Determination of Optimum Window to External Wall Ratio for Offices in a Hot and Humid Climate

21 Pages·2016·5.77 MB·English

by  Halil Alibaba

sustainability
Article
Determination of Optimum Window to External Wall
Ratio for Offices in a Hot and Humid Climate
HalilAlibaba
FacultyofArchitecture,DepartmentofArchitecture,EasternMediterraneanUniversity,Mersin10,Turkey;
[email protected];Tel.:[phone];Fax:[phone]
AcademicEditor:AdrianPitts
Received:7January2016;Accepted:17February2016;Published:20February2016
Abstract: Heatlossandgainthroughwindowshasaveryhighimpactonthethermalcomfortof
offices. Thispaperanalyzesastandardlowenergyconsumptionuniversityofficethathasastandard
envelope. Dynamic thermal simulations with EDSL Tas software, a predicted mean vote (PMV),
and a predicted percentage of dissatisfied (PPD) with all local discomfort as stated in ASHRAE,
ISO 7730: 2005, EN 15251: 2007 were used for thermal sensation, in order to optimize the best
windowtoexternalwallproportioninahotandhumidclimatethatexistsintheFamagustacase
study. Asimulatedofficebuildingisorientedeasttowestinordertotakeadvantageofthewind
direction. InMay45%(PPD<6%–0.7%openwindow),93%(PPD<10–0.2openwindow),and97%
(PPD<15%–0.1%openwindow)thermalcomfortscoresareobtainedwhenthewindowtoexternal
wallratio(WWR)is10%. InOctober43%(PPD<6%–0.7%openwindow),86%(PPD<10–0.2open
window),and92%(PPD<15%–0.1%openwindow)thermalcomfortscoresareobtainedwhenthe
WWRis10%. InSeptember49%(PPD<10%fullopenwindow)and51%(PPD<15%–0.1%open
window)thermalcomfortscoresareobtainedwhentheWWRis10%.
Keywords: PMV-PPD;ISO;ASHRAE;EDSLTas;lowenergydesign;sustainablebuildings;thermal
comfort;hot-humidclimate
1. Introduction
Dynamicthermalsimulationmethodsareusedbyacademicsforassessingbuildingperformance.
Forofficewindowsinhotclimates,thermalcomfortcanbeachievedthroughsimulationsforlosingor
gainingheat. EDSLTassoftware[1]isoneoftheoptionsfordynamicthermalsimulationgeneration
withASHRAE[2],ISO7730: 2005[3]andEN15251: 2007[4]standards.
Pinoetal.[5]foundthatbyusingEDSLTassoftwareforafully-glazedfaçadeinSantiago,the
cooling and heating energy demand may reach 115 kWh/m2 in one year. Moreover, if the WWR
is20%withexternalsolarprotectionandselectedglazing,thecoolingandheatingdemandwillbe
25 kWh/m2. If night ventilation is applied during cooling periods, a further 37% reduction will
beachieved.
Incoldclimates,artificialenergyisneededtoprovidethermally-comfortablespaces. Additionally,
theindoorclimateisaffectedbythebuildingformandenvelope[6]. InwarmpartsofEurope,froman
energysavingpointofview,windowsareweakpointsofthebuildingenvelope,especiallyforcooling.
Theperformanceofclearglassformaintainingcoolingloadsisverygoodifitsthermaltransmittance
isbetween2.00W/m2Kand3.00W/m2K[7]. Operatingthewindowshasgreatimportanceonthe
physicalconnectionwiththeoutsideandtheuseofnaturalventilationforcontrollingthermalcomfort
conditionstoreducecoolingloads. Moreover,naturalventilationwillimproveindoorairquality[8,9].
Theopeningproportionofthewindowshouldbebasedupontheoutdoorairtemperature,season,
time, and occupancy pattern [10–13]. HVAC energy can be reduced by up to 17%–47% by using
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mixed-modeventilationforsummertimeinvariousclimates[14]. Inmoderateclimateconditionssuch
asinGermany,Italy,andTurkey,theindoorairqualitycanbecontrolledbyopeningtypologiesand
summercoolingdependinguponthenaturalventilationstrategy[15].InallclimatesoftheUSA,annual
coolingenergyusecanbereducedbyusingthermalresistanceenvelopematerials(RSI-0.5/RSI-2.5)
from15%to39%. Annualheatingenergycanalsobesavedbyupto10%dependingonthewindow
size and internal heat gains [16]. Designing large windows for offices can allow more daylight to
enter and creates a balance between the energy consumed for lighting and cooling systems [17].
Althoughwindowsareusedforvisualcontactandforthegenerationofdaylightintospaces,theyhave
disadvantages,suchascreatingweakpointsinthebuildingskinforheatlosses[18]. Highlevelsof
solarradiationduringthesummerperiodinhotandhumidenvironmentsincreasecoolingloads[19].
Thecorrectproportionofwindowtoexternalwallandthecorrectopeningproportionofthewindow
willreducecoolingloadsandincreasethermalcomfort.Inordertodesignsustainableoffices,architects
shouldbeofferedguidanceastothecorrectsizeofwindowsonexternalwallsandthecorrectwindow
openingproportioninrelationtothewholeyear’sperformance. Theareaofawindowisadecision
takenbythedesignersattheearlystagesofarchitecturaldesign;therefore,itisdifficultorimpossible
tochangeitlater. Itisobviousthatwindowshaveaveryimportanteffectontheenergyuseofthe
building[20].
Theconstructionofpassivebuildingrequiressmallwindowsonthenorthfaçadeduetopotential
heatlosses. Howeverhavinglargewindowsonthesouthfaçadeleadstosolarheatgain. Adynamic
simulationtoolcalledDEROB-LHshowedthatthesizeofwindowsisnotimportantforwinterheating
butisveryimportanttomeetthecoolingdemandduringsummer[21]. InAmmancity,usingalarger
area of glass on the south, east, and west elevations saves energy and decreases the heating load
forthewinterseasonifinsulatingglassof6mmclearglassontheouterpane,12mmairspaceand
6mmclearglassontheinnerpaneisused. However,energyissavediftheglazingareaisdecreased
withinsulatingglassof6mmclearglassontheouterpane,12mmairspace,and6mmclearlow-E
(Pilkington)isusedonthenorthelevation[22].
Thequalityoftheindoorenvironmentrequiresthermalcomfortbecauseofitseffectsonwell-being,
the performance of people, and energy requirements [23]. For the thermal sensation of people,
meanradianttemperatureisoneoftheimportantvariables.[24]. Inordertoinvestigatetheenergy
behavior of buildings, a thermal infrared imaging tool is useful. This tool is used for the thermal
insulationoftheenvelope,ventilation,airleaks,andmechanicaldevicesperformance[25]. Thechoice
ofwindowsystemsisveryimportantforbuildingenergysavingduetotheUvalueandsolarheat
gaincoefficientofwindows[26]. Whenvenetianblindsareinstalledonwindowsintropicalclimates,
thesatisfactionofpeoplewhoaresittingnexttoglassdependsonthelevelofsolarradiationstriking
thebody[27]. Avirtualwindowwasdesignedwithanarrayof32LEDtilesandalineofLEDlinear
fixtureswithadjustablecolortemperaturestoprovidedirectlightintothetestroom. Asaresulta100%
viewfromthewindowisachieved;moreover,theaverageworkplaneluminancereached239lxand
11%oftotalareabecame500lx[28]. Thisstudyuseddaylightmetricsandlightingenergythatare
influencedbywindowtowallratio,wallreflectance,andwindoworientationinatropicalclimate.
Asaresult30%ofthewindowtowallratiowith0.8wallreflectanceonthesouthorientationledtothe
optimumsolution[29]. InordertocalculatethePMVandPPDISO7730: 200andEN15251[3,4]with
airtemperature,meanradianttemperature,airvelocity,andrelativehumidityarerequired[30].
2. Objective
ThisresearchreportsontheoutcomesofdynamicthermalsimulationsviaEDSLTassoftware[1]
forfindingthethermalcomfortofnaturallyventilatedofficeenvironmentsviaanoptimalproportion
ofwindowtoexternalwallwithanoptimalwindowopeningpercentage. Moreover,itunderlinesthe
factthataverageacceptablePMVandPPDforyearly-basedthermalcomfortoftheofficeenvironment
should be achieved for sustainability. According to ISO 7730 [3] and EN 15251 [4] standards for
overall thermal comfort and local discomfort, there are a number of categories. First, category A
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isPPD<6%(PMV´0.20to0.20),thesecondcategory,B,isPPD<10(´0.50to0.50)andthethird
category,C,isPPD<15%(PMV´0.70to0.70). Thereisalsoafourthcategory,D,thatbeginsfrom
the minimum of category C. Natural ventilation is a sustainable solution for decreasing cooling
load in the summer season and the heating load for the winter season. This paper examines the
influenceofdifferentwindowtoexternalwallproportionswithdifferentwindowopeningpercentages
for averaged yearly and monthly thermal performances of naturally-ventilated sustainable office
environmentinFamagusta,Cyprus. Thegoalistoofferadvicetodesignersonthethermalcomfortof
officeenvironments.
3. AnOverviewofPreviousStudies
Ochoaetal.[20]developedacomputermodelforoptimizinglowenergyandvisualcomfortin
thetemperateclimateofAmsterdam,theNetherlandswithwindowtoexternalwallratiosfrom10%
to100%at10%intervalsoffourmainorientations. Thewindowusedinthisworkwaslocatedinthe
middleoftheexternalwallandwasdoubleglazedwithoutanyshadingdevice. Asaresultofthis
work,itwasconcludedthatlargewindowsshouldnotbeusedbecausetheyprovideheattransfer
duringwinterandsummerperiods. Thecoolingdemandislargeinasoutherlyorientationwithlarge
windowsandconverselytheheatingdemandisalsolargeinanortherlyorientation,againwithalarge
windowsize. Moreover,withlargesizedwindowstheleastelectricconsumptionwasobservedwith
30%WWRatthenorthdirectionand20%WWRatthesouth,east,andwestfaçades. Thewindowto
externalwallratiobetween50%and70%intheNorth,60%intheSouthand50%–60%intheeastand
westorientationswereobservedfortheintersectionofoptimumvisualcomfortandluminancecriteria.
Gasparellaetal.[31]usedTRNYSsoftwareforevaluatingtheeffectoftwodifferentdoubleglazing
andtwodifferenttripleglazingwindowswithsizesof16%,25%,34%,and41%ofwindowtofloorarea
fortheparametersoforientationofthewindow,internalgainsforwinterandsummerenergyneed
withpeakloads,ofawell-insulatedresidentialbuildingintheclimateofParis,Milan,Nice,andRome.
Theresultsofthesimulationsfoundthatalargeglazingareaincreasesthewinterperformanceofthe
buildingbuthavingapeakloadisadisadvantage. Moreover,thisdisadvantagecanbeaddressed
byusingshuttersduringthenight. Asoutherlyorientationperformsbestinwinter,aswintertime
windowswithlowthermaltransmittancearegoodwithhighsolartransmittance. Itshouldnotbe
forgottenthathighsolartransmittancecreatesadisadvantageinsummertime,andtheuseofshading
devicesduringthistimeisadvantageous.
Poirazisetal.[32]usedIDAICE3.0fordynamicenergysimulationsofasingleskinofficebuilding
in Sweden. Studies have been done when the building was occupied with 30%, 60%, and 100%
windowtoexternalwallarea. Moreover,buildingorientationandplantypewithshadingdevices
wereanalyzedforlowenergyuseandgoodthermalcomfort. Thestudyconcludesthatsingleskin
buildingsconsumemoreenergythanconventionalfaçadesduringoccupation. Inadditiontothis,
theimpactofusingshadingelementsandappropriatewindowtypescansave15%ofenergyforfully
glazedfaçadebuildings.
Thalfeldt et al. [33] studied costly optimal and energy efficient window to external wall ratio
and external shading device simulations in the cold climate of Estonia. The optimal window to
externalwallratiowas40%and60%. Inadditiontothis,thecostlyoptimalfaçadesolutionwashigh
transparenttriple,low-emissivityglazingwithwindowtoexternalwallratioof25%andtheexternal
wallinsulationof200mm(U=0.16). LimitedsimulationsstudiedinCentralEuropeconcludedthat
awindowtoexternalwallratioof40%withtripleglazinganddoublelow-emissivitycoatingleadsto
optimalcost.
Susorovaetal.[34]createdtypicalofficemodelsindesignbuildersoftwareandconcludedthat
thegeometryoffenestrationaffectsenergyconsumptionlike3%and6%,maximum10%and14%in
hotclimatesbutonly1%intemperateandcoldclimates.
Leeetal.[35]conductedresearchviabuildingthermalsimulationmodelsinordertoidentify
optimumannualheating,coolingandlightingbymeansofenergyconsumptionfordifferentwindow
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systemsonabuildingskinwithdifferentwindowtoexternalwallratiosandorientationsinManila,
Taipei,Shanghai,SeoulandSapporowhichallhaveanAsianclimate. Thestudyconcludedthatin
SMusataninilaabi,liStyh 2a0n16g, h8,a 1i8,7S eoul,andSapporo,only25%ofthewindowtoexternalwallproportiono4n otf h2e0 
southfaçadewaseffective. InSapporoandSeoul,solarheatgainhadapositiveeffectonincreasing
the indoor temperature during the heating season. The north façade is less affected from the 
theindoortemperatureduringtheheatingseason. Thenorthfaçadeislessaffectedfromthevariations
variations of window to external wall ratio with the solar heat gain coefficient and the visible 
of window to external wall ratio with the solar heat gain coefficient and the visible transmittance.
transmittance. However, the east and west façades are affected, and care is needed. From a U‐value 
However, the east and west façades are affected, and care is needed. From a U-value perspective,
pweirnsdpoewctisvyes, tweminsdwowith sy1.s5teWm/s mw2iKtht o1.50 .8WW/m/2mK2 tKo h0a.8v eWa/mgr2eKa thearveeff eac tgroenatreerd uefcfiencgt tohne rheedautcininggl othade 
heating load than the cooling load. For cold areas lower U‐values can be used for window systems. 
thanthecoolingload. ForcoldareaslowerU-valuescanbeusedforwindowsystems.
In cool climates, such as Lithuania, without any shading, a north direction is the most energy 
Incoolclimates,suchasLithuania,withoutanyshading,anorthdirectionisthemostenergy
efficient orientation for air conditioned buildings. The most energy efficient window to external wall 
efficientorientationforairconditionedbuildings. Themostenergyefficientwindowtoexternalwall
ratios for south, east, and west orientations are 20%, but for north orientation is 20%–40% [36]. 
ratiosforsouth,east,andwestorientationsare20%,butfornorthorientationis20%–40%[36].
When all existing researches are considered, it became clear that there is an absence of research 
Whenallexistingresearchesareconsidered,itbecameclearthatthereisanabsenceofresearch
relating to optimum averaged yearly and monthly effects of window to external wall ratios with 
relating to optimum averaged yearly and monthly effects of window to external wall ratios with
various window opening ratios for offices in hot and humid climates on thermal comfort issues. The 
various window opening ratios for offices in hot and humid climates on thermal comfort issues.
necessity of filling this gap motivated the author to carry out this research. The consequences of the 
Thenecessityoffillingthisgapmotivatedtheauthortocarryoutthisresearch. Theconsequencesof
study will guide architects during the determination process of window to external wall ratios for 
thestudywillguidearchitectsduringthedeterminationprocessofwindowtoexternalwallratiosfor
offices in hot and humid climates. 
officesinhotandhumidclimates.
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rweesureltos botfa ainlle PdMfoVr tahneda PnPalDy zwederoef ofibceta.ined for the analyzed office. 

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Categories A, B, C, and D, which are stated above, can be seen with all the details in Table 1. The 
Categories A, B, C, and D, which are stated above, can be seen with all the details in Table 1.
properties of opaque and glass construction layers with U‐values are given in Tables 2 and 3, 
The properties of opaque and glass construction layers with U-values are given in Tables 2 and 3
respectively, for simulated office buildings. 
respectively,forsimulatedofficebuildings.
The Percentage of Dissatisfied People (PPD) and Predicted Mean Vote (PMV) calculations are 
produced via EDSL Tas [1] software by using its macros section for thermal comfort prediction. The 
simulated office building has one zone and the PMV parameters are as follows; metabolic rate is 1.2 
met, air speed was between 0.15 m/s as the lower limit and 0.3 m/s as the upper limit. Clothing value 
was 0.6 clo as the lower value and 0.95 clo as the upper value. The schedule for the office environment 
is created for the whole year (365 days, 7 days, and 24 h).
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Table1.ClassificationofthermalenvironmentsproposedbyISO7730[3]andEN15251[4].
ThermalStateofTheBodyasaWhole LocalDiscomfort
Percentageof PDDueto PDDueto
Predicted PDDueto
PredictedMean Dissatisfied VerticalAir Radiant
Category Percentageof CoolorWarm
VoteRange (PD)Dueto Temperature Temperature
Dissatisfied(%) Floor(%)
Draught(%) Difference(%) Asymmetry(%)
1(A) <6 ´0.20to0.20 <10 <3 <10 <5
2(B) <10 ´0.50to0.50 <20 <5 <10 <5
3(C) <15 ´0.70to0.70 <30 <10 <15 <10
4(D)(EN15251) >15 <´0.70or>0.70
Table2.ShowsusedpropertiesofopaqueconstructionlayerswithU-valuesforthesimulatedoffice.
U-Value SolarAbsorptance Emissivity Conductance Time
Category
(W/m2K) Ext.Surface Int.Surface External Internal (W/m2K) Constant
Ground
0.283 0.760 0.500 0.910 0.900 0.297 127.999
floor
Walls 1.135 0.400 0.400 0.900 0.900 1.407 4.920
Ceiling 1.01 0.700 0.500 0.900 0.900 1.251 13.749
Table3.ShowsusedpropertiesofglassconstructionlayerswithU-valuesforthesimulatedoffice.
ExternalSolar InternalSolar
Absorptance Absorptance
U-Value Solar Light Time
(W/m²K) Transmittance Ext. Int. Ext. Int. Transmittance Constant
Surf. Surf. Surf. Surf.
Windows(clear6-12-6
1.803 0.498 0.173 0.135 0.227 0.097 0.760 0
doubleglazinglowE)
ThePercentageofDissatisfiedPeople(PPD)andPredictedMeanVote(PMV)calculationsare
produced via EDSL Tas [1] software by using its macros section for thermal comfort prediction.
ThesimulatedofficebuildinghasonezoneandthePMVparametersareasfollows;metabolicrateis
1.2met,airspeedwasbetween0.15m/sasthelowerlimitand0.3m/sastheupperlimit. Clothing
value was 0.6 clo as the lower value and 0.95 clo as the upper value. The schedule for the office
environmentiscreatedforthewholeyear(365days,7days,and24h).
TheASHRAEThermalsensationscale[2,3,37]canbesummarizedas;´3cold,´2cool,´1slightly
cool, 0neutral, 1slightlywarm, 2warm, and3hot. Providingthermalcomfortconditionsshould
includemetabolicrate(met),clothinginsulation(clo),airtemperature(˝C),radianttemperature(˝C),
airspeed(m/s),andhumidity(%)[3,37].
4.2. TASSimulationResultsandDiscussions
Inordertogeneratethebestwindowtoexternalwallratiowithdifferentwindowopeningratios,
dynamicsimulationsofEDSLTasarecarriedout. Macrosareusedforthermalcomfortpredictions
(PMV and PPD) for averaged yearly and monthly performance generation. For the results three
categoriesofISO7730[3]andEN15251[4]areused. Accordingtothesestandards,PPDandPMV
hoursarefoundforFamagustathathashotandhumidclimaticconditions. Asaresultofthefindings
forthesimulatedofficeduringthewholeyear(8760h)categoriesofISO7730[3]andEN15251[4]
whichprovidethermalcomfortconditionswithWWRandwindowopeningratiocanbefoundinthe
followingparagraphsandinFigures2–11respectively.
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Figure 2. Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied People (PPD) for categories A,B, and C by means of hours (out of 8760 h in a whole year) 
Figure2.PredictedMeanVote(PMV)andPredictedPercentageofDissatisfiedPeople(PPD)forcategoriesA,B,andCbymeansofhours(outof8760hinawhole
for WWR 10% with all window opening ratios (from 0.1 to 1) with M: 1.2 met, air speed of 0.15–0.3 m/s, clothing value with 0.6–0.95 clo. 
year)forWWR10%withallwindowopeningratios(from0.1to1)withM:1.2met,airspeedof0.15–0.3m/s,clothingvaluewith0.6–0.95clo.
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Figure 3. Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied People (PPD) for categories A,B, and C by means of hours (out of 8760 h in a whole year) 
Figure3.PredictedMeanVote(PMV)andPredictedPercentageofDissatisfiedPeople(PPD)forcategoriesA,B,andCbymeansofhours(outof8760hinawhole
for WWR 20% with all window opening ratios (from 0.1 to 1) with M: 1.2 met, air speed of 0.15–0.3 m/s, clothing value with 0.6–0.95 clo. 
year)forWWR20%withallwindowopeningratios(from0.1to1)withM:1.2met,airspeedof0.15–0.3m/s,clothingvaluewith0.6–0.95clo.
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Figure 4. Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied People (PPD) for categories A,B, and C by means of hours (out of 8760 h in a whole year) 
Figure4.PredictedMeanVote(PMV)andPredictedPercentageofDissatisfiedPeople(PPD)forcategoriesA,B,andCbymeansofhours(outof8760hinawhole
for WWR 30% with all window opening ratios (from 0.1 to 1) with M: 1.2 met, air speed of 0.15–0.3 m/s, clothing value with 0.6–0.95 clo. 
year)forWWR30%withallwindowopeningratios(from0.1to1)withM:1.2met,airspeedof0.15–0.3m/s,clothingvaluewith0.6–0.95clo.
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Figure 5. Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied People (PPD) for categories A,B, and C by means of hours (out of 8760 h in a whole year) 
Figure5.PredictedMeanVote(PMV)andPredictedPercentageofDissatisfiedPeople(PPD)forcategoriesA,B,andCbymeansofhours(outof8760hinawhole
for WWR 40% with all window opening ratios (from 0.1 to 1) with M: 1.2 met, air speed of 0.15–0.3 m/s, clothing value with 0.6–0.95 clo. 
year)forWWR40%withallwindowopeningratios(from0.1to1)withM:1.2met,airspeedof0.15–0.3m/s,clothingvaluewith0.6–0.95clo.
Sustainability2016,8,187 10of21
Sustainability 2016, 8, 187  11 of 20 

Figure 6. Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied People (PPD) for categories A,B, and C by means of hours (out of 8760 h in a whole year) 
Figure6.PredictedMeanVote(PMV)andPredictedPercentageofDissatisfiedPeople(PPD)forcategoriesA,B,andCbymeansofhours(outof8760hinawhole
for WWR 50% with all window opening ratios (from 0.1 to 1) with M: 1.2 met, air speed of 0.15–0.3 m/s, clothing value with 0.6–0.95 clo. 
year)forWWR50%withallwindowopeningratios(from0.1to1)withM:1.2met,airspeedof0.15–0.3m/s,clothingvaluewith0.6–0.95clo.