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Comparison of the Summer Thermal Performanceof Three Test Buildings with that Predicted by theAdmittance ProcedureKevan Heathcote aa University of Technology , Sydney, P.O. Box 123, Broadway, 2007, AustraliaPublished online: 09 Jun 2011.

To cite this article: Kevan Heathcote (2008) Comparison of the Summer Thermal Performance of Three Test Buildings withthat Predicted by the Admittance Procedure, Architectural Science Review, 51:1, 31-38

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ArchitecturalScienceReviewVolume51.1,pp31-38

Comparison of the Summer Thermal Performance of Three Test Buildings with that Predicted

by the Admittance Procedure

Kevan Heathcote

UniversityofTechnology,Sydney,P.O.Box123,Broadway,2007,AustraliaCorrespondingAuthor:Tel:(612)95148718;Fax:(612)98148051;Email:kevan.heathcote@uts.edu.au

Received22May2007;accepted19September2007

Abstract: Thispaperdetailstheresultsofthermaltestingcarriedoutonthreeexperimentalbuildingsduringthesummerof2007andcomparestheirperformancewiththatpredictedbyusingtheCIBSEAdmittanceprocedure.Thebuildings,onebrickveneer,onemudbrickandoneofautoclavedaeratedconcretewallpanelswereconstructedbytheauthorinSydney,Australia.ThefieldresultswerecomparedwiththeadmittanceprocedurebasedonpublisheddesignvaluesfordirectanddiffuseradiationinSydney.Theresultsofthisanalysisconfirmtherelativeperformanceofthethreewallingsystemsandprovideabasisforunderstandingthethermalbehaviourofthesebuildings.

Keywords:Admittanceprocedure,Autoclavedaeratedconcrete,Brickveneer,Extrudedpolystyrenefoam,Insulation,Mudbrick,Plasterboard,Thermalperformance,Thermalmonitoring,Thermo-cellularreflectiveinsulation

IntroductionThere is a vast body of knowledge relating to the thermal

performanceofbuildings. Oneonlyhas to read thepaperbyRees,Davies,SpitlerandHaves(2000),“QualitativecomparisonofNorthAmericanandUKcoolingloadcalculationmethods”to see that there is still no general agreement as to a standardapproach“thegreatestcommonalityinthetheoreticalbasisofthemethodsoccurredduringthe1960s”(Reeset al.,2000).

Thereisalsoagrowingtendencytowardstheuseofsupposedlysophisticated computer models to predict the performance ofbuildings,butasLebrunsays,“Thegrowingdangeristouseabuildingsimulationprogrammoreandmoreasablackbox;fewexplanationsaregiventotheuseraboutthephysicalmeaningofthesimulationbeingperformed”(Lebrun&Nusgens,2000).

Theexperimentalprogrambeingreportedherewasdesignedtoprovidedatatovalidatemanualandcomputeranalyseswithrespecttotwonon-standardformsofresidentialwallconstructioninAustralia,mud-brickandautoclavedaeratedconcrete(AAC)wallpanels.Threebuildingswerebuilt,identicalexceptfortheirwallingmaterial.

Thebrick veneerwall systemwas chosenbecause it is usedforthevastmajorityofnewfreestandinghousinginNSWandtherefore provides a reference for comparison with alternativesystems.Themudbrick-wallsystemwaschosenbecausethereisagrowingrevivalofancientbuildingmethodsthatisclaimedtorequiresignificantlylessheatingandcoolingenergyduetoits

high“thermalmass”.ThethirdtypeofconstructionchosenwaslightweightAACpanelsbackedbypolystyrenepanelsforaddedinsulation.Thiswasseenasahighthermalresistanceoptionasopposedtothehighthermalmassofmudbrickandwithbrickveneerconstructionsittingsomewhereinbetween.

Thispaperreportstheperformanceofthethreebuildingsduringlatesummerof2007andcomparesthisperformancewiththatpredictedbytheadmittanceprocedure.Theadmittancemethodwaschosenasasuitablebasisforthetheoreticalcomparisonasitcatersforunconditionedinternalspacesandisrelativelysimpleto apply. No measurements of incident radiation were madeduetocostlimitations.Publishedvaluesofaveragediffuseanddirectradiationwereusedintheanalysiswiththeintentionofverifyingtherelativeperformanceofthebuildingsandtoprovideaninsightintoheatmovementsinandoutofthebuildings.

The objective of this initial monitoring and evaluationof the buildings was to provide a baseline performance of thethreebuildings in termsof theirability tocontrol temperatureswingsinthesituationofunconditionedinternalspace.Furtherexperimentalworkisbeingcarriedouttoinvestigatetheeffectofventilationontheperformanceofthebuildings.

Description of BuildingsThe three test buildings are located on the Yarrawood

Property of the University of Technology, Sydney, which is

www.earthscan.co.uk/journals/asre doi:10.3763/asre.2008.5105

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ArchitecturalScienceReview Volume51,Number1,March200832

approximately half way between Richmond and Penrith onthe western edge of the Sydney Basin. The site was once aconferencecentrebutisnowlargelyderelict.

The three buildings are each 4.5 metres square in plan.Theyhaveaninternalareaof16squaremetresandaninternalvolumeof38.4cubicmetres.Thereisasingleglazeddooronthenorthernsidewithglasslouvresabove.Thelocationofthebuildingson the sitewasdeterminedby theneed toprovidesufficientspacingtoavoidshadingbyeachotherandbyexistingbuildingsaswellastheneedforaccesstoservicesonthesite.Figure1showsthecompletedthreebuildings.

Floor ConstructionThe floor is a conventional reinforced concrete slab on

groundwitha100mmthickslaband300mmby300mmedgethickenings.Somecuttingwasnecessarytoaccommodatetheslightfallfromwesttoeastonthesite.

Roof ConstructionTheroofwasconventionallyframedwitha22degreepitch

with gable ends on the east and west sides. The eaves are600mm on the north side and 300mm on the south side.

The ceiling is 10mm plasterboard and the roof sheeting iscorrugated metal sheeting in a light grey colour. Thermo-cellular reflective insulation was placed directly under theroofingandR2polyesterbattinsulationwasplacedbetweentheceilingjoistsandagainstthegableends.Thegablesweresheetedwithfibrecementboarding.Figure2showsasectionthroughtheroof.

Door DetailsThesinglelightdooronthenorthsideiscentrallylocated

andconsistsofan820mmtimberframewith4mmtoughenedglass.Abovethedooraretwoglasslouvreswithaglazeddepthof320mmandwidthof820mm. These louvreswereclosedduringthis test series. Thetotalglazedareaof thedoorandlouvres is around1.14m2with theoverall opening includingframingbeingaround2.11m2.

Wall DetailsThe walls of the brick veneer building are of typical

construction.ThestudwallswereexternallysarkedandR1.5fibreglassbattswereplacedbetweenthestuds.

The insulated AAC wall system consists of a normal studwallwith50thickextrudedpolystyrenerigidfoaminsulationand75thickAACwallpanelsattachedtothestudwallusingtophatsteelsections.Foilbackedsarkingwasplacedagainstthestudswiththeshinysidefacingthe25mmcavitybetweenthestudsandtheextrudedpolystyrenerigidfoaminsulation.R1.5fibreglassbattswereplacedbetweenthestuds.

The mud bricks were 350mm long by 250mm wide and100mmhigh.Theywerebitumenstabilisedandwerelaidinamortarconsistingofamixtureofsandandaclayeysoil.Jointswereapproximately20mm.Figure3showssectionsthroughthethreetypesofwalls.

Thermal Properties of Building EnvelopesTable 1 shows the assumed material properties of the

individual wall components. Table 2 shows the values oftransmittance,admittance,decrementfactorandtimelagthatwereassumedinthisstudyforthewalls,roof,flooranddoor.Except for the door, thermal bridging was not taken intoaccount.ValuescalculatedwereobtainedusingaspreadsheetdevelopedbytheauthorbasedonthematrixmethodoutlinedbyDavies(2004)usingthebasicmaterialdatagiveninTable1. An external surface resistance of 0.04 m2K/W and aninternalsurfaceresistanceof0.12m2K/Wwereassumed.Acavity resistanceof0.17m2K/Wwasassumed for thebrickveneerwalls, and0.35m2K/Wfor theAACwalls, allowingfor the added benefit of reflective foil insulation facing thecavity.

Simplified Measures of Building ResponseThethreebuildingswerechosenbecauseoftheirvariationin

mass.Szokolay(2004)definesthespecificmassofabuilding(sM)as:

(1)

5

using top hat steel sections. Foil backed sarking was placed against the studs with the shiny

side facing the 25 mm cavity between the studs and the extruded polystyrene rigid foam

insulation. R1.5 fibreglass batts were placed between the studs.

The mud bricks were 350 mm long by 250 mm wide and 100 mm high. They were

bitumen stabilised and were laid in a mortar consisting of a mixture of sand and a clayey soil.

Joints were approximately 20 mm. Figure 3 shows sections through the three types of walls

<Insert Figure 3 here>

Thermal Properties of Building Envelopes

Table 1 shows the assumed material properties of the individual wall components.

Table 2 shows the values of transmittance, admittance, decrement factor and time lag that

were assumed in this study for the walls, roof, floor and door. Except for the door, thermal

bridging was not taken into account. Values calculated were obtained using a spreadsheet

developed by the author based on the matrix method outlined by Davies (2004) using the

basic material data given in Table 1. An external surface resistance of 0.04 m2K/W and an

internal surface resistance of 0.12 m2K/W were assumed. A cavity resistance of 0.17 m

2K/W

was assumed for the brick veneer walls, and 0.35 m2K/W for the AAC walls, allowing for the

added benefit of reflective foil insulation facing the cavity.

<Insert Table 1 here>

<Insert Table 2 here>

Simplified Measures of Building Response

The three buildings were chosen because of their variation in mass. Szokolay (2006)

defines the specific mass of a building (sM) as:

)/( 2mkgbuildingtheofareafloor

buildingtheofmasstotalsM = (1)

Using this definition, the specific masses of the threebuildingsare:

Figure 1. Completed Buildings

Figure 2 Section Through Roof (Source www.air-cell.com.au)

Figure 1: Completed test buildings.

Figure 2: Section through roof (source www.air-cell.com.au; accessed 4 May 2007).

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33KevanHeathcote SummerPerformanceandAdmittanceProcedure

Brick veneer 743kg/m2

Mud brick 1105kg/m2

Insulated AAC 447kg/m2

Note that all three buildings would beclassifiedasbeingof “heavy”constructionaccordingtoSzokolay’sdefinition(sM>400).Thisismainlyduetothelargethermalmassof theconcretefloor. However,ascanbeseenfromthetablethedifferencebetweenthespecificmassesofthethreebuildingsisquite largeand this shouldbe reflected intheirrelativeperformance.

Mass on its own is not sufficient toensure reduction in swing temperaturesand Van Straaten (1967) identifies Mass×ThermalResistanceofExternalWalls (ameasureofdiffusivity)asameasureofthereduction in swing temperatures. For thethreebuildings,thevalueofsMtimesthewallresistance(R)isasfollows:

Brick veneer 1530

Mud brick 519

Insulated AAC 2087

According to Van Straaten, the higherthevalueofsM×Rthesmallertheswingandon this basis the insulated AAC buildingcouldbeexpectedtohavethelowestswing,

Figure 3: Sections through the three walls.

Table 2: ElementProperties.

Table 1:AssumedThermalPropertiesofMaterials.

22

Table 1. Assumed Thermal Properties of Materials

Material Density

(kg/m3)

Conductivity

(W/m.K)

Specific Heat

(J/kg.K)

Brick veneer 1700(1)

0.84(1)

800(1)

Batt insulation 25(1)

0.035(1)

1000(1)

Plasterboard 950(1)

0.16(1)

840(1)

Mud bricks 1650(2)

0.8(3)

1000(3)

Autoclaved aerated

concrete panels

536(4)

5% m.c. 0.153(4)

5% m.c. 1000(4)

Extruded polystyrene rigid

foam insulation

30(5)

0.028(5)

1400(1)

Thermo-cellular reflective

insulation

Thermal resistance

is 2.2 m2K/W down(6)

(1) Szokolay (2004)

(2) Measured by author

(3) Minke (2006)

(4) CSR Hebel Technical Manual (Jan 2006) – “Powerpanels”

(5) www.aeromfg.com.au (SMTG Styrofoam) – accessed 6 February 2006

(6) www.air-cell.com.au/pages/tech-values.htm -- accessed 22 February 2007. Value is

for a non-ventilated 22° metal pitched roof with flat ceiling and includes surface resistances.

23

Table 2 . Element Properties

Element U (W/m2.K)

Y

(W/m2.K)

Area

(m2)

Decrement

Factor

Time

Lag

(Hrs)

Roof 0.24 Down(1)

0.67(5)

18.0 1.00(2)

1(2)

Floor 1.22(3)

6(2)

18.0 0(2)

-

Door 4.1(4

) 4.1(4)

1.67 1.00(2)

0(2)

Brick veneer 0.49(5)

0.79(5)

39.13 0.77(5)

3.9(5)

Mud brick 2.12(5)

4.89(5)

39.13 0.41(5)

7.7(5)

Insulated AAC 0.23(5)

0.69(5)

39.13 0.83(5)

3.7(5)

(1) Table 1 + R2 insulation on ceiling

(2) Szokolay (2004)

(3) CIBSE (1986), Table A3.10

(4) Calculated using CIBSE (1986)

(5) Calculated using matrix program based on Davies (2004)

Figure 3 Sections through the Three Walls

(1) Szokolay (2004)(2) Measured by author(3) Minke (2006)(4) CSR Hebel Technical Manual (Jan 2006) – “Powerpanels”(5) www.aeromfg.com.au (SMTG Styrofoam) – accessed 6 February 2006(6) www.air-cell.com.au/pages/tech-values.htm -- accessed 22 February 2007. Value is for a non-ventilated 22° metal pitched roof with flat ceiling and includes surface resistances.

(1) Table 1 + R2 insulation on ceiling(2) Szokolay (2004)(3) CIBSE (1986), Table A3.10(4) Calculated using CIBSE (1986)(5) Calculated using matrix program based on Davies (2004)

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ArchitecturalScienceReview Volume51,Number1,March200834

followedbythebrickveneerbuilding.Notehoweverthattherelationshipisnotlinearsothedifferenceswouldnotbeaslargeastherawfiguressuggest.

Another simple measure of the thermal performance ofbuildings is the CIBSE response factor (fr). It is defined asfollows:

(2)

7

!

!

+

+

=

NvAU

NvAY

fr

3

1)(

3

1)(

(2)

where

Σ(AY) = sum of products of areas of all room surfaces and their appropriate admittances

Σ(AU) = sum of products of areas of all exposed surfaces and their appropriate

transmittances

N = Rate of air interchange (Taken as 1/hr based on Table A8.4 of CIBSE Guide)

v = room volume = 38.4 m3

Using this data, the response factors of the three buildings are

Brick veneer 4.0

Mud brick 3.0

Insulated AAC 5.3

According to the CIBSE Guide (1986), the brick veneer and the mud brick buildings

would be classified as “lightweight” (fr <=4) whilst the insulated AAC is bordering on

heavyweight” (fr >=6). This situation arises because of the high insulation of the insulated

AAC building and confirms the relative performance of the three buildings predicted based on

sM×R given above.

It is worth noting that both the response factor and the sM×R factors are based on the

resistance of the buildings to solar irradiance and are not dependent on the driving

temperature that can be dramatically changed depending on the absorptivity of the wall

surfaces.

Analysis of Buildings Using Admittance Procedure

The three buildings were analysed using the admittance method, described in Section

A8 of the CIBSE Guide (1986). The analysis was based on average Sydney solar irradiance

whereΣ(AY)=sumofproductsofareasofallroomsurfacesand

theirappropriateadmittancesΣ(AU)=sumofproductsofareasofallexposedsurfacesand

theirappropriatetransmittancesN=Rateofairinterchange(Takenas1/hrbasedonTable

A8.4ofCIBSEGuide)v=roomvolume=38.4m3

Usingthisdata,theresponsefactorsofthethreebuildingsare:

Brick veneer 4.0

Mud brick 3.0

Insulated AAC 5.3

AccordingtotheCIBSE Guide(1986),thebrickveneerandmud brick buildings would be classified as “lightweight” (fr<=4)whilsttheinsulatedAACisborderingonheavyweight”(fr>=6).ThissituationarisesbecauseofthehighinsulationoftheinsulatedAACbuildingandconfirmstherelativeperformanceofthethreebuildingspredictedbasedonsM×Rgivenabove.

It is worth noting that both the response factor and thesM×R factors are based on the resistance of the buildingsto solar irradiance and are not dependent on the drivingtemperature that can be dramatically changed depending ontheabsorptivityofthewallsurfaces.

Analysis of Buildings Using Admittance Procedure

The three buildings were analysed using the admittancemethod,described inSectionA8of theCIBSE Guide (1986).TheanalysiswasbasedonaverageSydneysolarirradiancedataforSydneygivenbySpencer(1975) for22January(Figure4)andexternaltemperaturesrecordedatthesite.ThevaluesgivenbySpencerfordiffuseradiationincludeanallowanceforreflectedradiation based on a reflectance of 0.2. The average externaltemperaturerecordedatthesitebetweenthe13thDecember2006andthe18thJanuary2007(23.6ºC)wasusedforcalculatingtheaverageinternaltemperaturesofthebuildings.

Theaimoftheanalysiswasnottogetexactcorrespondencebetweentheadmittancemethodandrecordedresults(sincesolarradiationwasnotmeasured)buttoseewhethertheadmittancemethod could give results which were consistent with thoserecordedinthethreebuildingsonarepresentativesummerday.

Brief Description of Admittance ProcedureTheadmittancemethodwasdevelopedbyLoudon(1970)

topredictsummertimetemperaturesinbuildingswithoutairconditioning.Themethodisusedtopredictpeaktemperaturesinabuildingbasedoncyclicinputsofoutsidetemperatureandirradiance.

The method uses the concept of “sol-air” temperaturedeveloped by Mackey and Wright (1943) to determine thedriverofheatinputthoughopaqueelementsofabuilding.Thesol–airtemperatureisdefinedasthetemperaturethat“wouldgive thesamerateofheat transferandthesametemperaturedistributionthroughthewallasexistswiththeactualoutdoortemperatureandincidentsolarradiation”(Mackey&Wright,1943,p.150).Forawallthesolairtemperatureisdefinedasfollows:

(3)

8

data for Sydney given by Spencer (1975) for 22 January (Figure 4) and external temperatures

recorded at the site. The values given by Spencer for diffuse radiation include an allowance

for reflected radiation based on a reflectance of 0.2. The average external temperature

recorded at the site between the 13th

December 2006 and the 18th

January 2007 (23.6 ºC) was

used for calculating the average internal temperatures of the buildings.

<Insert Figure 4 here>

The aim of the analysis was not to get exact correspondence between the admittance

method and recorded results (since solar radiation was not measured) but to see whether the

admittance method could give results which were consistent with those recorded in the three

buildings on a representative summer day.

Brief Description of Admittance Procedure

The admittance method was developed by Loudon (1970) to predict summertime

temperatures in buildings without air conditioning. The method is used to predict peak

temperatures in a building based on cyclic inputs of outside temperature and irradiance.

The method uses the concept of “sol-air” temperature developed by Mackey and

Wright (1943) to determine the driver of heat input though opaque elements of a building.

The sol –air temperature is defined as the temperature that “would give the same rate of heat

transfer and the same temperature distribution through the wall as exists with the actual

outdoor temperature and incident solar radiation” (Mackey & Wright, 1943, p 150). For a

wall the sol air temperature is defined as follows

teo = tao +α×IT×Rso (3)

where

teo = sol air temperature

tao = outside air temperature

whereteo=solairtemperaturetao=outsideairtemperature

0

200

400

600

800

1000

1200

6:00 AM 8:00 AM 10:00 AM 12:00 PM 2:00 PM 4:00 PM 6:00 PM

EST (Add 1 Hour for DST)

To

tal

So

lar

Irra

dia

nc

e (

W/m

^2

)

North/South/Diffuse East West Roof

Figure 4 Average Solar Irradiances for Jan 22, Sydney (Spencer, 1975) Figure 4: Average solar irradiances for January 22, Sydney (Spencer, 1975).

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35KevanHeathcote SummerPerformanceandAdmittanceProcedure

α=absorptivityoftheoutsidesurfaceforsolarradiationIT=intensityofsolarradiationincidentuponthesurfaceof

thewall.Rso=outsidesurfaceresistanceForroofs,theequationis

teo=tao+α×IT×Rso--E×Rso (4)

whereE=Radiantemissionterm=90W/m2foracloudlessskyThemethodisbrokenupintotwoparts:1.Inthefirstpart,itisassumedthatonaveragethereis

nonetheatflowintooroutofthebuilding.Averagevaluesarethenusedforsolarirradiance(IT)andoutsidetemperature(tt-

ao)andalltheheatflowsarethensummedandsettozero.Thisequationisthensolvedfortheaverageinsidetemperature(t-

ei). Figure5showsagraphicdepictionofheatflows intoandoutofthebuildings.

2.Inthesecondpart,itisnecessarytoguessthetimeofdaywhenthepeakindoortemperatureislikelytooccurandthentocalculatethe“swing”heatgainsassociatedwiththat“peakhour”. Theswingheatgainsarecalculatedas for theaveragevaluesexceptthat:

a) Dynamic transmittances are used instead of meanvalues. Dynamic transmittances are a measure ofheat input to the enclosure due to cyclical variationsinoutdoortemperature.TheyarelessthanthemeanU values and are represented by f×U, where f is the

“decrement factor”. Note that this only applies toopaqueelements.

b) Alternatingsolargainfactorsareusedforglazedareasinsteadofmeanvalues

c) Foropaqueelementstherelevantoutsidetemperatureandsolarirradiancearetakenatthepeakhourminusany“thermallag”associatedwiththematerial

d) Fortransparentmaterials,asolarirradiancetimelagofonehourisassumedforheavyweightconstruction

The total swing heat gain so calculated can be separatedcan be separatedintoaventilationexchangecomponent(0.33×N×v×t~

ei)andaconvective/radiativecomponent(ΣAY×t~

ei)wheret~eiisthe

insideswingtemperature.Theadmittance(Y)oftheinternalsurfacesofthebuildingreflectstheresponseofthestructureto heat input. It is dominated by the material nearest theinside surface of the construction. When combined withthedynamictransmittancesoftheexternalenvelopeandtheventilationexchangeitpresentsameansoftranslatingcyclicalheatinputsintointernalenvironmenttemperatures.

The total swing heat gain is then equated to the twocomponents given above and the equation solved to yieldthe swing temperature at the peak hour (t~

ei). The totaltemperatureatthepeakhouristhent-

ei+t~ei.

The value tei so calculated is not the inside temperaturebutwhatiscalledthe“internalenvironmentaltemperature”,definedas2/3ofthemeaninternalsurfacetemperatureplus1/3oftheinternalairtemperature.

Figure 5 Graphic of Heat Flows In and Out of Buildings

Qv=0.33Nv(tei-tao)

Indoor Temperature tei

Qff=AffUff(tei-tao)

Qfw1=AfwUfw(teo-tei)

Qs=AgSeIT

teo

tao

Outdoor Temperature tao

IT

Solar Irradiance IT

Sol-Air Temperature teo

Surface

Absorptance

and

Resistance

Qg=AgUg(tei-tao)

Qfwr=AfrUfr(teo-tei)

Nomenclature:

A = Area of element

U = Element Transmittance

N = No of air changes per hour

v= Room Volume

S= Glass Solar Gain Factor

Figure 5: Graphic of heat flows in and out of buildings.

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ArchitecturalScienceReview Volume51,Number1,March200836

Figure 6: Recorded temperatures on 9th January 2007.

Calculated Internal Environment TemperaturesThe design values for irradiance and the external

temperatures for the9th January2007are shown inTables3 and 4 together with the values of sol-air temperaturecalculated using equations (3) and (4). Because of theoverhangsonthenorthandsouthsides,itwasassumedthatthese walls only received diffuse radiation during the test

period.Forconvenience,Table3onlyshowsvaluesfortheEastwalls.

The mean diffuse irradiance for the northern door wastakenas66W/m2,withpeakirradiancesof104W/m2forthebrickveneerbuilding(4pmEST),42W/m2forthemudbrickbuilding (6pm EST) and 137 W/m2 for the insulated AACbuilding(3pmEST).

Table 3:DesignValuesforExternalTemperatureandIrradianceforEastWalls.

Table 4:DesignValuesforExternalTemperatureandIrradianceforRoof.

25

Table 4 . Design Values for External Temperature and Irradiance for Roof

Brick veneer

Building

Mud brick

Building

Insulated

AAC

Building

Average

Irradiance362 (W/m

2) 362 (W/m

2) 362 (W/m

2)

Average Sol-

Air Temp.27.2 ºC 27.2 ºC 27.2 ºC

Peak Hour 4 pm EST 6 pm EST 3 pm EST

Peak Hour Ext.

Temperature29.7 ºC 26.2 ºC 28.7 ºC

Time Lag 1 hr 1 hr 1 hr

Lagged Wall

Irradiance

593 W/m2

(3pm EST)

156 W/m2

(5 pm EST)

791 W/m2

(2 pm EST)

Lagged

External

Temperature

28.7 ºC 29.7 ºC 28.2ºC

Lagged Sol Air

Temperature37.0 ºC 26.2 ºC 40.9 ºC

19.0

20.0

21.0

22.0

23.0

24.0

25.0

26.0

27.0

28.0

29.0

30.0

31.0

12:00 PM 4:00 PM 8:00 PM 12:00 AM 4:00 AM 8:00 AM 12:00 PM

DST Commencing 12pm on the 9/1/2007

Te

mp

era

ture

De

gre

es

Ce

nti

gra

de

Outside Hebel Mud Brick Brick Veneer

Mud Brick

AAC

Brick Veneer

Figure 6 Graph of Recorded Temperatures on 9th January 2007

24

Table 3 . Design Values for External Temperature and Irradiance for East Walls

Brick veneer

Walls

Mud brick

Walls

Insulated

AAC Walls

Average

Irradiance200 (W/m

2) 200 (W/m

2) 200 (W/m

2)

Average Sol-

Air Temp.29.2 ºC 30.0 ºC 26.8 ºC

Peak Hour 4 pm EST 6 pm EST 3 pm EST

Peak Hour Ext.

Temperature28.7 ºC 26.7 ºC 28.7 ºC

Time Lag 4 hrs 8 hrs 4 hrs

Lagged Wall

Irradiance

193 W/m2

(12 pm EST)

649 W/m2

(10 am EST)

441 W/m2

(11 am EST)

Lagged

External

Temperature

26.2ºC 23.7 ºC 24.7ºC

Lagged Sol Air

Temperature31.6 ºC 44.5 ºC 31.8 ºC

Brick Veneer Walls

Mud Brick Walls

Brick Veneer Walls

Mud Brick Walls

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37KevanHeathcote SummerPerformanceandAdmittanceProcedure

Asteadystateglasssolargainfactorof0.76wasassumedforaveragecalculationsandanalternatingsolargainfactorof0.54wasusedforswingcalculations.Anoutsidesurfaceresistanceof0.04m2K/Wwasassumedforboththewallsandtheroof.Aroofabsorptivityof0.5wasassumedwithwallabsorptivityof0.4fortheinsulatedAACbuilding,0.7forthebrickveneerbuilding and 0.8 for the mud brick building. These werechosenbasedonvaluesgiveninSzokolay(2004).

AventilationexchangerateofoneairchangeperhourwasassumedbasedonTableA8.4oftheCIBSEGuide(1986).Thisequatestoanairvelocityofaround0.5m/secpassingthroughanopeningof0.02m2.

Table5 shows the calculateddistributionofheatflows inthe average condition together with the predicted average

environmental temperature and Table6 shows the distribution and calculatedswingtemperatures.

Measured Performance of Buildings

Temperatureswererecordedexternallyand internally in the three buildingsduring the period 13th December 2006and the 18th January 2007 using singletemperature/humidity data loggers (DS1923 iButton® Hydrochrons®) whichrecord toanaccuracyof+/-0.5ºC. Theexternal logger was placed in a smallwooden box mounted on the side of abuildingdirectlytothenorth(approx1.5metresabovegroundlevel).Theboxisa150mmcubeandhasa50mmdiameteropeningonthesouthside.

The internal loggers were hung fromtheceilingsothattheyweregeometricallyin the centre of each building. Duringthisperiod,therewasaconsistentpatternof relative performance of the threebuildings. The 9th January was chosenfor comparison with the admittancemethodasitwasinaperiodofnegligiblecloud cover, had a good range ofexternal temperature, had a maximumtemperature that was representative ofsummer conditions in the region, andwasprecededbysimilardaysofexternaltemperature.

Figure 6 shows a graph of thetemperatures recorded externally andinthecentreof thebuildingsonthe9thJanuary2007.

Figure 6 clearly indicates very littlelag between peak outside temperatureandpeakindoortemperatureinthecaseoftheinsulatedAACbuilding.Alagofaround 1 hour is evident for the brickveneerbuildingandaround4hours forthemudbrickbuilding.

The measured average temperatures(horizontallines)shownonFigure6arethoserecordedduringthe period 13th December 2006 and the 18th January 2007andappeartocorrespondfairlywellwiththemeanvaluesforthe 9th January. The difference between these averages andthemaximumvalues(“swing”)arefairlysimilarinthecaseoftheinsulatedAACandbrickveneerbuildings(1.7ºC)withaslightlylowervalue(1.5ºC)forthemudbrickbuilding.

Comparison between Theory and PracticeTable 7 shows the difference between the temperatures

calculated by the admittance method and the average andmaximum temperatures recorded in each building on the9th January 2007. It must be remembered that calculatedresultsare“environmental”temperaturesandthesearebeing

Table 5:AnalyticalAverageHeatFlowsandTemperatures.

26

Table 5. Analytical Average Heat Flows and Temperatures

Brick veneer Mud brick Insulated AAC

Heat Flows (Watts) – In Positive

Door Solar Gain 57 57 57

Walls 33 91 5

Roof 8 2 11

Ventilation -18 -28 -20

Floor -53 -81 -39

Door Fabric -27 -41 -14

Predicted

Average

Temperature

25.7 ºC 26.9 ºC 25.2 ºC

Variation from

Outside Average

(23.6 ºC)

2.1ºC 3.3 ºC 1.6ºC

Table 6:AnalyticalHeatFlowsandSwingTemperatures.

27

Table 6. Analytical Heat Flows and Swing Temperatures

Brick veneer Mud brick Insulated AAC

Heat Flows (Watts) – In Positive

Door Solar Gain 23 -15 44

Walls 55 166 21

Roof 47 -5 66

Ventilation 65 39 65

Floor 0 0 0

Door Fabric 44 53 40

TOTAL 234 238 236

∑AY + Cv 188 358 185

Swing

Temperature1.2 ºC 0.7ºC 1.3ºC

Average + Swing

Temp26.9 ºC 27.6 ºC 26.5 ºC

Table 7: CalculatedandRecordedTemperaturesinBuildingsduringTestPeriod.

28

Table 7 . Calculated and Recorded Temperatures in Buildings during Test Period

Average Temperatures

Brick veneer Mud brick Insulated AAC

Calculated Values 25.7 ºC 26.9 ºC 25.2 ºC

Recorded Values 25.4 ºC 26.6 ºC 25.0 ºC

Difference +0.3 ºC +0.3 ºC +0.2 ºC

Swing Temperatures

Calculated Values 1.2 ºC 0.7 ºC 1.3 ºC

Recorded Values 1.7 ºC 1.5 ºC 1.7 ºC

Difference -0.5 ºC -0.8 ºC -0.4 ºC

Combined Average and Swing Temperatures

Calculated Values 26.9 ºC 27.6 ºC 26.5 ºC

Recorded Values 27.1 ºC 28.1 ºC 26.7 ºC

Difference -0.2ºC -0.5 ºC -0.2 ºC

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ArchitecturalScienceReview Volume51,Number1,March200838

comparedwithinternalroomtemperatures,howeveranalysisof another period when wall temperatures were recordedindicatesarelativelysmalldifferencebetweentheinternalandenvironmentalvalues.

It is clear fromTable 7 that the admittance method hasbeenabletopredictquiteaccuratelythedifferenceinaveragetemperaturesbetweentheoutsideandtheinsideofthethreebuildings. The maximum difference between the predictedaveragetemperaturesandtherecordedaveragesisonly0.3ºC,which is about 1.2% of the recorded values This accuracyishelpedbythefactthattheanalysesuses“average”climaticproperties,andthoseassumedintheanalysiscouldbeexpectedtobesimilartotheactualaveragesfortherecordingperiod.

Intermsofpredictingswingtemperatures,itseemsthattheadmittancemethodpredictsmuchlowerswingsthanoccurredinpractice,especially for themudbrickbuilding,wheretheerroris53%oftherecordedvalue.Partofthereasonforthismaybedue to the smallvaluesof swing involvedcombinedwiththeaccuracyoftherecordingloggers.Anotherpossiblereason is the steepness of the East andWest wall irradiancecurvesshowninFigure4ataroundmidday,whichiswhenthelaggedpeakirradianceswereassumedtooccur.Atthattime,anerrorof1hourinthetimelagofthewallsleadstoadoublingofthepeaksolarirradianceusedinthecalculations,andthiscouldhavea significant effecton the resultingpredictionofswingtemperatures.Otherpossibleerrorsintheanalysiscouldbedue to thevariationbetweenassumedvalues formaterialpropertiesandtheactualvalues,andontheassumedvaluesforwallabsorptivityvalues.Adetailedanalysisoftheseerrorsisoutsidethescopeofthispaperbutinitialcomparisonsindicatethat the effect of changes in these on swing temperatures ismuchsmallerthanthatofincidentradiation.

ConclusionThisstudyhasshownthattheadmittancemethodisauseful

tooltogainanunderstandingoftheheatflowsintoandoutofabuilding.Ithasproventobeareasonablyaccuratemethodfor determining average inside temperatures for the threebuildingsstudiedbasedonassumedvaluesofsolarirradianceandmaterial thermalproperties. Although the total internaltemperaturespredictedonthechosensampledayweresimilarto those recorded, the admittance method appears likelyto underestimate swing temperatures when applied to highthermalmass/insulationbuildings.

Acknowledgement and Disclaimer

The author would like to acknowledge the generous monetaryassistanceprovidedbyCSRHebel,withoutwhomthisprojectwouldnot have been possible. I would also like to thank Austral bricksfor providing and laying the bricks for the brick veneer buildingandtoPeterJirgensof“Makeitmudbricks”forprovidingthemudbricks. Special thanksmustalsobegiven tomembersof theEarthBuilding Association of NSW for their work on the constructionofthebuildings.Theauthorwouldliketomakethepointthattheresultspresentedhereareforaparticularconfigurationandmethodofoperationofthetestbuildingsonlyandshouldnotatthisstagebeinterpreted as conferring any particular preference for one or otherformofconstruction.

References

CIBSE (1986). CIBSE Guide, Volume A: Design Data. London:CharteredInstitutionofBuildingServicesEngineers.

Davies,M.G.(2004). Building Heat Transfer. NewYork:Wiley.Lebrun,J.J.,&Nusgens,P.J.(2000).Simplifiedanalysisofbuilding

thermalstorageeffects.Transaction of the American Society of Civil Engineers, 106,801-810.

Loudon, A.G. (1970). Summertime temperatures in buildingswithoutairconditioning.Journal of the Institution of Heating and Ventilation Engineers, 37,280-229.

Mackey, C.O. & Wright, L.T. (1943). Summer Comfort Factorsas Inflenced by the Thermal Properties of Building Materials,Transactions of the American Society of Heating and Ventilation Engineers,49,148-169.

Minke,G.(2006).Building with EARTH: Design and Technology of a Sustainable Architecture. Basel:Birkhauser.

Rees,S.J.,Davies,M.G.,Spitler,J.D.,&Haves,P.(2000).QualitativecomparisonofNorthAmericanandU.K.coolingloadcalculationmethods. International Journal of Heating, Ventilation, Air-Conditioning & Refrigeration Research, 6,75-99.

Spencer,J.W.(1975).Sydney Solar Tables,BuildingResearchTechnicalPublication No 8. Melbourne: Commonwealth Scientific andIndustrialResearchOrganisation

Szokolay,S.V.(1987). Thermal Design of Buildings.Canberra:RoyalAustralianInstituteofArchitectsEducationalDivision.

Szokolay,S.V.(2004). Introduction to Architectural Science. Oxford:ArchitecturalPress.

Van Straaten, J.F. (1967). Thermal Performance of Buildings. Amsterdam:Elsevier.

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