20/03/2013 - wag & paws · 20/03/2013 comparative analysis of the optimal void depth of a...

HISTORY

ConduCtionConduCtion oCCurs in situations where a body is heated on one side. as a result the atoms on this side will yield heat Continously to their neighbouring atoms whiCh are Cooler. in situations where the other side is Cooled then no thermal equilibrium Can be aChieved. however, heat will Continue to be transferred from the warmer side to the Cooler one.

ConveCtionConveCtion oCCurs in situations relating to fluids and gases as there is further meChanism for heat transmission. the atoms have the ability to move and as a result Can transfer their heat to other loCations.

radiationradiation is the only possible form of heat transmission through a vaCuum. this radiation is emitted by all atoms with a temperature greater than absoloute zero (-273.15˚C or 0 Kelvin).

Double-sKin FaçaDe thermal PerFormanCein orDer to unDerstanD the FaCtors aFFeCting the thermal PerFormanCe oF a Double-sKin FaçaDe it is neCessary to investigate the prinCiples of heat transfer and fluid meChaniCs.the area oF thermoDynamiCs Known as heat transFer is the FaCtor whiCh Determines anD CharaCterises thermal behaviour anD PerFormanCe. the CalCulation oF heat transFer within a Double-sKin FaçaDe is a ComPlex ProCess as there is a wide range of heat transfer methods oCCurring simultaneously. these methods of heat transfer inClude laminar and turbulent flows, temperature differentiation, density stratifiCations and varying air-veloCities (tasCón & hernanDez., 2008).

dissertation ConCeptFor my teChniCal Dissertation i have DeCiDeD to examine what is the oPtimal voiD DePth oF a Double-sKin FaçaDe in relation to its thermal performanCe in a temperate Climate. in order to Carry out an aCCurate evaluation i have DeCiDeD to imPlement anD examine my FinDings using a ProPoseD Design CarrieD out on hawKins house, hawKins street, Dublin two. as the basis For my examination.

i have Chosen to aPPly the Double-sKin FaçaDe to a ProPoseD extension, ‘‘the Drum’’, on the south FaçaDe oF the hawKins house DeveloPment. it is CirCular in Plan anD is Primarily to be useD as an oFFiCe sPaCe along with its loCation to the south oF the DeveloPment i believe this is the most suitable area to examine For my Dissertation.

there are many methoDs oF ClassiFiCation oF a Double-sKin FaçaDe. eaCh one is DePenDent on Design PrinCiPles suCh as the origin and direCtion of airflow, Configuration and aCCording to the form in whiCh the intermediate spaCe is DiviDeD. however, the PrinCiPle FaCtor whiCh Determines the FaçaDes ClassiFiCation is aCCorDing to the DesireD ventilation funCtion.there are four main Categories as follows:

1. bow windows2. shaFt-box FaçaDes3. CorriDor FaçaDes4. multi-storey FaçaDes

there are many ConsiDerations whiCh must be assesseD when seleCting the methoD oF Double-sKin FaçaDe ConstruCtion. these inClude the following:

• heat & mass• natural ventilation• aCoustiCs• lighting• fire performanCe• Cost• sustainability

in orDer to evaluate the PerFormanCe oF the DiFFerent tyPes oF Double-sKin FaCaDe ConstruCtion i will PerForm a number oF simPle ComPutational exPeriments oF eaCh oF the resPeCtive tyPes. i will examineD both the thermal PerFormanCe anD airFlow rate oF eaCh resPeCtive system at a number oF varying DePths, ie. 1000mm, 800mm, 600mm, 400mm anD 200mm. in orDer to aCCurately assess anD examine these PerFormanCe CharaCteristiCs by using ComPutational FluiD DynamiCs (CFD).

Computational fluid dynamiCsComputational fluid dynamiCs is ConCerned with the numeriCal simulation of fluid flow and heat transfer proCesses. the objeCtive of Cfd applied to buildings is to provide the designer with a tool that enables them to gain greater unDerstanDing oF the liKel air Flow anD heat transFer ProCesses oCCuring within anD arounD builDing sPaCes given speCifiC boundary Conditions whiCh may in Clude the effeCts of Climate, internal energy sourCes and hvaC systems. in summary Cfd involves the numeriCal solution of the following governing equations:

• momentum• energy• mass Continuity• turbulenCe• sCalar / mass fraCtion

aaron regazzolidt 175a20/03/2013

ComParative analysis oF the oPtimal voiD DePth oF a ventilateD Double-sKin FaçaDe in relation to its thermal PerFormanCe

box winDowsthe box winDow is one oF the olDest Forms oF a Double-sKin FaçaDe.it is Comprised of:

•a frame with inward opening Casements.•the exterior single-glazeD sKin Contains oPenings in order to allow the ingress of fresh air and the egress of stale air, and as a result allows the ventilation of both the intermediate spaCe and the internal rooms.•the intermeDiate sPaCe between the exterior anD interior sKin are either DiviDeD horizontally along the ConstruCtional axis on or on room-to-room basis.•vertiCal division oCCurs as a result of separation between stories or between individual window elements.•the ConCept of Continuous division provides proteCtion against the transmittanCe of sounds and smells between bays and rooms.

shaFt-box FaçaDesthe shaFt-box FaçaDe is a unique variation oF box window ConstruCtion with a Combination of a double-sKin FaçaDe with a multi-storey Cavity anD one with a single-storey Cavity.it is Comprised of:

•an alternating layout oF box winDows anD vertiCal shaft Components.•at eaCh storey the vertiCal shaFts are linKeD with the aDjoining box winDows through an airFlow oPening•as a result the staCK eFFeCt Draws the air From the box winDows ComPonents in the vertiCal shaFt anD uP to the toP oF the shaFt where it is exhausteD.•in the situation where thermal uplift requires aDDitional suPPort, airFlow may be meChaniCally suCKeD out via (hybriD ventilation) the vertiCal shaFts.

CorriDor FaçaDesin CorriDor FaçaDes the air Channels are seParateD horizontally at eaCh intermediate floor. it is Comprised of:

•CloseD intermeDiate sPaCes between both sKins at the level of eaCh floor.•divisions are loCated along the horizontal length of the Corridor only where it is required for aCoustiC, fire-proteCtion or ventilation reasons.•the air intaKe anD extraCt oPenings in the exterior sKin shoulD be loCateD near the Floor anD Ceiling respeCtively.•they are usually positioned in a staggered format from bay to bay in orDer to Prevent stale air extraCteD on one floor entering the spaCe of the floor immediately above.

multi-storey FaçaDesin a builDing a multi-storey FaçaDe the Cavity is not seParateD at eaCh level, it extenDs over the whole height of the building.it is Comprised of:

•the intermediate spaCe is ConneCted vertiCally and horizontally by a number of internal rooms.•in Certain Cases, the sPaCe Can extenD arounD the whole building without and intermediate separations.•ventilation is aChieved by large openings near the ground floor and the roof respeCtively.•while the air is heated, the intermediate spaCe Can be CloseD at both the toP anD bottom to exPloit the Conservatory effeCt and to optimise the solar-energy gains.•multi-storey FaçaDes are mostly suiteD where external noise levels are high anD aCoustiC insulation is a Key Design requirement.

part plansCale 1:150

offiCe spaCe

part seCtionsCale 1:50

parapet detailsCale 1:20

floor junCtionsCale 1:20

Double-sKin base DetailsCale 1:20

suspended Ceiling system

Composite Cladding panel

raised floor system

fire stop

external rigiD insulation

alluminium louvres

perimeter gutter

stainless steel struCture

offiCe spaCe

ConCrete paving system

ConCrete Column

laminated safety glass wall system

double glazed Curtain wall system


textureD aluminium Cladding panel

aluminium louvres

spandrel panel








raised floor system

fire stop


alluminium louvres

perimeter gutter


offiCe spaCe


ConCrete Column





aluminium louvres

spandrel panel








raised floor system

fire stop


alluminium louvres

perimeter gutter


offiCe spaCe


ConCrete Column





aluminium louvres

spandrel panel








raised floor system

fire stop


alluminium louvres

perimeter gutter


offiCe spaCe


ConCrete Column





aluminium louvres

spandrel panel

grateD walKway

aluminium louvres


intermediate spaCe

laminated safety glass Curtain wall system

offiCe spaCe


intermediate spaCe


vertiCal divisionoffiCe spaCe


shaft spaCe


vertiCal division

box FaCaDe system

offiCe spaCe



vertiCal division

box FaCaDe system

grateD walKway

aluminium louvres

grateD walKway

aluminium louvres

air intaKe air extraCt

proposed south elevationsCale 1:200

ProPoseD ‘‘Drum’’

to maKe these invisible ProCesses more easily ComPrehenDible, it is neCessary to initially looK at the Constituent atoms. atoms form solid bodies, liquids and gases depending on their respeCtive Cohesive forCes. aCCording to (oesterle, et al., 2001) there are three main methoDs oF heat transFer between atoms as Follows:

Diagram oF heat transFer through a Doouble-sKin FaçaDesCale: nts

radiation

Con

duC

tio

n

Con

veCt

ion

resulting heat transfer

radiation

Cavity internal

ConduCtion

solar radiation

refleCted radiation

ConveCtion

various standard values defining thermal transmission are used in building physiCs. the CoeffiCient of thermal transmission (u-value) is the stanDarD that is useD to DesCribe the transFer oF heat through a ConstruCtion element in terms of the ambient temperature differential on both sides of the ConstruCtion element. the unit of measurement oF the u-value is w/m²K (oesterle, et al., 2001).

(gan, 2001) PresenteD an analytiCal solution moDel oF heat transFer through a multiPle layereD glazing system derived from a double-glazing unit. the thermal transmittanCe in multiple glazing was translated by the author with the following equation:

where: 1 u = w/m²K u= 1 1 1 he = external heat transFer CoeFFiCient (w/m²K) he hi ht hi = internal heat transFer CoeFFiCient (w/m²K) ht = ConDuCtanCe oF multiPle glazing units (w/m²K)

the main heat Fluxes through a multiPle glazing unit are shown above. the heat sourCe From the exterior is the solar raDiation, whiCh is initially reFleCteD on aPProximately 15% oF the external glazeD sKin. this ProCess, whiCh is DePenDant on the external ConDitions, Determines the external heat transFer CoeFFiCient (he) anD the remaining radiation passes through the glass.

the reFleCtion on the internal glazeD sKin anD inner walls oF the Cavity Creates ProCesses oF ConveCtion anD ConDuCtion, whiCh Determine the heat transFer CoeFFiCient within the Cavity (h), the aCCumulateD anD remaining heat by raDiation anD ConDuCtion reCeiveD by the room Determines the heat transFer CoeFFiCient (ht).

thermal buoyanCythe ConCePt oF a Double-sKin FaçaDe was DeveloPeD to Create a greenhouse eFFeCt between two Parallel surFaCes of glass in order to improve thermal insulation. thermal buoyanCy is defined as the proCess whiCh oCCurs when the Density oF the air between the exterior anD interior layers oF a Double-sKin FaçaDe is inCreaseD Due to the heat generated from the greenhouse effeCt. as the density of the air inCreases inside the intermediate spaCe pressure and temPerature DiFFerenCes DeveloP along the height oF the FaçaDe. this is DePenDent uPon the averaging temPerature differenCe between the Column of warm air. this pressure differenCe is given by the equation:

where: P = air Pressure (PasCals Pa) P = 0.43h t h = height oF the Column (mm) t = mean temPeraure DiFFerenCe (˚C)

then the resulting airflow is given by the equation:

v = 0.121a(h t) ⁰⁵ where: v = volume Flow rate (m³/s) a = area oF eaCh oPeneing (mm ²)

external

hawKins house sKetChsCale nts

exPeCteD exPerimental resultsin orDer to analyze the oPtimal Double-sKin FaçaDe DePth i will examine eaCh Cavity DePth unDer the PerFormanCe Criteria oF thermal PerFormanCe anD thermal uPliFt. in orDer to outline the exPeCteD results the two Diagrams below are taKing From ‘‘exPerimental anD ComPutational evaluation oF thermal PerFormanCe anD overheating in Double-sKin FaçaDes’’ by mauriCio hernanDez tasCon.

the author found that when the Cavity was ventilated the reduCtion in the Cavity depth inCreased the overall temperatures measured. the table below shows how the thermal performanCe rose and remained to relativey steady levels. however, when the DePth was DeCreaseD to 100mm the Cavity began to behave liKe a sealeD Cavity whiCh indiCates that the airflow is not adequate and as a result the heat removal rate fell.

one interesting point of note is that although the reduCtion in Cavity depth had a direCt effeCt on inCreased temperatures in the Cavity, the internal room temperautre was more influenCed resultant heat load radiation and ConDuCtive laoDs through the inner sKin.

800mm 600mm 400mm 200mm 100mm

veloCity magnitute Contours (m/s) For verying Cavity DePths

Cavity air temPerature (˚C) For verying Cavity DePths

thermal performanCe and airflow veloCity for varying Cavity depths

airF

low v

elo

City

(m³/

s)

hea

t tr

ansF

er C

oeF

FiCi

ent

(w/m

²K)

optimal Cavity depth

Determining the oPtimal Double-sKin FaçaDe DePthin orDer to Determine the oPtimal FaçaDe DePth i will Create a graPh Plotting the values oF the Double-sKin FaçaDes overall heat transFer CoeFFiCient (w/m²K) against the FaçaDes thermal uPliFt (m³/s) in relation to the resPeCtive DePths oF Cavity to be testeD, ie. 1000mm, 800mm, 600mm, 400, anD 200mm.

in order to obtain aCCurate results i will Create four graphs outlining the above mentioned performanCe Criteria in relation to eaCh of the main ClimatiC seasons whiCh are as follows:

• sPring equinox• summer solstiCe• autumn equinox• winter solstiCe

Cavity DePth (mm)

box FaCaDe sKetCh uP moDelsCale nts

shaFt-box FaCaDe sKetCh uP moDelsCale nts

CorriDor FaCaDe sKetCh uP moDelsCale nts

multi-storey FaCaDe sKetCh uP moDelsCale nts

horizontal division

internal glazing

airflow opening

external glazing

vertiCal division

horizontal divisioninternal glazing

airflow opening

external glazing

vertiCal division

airflow opening

horizontal division

internal glazing

airflow opening

external glazing

vertiCal division

horizontal division

internal glazing

airflow opening

external glazing

vertiCal division

20/03/2013 - wag & paws · 20/03/2013 comparative analysis of the optimal void depth of a...

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