuse(TheRadiantCity),firstpublishedinFrance,1933)

7.17 ©UlrikePasse,drawingbySuncicaJasarovic

7.18 ©UlrikePasse,drawingbySuncicaJasarovic

7.19 ©UlrikePasse,drawingbySuncicaJasarovic

7.20 AdaptedfromEvyatarErell,DavidPearlmutter,andTerryWilliamson,UrbanMicroclimate:DesigningtheSpacesbetweenBuildings,1sted.(London;Washington,D.C.:Earthscan,2011),p.16,Fig.1.1

7.21 AdaptedfromT.R.Oke(1987),BoundaryLayerClimates,p.265,Fig.8.1(a)

7.22 AdaptedfromT.R.Oke(1987),BoundaryLayerClimates,p.265,Fig.8.1(c),8.1(d)

7.23 AdaptedfromEvyatarErell,DavidPearlmutter,andTerryWilliamson(2011),UrbanMicroclimate,p.28,Fig.2.1

7.24 AdaptedfromEvyatarErell,DavidPearlmutter,andTerryWilliamson(2011),UrbanMicroclimate,pp.92–93,Fig.4.7–10

7.25 AdaptedfromT.R.Oke(1987),BoundaryLayerClimates,p.267,Fig.8.2(a)

7.26 AdaptedfromT.R.Oke(1987),BoundaryLayerClimates,p.267,Fig.8.2(b)

7.27 Redrawn.AdaptedfromT.R.Oke(1987),BoundaryLayerClimates,p.267,Fig.8.2(c).

7.28 Redrawn.AdaptedfromEvyatarErell,DavidPearlmutter,andTerryWilliamson(2011),UrbanMicroclimate,p.94,Fig.4.11.

7.29 Redrawn.AdaptedfromEvyatarErell,DavidPearlmutter,andTerryWilliamson(2011),UrbanMicroclimate,p.96,Fig.4.12.

8.1 ©UlrikePasse

8.2 ©UlrikePasse

8.3 ©UlrikePasse

8.4 ©UlrikePasse

8.5 ©UlrikePasse

8.6 ©UlrikePasse

8.7 ©UlrikePasse

8.8 ©UlrikePasse

8.9 ©UlrikePasse

8.10 ©FrancineBattagliaandMichaelDetaranto

8.11 ©UlrikePasse

8.12 ©UlrikePasse

8.13 ©UlrikePasse

8.14 ©UlrikePasse

8.15 ©UlrikePasse

8.16 ©UlrikePasse

8.17 ©UlrikePasse

8.18 ©UlrikePasse

8.19 ©UlrikePasse

8.20 ©UlrikePasse

8.21 ©UlrikePasse

8.22 ©UlrikePasse

8.23 ©UlrikePasse

8.24 ©UlrikePasse

8.25 ©UlrikePasse

8.26 ©UlrikePasse

8.27 ©UlrikePasse

8.28 ©UlrikePasse

8.29 ©UlrikePasse

8.30 ©UlrikePasse

8.31 ©UlrikePasse

8.32 ©AgaKhanAwardforArchitectureandAlhadiAlbaridi

8.33 ©AgaKhanAwardforArchitectureandAlhadiAlbaridi

8.34 ©AgaKhanAwardforArchitectureandAlhadiAlbaridi

8.35 ©UlrikePasse.ShuaibuKenchi.

8.36 ©UlrikePasse.ShuaibuKenchi.

8.37 ©NinaMaritz.NinaMaritzArchitects.

8.38 ©NinaMaritz.NinaMaritzArchitects.

8.39 ©NinaMaritz.NinaMaritzArchitects.

8.40 ©UlrikePasse.SuncicaJasarovic.

8.41 ©UlrikePasse.SuncicaJasarovic.

8.42 ©UlrikePasse.SuncicaJasarovic.

8.43 ©UlrikePasse.SuncicaJasarovic.

8.44 ©UlrikePasse.SuncicaJasarovic.

8.45 ©UlrikePasse.SuncicaJasarovic.

8.46 ©UlrikePasse.SuncicaJasarovic.

8.47 ©UlrikePasse.SuncicaJasarovic.

8.48 ©UlrikePasse.SuncicaJasarovic.

8.49 ©UlrikePasse.SuncicaJasarovic.

8.50 ©UlrikePasse

8.51 ©UlrikePasse

8.52 ©UlrikePasse

8.53 ©UlrikePasse.SuncicaJasarovic.

8.54 ©UlrikePasse.SuncicaJasarovic.

8.55 ©UlrikePasse.SuncicaJasarovic.

8.56 ©UlrikePasse

8.57 ©UlrikePasse

8.58 ©UlrikePasse

8.59 ©UlrikePasse.SuncicaJasarovic.

8.60 ©UlrikePasse.SuncicaJasarovic.

8.61 ©UlrikePasse.SuncicaJasarovic.

9.1 ©UlrikePasse,adaptedfromCISBEApplicationsManual(2005),p.26,Table3.2

9.2 ©UlrikePasse

9.3 ©UlrikePasse

9.4 ©ShanHe.Photo:ShanHe.

9.5 ©UlrikePasse

9.6 ©Photocredit:PiaSchneider

9.7 ©UlrikePasse

9.8 ©UlrikePasse,drawingbySuncicaJasarovic

9.9 ©UlrikePasse

9.10 AdaptedfromBaruchGivoni,ClimateConsiderationsinBuildingandUrbanDesign(NewYork:JohnWiley&Sons,1998),p.102,Fig.2–15

9.11 ©UlrikePasse.SuncicaJasarovic.

9.12 ©UlrikePasse.SuncicaJasarovic.

9.13 ©UlrikePasse.SuncicaJasarovic.

9.14 ©UlrikePasse.SuncicaJasarovic.

9.15 ©FrancineBattagliaandPrestonStoakes

9.16 ©FrancineBattagliaandPrestonStoakes

9.17 ©FrancineBattagliaandPrestonStoakes

9.18 ©FrancineBattagliaandPrestonStoakes

9.19 ©UlrikePasse

9.20 ©UlrikePasse

9.21 ©UlrikePasse,adaptedfromLorenzoLignarolo,CharlotteLelieveld,andPatrickTeuffel,“ShapeMorphingWind-ResponsiveFacadeSystemsRealizedwithSmartMaterials,”in:AdaptiveArchitectureConference(2011),p.2,Fig.1

9.22 ©UlrikePasse,phototakenonJune8th,2014

9.23 ©PaulMcMullin,ArchitecturalPhotographer,www.paulmcmullin.com

9.24 ©UlrikePasse,phototakenonJune8th,2014

9.25 ©UlrikePasse

9.26 ©IrenaVezin.PhotoCredit:IrenaVezin,Hamburg&Goa.

9.27 ©UlrikePasse

9.28 ©UlrikePasse

10.1 ©2015CalderFoundation,NewYork/ArtistsRightsSociety(ARS),NewYork

10.2 ©ShanHe

10.3 ©ShuaibuKenchi

10.4 ©SecretArchiveoftheVatican(ArchivoSegretoVaticano)

10.5 ©ShanHe

10.6 ©UlrikePasse

10.7 ©UlrikePasse,drawingbySuncicaJasarovic

10.8 ©UlrikePasse

10.9 ©UlrikePasse,drawingbySuncicaJasarovic

10.10 ©UlrikePasse,drawingbySuncicaJasarovic

10.11 ©UlrikePasse,drawingbySuncicaJasarovic

10.12 ©UlrikePasse,drawingbySuncicaJasarovic

10.13 ©UlrikePasse

10.14 ©UlrikePasse

10.15 ©UlrikePasse,drawingbySuncicaJasarovic

10.16 AdaptedfromCIBSEApplicationsManual(2005),p.10,Fig.2.9

10.17 ©UlrikePasse

10.18 ©UlrikePasse

10.19 ©UlrikePasse

10.20 ©ShuaibuKenchi,adaptedfromNorbertLechner,Heating,Cooling,Lighting(NewYork:Wiley,2009)

12.1a ©FrancineBattagliaandMichaelDetaranto

12.1b ©FrancineBattagliaandMichaelDetaranto

12.2 ©FrancineBattagliaandMichaelDetaranto

12.3a ©FrancineBattagliaandDavidPark

12.3b ©FrancineBattagliaandDavidPark

12.4 ©FrancineBattagliaandMichaelDetaranto

12.5 ©FrancineBattagliaandMichaelDetaranto

12.6a ©FrancineBattagliaandMichaelDetaranto

12.6b ©FrancineBattagliaandMichaelDetaranto

12.7 ©FrancineBattagliaandMichaelDetaranto

12.8a ©FrancineBattagliaandDavidPark

12.8b ©FrancineBattagliaandDavidPark

12.8c ©FrancineBattagliaandDavidPark

12.9a ©FrancineBattagliaandDavidPark

12.9b ©FrancineBattagliaandDavidPark

12.10 ©FrancineBattagliaandPrestonStoakes

TableCredits3.1 ©UlrikePasse

3.2 ©ASHRAE,www.ashrae.org,ASHRAEStandard:62.2(2013)

4.1 AdaptedfromOke,BoundaryLayerClimates(1987),p.57

4.2 AdaptedfromOke,BoundaryLayerClimates(1987),pp.167–170,290

5.1 ©UlrikePasse

6.1 ©ASHRAE,www.ashrae.org,ASHRAEStandard:55(2013)

6.2 ©ASHRAE,www.ashrae.org,ASHRAEStandard:55(2013)

6.3 ©ASHRAE,adaptedfromF.Nicol,MichaelA.Humphreys,andSusanRoaf,AdaptiveThermalComfort:PrinciplesandPractice(London:NewYork,2012),Table8.1

6.4 ©ASHRAE,www.ashrae.org,ASHRAEStandard:55(2013)

6.5 ©ASHRAE,www.ashrae.org,ASHRAEStandard:55(2013)

7.1 ©UlrikePasseandFrancineBattaglia

7.2 ©UlrikePasseandFrancineBattaglia

7.3 ©UlrikePasse

7.4 AdaptedfromJonWieringa,“RepresentativeRoughnessParametersforHomogeneousTerrain,”Boundary-LayerMeteorology,63(4),1993,p.348,TableVIII;andChristianGhiausandFrancisAllard(eds),NaturalVentilationintheUrbanEnvironment(London:James&James,2005),p.62

7.5 AdaptedfromWieringa,“RepresentativeRoughnessParameters”(1993),p.327

7.6 AdaptedfromC.S.B.GrimmondandT.R.Oke,“AerodynamicPropertiesofUrbanAreasDerivedfromAnalysisofSurfaceForm,”JournalofAppliedMeteorology,38(9),1999,p.1,281,Table6,Fig.7,8

7.7 AdaptedfromGrimmondandOke,“AerodynamicPropertiesofUrbanAreas”(1999),p.1,281,Table6,Fig.7,8

7.8 ©UlrikePasse.ThankyoutoKellyKalvelageforcompilingtheoverview.

IndexAalto,Alvar3,7,34–7,60,101–4,119,233,244,272

Aalto,Elissa101

acceleration42–3,139;gravitational46

Ackerman,Marsha139,140,255–6

Acropolis109

actuators245,261–2

adaptiveprinciple132

adaptivethermalcomfortmodel2,131,134–5,137

adhesives65

Aeneas79

Aeneid79

AeolianVillas98

Aeolus79,99

AffleckHouse22,24–6,149,293,296,298,299

air1,8,12,58–60,96,100,104,115,145,150,153,156,160,204,239,240,272,307;ageof259–61;compositionof56–7;exhaust29,156,179,239,259,273;fresh2,7,9,20,55,60–2,94,118,146,152,159,161,170,179–80,198,217,236,251,259–60;andmoisture52;propertiesof43,44–5;stale7,9,20,57,108,113,146,150,198,217,236,299;visualizationof12

airchangeefficiency260

airchangerate(airchangesperhour;ACH)62,146,151,153,154,156,157,204,205,228,237,250,260,265,266,269,274,276,302–3,304

air-conditioning2,5,20,65,124,126,127,132,139–41,197,208,220,256

airdensity22,44,45,148,288,300

airexchange1,8,304;ratesof9,198,227,228,266

airflow7–10,17,20,22,25,28,32,33,38,63–4,84–5,119,165,179,193,198,220,229,236,238,239,241,245,246,252,260,277,281,289,294,297–303;buoyancy-driven300–1,302;physicsof41,237,281;pressure-driven301–3;wind-driven23,149,193,299–300,302,303

airmovement4,6,7,8,9,19,21,27–8,31,58,62,92–3,145,165,241,255–7,271,304

airpollution7,9,49–50,55,57,65,173,174,179,259,273–4,286,287

airportwinddata175

airquality1,5,8,9,10,21,50,55,63–5,113,124,139,161,170,180,266

airtightness265–6,270,272

airvelocity2,4,7,9,32,131,165,210,239,241,244,248,249,250,256,292,294,303,304,305

Alberti,LeonBattista100

Ali-ToudertDortmund176

Allard,Francis42,50

allergies57,62

alliesthesia140

Alps75,186

Ames164

AnasaziPueblos93

Anaximenes59

anemoi80

anemometers257–8,282

angels80

arcades35,37,107–8,112,150

Archimedes’law51

architecturaldesign6–9,20,170–4

architecturalspace13,68,90

architecturaltypology17

architecture5,10–11,21,82,108,125,240,246,251;Baroque100;green119;kinetic245;Renaissance100;traditional8,28,35,90–2,95,111,115,119,129,228,234,252;vernacular90–2,103,105,108,119

Aristotle58,76,78,80

ASHRAE74,126,128,136,138,302

asthma55,57,62

Athens78,258

AthensCharter,The159,161,165

Atlas99–100

atmosphericscience52,255

atria33–4,39,101,115,118,146–7,153,193,196,198,202,203,263,274,275

Babylonianmythology58

Bachelard,Gaston90,93,109–10

bacteria57,60

badgir111

Bagnaia18

balconies60,237,238,246,247–8,306

Banham,Reyner92,110,267

Barcelona163,164

basilicaS.Giovanni80,81

baskets93

Bauhausbuilding(Dessau)234–5,262

Beaufort,Francis77

Beaufortscale77

Berlin162,163,164,181,182,213–6,245,249

Bernoulli’sprinciple47,48,285

bi-metalstripfaçades245

BirthofVenus,The79–80

blinds31,239,263;solar262

blowerdoortest265–6

Boccaccio,Giovanni60

Bologna107

Bonine,Michael111

Boreas80

Borromini,Francesco80,81,100,101,108

Botticelli,Sandro79–80

boundaryconditions47,48,50,300

boundarylayer50,85,163,173,282;atmospheric47,69–72,171;laminar72–3;planetary68,171;androughnesslength70,171,173;turbulent72,247;unstable50;urban165,166,171

Boussinesqmodel288,294

Boyle,Robert59,77

Brandes,HeinrichWilhelm77

breezes3,34,62,83,105,107–8,110,128,136,137,139,150,169,188,190,220

Buckinghampitheorem284

Buddhism58,59

buildingmanagementsystems(BMS)263

buildingenvelopes8,57,118,218,221,227,237,246,265–6,268,270,272

BuildingResearchEstablishment’sEnvironmentalBuilding204

buoyancy9,17,21,49,51,53,69,70,71,146–7,149,156,282–6,288,289,294,299,300–1,302,303,305

Calder,Alexander255

cancer57,60,62

canopyzone165,167

CanyonAirTemperatureModel(CAT)176

CapeTown162,164

carbondioxide(CO2)1,5,8,56–7,63

carbonmonoxide1

Carrier,Willis127

CasadePilatos106

CasaGiuliani182–7,300,306

casestudies10–12,180,182,185–224

caves93,95,98,110

CFX292

CharlesdeGaulleSchool(Damascus)205–8

Chicago76,163,164

chimneys93,115–17,196,205,248;solar146,204–7

China93,103–4,236

Chinesephilosophy58,77

Christianity77,80

Circignani,Nicolò80,258–9

climate2,10,11,17,19–22,27,34–6,39,41,52,62,66,68–78,82,87,90–1,101–5,118,124,128,132,158,202–3,211,220,228,268,271–2;internal17

climatechange5,119,140

ClimateConsultant76–77

climategroups73–4

climaticcoolingpotential(CCP)171

climatology71,128,170–4

clothing112,127,134–5,137,139,179,256

clouds49,52,69,77,82,190

Columina,Beatrix21

Commerzbank(Frankfurt)193–7

Como182–7

composites65

computer-aideddesign292–3,307

condensation82,139,227,266

conduction62,71,82,98,298

conductivity288–9

CongrèsInternationauxd’ArchitectureModerne(CIAM)159,161,165

ConjunctionofMultizoneInfiltrationSpecialists(COMIS)287

Connor,Steven55

conservationofmass9,46,52,284,286,288,292

conservationofmomentum46,52,288,292

CONTAM287

convection12,29,71,105,124,136–7,239,283,286–7;forced52,299,300;free283–4;natural8,9,29,52,295,301;wind246

“CoolBiz”campaign135

coolingstrategies19,62,95,220,264–5,269,271,299,303,307

coolingtechnology17,100,124,246

Corioliseffect52,70

Correa,Charles10,34–5,188–92

corridors19–20,64,182,183,184,186,217,308;circulation181

Costozza98

Courant–Friedrichs–Lewy(CFL)number297–8

courtyards34–9,93,101–7,112,115,117,118,130,153,176,179,194,199,201,205–7,213,269–70

cross-connections22

culture10,58,59,68,77,90–1,106,118,119,129,139,255

Dalton,James94

Damascus205–8

Danti,Ignazio80,258

Daoism236

Davos60,115,117,234

daylighting5,6,9,33,102,147,153,182,185,196,199–202,209,217,220,230,233,242,251,268,269

deDear,Richard127,128,132,140,141

desert70,73,82,94,111,112,118,173,207

Dessau234–5,262

developingworld,the10,161

discretization295

displacementzone165,167

domes94,96–8

doors19,33,104,110,149,228,291,293,296,297,298,307–8

doubleheightspaces21,23,29,30,31,39,188,190,191,239,240,241

double-skinfaçades39,60,108,153,193,194,203,217,220,243–4,249,274

drowsiness1,8

Dubai111

dust161,250

How,JamesEads,27

Earth,rotationof52,69,70

Eastgateshoppingcenter198–9

Eberswalde268–71

Eco,Umberto92

Egypt111

Egyptianphilosophy58

Eisenman,Peter182

Classicalelements(Greek)1,58

Elgin,IL200–2

energy1,2,163;conservationof52,71,284,286,288,292;consumptionof4–5,9,95,124,127,135,140,197,203,211,220,265–7;electrical2;formsof71,82;savingof3,224,264–5;solar69,71,82;transferof52;transportof9

energyefficiency6,95,200,308

EnergyPlus7,287

energyuse9

England115,118,159

environmentalforces17,21,53,107,124,126,227

EsherickHouse22,29–33,239–43

Estonia231

Euleriandescriptionofflow42–3,45

Evans,Robin20

evaporation2,57,62,106,124,134,137,176,256

“façadeasfilter”12

Fanger,Ole127

fans17,52,134,204,266

farmsteads35

Fewkes,Walter94

Fibonaccisequence11

Finland60,101,103,104,129,130,233,244

fire58,90,197,220,274

floorlayouts20

flowfields170,297

flowpaths11–12,20–1,28,85,153,179,186–7,192,198,199,203,208,212,215,219,221,222,228,274

flowpatterns9,49,53,82–6,103,154,158,165,167,170,171,173,179,236,237,241,245,281,286,289,299,300,301,304

flowrates12,154

Fluent292

fluiddynamics9,17,41–2,47,49,53,96,288;computational(CFD)7,8–9,43,47,152,241,242,246,281,286,289,292–307;ofweather52;ofwind112

fluidparticles46

forests60,70,83,173

formaldehyde57,60,273

Foster,Norman193–7

Fourier,Charles159

FraAngelico36

France83,93,208,228

Francis,St77

Frankfurt193–7,217–20

free-flowopenspace21

FreieUniversitätBerlin213–6

Frenchdoors228

Fuller,Buckminster10

Functionalism60

GardenCitymovement159,160

gardens18,33,34,35,98,106,107,110,129,175,188,242;sky193–7

gazebos130

Genoa162,163,164

geometry9,11,20,22,31–2,240,241

Germany4,10,83,126,182,193–7,205,213–20,228,234–5,243–5,249,268–71

Ghiaus,Christian42

Giedion,Andres234

glass21,27,31,35,52,60–1,82,108,193–4,197,202,204,217,230–5,239,244–5,251,268,275

glues65,273

Goa19,251

God77,80

Golden,CO272

golfballs247

GrandCanyon17

Grashofnumber283–4,285,299,300,301,302,303

gravity17,21,43,51,52,69,70,283,286,294

Greekphilosophy/mythology58,78–80,99

greendesign6,10

Green-Gaussbasedmethod295

greenhouses234

Gregotti,Vittorio101

Gretsky,Wayne263

Gropius,Walter234–5

GSWbuilding245,249

HabitatResearchandDevelopmentCenter(HRDC)(Windhoek)208–12

HafenCity(Hamburg)243–4

Hamburg107,243–4,275

Hansaviertel160,181

Harare198–9

HarmA.WeberAcademicCenter200–4,274,277

Harranhouses95,96,118

HausMarxen5,10–12

health2,8,9,11,28,55,57,59–62,100,139;criteriafor65–6;public21,55,62,134

hearths101

heat,transportof1–2

heatbalance134

heatcapacity268,270,271

heating104,263–4

heatingrate264

heating,ventilation,andair-conditioning(HVAC)systems124,126

heatislands83,84,85,159,163,176,270

heatrecovery269

heattransfer7,93,134,137,139,281,283,286,292,295,298,305

Helsinki233

Hermes80

Heschong,Lisa20,128–9

high-risebuildings102,160,161,163,175,176,193,243,246,247,249

HildegardofBingen78

Hinduism58,77

Homer78

Hooke,Robert77

HooverDam17,18

Howard,Ebenezer159,160

HowHouse22,27–8

humidity1,2,17,19,50,52,57,60,68,82,90,108,113,131,137,139,189,191,196,202,238,256,268,271;relative52,57,82,85,127,137,186,190,191,196,207,216,220

hurricanes70,77,83

illumination68,126

immeublevilla160

indexofthermalstress(ITS)137

India10,34–5,118,158,188–92,251–3

IndoorairPLUS65

IndoorAirQualityBuildingEducationandAssessmentModel(I-BEAM)65

indoorenvironmentalquality(IEQ)57,202,271

infiltrationrates265–6

insects250,273,276–7

insulation74,134–5,205,231,268;noise243;vacuum227

integrativedesign6

interconnectivity19,20,272–3

interiorcomfort2,136

Iran94,97,111–13,118,207

Iraq111

Islamicworld77,129

isolatedroughnessflow168–9

Italy18,20,78,80,83,93,185,208,232

Ito,Toto246

Japan104,118,135

Japanesephilosophy58,77

jetstreams47,83

JudsonUniversity274

Jung,CarlG.90

Juno79

Kahn,Louis22,29,30–1,239–40

KanchanjungaApartmentbuilding34,188–92

k-epsilonmodel50

kivas93–4

Klee,Paul1

Klein,Yves10

Koeppenclimateclassifications73

Köppen,Wladimir73

KreditanstaltfürWiederaufbau(KfW)153,217–20

Lagrangiandescriptionofflow42–3,45

laminarflow49–50,72,242,247,283

Landsberg,Helmut163

largeeddysimulation(LES)294

Laugier,Marc-Antoine124

leastsquarescellbased(LSCB)method295

LeCorbusier10,21,119,159,160,161,181,188

Ledigenheim(Breslau)181

Leeds,Lewis21,55–6

Levante78

Lewcock,Ronald90,92

light4,9,10,21,31,32,35,68,90–1,96,100,159,160,188,217,227,240,241,251–3

LiTiegui236

loggias35,93,107–8,190

Lomas,Kevin150

London162,163,164

Loomis,Elias77

LoopDA287

Loos,Adolf27

louvers10,147,228,232,250,274,276

Mahajanexperiments297,298

Manchester159

Mann,Thomas60

mapping87

Maritz,Nina208–9

Mascherino,Ottaviano80,258

McCoy,Esther110

mechanicalventilation2–5,10,63,124,140,180,196,197,202,213,221;drawbacksof5

MediterraneanSea75,83,95,108,118

Meir,IsaacA.91

Mercurio80

metabolicequivalentoftask(MET)133

metabolism62,127,132–4,136,137,39

meteorology255

Michelangelo108

Michelozzo34

MickPearceArchitects198

microclimate35,39,70,71,72,82,103,136,205

Miller,Henry139

mistral83

modelpredictivecontrols(MPC)264–5

ModernMovement19,21,22,60,119,159

mold57,60,139,227,266

Mumbai34–5,158,188–92,251–3

Mumford,Lewis139

Namibia208–12

Naples98

NationalRenewableEnergyLaboratory(NREL)75;officebuildingof272

nativeAmericans77

naturalventilation2,6,9,12,17,19,22,27,34,39,53,57,63,65,68,72,82,117,127–8,131–2,140,145,149,151,158,170,177,179,183,186,191,196,200,202,207,209,213,219,220,223,224,228,239,240,246,247,273–4,281,304,306,308;andacousticchallenges273;benefitsof2;andclimate87;andcontrolsystems/strategies3–4,261–71;anddesign2–4,8;drivingforcesof20–1;evaluationof9;limitationsof271–7;literatureon6–7;modellingof289;needfor1–2,6;physicsof41;andspace32;andusersatisfaction266–7

nausea57

Navier-Stokesequations47

Netherlands,the228

net-zeroenergybuildings6

neutralpressurelevel(NPL)147

Newton’slawsofmotion43–4,45,47

noise173,179,243,250,273,274

Norway103

NottinghamJubileeCampus249

Nova,Alessandro76,77,80

NOX246

oasthouses115

Odyssey78

odors2,55,57

off-gassing55,65

OpenFOAM292

open-to-the-skyspaces34,39

Owen,Robert159

oxygen1,7–8,56–7

ozone62

PaimioSanatorium36,60,61,244,272

Pakistan111

PalazzoMediciRiccardi34

Palladio,Andrea98,99

PalmyraHouse251–2

ParametersforMBDC’sMaterialsAssessmentProtocol65

partialenclosure21

particleload2

passages93

PassivHausStandard266

PaulWunderlichHaus268–71

pedestriancomfort82,163

Persia,ancient77

Pettenkofer,Max(von)21,62,256

phasechangematerials270,271

PhilipofMedma76

photovoltaicarrays200,201

PietrodellaValle251

Plato58,76

PlinytheYounger108

Pneuma59

pneumatology100

pollen250

porches19,23,24,26,110,128,251,255,277

Portugal109,115,116

prairiehouses22

Prandtlnumber284,295

predictedmeanvoteorpredictedpercentdissatisfied(PMV/PPD)model127,131,134

pressure9,12,18,21–3,41–2,44,281,284,292,294,303,304;differencesin2,8,17,19,21,23,29,41,69,70,85,145–51,153,165,179,285,287,307;andneutralplanes145–6

PREssureSTaggeringOption(PRESTO!)295

privacy19–20

psychrometriccharts52,53,82

RadiantCity(LaVilleRadieuse)160,161

radiation71;long-wave71;short-wave71;solar9,68,72,82,96,101,104,105,110,124,136–7,146,148,169,171,172,188,220,245

radon62,65

rain228,250,251,252,262,273

Raumplan27,28

Rayleighnumber284

recirculationzones152,299,301,303,306

refrigeration2

renormalizationgrouptheory(RNG)294

Reynolds-averagedNavier-Stokes(RANS)equations294

Reynoldsnumber50,283,285,299,300,301,302

Roaf,SusanC.91,111,248

RockyMountains75

Romancivilization78–80

Rome20,77,80,98,108,267

roofgeometry95–7,251

Rossi,Aldo90

roughness20,71,166,168–9,171,173–6,246–8,282

roughnessfactor70,71

roughnessheight171,173

roughnesslength70,71,171,173

Rudofsky,Bernard90,91–2,111

SanFranciscoFederalBuilding220–4,275–6

SaoPaolo162,163,164

Sartre,Jean-Paul255

SaudiArabia111

SäynätsaloTownHall36–9

Scamozzi,Vincenzo78,100

Scharoun,Hans181

Schindler,RudolphM.22,27,28

SchindlerFrame28

Scirocco78

semi-implicitmethodforpressure-linkedequations(SIMPLE)294

Semper,Gottfried90,101,108,124

Shakespeare,William81

Sharag-Eldin,Adil94

shutters29,30,32,232,236,239,240,242

sickbuildingsyndrome(SBS)10,57,63

SidwellFriendsSchool204

simulationtools12–13

SintraPalace115–16,118,248

skimmingflowregime169–70

smoke55,57,94,101,115,193,197,204,274–5,286

smokepen260

smoketests260

solargain102,230,268

solarorientation9,68,91,209

solarradiation9,68,72,82,96,101,104,105,110,124,136–7,146,148,169,171–2,188,220,245

solids41–2

Spain93,106,107,109

spatialarchetypes90–1,108–9

spatialcomposition11,20–1,25,31,38,240–1

spatialdesign6,11,12,124,126,182,185,188,196,202,207,209,213,217,221

spatialenvelope31,240

spatiallayout9,94,180

Spyridaki,George109

stackeffects8,9,20,22,29,93,105,117,146,147,156,180,198,204,217,239,274,304,305;andbuoyancy51

stairs21,36,146,180–3,198,222,292–3,296

streetcanyons41,85,149,151,163–73,175–6,194,237,270

StudioMumbai251–2

suburbs22–3,173,175,213,282“SuperCoolBiz”campaign135

sustainablebuildings119,268

sweat112,134,137,139

Sweden102,103

Switzerland60,102,115,234

Syria94,97,205–8

TelAviv163

temperature41,44,62,63,82,127,131,132,137–8,141,145,148,163,171,179,191,198,211,220,224,238,245,256,262–4,267,281,283,284–8,292,298–302,303–7;distributionsof9,10,12,70,305

Tempest,The81

Terragni,Giuseppe182–7

thermalcomfort1,2,4–5,8,10,52,82,124,126–41,268;outdoor136–7;andparameters127;researchon127

thermalbridges227

thermaldelight128–9

thermalenergy8

thermalmass2,93,96,98,111,113,118,202,213,264,265,267–8,270,271,273

thermodynamics7,53,71;lawsof44,45,71

thermoregulation132

ThesisAnemon76

ThimostenesofRhodos76

Thompson,D’ArcyWentworth78

Tiber78,108

Tibetanphilosophy58

Timberlake,Kieran204

tipis94

Tokyo162,163,164,246

Topkapipalace117

topographicalfactor71

topography72,85,86,92

TorredeiVenti(ToweroftheWinds,theVatican)78,80,258–9

ToweroftheWind(Tokyo)246

ToweroftheWinds(Athens)258

TownEnergyBudget(TEB)Model176

Trento,Francesco98

troposphere47,68

tuberculosis60,61,159

turbulence7,9,18,47,49–50,69,83,156,165,167,169,170,242,282,284,285,289,292,294

turbulentenergyspectrum50

turbulentflow47,49–50,72,247,283

turbulentdissipationrate294

turbulentkineticenergy294

Turkey93–4,97,117,118,130

UnileverBuilding(Hamburg)244,275

UnitedKingdom126,127,150,202,204,208

UnitedStatesofAmerica5,17,23,27,28,55,62,65,74–5,76,83,87,93,110,118,126,127,139,200–2,220–4,239,256,272

UnitedStatesEnvironmentalProtectionAgency65

urbancanopylayer(UCL)166,168

urbandensity158,159,161–3,173–6

urbanenvironment60,128,136,158,159,161,171,173,243,285

urbangrowth158

urbanheatisland(UHI)effect84–5,159,163,176,270

urbanism161

urbangeometry174

urbanmeteorology163

urbanmorphometry162,163,164,174–5

urbanpatterns159–62

URBVENTproject71,238

UsonianHouses22–3

UtsavHouse251–2

Vatican,the78,80,258–9

Vayu77

Veneto99,100

ventiducts98,99

ventilation1,9,24,28,55,57,65,68,85,93,99,100,109–10,118,139,163,167,170,183–4,214,227,244,252,259,289,298,304;computationalmodelsof286–9;cross-9,19,23,63–4,151–6,175,179–83,185,188,193,196,199,200,202–6,209,217,220,232,233,238,245,249,250,269,271,282,286,299,301–3;definitionof7–8,9;empiricalmodelsof281,284–5;engineered1;fan-assisted204;goalsof57,146;hybrid180;nightflush268,270;nighttime3,87,146,163,171,250,265,267–72;numericalmodellingof50,292–9;patternsof35;single-sided156–7,193,196,197,271,282,298,302,303;stack19,85,117,118,145–8,150,153,181,193,196,198,200,202–8,230,249,272,296;studyof281;zonalmodelsof287seealsomechanicalventilation;naturalventilation

ventilationholes236

ventilationpaths12,21,84,152,180,197

ventilationrate9,21,60

ventilationshafts93–4,115,202,204

ventilationstandards126

ventilationstrategies11,49,50,55,62,72,74,83,91,94,96,98,105,111,117,118,145,148–51,153,156,173,179–80,185,188,196–7,200,202,207,209,213,216,217,221,227,228,237,243,247,259,260,265,267,272–3,286,308

vents19,31,32,111–12,115,147,149,170,198,203,221,240,261,262–3,273,274;trickle250

Venturieffect9,210

verandas35,188,251

Vergil79

Vicenza98

Vignola,JacopoBarozzida18

Viipurilibrary7,36,307–8

VilladaSchio98

VillaEmo98,99

VillaMadama20

VillaPoiana98

VillaRotonda98

VilaTrento100

VilleRadieuse(RadiantCity)10

viruses57,60

viscosity43,46,47,49,50,283,288,289,295

visualizationtools9

Vitruvius51,77,78,258

volatileorganiccompounds(VOCs)1,2,57,60,62,273

vonPettenkofer,Max21,62,256

wake165,167

wakefactor71

wakeinterference169,174,176

water17,23;flowof18

weather2,9,68–9,131,176,287

weatherforecasting77,78

weathermaps77

well-being2,60,100,128,158

Wells,H.G.255

whales246

wind8,9,12,17,21,29,39,41,52–3,69,70,72,74–7,80,82–4,91,102,115,145,148–51,155–8,163,165,167,177,190,197,198,202,205,207,209,218,222,228,236,239,245,259,262,281,285,294,298,300;personificationof77–81

windcatchers22,28,39,93,111–14,209,211,248,272

windchannelling100

windchimes255

Windhoek208–12

windmaps75

windows2,3,4,21,23,24,26,33,147,154,160,183–4,188,196,200,203,209,213,220,227–42,244,251,256,259,268–9,273,276–7,292,293,298–9,301–3,308;bay237;box231;casement228;controlof262–5;French228;hopper230;Laeuferli234;louver228;orientationof237;pivot228,234–5;sash193,229;soundproofed273;stylesof228;Roman232;ventilation233

windpatterns9,21,41,74,83–5,158,163,168,237

windroses26,29,39,76–7,78,80,85,190,196,202,207,211,215,218,222,258

windspeed111,137,149,151,154,156,167,169,171,173,180,185,189,196,202,207,211,216,220,224,238,257,264,270,282,283,298–9

windsystems70,72,82,83–4

windtowers112,208–12

windtunnels238,282–4

windvanes256–9

windvelocity23,39,47,82,112,148,151–2,154,157,170,173,175,237,243,244,257,258,271,272,282,284,298,299

wingwalls236

wovenscreens108

Wright,FrankLloyd22–3,24,119

Wright,Joseph59

Yazd111–14

Yemen118

Ziegenhagen,Heinrich159,160

Zimbabwe198–9