single and double skin glazed ofﬁce buildings

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Division of Energy and Building Design

Department of Architecture and Built Environment

Lund UniversityFaculty of Engineering LTH, 2008Report EBD-T--08/8

Harris Poirazis

Single and Double SkinGlazed Office Buildings

Analyses of Energy Use and Indoor Climate


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Lund UniversityLund University, with eight faculties and a number of research centres andspecialized institutes, is the largest establishment for research and higher

education in Scandinavia. The main part of the University is situated inthe small city of Lund which has about 103 700 inhabitants. A number ofdepartments for research and education are, however, located in Malm.Lund University was founded in 1666 and has today a total staff of 5 500employees and 40 000 students attending 140 degree programmes and1 600 subject courses offered by 66 departments.

Division of Energy and Building DesignReducing environmental effects of construction and facility management isa central aim of society. Minimising the energy use is an important aspect ofthis aim. The recently established division of Energy and Building Designbelongs to the department of Architecture and Built Environment at theLund University, Faculty of Engineering LTH in Sweden. The divisionhas a focus on research in the fields of energy use, passive and active solardesign, daylight utilisation and shading of buildings. Effects and requi-rements of occupants on thermal and visual comfort are an essential partof this work. Energy and Building Design also develops guidelines and

methods for the planning process.


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Single and Double Skin

Glazed Office Buildings

Analyses of Energy Use and Indoor Climate

Harris Poirazis

Doctoral Dissertation


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Single and Double Skin Glazed Office Buildings

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Keywords

Glazed office buildings, single skin faades, double skin faades,building simulations, building performance, energy use, indoorclimate, thermal environment, thermal comfort.

copyright Harris Poirazis and Division of Energy and Building Design.Lund University, Lund Institute of Technology, Lund 2008.The English language corrected by L. J. Gruber BSc(Eng) MICE MIStructE.Layout: Hans Follin, LTH, Lund.Cover photo: Harris Poirazis

Printed by KFS AB, Lund 2008

Report No EBD-T--08/8

Single and Double Skin Glazed Office Buildings. Analyses of Energy Use and Indoor Climate.Department of Architecture and Built Environment, Division of Energy and Building Design,Lund University, Lund

ISSN 1651-8136ISBN 978-91-85147-23-6

Lund University, Lund Institute of TechnologyDepartment of Architecture and Built EnvironmentDivision of Energy and Building Design Telephone: +46 46 - 222 73 52P.O. Box 118 Telefax: +46 46 - 222 47 19SE-221 00 LUND E-mail: [email protected]

Sweden Home page: www.ebd.lth.se


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To UsoaIve only gone this far because you tied my shoe laces


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Abstract

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Abstract

The energy efficiency and thermal performance of highly glazed officebuildings are often questioned. However, nowadays glazed buildings areincreasingly being built around the world, because (a) there is a growingtendency among architects to use large areas of glass in the faade, often

with the aim of contributing to a better view of the outside and access todaylight, (b) users often like the idea of increased glass area, relating itto a better view of the outside and a more pleasant indoor environmentand (c) many companies prefer the distinctive image of themselves (e.g.transparency or openness) that a glazed office building can provide. Due toinsufficient knowledge concerning function, energy use as well as indoorenvironment of glazed office buildings for Scandinavian conditions, aproject was initiated in order to gain knowledge of their possibilities andlimitations.

The aim of this thesis is to clarify and quantify how highly glazed faadesaffect the energy use and thermal comfort of office buildings. Another aimwas to validate or identify the needed improvement of building energysimulation tools, in order to ensure the precision of the simulations. Fi-nally, suggestions have been given for determining how the design can beimproved with regard to energy efficiency and thermal comfort.

The first part of this project involved establishing a reference buildingwith different single skin glazed alternatives, choosing simulation tools andcarrying out simulations for the determined alternatives. As the referencebuilding, a moderately glazed office building representative of the late

nineties was chosen. Using this building as a starting point, the windowarea to external wall area ratio was increased gradually, in order to meeta fully glazed office building. Results were obtained through varying thebuildings orientation, the interior layout (open plan and cell type offices)and the type of glazing and solar shading devices. The different buildingalternatives were compared with different indoor environment classifica-tions and a sensitivity analysis was presented regarding the occupantscomfort and the energy used for operating the building.

In the second part of the project parametric studies were carried outregarding the performance of various double skin faade cavity alterna-


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Contents

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Contents

Keywords 2

Abstract 5

Contents 7

Acknowledgements 13How to read this thesis 15

1 Introduction 19

1.1 General 191.2 Energy efficiency in the building sector 201.3 Energy efficient building design 211.4 The Glazed Office Building project 221.5 Aim of the thesis 221.6 Limitations of the thesis 23

1.7 Definitions and symbols 252 Background 31

2.1 General 312.2 The performance and quality of a building as a system 322.3 Building Environment 342.3.1 Design Criteria 342.3.2 Indoor Environment 352.3.2.1 Thermal Comfort 352.3.2.2 Conditions of thermal comfort 362.3.2.3 Thermal comfort and productivity 432.3.2.4 Other indoor climate parameters that influence the occupants

health and productivity 452.3.3 Architectural quality 462.3.4 Environmental performance 472.3.5 Costs 48

2.4 Building technology 492.4.1 Glass in buildings 492.4.1.1 General 492.4.1.2 Basic physics of the glass 502.4.1.3 Thermal functions of the glass 52


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2.4.2 Single skin faades 542.4.2.1 Glazing 542.4.2.2 Shading devices 552.4.3 Double skin faades 57

2.4.3.1 General 572.4.3.2 Classification of double skin faades 572.4.3.3 Technical description of the cavity 582.4.3.4 Advantages and disadvantages of double skin faades 58

3 State of the art 63

3.1 Glazed office buildings in Nordic climates 633.1.1 General 633.1.2 Layout of typical office buildings 643.1.3 Office buildings in Sweden 653.1.4 Energy performance of Swedish office buildings 66

3.1.5 Glazed office buildings in Sweden 683.2 Double skin faades 703.2.1 Building physics of the double skin faade cavity 703.2.1.1 General 703.2.1.2 Modelling approaches 713.2.1.3 Measurements test rooms and real buildings 753.2.2 Integration of double skin faades 773.2.2.1 Contribution of double skin faades to the HVAC strategy 783.2.2.2 Examples of coupling double skin faades and HVAC 813.2.2.3 Control strategy 85

3.2.3 Energy performance of buildings with integrated double skin faades 863.2.4 Typical constructions - Examples of buildings 89

3.3 Building simulation software 913.3.1 Building energy simulation tools 923.3.2 Software for DSF modelling 963.3.2.1 Faade simulation software 963.3.2.2 Building simulation software 97

4 Methods 99

4.1 Generation of building alternatives 99

4.1.1 Reference building (30% window to external wall area ratio) 1004.1.2 Single skin alternatives (60% and 100% window to external

wall area ratios) 1024.1.3 Double skin alternatives (100% window to external wall area ratio) 1044.1.3.1 Pilot study on component level using WIS 3 1044.1.3.2 Study on a zone level using IDA ICE 3.0 1104.1.3.3 Study on a building level using IDA ICE 3.0 113

4.2 Description of the studied parameters 1134.2.1 Single skin alternatives (30%, 60% and 100% glazed alternatives) 1134.2.1.1 IDA ICE 3.0 output (zone level) 1144.2.1.2 IDA ICE 3.0 output (building level) 114


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4.2.2 Double skin alternatives 1164.2.2.1 WIS 3 simulations (component level) 1164.2.2.2 IDA ICE 3.0 Simulations (zone level) 1194.2.2.3 IDA ICE 3.0 Simulations (building level) 119

4.3 Description of the simulation tools 1194.3.1 Simulations using WIS 3 1194.3.1.1 Temperatures at the centre of each layer 1204.3.1.2 Temperatures at different heights of the cavity 1214.3.2 Simulations using IDA ICE 3.0 1244.3.2.1 General description 1244.3.2.2 Description of double faade model 1254.3.2.3 Validation of IDA ICE 3.0 Double Faade model

(IEA SHC Task 34/ECBCS Annex 43) 126

5 Description of the building model 129

5.1 Description of the reference building 1295.1.1. Geometry of the building 1295.1.2. Office layouts 1305.1.3 Description of building elements 1345.1.4 Special modifications for the simulated model 1385.1.5 Control set points for indoor air temperature 1405.1.6 Occupancy 1415.1.7 Lights 1455.1.8 HVAC 1465.1.8.1 Heating and cooling 1465.1.8.2 Ventilation 1465.1.8.3 Equivalent heat recovery efficiency 1475.1.8.4 Use of electricity 1495.1.9 Electrical equipment 149

5.2 Description of single skin glazed alternatives 1505.2.1 Description of 60% glazed building 1505.2.1.1 Faade construction 1505.2.1.2 Window properties 1525.2.2 Description of 100% glazed building 155

5.3 Description of double skin glazed alternatives 1575.3.1 WIS 3.0 simulations 1575.3.1.1 Geometry of the standard double faade box 1575.3.1.2 Geometry of the airflow window 1575.3.2 IDA ICE 3.0 Input (zone level) 1595.3.2.1 Office description (IDA ICE 3.0 - zone level) 1595.3.2.3 Geometry of the multi storey high faade 1605.3.2.4 Properties of the inner and outer skin 1605.3.2.5 Shading devices 161

5.4 Assumptions made during the calculations 163


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6 Results and discussion 165

6.1 Reference building 1666.1.1 Energy use 1666.1.1.1 Impact of floor plan type 1666.1.1.2 Impact of orientation 1696.1.1.3 Impact of control set points 1696.1.2 Indoor climate on a building level 1706.1.2.1 Weighted average mean air temperatures 1706.1.2.2 Perception of thermal comfort 1746.1.3 Indoor climate on a zone level 1816.1.3.1 Mean air temperatures and potential overheating problem 1826.1.3.2 Directed operative temperatures 1866.1.3.3 Perception of thermal comfort 190

6.2 Single skin glazed alternatives (60% and 100% window

to external wall area ratios) 1996.2.1 Energy use 1996.2.1.1 Impact of floor plan type and orientation 2006.2.1.2 Impact of windows and shading devices for the 60% and 100% glazed alternatives 2026.2.2 Indoor climate on a building level 2096.2.2.1 Weighted average mean air temperatures 2096.2.2.2 Impact of window and shading type on the perception of thermal

comfort for the 60% and 100% glazed alternatives 2106.2.3 Indoor climate on a zone level 2246.2.3.1 Directed operative temperatures 2246.2.3.2 Perception of thermal comfort 2266.3 Double skin faades 2336.3.1 Simulations on a component level (pilot study using WIS 3) 2336.3.1.1 Pre study: reducing the number of standard double faade alternatives 2346.3.1.2 Parametric study: influence of cavity geometry on system performance 2416.3.1.3 Performance of the glazing alternatives 2526.3.2 Parametric studies on a zone level (IDA ICE 3.0) 2656.3.2.1 Standard double faade mode (naturally ventilated cavity) 2666.3.2.2. Standard double faade mode (mechanically ventilated cavity) 2706.3.2.3 Standard double faade mode (hybrid ventilated cavity) 274

6.3.2.4 Airflow window mode 2776.3.2.5 Impact of the ventilated faade concept 2826.3.2.6. Impact of shading device type 2916.3.3 Parametric studies on a building level (IDA ICE 3.0) 2956.3.3.1 Energy use 2976.3.3.2 Thermal comfort 300

6.4 Comparison of single and double skin faade building alternatives 3026.4.1 Impact of glazing size on energy use and thermal comfort of

single skin buildings 3026.4.2 Impact of glazing type on energy use and thermal comfort 304

6.4.3 Comparison of buildings with single and double skin faades 306


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Appendix J 391

Appendix K 393

Appendix L 397

Appendix M 403


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Acknowledgements

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Acknowledgements

I wish to thank my supervisors Maria Wall and ke Blomsterberg for theirguidance and the useful advice that they gave me during the research workand for the compilation of this report. I would also like to thank my col-leagues at the Division of Energy and Building Design; especially Gunilla

Kellgren for being so kind and helpful, Bengt Hellstrm for all the adviceon technical issues, and Johan Nilsson for his support and friendship dur-ing the past years and Henrik Davidsson for just introducing the "Con-stanza" concept to me. The contribution and support of Per Sahlin andMika Vuolle proved to be substantial for meeting the (reasonably delayed)deadlines. Special thanks to Jean Rosenfeld for believing in me and beingthe main driving force for starting a PhD. Along the way several peopleand organizations contributed to this work; I thank all of you. Finally, Iwould like to thank all the experts who, by making available their theses,reports and articles, have provided easy access to knowledge.

I would like to express my greatest gratitude to my parents Kaiti andStathis for their support during all the years of my study. Last but defi-nitely not least, I wish to thank Usoa for always believing in me and forsupporting my choices without considering any cost.

The project was funded by the Swedish Energy Agency and SBUF(Development Fund of the Swedish Construction Industry), and sup-ported by Skanska and WSP.

Lund, December 2007

Harris Poirazis


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How to read this thesis

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How to read this thesis

When writing this thesis, a main aim was to provide enough backgroundknowledge so that a new reader, less knowledgeable in this field, can read

it. Since the findings of this thesis are primarily addressed to architects,HVAC engineers, glazing/faade experts and consultants in the buildingindustry, a common language had to be established. Thus, the first threechapters were quite extensive covering different aspects of the field.

In the first (Introduction) chapter a brief description is given of whatenergy efficient design means and why energy savings in the building sec-tor are important. Then, the contribution of the Glazed Office Buildingproject to the field is briefly explained and the main aims and limitationsof this thesis (as a part of the whole project) are described. Finally, defini-tions and symbols used during the thesis are briefly explained.

The main aim of the second (Background) chapter is to provide atheoretical background regarding different aspects of the building systemand their impact on building performance. The building is described as asystem consisting of the building environment and the building technol-ogy. The parameters that the building environment and the buildingtechnology comprise are described briefly in a top down organization.Emphasis is given to the aspects studied further in this thesis (such asconditions of thermal comfort and other indoor climate parameters thatinfluence the occupants health and productivity), while other parameters,

such as architectural quality, environmental performance and costs aredescribed briefly.

The third chapter (State of the art) aims to inform the reader about theresearch already carried out in the field, focusing mainly on three topics:(a) glazed office buildings in Nordic climates, (b) double skin faades and(c) building simulation software. In the first part a description of typical(glazed) office buildings in Sweden with regard to energy performance isprovided. The second part deals with building physics of the double skinfaade component (such as modelling approaches of the cavity) and integra-tion techniques of double skin faades in buildings. Finally a description


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stage the goals to be achieved, the design team can improve the buildingperformance and fulfil the design requirements.

This thesis aims to compare the performance (as to energy use andindoor climate issues) of conventional and highly glazed faades. Through

extensive parametric studies the impact of design parameters on buildingperformance is studied. Optimizing energy and indoor climate perform-ance of single skin highly glazed buildings is the first goal to be achieved.The proper integration of double skin faade systems is also investigatedwith the aim of further improvements.

When large proportions of glazing are used in the faade, it is essentialto know from the early design stage what is to be achieved and how toachieve it. Clear goals and sufficient knowledge of the calculation toolsthat should be used for predicting building performance are essential for

a successful building design.

1.2 Energy efficiency in the building sectorEnergy use in the building sector accounts for a large proportion of thetotal energy use in most countries around the world. Particularly for theEU, the building sector accounts for more than 40% of the energy use andis expanding (directive 2002/91/EC). Consequently, the building sector

has a major energy-saving potential. According to the Energy EfficiencyAction Plan (2006) the largest cost effective savings potential lies in theresidential and commercial building sector. The full saving potential isestimated around 27% and 30% respectively. In order to achieve this, theBuildings Directive was introduced in 2002 with the aim to reduce energyuse by implementing energy conservation measures in the building sec-tor. It states that (almost all) buildings sold or rented within the EU shallhave an energy performance certificate not older than 10 years. Moreover,public authority buildings and buildings frequently visited by the publicshould set an example by taking environmental and energy considerationsinto account and therefore should be subject to energy certification on aregular basis (i.e. every 10 years).

According to the directive 2002/91/EC, the energy performance ofbuildings should be calculated on the basis of a methodology, which maybe differentiated at regional level, taking into account climatic and localconditions as well as indoor climate environment and cost effectiveness.Some of the factors which determine building performance are thermalinsulation, the heating and air-conditioning installations, the applicationof renewable energy sources and the design of the building. More specifi-

cally, according to the 2002/91/EC directive, the energy performance of a


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the directed operative temperatures and the perception of thermal comfort(PMV and PPD values). Daylight was taken into consideration only inorder to keep a minimum and maximum illuminance level intensity at theworking surface; when the illuminance exceeds these levels, artificial light

was considered. A detailed separate study analyzing daylight and visualcomfort was carried out within the Glazed Office Buildings project(Blow-Hbe, 2007). Investment cost and LCC analysis were also carriedout separately (Sjodin, 2007).

Different office building alternatives i.e. different faade alternatives foroffice buildings were simulated and analyzed for this report. A virtual refer-ence building was created, a building representative of office buildings builtduring the ninties in Sweden. The faade of this building was changed fordifferent glazed faade alternatives. All the building elements were chosen

based on commercially available products. Some of the building designparameters were assumed to remain the same during the simulations andsome were changed. The parameters that were kept the same were:

the shape of the building the roof, ground floor, interior wall and intermediate floor construc-

tion external obstructions to the building infiltration and exfiltration of the building envelope

Parameters that varied during the simulations were: building orientation office layout (cell type and open plan type) internal loads (number of occupants and equipment) occupancy proportion of the glazed faade area (30%, 60% and 100% glazing) glazing and frame type shading devices (type and position) thermal transmittance of the faade elements

heat recovery efficiency specific fan power control set points (temperature, lighting) HVAC installations


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Heat Recovery Efficiency (or Heat Recovery Effectiveness): The propor-tion of heat recovered from otherwise waste heat passing through a heatrecovery system. Normally it is expressed as a percentage (Limb, 1992).

Humidity, absolute (dv): The ratio of the mass of water vapour to thetotal volume of the sample.

Humidity, relative (): The ratio of the mole fraction of water vapour ina given moist air sample to the mole fraction in an air sample saturated atthe same temperature and pressure.

Indoor Climate (or Indoor Environment): The synthesis of day to dayvalues of physical variables in a building e.g. temperature, humidity, airmovement and air quality, etc, which affect the health and/or the comfortof occupants (Limb, 1992).

Illuminance (E): Expresses the amount of luminous flux that arrives at asurface and is measured in lux.

Illuminance and luminance distribution: A measure of the light varia-tion from a point to another point across a plane or a surface.

Luminance: Expresses the light reflected off a surface and is measuredin lumens per square meter per steradian or in candelas per square meter

(cd/m). In a way the luminance is directly related to the perceived bright-ness of a surface in a given direction.

Luminous Efficacy: Refers to the ratio of total luminous flux emittedby a lamp to the energy used. It is expressed in lumens per watt (lm/W).According to Erhorn and Stoffel (1996),

systemlightingofpowertotal

spaceconsideredofareaflooreilluminancsurfacedesiredn

= (lm/W)

Mechanical Ventilation: Ventilation by means of one or more fans (Limb,1992).

Multizone: A building or part of a building that comprises a number ofzones or cells (Limb, 1992).

Natural Ventilation: The movement of outdoor air into a space throughintentionally provided openings such as windows and doors, or throughnon powered ventilators or by infiltration (Limb, 1992).


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Temperature, Dry Bulb: The air temperature indicated by a dry tempera-ture sensing element (such as the bulb of a mercury in glass thermometer)shielded from the effects of radiation (Limb, 1992).

Temperature, Effective (eff): The temperature of a still, saturatedatmosphere that would produce the same effect as the atmosphere inquestion.

Temperature, Environmental: The temperature of the air outside a roomor zone (Limb, 1992).

Temperature, Operative (op): The operative temperature empiricallycombines the dry bulb and the mean radiant temperatures. The operativetemperature is the temperature at which a person emits the same heat

output as before, but when air temperature (a) = radiant temperature(r) = operative temperature (op). op does not have the same value forall the parts of the room (when the weighting method is used) (Peterson,1991).

Temperature, Directed Operative: It is calculated in the same way as theoperative temperature, the only difference being that the weighting is doneonly for the point where the occupant is placed and towards the surfaceof interest as shown in Figure 2.6, Subsection 2.3.2.2.

Temperature, Radiant (or Surface) (r): Radiant or surface temperatureis the temperature of an exposed surface in the environment. The tem-peratures of individual surfaces are usually combined into a mean radianttemperature.

Temperature, Resultant: It is similar to the effective temperature but itincludes humidity effects.

Temperature, Wet Bulb: The air temperature indicated by a sensingelement kept wet (usually by a wick), the indicated temperature thus

being related to the rate of evaporation from the wetted bulb. This wetbulb temperature is used by psychrometers to measure relative humidity(Limb, 1992).

Thermal Comfort: A condition of satisfaction expressed by occupantswithin a building regarding their thermal environment. Since the thermalcomfort condition is a subjective feeling of satisfaction, building designersattempt to satisfy as many of the occupants as possible (usually 80% ormore) (Limb, 1992).


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Background

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Building Environment

Indoorenvironment

Architecturalquality

Costs

Energyperformance

Bui lding T echnology

Integration ofpassive systems

Integration ofactive systems

Buildingsimulationsoftware

Output

Input

Environmentalperformance

Figure 2.1 The building system.

The design team should take into account the design constraints at anearly stage of the decision making process, in order to achieve an overallapproach and more accurate predictions. Thereby, unpleasant surprisesresulting in an increase in the buildings life cycle cost and/or impairmentof its performance as to energy use and indoor climate can be avoided.These constraints (stated as input in Figure 2.1) are:

Climate (solar radiation, outdoor temperature, etc) Site and obstructions of the building (latitude, local daylight availabil-

ity, atmospheric conditions, exterior obstructions, ground reflectance,etc)

Use of the building (operating hours, occupant density, schedule andactivity, etc)

Building and Design Regulations

It is obvious that optimum building design (maximization of the output)can not be achieved, since the overall goodness can be defined in differentways depending both on the design constraints and on the way that the

design team prioritises its goals and needs (Andersen, 2000). In sustainable


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T hermalC omfort

PrimaryFactors SecondaryFactors

Figure 2.4 Main aspects of thermal comfort.

2.3.2.2 Conditions of thermal comfort

As outlined above, the factors influencing thermal comfort are dividedinto primary and secondary ones. The primary factors are shown in Figure

2.5:

PrimaryFactors

T emperatureand radiation

(dry bulb, meanradiant)

O perativeand resultanttemperatures

Relativehumidity

Air speed andturbulence

Clothing Perceptionof thermalcomfort

Figure 2.5 Primary factors of thermal comfort.

Temperature and radiation (dry bulb, mean radiant): The thermalsensation is dominated by the surrounding temperature. However,the standard dry bulb temperature is not always a sufficient indicatorfor establishing a good indoor thermal environment, since it does nottake into account the influence of radiant energy. The mean radianttemperature, however, is a more appropriate thermal comfort indica-tor, since it is a measure of the average radiation exchange between the

occupant and the surrounding surfaces.

Operative and resultant temperatures: The operative and mean re-sultant temperatures empirically combine the dry bulb and the meanradiant temperatures. The operative temperature is the temperatureat which a person emits the same heat output as before, but when airtemperature (a) = radiant temperature (r) = operative temperature(op) (Peterson, 1991). The op does not have the same value for allthe parts of the room (when the weighting method is used).


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Figure 2.10 Correlation between air temperature and the number of accidents,

productivity of manual work, finger dexterity, number of breaks, andmental performance (reference: Wyon, 1986).

It is obvious that it is not always easy to evaluate and improve the thermalconditions in order to increase the comfort and productivity of the oc-cupants. Advanced computer simulation programs often predict

operative temperatures temperature swings relative humidity and air velocity

in a building with predictable occupants. However, the behaviour andadaptability of occupants in reality are far harder to predict. A quite prac-

tical approach in order to ensure acceptable indoor thermal environmentcould be to ensure that the air temperature and the cold draught fromwindows stay within acceptable limits.


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2.4.2 Single skin faades

Nowadays, there is a growing interest in using highly glazed facades in

commercial buildings. The trend of covering large portions of the faadeor even the entire faade by glass has its origin in Europe and is expandingto other regions. As with many other architectural trends, understandingand improving the building performance of highly glazed buildings is veryimportant. Prior simulation studies have shown that it should be technicallypossible to produce an allglass faade with sufficient energy and indoorclimate performance although it is not a simple challenge (Lee, et al., 2002).This Subsection gives a brief background to the problems often met andthe solutions given, in order to improve the buildings performance.

When glazed faades are designed, several devices are often imple-

mented, in order to keep the heat losses low and to avoid undesired heatgains through solar radiation (during summer). According to Compagno(2002) the two main criteria when designing a fully glazed faade are thenumber of glazing skins incorporated in the design (single or multipleskin faades) and the positioning of shading devices.

2.4.2.1 Glazing

In energy efficient design the proper selection of glazing elements is prob-

ably the most complex task. Glazing and window design are two areas inwhich great technical developments have occurred over the last years. Inorder to achieve good window design, it is essential to find the balancebetween demands which are often conflicting such as passive heating andcooling functions, e.g. allow solar gains but avoid excessive solar heat,provide sufficient daylight without causing glare, allow controllable ven-tilation into the building but keep out the noise, allow visual contact withthe surroundings but ensure acceptable privacy levels (A Green Vitruvious,1999). This Subchapter focuses on the thermal insulation that glazing canprovide and suggests a number of ways to decrease heat loss through it.

Single glazing provides relatively little resistance to loss of heat, since theglass is a poor insulator. To decrease the thermal transmittance, a secondpane of glass separated from the first pane by an air space can be added.This layer of enclosed air provides extra thermal resistance to long waveradiation exchange.

The incorporation of an air space provides several opportunities forincreasing the thermal resistance of glazing:

increasing the width of the air space: by increasing the width of the

air space, extra resistance is provided. There is a limit due to convec-


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Background

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2.4.3 Double skin faades

2.4.3.1 General

The double skin faade is a system consisting of two glass skins (single ordouble) placed in such a way that air flows in the intermediate cavity. Thedistance between the skins usually varies from 0.2 m up to 2 m. For protec-tion and heat extraction reasons the solar shading devices are placed insidethe cavity. The ventilation of the cavity can be natural, fan supported ormechanical; the origin and destination of the air can also vary dependingon the location, the use and HVAC strategy of the building.

The advantages of double skin faades compared with single skinfacades are improved acoustic insulation, protection of shading devices

and provision of natural ventilation in the office spaces. However, energyreduction and provision of an improved indoor thermal environment canalso be achieved, when these are designed and integrated properly. Dueto the additional skin, a thermal buffer zone is formed which reduces theheat losses and enables passive solar gains. During the heating period, thesolar preheated air can be introduced inside the building providing naturalventilation with a good indoor climate retained. On the other hand, duringthe summer overheating problems are often referred to when the faadeis poorly ventilated (Poirazis, 2004). Different configurations can resultin different ways of using the faade, proving the flexibility of the systemand its adaptability to different climates and locations.

A detailed description of this system can be found in the Literaturereview for Double skin faades for office buildings by Poirazis (2004).

2.4.3.2 Classification of double skin faades

The most common way to categorize the system is according to the type(geometry) of the cavity, as described below.

Multi storey: In this case no horizontal or vertical partitioning existsbetween the two skins. The air cavity ventilation is provided vialarge openings at the bottom and top of the cavity.

Corridor: The cavity is partitioned horizontally for acoustical, firesecurity or ventilation reasons.

Box window: In this case horizontal and vertical partitioning dividesthe faade into smaller and independent boxes.

Shaft box: In this case a set of box window elements are placed inthe faade. These elements are connected via vertical shafts situated

in the faade. These shafts ensure an increased stack effect.


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Background

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Acoustic insulation: In the view of some authors sound insulation can beone of the most important reasons to use a double skin faade. Reducedinternal noise levels inside an office building can be achieved by reducing

both the transmission from room to room (internal noise pollution) andthe transmission from outdoor sources i.e. heavy traffic (external noisepollution). The type of double skin faade and the number of openingscan be really critical for sound insulation concerning the internal and theexternal noise pollution.

Thermal insulation: During the winter, the external additional skin pro-vides improved insulation by increasing the external heat transfer resistance.The reduced air flow and the increased temperature of the air inside thecavity lower the heat transfer rate on the surface of the glass,which leadsto reduction of heat losses.

During the summer, the warm air inside the cavity can be extractedby mechanical, fan supported or natural ventilation. Certain faade typescan cause overheating problems. However, a completely openable outerlayer can solve the overheating problem during the summer months, butwill certainly increase the construction cost.

Night time ventilation: During the hot summer days, when the externaltemperature is higher than 26C, the interior spaces may easily become

overheated. In this case, it may be energy saving to pre-cool the officesduring the night using natural ventilation. In this case, the indoor tem-peratures will be lower during the early morning hours, providing thermalcomfort and improved air quality for the occupants.

Energy savings and reduced environmental impacts: In principle, doubleskin faades can save energy when properly designed. Often, when theconventional insulation of the exterior wall is poor, the savings that canbe obtained with the additional skin may seem impressive.

Better protection of the shading or lighting devices: Since the shadingor lighting devices are placed inside the intermediate cavity of the doubleskin faades, they are protected from both the wind and rain.

Reduction of the wind pressure effects: The double skin faades aroundhigh rise buildings can serve to reduce the effects of wind pressure.

Transparency Architectural design: In almost all the literature, refe-rence is made to the desire of architects to use bigger proportions of glazedsurfaces.


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3 State of the art

3.1 Glazed office buildings in Nordicclimates

Subchapter 3.1 is based on personal communication with ke Blom-

sterberg at the Division of Energy and Building design, Department ofArchitecture and Built Environment, Lund University.

3.1.1 General

The office buildings as known today are likely to retain their validity inthe foreseeable future. Although there has been, and still is, a dramaticdevelopment of the infrastructure for communications (mobile phones,laptops, e-mails, etc.), the change in office practice is far less dramatic

(Kleibrink, 2002). Nowadays, the exchange of information between andwithin organizations is very often achieved by e-mail and the activitiesare increasingly dominated by discussions and flow of information atall levels. High interaction levels may however lead to reduced occupantproductivity, due to acoustic disturbance. The increase in teamwork andcommunication, however, can lead to activities and persons disturbingeach other, especially if the spatial organisation is not appropriate. Theplan of an office environment establishes the privacy (both acoustic andvisual) level at which the office functions. Therefore, it is still necessaryto perform concentrated individual work in undisturbed surroundings.Modern office work is characterized by quick changes between these twotypes of activity, so the challenge today is to provide for a combinationof individual work and teamwork, while also providing for flexibility forunforeseen developments.

Moreover, in new constructions the conventional envelope of officebuildings tends to be replaced by a highly glazed one that can lead toa pleasant visual indoor environment. The recent trend of transparentbuildings is often initiated by architects, in order to provide more day-light and view to the occupants. Depending on the task of the occupants

this can increase their productivity (as stated in the Sustainable Building


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Functional efficiency: the working space should meet physiologicalrequirements, ergonomic standards and statutory requirements, inorder to support optimal working conditions.

Contact quality: the working spaces should contribute to the transpar-

ency of the activities, carried out in the office and encourage commu-nication and synergetic effects between employees and departments

Corporate culture: the message conveyed by the working spaces shouldpromote the employees identification with the company and its pro-ducts and communicate company values internally and externally.

Typical depths for office buildings are

12 to 13 metres for a cell-type office 13. 5 to 15.5 metres for a combination office

3.1.3 Office buildings in Sweden

Office buildings account for a significant proportion of the floor area innon-industrial buildings in Sweden. The total floor area in office build-ings is approximately 30 million m2 (usable area to let) (SCB, 2001). Thecompleted floor area is almost evenly distributed over the decades, but withless construction during the last decade (as shown in Table 3.1).

Table 3.1 Floor area, millions m2, broken down by year of completion(SCB, 2001).

Year -1940 1941-1960 1961-1970 1971-1980 1981-1991 1991- Sum

Floor area 7,1 4,6 4,9 5,4 5,4 2,8 30,2

Most (65%) of the existing office buildings are rather small, between 200and 1000 m2. Many office buildings are between 1000 and 5000 m2 and

some are bigger than 20 000 m2 (see Table 3.2).

Table 3.2 Number of office buildings within a certain range of floor area,m2 (SCB, 2001).

Floor area (m2) 200-999 1000-4999 5000-19999 20000- Sum

Number of buildings 11 505 4 719 1 415 170 17 809


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Table 3.5 Average energy use for space heating, district cooling and electric-ity for cooling in Swedish office buildings (SCB, 2001).

Year of -1940 1941-1960 1961-1970 1971-1980 1981-1991 1991- Averagecompletion

Use of district 146 143 156 127 114 127 135heatingkWh/m2a

An analysis of energy use for heating and use of electricity in premisesshowed that the heating energy use has been reduced, while the total use ofelectricity has increased, during the last decades (Energiboken, 1995). The

reduction in heating energy use is due to the improved thermal insulation(lower thermal transmittance) and introduction of heat recovery on theexhaust air flow, required by the building regulations. New premises have alower total use of energy than older ones, but a higher share of use of elec-tricity (see Figure 3.1). In new office buildings, i.e. those built after 1980,the use of electricity often accounts for 70% of the use of energy (Nilson,1996). The previous building regulations, before 2006, did not have anyreal requirement for the use of electricity or the total energy use.

0

20

40

60

80

100

120

140

160

180

200

220

240

260

280

0 10 20 30 40 50 60 70 80 90 100 110 120 130

Electricity (kWh/am)

Hea

ting

(kWh/am

)

Typical office buildings Refurbished office buildings New office buildings

1970

1990

1980

Figure 3.1 Relation between use of energy for space heating and use of electric-ity in Swedish office buildings, as a function of year of completion(Energiboken, 1995).


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ties the air is brought into the cavity and exhausted by two means: windpressure and/or the stack effect. According to the author the wind effect isdominant all the year round. As the author mentions, natural ventilationsystems in urban environments may also experience significant problems of

noise transmission and pollution and may result in uncomfortable indoorenvironments in extreme weather conditions.

The mechanically ventilated double skin faades often use an underflooror overhead ventilation system in the building to supply or exhaust thecavity air to ensure good distribution of the fresh air. In this case the airis forced into the cavity by mechanical means. This air rises and removesheat from the cavity and continues upwards to be expelled or re-circulated.The mechanically assisted ventilation systems allow the building to besealed, thereby providing more protection from traffic noise than naturally

ventilated systems. In areas with severe weather conditions or poor airquality, the mechanically assisted ventilation system can keep conditionsin the buffer zone nearly constant to reduce the influence of the outdoorair to the indoor environment.

If the airflow in the DSF cavity is mechanically driven, the amount ofair passing the cavity is known; in the case of a naturally ventilated cav-ity, however, it is necessary that the flow is calculated. In addition, theairflow in the cavity can be limited to maintain the necessary airflow ratein the room. Knowledge of air temperature in the double faade cavityis essential if one wants to maintain a comfortable indoor environment,

especially when the cavity air is directly used for ventilation indoors. Theair temperature and the airflow in the cavity are interrelated parametersand one can not be estimated properly without the other. Knowledge ofthe flow regime is also essential for prediction of the air temperature andair flow.

3.2.1.2 Modelling approaches

This part is based on the DSF Modelling Approaches subchapter of the

Literature review written by Poirazis (2006).Nowadays, building simulation software and developed mathematical

models vary over a wide range of complexity. The simplest model is de-scribed by a few equations and the most complex one is the CFD modelsolving the conservation equations for mass, momentum and thermalenergy.

According to Champagne (2002), in the HVAC field there is a needto validate a proposed design to ensure proper performance. The twomethods typically used are experimental or numerical. According to the

author the experimental values are very reliable, when performed in a


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controlled environment; however, there are several major drawbacks tothis approach since, for instance, it is expensive and time consuming.Numerical approaches such as computational fluid dynamics (CFD) areinformative and when applicable can also save time and money.

At the same time, Hensen (2002) categorizes building simulation ap-proaches by level of resolution into macroscopic and microscopic. Accord-ing to the author the macroscopic approaches deal with entire buildingsystems, indoor and outdoor conditions over some periods, while micro-scopic approaches use much smaller spatial and time scales. The buildingsimulation software is normally related to the macroscopic approaches,while the CFD has the microscopic technique which is usually restrictedto the steady state condition. The macroscopic (network) method is moresuitable for the time series considerations.

Another direction is taken by Djunaedy, et al. (2002), which categorizesthe main air flow modelling levels of resolution and complexity as:

Building Energy Balance (BEB) models that basically rely on airflowguesstimates.

Zonal Airflow Network (AFN) models that are based on (macro-scopic) zone mass balance and inter-zone flow pressure relationships;typically for a whole building.

CFD that is based on energy, mass and momentum conservationin all (minuscule) cells that make up the flow domain; typically a

single building zone.

Hensen, et al. (2002), explain that although airflow is obviously an im-portant issue for building performance assessment, the development ofits treatment in modelling methods often lags behind the treatment ap-plied to the other important issues, such as energy flow paths. Nowadaysemphasis has been given to airflow simulations which mostly focus on thefollowing two approaches:

Computational Fluid Dynamics (CFD) based on conservation

equations for mass, momentum and thermal energy for all nodes ofa two- or three-dimensional grid inside or around the object underinvestigation. The CFD approach is applicable to any thermo fluidphenomenon; however, in building physics applications, there areseveral problematic issues, such as the amount of necessary comput-ing power, the nature of the flow fields and the occupant-dependentboundary conditions. This has often led to CFD applications beingrestricted to steady-state cases or very short simulation periods.

The network method, in which a building is treated as a network of

nodes representing rooms, parts of rooms and system components,


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with inter-nodal connections. According to the authors, the as-sumption is made that for each type of connection there exists anunambiguous relationship between the flow through the componentand the pressure difference across it. Conservation of mass for the

flows into and out of each node leads to a set of simultaneous, non-linear equations, which can be integrated over time to characterizethe flow domain.

The position of Park, et al. (2003), Gertis (1999), Hensen, et al. (2002),and the work of many other researchers indicates that it is very difficult tofind a simple model that would describe the DSF performance appropri-ately. As explained in Hensen, et al. (2002) predicting the performance of adouble skin faade can be quite difficult, since highly transient parameters

such as cavity temperature, ambient temperature, wind velocity and di-rection, transmitted and absorbed solar radiation and angles of incidencegovern the main driving forces.

Manz and Frank (2005), point out that the thermal design of buildingswith the DSF type of envelope remains a challenging task. As yet, there isno software tool that can accommodate all the following three modellinglevels: optics of layer sequence, thermodynamics and fluid dynamics ofDSF and building energy system. The complexity of the prediction task isthe main reason for the long lasting research and application of simplify-ing techniques. The iterative approach of the network method became the

reason to distinguish the three main issues in the DSF modelling:

Optical element responsible for the optical properties of the DSFmaterials

Heat transfer element responsible for the heat transfer processesin the DSF

Flow element responsible for the motion of the fluid in theDSF

In various network methods these elements are defined differently in terms

of nomenclature. In some methods they even stay undefined. The elements(the physical processes behind them) influence each other and, as has beenargued, together they govern the main heat and mass transfer processes inthe DSF. Several researchers (Saelens, Faggembauu, van Paassen, Di Maio,Manz and others) suggested the separation of the flow element and theheat transfer element in the predictions, which makes for better accuracyof wind influence predictions and advanced calculations of the convectiveand radiative heat transfer (Saelens, 2002).

Saelens (2002), performed an investigation of an accuracy change with

stepwise enhancement of the network model. The diagram, depicted in


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Ventilated Active Envelopes (2001), the driving forces are usually small andbecause of the high flow resistance of the orifice, the flow in the cavity would betoo much affected. Furthermore, it would be difficult to find a suitable placefor the orifice as no exhaust duct is available.

Saelens (2001) after studying reports of Park et al. (1989) and Faist(1998), described a second method to estimate the airflow rate by meas-uring the air velocity with anemometers. The author concluded thatthe determination of the airflow rate from velocity measurements seemsobvious, but is likely to produce erroneous results, since the velocity in anaturally ventilated channel is not uniform and is influenced by loweringor raising the shading device. Furthermore, according to the author, thereis no guarantee that the resulting velocity vector is perpendicular to thereference surface. Detailed information about the velocity vectors may be

obtained by placing an array of individual velocity measuring points, whichmay however affect the development of the airflow in the cavity. Hence,determining the airflow rate in naturally ventilated active envelopes frommeasured velocities is a less recommendable method.

A third, less common method, is the use of tracer gas measurements(Ziller (1999); Busselen and Mattelaer (2000)). Tracer gas techniques such asthe constant concentration, constant emission and tracer dilution method(Raatschen, 1995 and ASHRAE, 1997) make it possible to determine theairflow rate in both naturally and mechanically ventilated active envelopeswithout interfering with the driving forces.

In Modelling of air and heat transport in active envelopes, Saelens,Carmeliet and Hens (2001) compare (using measurements) five models,of varying complexity, of a mechanically ventilated active envelope. Theauthors claim that radiation and convection in the cavity have to bemodelled separately in order to obtain reliable results. According to theauthors, for an accurate prediction of active envelope performances, thevertical temperature profile has to be implemented properly (e.g. by anexponential expression). A sensitivity study performed with the numericalmodel reveals that the air temperature at the inlet of the cavity, the airflow

rate, the distribution of the airflow in the cavity and the angle of solarincidence are the governing parameters.Saelens (2002) describes in his thesis measurements carried out at the

Vliet test building (two one storey high multiple-skin faades and a tradi-tional envelope).According to the author there are two main aims of themeasurements: (a) the measurement set-up is used to extend knowledgeof the thermal behaviour of multiple skin faades and (b) the data is usedto evaluate modelling assumptions and to derive and check relationshipsfor modelling parameters.

The author compares different models for the convective heat transfer

coefficient with the measurements. Additionally, the measurements are


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used to evaluate the numerical model and to assess the reliability of modelswith different levels of complexity. Finally, the data are used to assess howthe inlet temperature should be determined.

Shiou Li in 2001 wrote an MSc thesis which proposes a protocol for

experimentally determining the performance of a south facing doubleglazed envelope system. The protocol was applied to an experimentalstudy of a south-facing, single story double glazed ventilated system. Inorder to achieve that, two modular full-scale double glazed window modelswith naturally or mechanically assisted ventilation were constructed andmonitored. The main goal was to develop and apply the test protocol bymonitoring and analyzing the thermal performance of double faades. Byusing this test protocol the author claims average cavity heat removal rateapproximately 25% higher for the active system when compared to the

naturally ventilated one. Also, the passive system has a higher temperaturedifference between the indoor glass surface and the indoor air than theactive system.

3.2.2 Integration of double skin faades

The integration of the double skin faade systems in office buildings iscrucial for thermal performance and energy use during the occupationphase. Stec & Paasen (2003) presented a paper in which they describe

different HVAC strategies for different double skin faade types. Accord-ing to the authors, the integration procedure of double skin faades inthe building should include (a) defining the functions of the double skinfaade in the building, (b) selecting the type of the double skin faade,its components, materials and dimensions of the faade that fulfil therequirements, (c) optimizing the design of the HVAC system to coupleit with the double skin faade, and (d) selecting the control strategy tosupervise the whole system.

The authors briefly introduce the concept of different cavity depths anddescribe its influence on the air temperatures inside the cavity. According

to them, the dimensions of the faade together with the openings deter-mine the flow through the faade; narrower cavities result in higher flowresistance and smaller flow through the cavity and a higher increase in airtemperature in the cavity. The authors conclude that (a) in the cold periodit is more suitable to use narrow cavities to limit the flow and increasethe cavity temperature and (b) in the hot period the double skin faadeshould work as a screen for the heat gains from radiation and conduction.It is difficult to claim in general whether the narrow or deep cavities willperform better because in one case the cavity temperature and in the other

case the temperature of the blinds will be higher.


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Examples concerning the influence of different depths on the propertiesof the cavity are shown in Second Skin Faade Simulation with SimulinkCode by Di Maio and van Paassen in (2000). In Modelling the Air Infil-trations in the Second Skin Faade in (2001) the same authors conclude

that narrow cavities are more useful, because they can deliver a higher andhotter air flow compared to the air flow delivered by wide ones.

3.2.2.1 Contribution of double skin faades to the HVACstrategy

As Stec et al. (2003) describe, an HVAC system can be used in the follow-ing three ways in a double skin faade office building:

full HVAC system (the double faade is not a part of the HVAC)which can result in high energy use. The user can select wheneverhe/she prefers mechanically controlled conditions inside or naturalventilation with the use of the double skin faade).

limited HVAC system (the double faade contributes partly to theHVAC system or plays the major role in creating the right indoorclimate). In this way the double faade can play the role of:

o pre-heater for the ventilation airo ventilation ducto pre-cooler (mostly for night cooling)

no HVAC. The double faade fulfils all the requirements of anHVAC system. This is the ideal case that can lead to low energyuse.

During the heating periods the outdoor air can be inserted from the lowerpart of the faade and be preheated in the cavity (Figure 3.3). The exterioropenings control the air flow and thus the temperatures. Then, throughthe central ventilation system the air can enter the building at a propertemperature. During the summer, the air can be extracted through the

openings from the upper part of the faade. This strategy is usually appliedto multi storey high double skin faades.


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AHU

Winter Summer

Figure 3.3 Double skin faade as a central direct pre-heater of the supply air.

During the whole year, the double skin faade cavity can work only asan exhaust duct without the possibility of heat recovery for the HVACsystem (Figure 3.4). It can be applied both during winter and summerto the same extent. The main aim of this configuration is to improve theinsulation properties in the winter and to reduce the solar radiation heat

gains during the summer. There are no limitations to individual controlof window opening.

AHU

Winter/Summer

Figure 3.4 Double skin faade as an exhaust duct.


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It is also possible to use the double skin faade as an individual supply ofthe preheated air (Figure 3.5). This strategy can be applied in both themulti-storey and box window types. An exhaust ventilation system im-

proves the flow from the cavity to the room and to the exhaust duct. Extraconditioning of air is needed in every room by means of VRV system orradiators. This solution is not applicable for the summer conditions, sincethe air temperature inside the cavity is higher than the thermal comfortlevels. Also in this case there are no limitations to individual control ofwindow opening.

Box windowMulti-storey

Figure 3.5 Double skin faade as an individual supply of the preheated air.

Finally, the double skin faade cavity can be used as a central exhaust ductfor the ventilation system (Figure 3.6). The air enters through the lower partof the cavity and from each room. The supply ventilation system stimulatesthe flow through the room to the cavity. Heat can be recovered by meansof heat pump or heat regenerator at the top of the cavity. Because the air

in the cavity is not fresh air, the windows cannot be operable.


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the ventilation strategy of the cases studied differs. Provision of naturalventilation in the rooms during spring and autumn months is oftenachieved; in extreme weather conditions solutions were given so as not tocompromise the (thermal) comfort of the occupants. In two of these cases

it was stated that by using the preheating mode of the cavity, the buildingcan be naturally ventilated during long periods of the year (70-75% for theDsseldorf City Gate and 50-60% for the ARAG 2000 Tower). In othercases (e.g. GSW Headquarters) the warm air inside the cavity is returnedto the central plant for heat recovery purposes. Generally, in the mentionedcases the ventilation can be natural, mechanical or even fan supported; insome cases the airflow (and consequently the air temperature) inside thecavity is regulated in such a way that natural ventilation can be sufficientfor long periods during the year.

The depth of the cavity varies in all the cases described above. Thenarrowest cavities are in Galleries Lafayette and Posdamer Platz 1 (approxi-mately 0.2m deep), both located in Germany, while the deeper one is thein the Korona building in Finland (2m). In the examples given the cavitiesin Finland tend to be somewhat deeper although there is not any specificreasoning for that; the opposite could be expected since deeper cavities arerequired in warmer climates for more efficient heat extraction.

A typical construction of a double skin faade in Germany consists ofa single outer and a double inner glazing unit. The outer pane of glassis in most cases an 8 or 12mm toughened pane; usually the glazing is a

clear pane, while in some others (e.g. Victoria Life Insurance Buildings) alaminated solar control glass is used as an outer pane . In some of the casesstudied the outer skin is openable for more efficient heat extraction. Theinner skin is in almost all the cases a low E glazing unit. Similar numbersand types of panes (single outer and double inner with low E skin) areused for the cases in Sweden. In Finland, however, the cases mentioneddiffer. In some cases the construction is similar to that in Germany (singleouter and double inner skin; e.g. Martela, Itmerentori, Nokia Ruoholahti,Nokia K2, etc). In some other cases the number of panes in the inner and

outer skin is larger. For example, the faade of the Sanomatalo buildingconsists of a triple pane inner skin (toughened 6mm inner, toughened 4mm intermediate and solar control 6mm outer) and a double pane outerone (toughened and laminated 6+6 mm panes); the construction of theSonera faade is similar (triple inner and double outer). The faade of theJOT Automation Group building consists of a triple inner envelope (6mm solar control glass (outer), 4 mm clear glass (middle), 4 mm clear glass(inner)) and a single outer one (10 mm tempered, green solar protectiveglass pane); the construction of the Radiolinja faade is similar (tripleinner and single outer). Unfortunately, values such as thermal and solar


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transmittance of the inner or outer skin for the faades mentioned abovecould not be found in the literature.

In almost all the cases (regardless of country or construction) the shad-ing devices, usually venetian blinds, are placed inside the ventilated cavity

(in most cases closer to the outer skin).From the constructions studied it appears that it is hard to describe a

typical double skin faade construction when performance evaluation foreach building is not accessible. The faade constructions described above(and in more detail in the literature review report Double Skin Faadesfor Office Buildings by Poirazis (2004)), can however be considered agood starting point for analyzing the tendencies, when deciding the casesto be simulated in this thesis.

3.3 Building simulation softwareThe use of simulation tools during the design stage can help the designerimprove the overall building performance. The system building instal-lations can be optimised with regard to indoor climate and energy use.Different alternatives can be studied, compared and optimized in termsof energy use and indoor environment at a low cost (avoiding full scaleexperiments), since the performance can be analysed and predicted at anearly stage. The simulations can also be used to predict the energy use

and indoor climate of an existing building (in the case of a refurbishmentproject).According to Jacobs and Henderson (2002) the building simulation

software can be divided into the following categories:

Practitioner Design Tools: Software used by architects, engineers, andother practitioners to automate common tasks that are part of the day-to-day design process (often integrated into CAD environments).

Whole Building Energy Analysis Tools: Software that predict annual

energy use (and often operating costs) by simulating operating condi-tions. These detailed hour-by-hour building simulation tools are usedby some practitioners as part of the design process and for energy codecompliance.

Energy and Environmental Screening Tools: Software focusing onthe economic and environmental impacts of using new energy-efficienttechnologies in buildings.

Specialized Analysis Tools: Software used most often for research pur-

poses and include technically accurate simulation models; they are often


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developed for academic study of a building science problem. These toolsfocus on building or system performance details.

3.3.1 Building energy simulation toolsOver the last 50 years a great number of dynamic Building Energy Analysistools has been developed. These tools provide the user with indicators es-sential for the building performance such as energy use, temperature andcosts. Below, some of these tools that were considered during the earlystage of the Glazed Office Buildings project are presented and brieflydescribed. This description is based on the report Constructing the Ca-pabilities of Building Energy Performance Simulation Programs writtenby Crawley, Hand, Kummert and Griffith in 2005.

BLAST: The BLAST program was developed by the USA CERL and theUniversity of Illinois. The BLAST (Building Loads Analysis and SystemThermodynamics) software is a set of programs that aims to predict theenergy consumption, energy system performance and cost of buildings.The tool contains the major subprograms: (a) Space Loads Prediction, (b)Air System Simulation and (c) Central Plant. BLAST can both estimatethe annual energy performance and perform peak load (design day) cal-culations for mechanical equipment design.

BSim 4: BSim 4 was developed by the Danish Building Research Institute(SBI) in 2004. It is a user friendly tool used for energy design of buildingsand moisture analysis. The tool comprises several modules: (a) tsbi 5: acombined transient thermal and transient indoor humidity and surfacehumidity simulation module, (b) SimView: graphic model editor andinput generator, (c) SimLight: tool for daylight analysis conditions insimple zones, (d) XSun: graphical tool for analysis of direct sunlight andshadowing, (e) SimPV: a simple tool for calculating electrical yield fromPV systems, (f) NatVent: a simple tool for one zone natural ventilation

and (g) SimDxf: a simple tool for importing CAD drawings.DEROB-LTH: DEROB-LTH was originally developed at the Numeri-cal Simulation Laboratory, University of Texas, Austin, USA. Since thebeginning of the 1980, the program has been further developed at LundUniversity, under the name DEROB-LTH. Building energy simulation toolused to explore the complex dynamic behaviour of buildings for differentdesigns. The behaviour is expressed in terms of temperatures, heating andcooling loads and different comfort indices. The form of the building canbe modelled in a flexible way. The model for assessing the solar insulation

of building surfaces is detailed and includes the influence of different types


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of shading devices. The window model has been improved and accuratelycalculates the properties of a window package. The simulation uses a timestep of one hour and calculates values in response to hourly values forclimatic data, internal loads and airflows. DEROB-LTH is very good at

calculating the energy balance regarding solar energy, taking into accounttransmittance, absorptance, and reflectance in and out from a volume (andto adjacent volumes).

DOE-2.1E: DOE-2 was developed by Lawrence Berkeley National Labora-tory. The DOE-2.1E software has been widely used for the past 25 yearsto predict the hourly energy use and energy cost of buildings. The toolconsists of one module for translation of input (BDL processor) and foursimulation subprograms (LOADS, SYSTEMS, PLANT and ECON). The

LOAD subprogram calculates the sensible and latent components of thehourly or cooling load for each constant temperature space, taking intoaccount weather and building use patterns. The output of LOADS is theinput for SYSTEMS, which handles the secondary systems (calculates theperformance of fans, coils and ducts). The output of SYSTEMS is airflowand coil loads. PLANT calculates the behaviour of boilers, chillers, coolingtowers, etc, according to the secondary systems cooling and heating loads.Finally the ECONOMICS subprogram calculates the cost of energy.

ECOTECT: ECOTECT is a highly visual and interactive building design

and analysis tool, covering thermal, energy, lighting, shading, acoustics andcost aspects, developed by Square One. The main aim of the tool is to allowdesigners to take a holistic approach to the building design (rather thansizing a HVAC system), by providing continuous interactive and visualfeedback. The software is entirely designed and written by architects andis intended mainly for use by architects.

EnergyPlus (Version 1.2.2): EnergyPlus is a tool based on the mostpopular features and capabilities of BLAST and DOE-2.1E which aimsto provide an integrated (simultaneous loads and systems) simulation for

accurate energy, temperature and comfort predictions. The EnergyPlusmodule calculates the system response of heating and cooling systems (withvariable time step) providing more accurate space temperature prediction,crucial for system and plant sizing, occupant comfort and occupant healthcalculations. EnergyPlus has two basic components: (a) a building systemssimulation module and (b) a heat and mass balance simulation module.The building systems simulation manager handles communication betweenthe heat balance engine and various HVAC modules and loops, such ascoils, boilers, chillers, pumps, fans, and other equipment components. The

heat balance module manages the surface and air heat balance modules


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and acts as an interface between the heat balance and the building systemssimulation manager. The heat and mass balance calculations are based onIBLAST (a research version of BLAST).

ESP-r Version 10.1: ESP-r has been under development for more than25 years. It follows the pattern of simulation follows description whereadditional technical domain solvers are invoked as the building and systemdescription evolves. It works with third party tools such as Radiance tosupport higher resolution assessments as well as interacting with supplyand demand matching tools. Although ESP-r has a strong research herit-age (e.g. it supports simultaneous building fabric-network mass flow andCFD domains), it is being used as a consulting tool by architects, engineersand multidisciplinary practices and as the engine for other simulation

environments.IDA ICE Version 3.0: IDA Indoor Climate and Energy (IDA ICE 3.0) isa building energy simulation program for the simulation of energy use forheating, cooling, lighting etc., thermal comfort and indoor air quality inbuildings. The tool is a multi-zone dynamic energy simulation program,which in a detailed manner takes into account HVAC equipment, whichis simulated as well. The tool is based on a general simulation platformfor modular systems, IDA ICE 3.0 Simulation Environment. In IDA ICE3.0, physical systems from several domains are described using symbolic

equations, stated in either or both of the simulation languages NeutralModel Format (NMF) and Modelica. The user defines the tolerance controlsolution accuracy, allowing complete isolation of numerical errors frommodelling approximations.IDA ICE 3.0 offers 4 types of interfaces for different user categories:

Wizard level: leading the user through the steps of building a modelfor a specific type of study.

Standard level: the user is expected to formulate a model usingdomain specific concepts and objects (zones, radiators, windows,etc).

Advanced level interface: the user is able to browse and edit themathematical model of the system.

NMF and or Modelica programming: for developers.

It can be used to provide an integrated (simultaneous loads and systems)simulation for accurate energy, temperature and comfort predictions.

PowerDomus Version 1.5: PowerDomus is a whole building simulationtool for thermal comfort and energy use analysis. The tool visualizes the


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solar path and inter-building shading effects and provides reports withgraphical results of zone temperature and relative humidity, PMV and PPD,thermal loads statistics, temperature and moisture content within user-selectable walls-roofs, surface vapour fluxes and daily-integrated moisture

sorption-desorption capacity. PowerDomus is a user friendly software thathas the aim of being used by a large number of users.

Tas Version 9.0.7: Tas is a software that simulates the dynamic thermalperformance of buildings and their systems using different modules. Thecore module is the Tas Building Designer, a dynamic building simulationtool with integrated natural and forced airflow. The module has a 3Dgraphics based geometry input that includes a CAD link. Tas has beenused for over 20 years in the UK and around the world. It has a reputa-

tion for robustness, accuracy and a comprehensive range of capabilities.Developments are regularly tested against ASHRAE, CIBSE and ISO/CENstandards.

TRNSYS Version 16.0.37: TRNSYS is a software with a modular structurethat was designed to solve complex energy system problems by breakingthe problem down into a series of smaller components. The componentscan be simple (such as a pump or pipe) or more complicated (such as amulti-zone building model). These components are configured and assem-bled using the TRNSYS simulation studio integrated visual interface, and

the building input data is entered through the visual interface TRNBuild.The simulation engine then solves the system of algebraic and differentialequations that represent the whole system. The time steps usually consid-ered by the program are 1 hour or 15 min but can also achieve 0.1sec timesteps. Apart from the detailed multizone building model, the library ofTRNSYS includes components commonly found in thermal and electricalenergy systems (such as solar thermal and photovoltaic systems, low energybuildings and HVAC systems, renewable energy systems, etc).

TRNSYS, DOE 2.1E, IDA ICE 3.0, and ESP-r were validated within IEA

Task 22 (Building Energy Analysis Tools). The test cases developed for theRADTEST (Radiant Heating and Cooling Test Cases byAchermann andZweifel, 2003) were based on the ENVELOPE BEST TEST from IEATask 12 (Judkoff and Neymark, 1995). TRNSYS, DOE 2.1E, IDA ICE3.0 were empirically validated by Travesi, Maxwell, Klaassen, and Holtz(2001), as described in the IEA report Empirical Validation of IowaEnergy Resource Station Building Energy Analysis Simulation Models.DOE 2.1 D, BLAST 3.0, ESP and TRNSYS have been validated by theInternational Energy Agency Building Energy Simulation Test (BESTEST)

and Diagnostic Method (Judkoff and Neymark, 1995).


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3.3.2 Software for DSF modelling

In this part a description is given of the available software for double

skin faades based on the report Ventilated double faades written byFlamant, et al. (2004). The authors distinguish these tools into: (a) com-ponent simulation software and (b) building simulation software. Thecomponent simulation software simulate the thermal, energetic and visualbehaviour and performance of the faade component while the buildingsimulation software simulate the whole building (faade included) inorder to predict the thermal dynamic behaviour of the building, indoortemperatures, energy use , etc.

3.3.2.1 Faade simulation softwareWIS 3: WIS (Window Information System) is a freeware software devel-oped to calculate the thermal and solar characteristics of window systemsand components. One of the unique elements of this tool is the combina-tion of glazing and shading devices, with the option of free or forced cir-culation between both. This makes the tool suited to calculate the thermaland solar performance of double skin faades. WIS performs calculationof the transfer of short wave radiation for all angles of incidence, but isunable to perform dynamic calculations. It is possible to model natural

convection, caused by stack effect, but wind induced convection is notcovered. The WIS algorithms are based on international standards suchas the ISO Standard 15099.

BISCO/TRISCO/VOLTRA: These tools were developed by Physibeland aim to model heat transfer of building elements. The unique featureof this software group is the potential to perform thermal calculations incombination with thermal bridging effect with the components. In greaterdetail, BISCO calculates two dimensional steady state heat transfer inobjects with any shape. TRISCO performs the same kind of calculation

but for three dimensional objects, while VOLTRA is an extension for timedependent boundary conditions of the steady state TRISCO. It is possibleto model forced ventilation (ventilation fluxes should be defined a priori),but not natural ventilation. Control system and building modelling arenot considered in the tool. These three software tools can calculate bothtemperature distribution along the cavity and heat loss.


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ReferenceBuilding

(SS-30%)

CellType

SS-30%-Cell

OpenPlanType

SS-30%-O

en

North-South

SS-30%-O

en-NS

North-South

SS-30%-Cell-NS

North-South45

SS-

30%-Cell-NS45

East-West

(SS-30%-Cell-EW)

North-South45

SS-30%-O

en-NS45

East-West

SS-30%-O

en-EW

StrictControl

(SS-30%-Cell-

NS-strict)

NormalControl

(SS-30%-Cell-NS

-

normal)

Poorcontrol

(SS-30%-Cell-

NS-poor)

StrictControl

(SS-30%-Cell-

EW-strict)

Norm

alControl

(SS-30%-Cell-EW-

normal)

Po

orcontrol

(SS

-30%-Cell-

EW-poor)

StrictControl

(SS-30%-Cell-

NS45-strict)

NormalControl

(SS-30%-Cell-

NS45-normal)

Poorcontrol

(SS-30%-Cell-

NS45-poor)

StrictControl

(SS-30%-Open-

NS-strict)

NormalControl

(SS-30%-Open-NS-

normal)

Poorcontrol

(SS-30%-

Open-NS-poor)

StrictControl

(SS-30%-Open-

NS45-strict)

NormalControl

(SS-30%-Open-

NS45-normal)

Poorcontrol

(SS-30%-Open-

NS45-poor)

StrictControl

(SS-30%-Open

-

EW-strict)

NormalControl

(S

S-30%-Open-

EW-normal)

Poorcontrol

(SS-30%-Open

-EW-poor)

Figure 4.1 Tree diagram for reference building alternatives (SS=single skin

faade, NS=Nort-South).


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4.1.2 Single skin alternatives (60% and 100%window to external wall area ratios)

Seven alternatives were initially created for the parametric studies with60% and 100% window to external wall area ratios. For these alternativesdifferent window and shading device types and positions were appliedand for each one 3 control set points and 2 plan types were simulated.The 42 (60% glazed) generated alternatives were compared on a build-ing level. The same number of alternatives was simulated for the 100%glazed alternatives and conclusions have been drawn both on building andzone level. A flow chart for the selection of the alternatives, as the firststep of the parametric studys methodology, is set out below (Figure 4.2).Comme

single and double skin glazed ofﬁce buildings

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