Simulation-based decision support tool for early stages of zero-energy building design

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ContentslistsavailableatSciVerseScienceDirect

Energy

and

Buildings

jo u rn al h om epa g e :w w w . e l s e v i e r . c o m / l o c a t e / e n b u i l d

Simulation-based

decision

support

tool

for

early

stages

of

zero-energy

building

design

Shady

Attia

a,∗

_,

_Elisabeth

_Gratia

a

_,

_André

_De

_Herde

a

_,

_Jan

_L.M.

_Hensen

b a_Architecture_et_Climat,_Université_Catholique_de_Louvain,₁₃₄₈_Louvain_La_Neuve,_Belgium

b_Building_Physics_and_Services,_Eindhoven_University_of_Technology,_The_Netherlands

a

r

t

i

c

l

e

i

n

f

o

Articlehistory:

Received12October2011

Receivedinrevisedform17January2012 Accepted28January2012

Keywords:

Designdecisionsupport Zeroenergybuilding Sensitivityanalysis Energysimulation Thermalcomfort Hotclimates

a

b

s

t

r

a

c

t

Thereisaneedfordecisionsupporttoolsthatintegrateenergysimulationintoearlydesignofzero energybuildingsinthearchitecturalpractice.Despitetheproliferationofsimulationprogramsinthe lastdecade,therearenoready-to-useapplicationsthatcaterspeciﬁcallyforthehotclimatesandtheir comfortconditions.Furthermore,themajorityofexistingtoolsfocusonevaluatingthedesignalternatives afterthedecisionmaking,andlargelyoverlooktheissueofinformingthedesignbeforethedecision making.Thispaperpresentsenergy-orientedsoftwaretoolthatbothaccommodatestheEgyptiancontext andprovidesinformativesupportthataimstofacilitatedecisionmakingofzeroenergybuildings.A residentialbenchmarkwasestablishedcouplingsensitivityanalysismodellingandenergysimulation software(EnergyPlus)asameansofdevelopingadecisionsupporttooltoallowdesignerstorapidlyand ﬂexiblyassessthethermalcomfortandenergyperformanceofearlydesignalternatives.Validationof theresultsgeneratedbythetoolandabilitytosupportthedecisionmakingarepresentedinthecontext ofacasestudyandusabilitytesting.

Contents

Introduction. . . ... 3

DesignprocessandtoolsofNZEBs... 4

NZEBdesignapproaches. . . ... 4

ConceptualearlydesignstagesofNZEBs... 4

BarrierstointegratingBPSduringearlydesignphases ... 5

Geometryrepresentationinsimulationtools... 5

Fillinginput ... 5

Informativesupportduringthedecisionmaking... 5

Evaluativeperformancecomparisons ... 6

Interpretationofresults... 6

Informediteration... 6

Simulationtoolsreview... 6

Tooldescription... 7

Simulationbenchmarkanddatabase... 7

Thermalcomfortinhotclimates... 7

Renewablesystems... 7

Decisionsupportlogicandsensitivityanalysis... 8

Implementation,Interface,input,outputanddesignﬂowanddesigncontinuation... 9

Casestudy... 9

Resultsvalidity... 12

Usabilitytesting... 12

∗ Correspondingauthorat:ArchitectureetClimat,UniversitéCatholiquedeLouvain,1348Louvain-la-Neuve,BelgiumTel.:+32010472334;fax:+32010472150. E-mailaddress:shady.attia@uclouvain.be(S.Attia).

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Discussionandconclusion... 13

Summaryofmainﬁndings ... 13

Strengthandlimitations... 14

Comparisonwithexistingtools... 14

Futureresearch... 14

Acknowledgements... 14

References... 14

Introduction

Themodellingofnetzero-energybuildings(NZEBs)isa chal-lengingproblemofincreasing importance.TheNZEBs objective hasraisedthebarofbuildingperformance,andwillchangethe waybuildingsaredesignedandconstructed.Duringthecoming years,thebuildingdesigncommunityatlargewillbegalvanisedby mandatorycodesandstandardsthataimtoreachneutralor zero-energybuiltenvironments[1–3].Atthesametime,lessonsfrom practiceshowthatdesigningarobustNZEBisacomplex,costly andtedioustask.TheuncertaintyofdecisionmakingforNZEBsis high.Combiningpassiveandactivesystemsearlyonisachallenge, asis,moreimportantly,guidingdesignerstowardstheobjective ofenergyandindoorcomfortofNZEB.Table1showsthesixmain buildingdesignaspectsthatdesignersshouldaddressearlyon dur-ingtheconceptualstage.Theintegrationofsuchdesignaspects duringtheearlydesignphasesisextremelycomplex,time consum-ingandrequiresahighlevelofexpertise,andsoftwarepackages thatarenotavailable.Atthisstage,thearchitectsareinaconstant searchforadesigndirectiontomakeaninformeddecision. Deci-sionstakenduringthisstagecandeterminethesuccessorfailure ofthedesign.Inordertodesignandconstructsuchbuildingsit isimportanttoassureinformeddecisionmakingduringtheearly designphasesforNZEBs.Thisincludestheintegrationofbuilding performancesimulation(BPS)toolsearlyoninthedesignprocess [4,5].

BPS is ideal to lower such barriers. BPS techniques can be supportivewhenintegratedearlyonin thearchitectural design process. Simulation in theory handles dynamic and iterative designinvestigations,whichmakesiteffectiveforenablingnew knowledge,analyticalprocesses,materialsandcomponentdata, standards, design details, etc., to be incorporated and made accessible topracticing professionals. In the last tenyears, the BPS discipline hasreached a high level of maturation, offering a range of tools for building performance evaluation [6]. Most importantly,theyopenthedoortoothermainstreamspecialism, includingarchitectsand smallerpractices,duringearlier design phases.

However,despitetheproliferationofBPStools,thebarriersare stillhigh.Despitetheproliferationofsimulationprogramsinthe lastdecade,therearenoready-to-useapplicationsthatcater specif-icallyforthehotclimatesandtheircomfortconditions.Current designanddecisionsupporttoolsareinadequatetosupportand informthedesignofNZEBs,speciﬁcallyduringearlydesignphases. Mostsimulationtoolsarenotabletoadequatelyprovidefeedback regardingthepotentialofpassiveandactivedesignand technolo-gies,northecomfortusedtoaccommodatetheseenvironmental conditions[7].Severalstudiesshowthatcurrenttoolsare inad-equate,userhostileandtooincompletetobeusedbyarchitects duringtheearlyphasestodesign NZEBs[8–10].Architects suf-ferfromBPStoolbarriersduringthisdecisivephasethatismore focusedonaddressingthebuildinggeometryandenvelope.Infact, architectsarenotonboardconcerningtheuseofBPStoolsforNZEB design.Outofthe392BPStoollistedontheDOEwebsitein2011, lessthan40toolsaretargetingarchitectsduringtheearlydesign phases,asshowninFigs.1and2[11].

Ontheotherhand,theintegrationofBPSinthedesignofNZEB ischallenging,andrequiresmakinginformeddesigndecisionsand strategicanalysisofmanydesignsolutionsandparameterranges andsimulatingtheirperformance.Arecentstudybytheauthor [12],aimingatrankingBPStools’mostimportantselectioncriteria, showedthatarchitectsrankedintelligenceaboveusability, inter-operabilityandaccuracy,asshowninFig.3.Architectsidentified intelligenceastheBPStools’abilitytoinformthedecision mak-ingandallowdecisionmakingonbuildingperformanceandcost. Alsoarchitectsindicatedalackofintelligencewithinthetools com-pared.Thestudyrevealedthatarchitectsandnon-specialistusers whowanttodesignNZEBsfrequentlythereforefinditdifficultto integrateBPStoolsintothedesignprocess.

Therefore,inordertodeliverNZEBswemustlowerthebarrier betweenbuildingdesignandperformance,ensuringthebest guid-anceisavailableduringthecriticaldecisionmakingstagesofNZEB design.Architects’decisionstodesignNZEBsshouldbeinformed. Researchinvestigationsintheliteraturedescribethereasonsfor thesebarriers,butlittleefforthasbeendonetodeveloptherequired methodsandtoolsthatcanpredictthebuildingperformancein

Fig.1.EvolutionofBPSToolsinthelast10years.

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Table1

ThesixmainbuildingdesignaspectsofNZEBsdesign.

1.Metric ThereareseveraldeﬁnitionsforNZEBsthatarebasedonenergy,environmentaloreconomicbalance.Therefore,a NZEBsimulationtoolmustallowthevariationofthebalancemetric

2.Comfortlevelandclimate Thenetzeroenergydeﬁnitionisverysensitivetowardsclimate.Consequentially,designingNZEBsdependsonthe thermalcomfortlevel.Differentcomfortmodels,e.g.staticmodelandtheadaptivemodel,caninﬂuencethe‘netzero’ objective

3.Passivestrategies PassivestrategiesareveryfundamentalinthedesignofNZEBincludingdaylighting,naturalventilation,thermalmass andshading

4.Energyefficiency Bydefinition,aNZEBmustbeaveryefficientbuilding.Thisimpliescomplyingwithenergyefficiencycodesand standardsandconsideringthebuildingenvelopeperformance,lowinfiltrationrates,andreduceartificiallightingand plugloads

5.Renewableenergysystems(RES) RESareanintegralpartofNZEBthatneedstobeaddressedearlyoninrelationtobuildingfromaddressingthepanels’ area,mountingposition,rowspacingandinclination

6.Innovativesolutionsandtechnologies Theaggressivenatureof‘netzero’objectiverequiresalwaysimplementinginnovativeandnewsolutionsand technologies

useandsupportthedesigndecisionmakingofbuildings[10].In ordertoovercomethebarriersandachievetheaimsidentiﬁed ear-lierthisresearch,acontextualdecisionsupporttoolisproposed forNZEB design. Thisstudyis partof a largerresearchproject thataimstolowerthebarriersofintegratingBPSduringtheearly phasesindesign.Thispaperpresentsamethodanddecision sup-portbuildingsimulationtoolunderdevelopmentthatcanbeused asaproactiveguideintheearlydesignstagesofresidentialNZEB designinhotclimates.Thepaperproposesasensitivityapproach methodembeddedinatooltoprovidebetterguidancefordesign decisionstodeliverNZEBs.Thisisachievedthroughenabling sensi-tivityanalysistoinformthedecisionmakingandallowingavariety ofalternativestobecreatedinshorttime.

Section2 presentsan overview on the existing design pro-cessandsimulationtoolsforzeroenergybuildings.ThenSection 3presentsa tooldescriptionand mechanics.Section4isacase studythatincludesthevalidationoftheresultsandusability test-ing.Finally,Section5summarizestheresearchﬁndingsandtools strengthandweaknesssuggestingfutureimprovements.

DesignprocessandtoolsofNZEBs

Abuildingdeliveryprocesshastraditionallybeenadiscreteand sequentialsetofactivities.Designersstartwithrulesofthumbto createadesign,andthenmodelittoverifyitscompliancewiththe performancegoals.Iftheproposeddesigndidnotmeetthegoalsthe designerswouldgobackandstartagain.Thistedioustrialanderror approachcontinuesuntilﬁndingthedesignthatmeetsthe perfor-manceconditions.However,the“netzero”objectiveisanenergy performance-baseddesigngoalthatembracestheintegrationof energy-performancegoalsearlyinthedesignprocess.Architects

Fig.3.Architectsrankingthemostimportantfeaturesofasimulationtool[14].

areforced toexpand theirscopeof responsibilitybeyond func-tionandaesthetics.ThedesignprocessofsmallscaleNZEBs,with noenergyspecialistonboard,showsthatthedesignisnot intu-itiveandenergyperformancerequirementsmustbedetermined intheearlydesignstages.Therefore,BPStoolsarea fundamen-talpartofthedesignprocess[13–15].Duringearlydesignphases, 20%ofthedesigndecisionstakensubsequentlyinﬂuence80%of alldesigndecisions[15].Inordertoapplysimulationduringearly designphasesitisbettertounderstandthecurrentbuildingdesign anddeliveryprocessofNZEBs,becausetheeffectivenessoftools areaffectedbytheprocess.Thissectionelaborates onprevious attemptsatsolvingintegrationissuesrelatedtotheNZEBdesign deliveryprocessandtheuseofsimulationtools.

NZEBdesignapproaches

ANZEBisagrid-connectedandenergy-efficientbuildingthat balances its total annual energy needs by on-site generation [16]. The main concernof NZEBs design is robustness through themetric-baseddesignortheperformance-baseddesign (PBD) approaches.AsformulatedbyKalay,thePBDapproachemphasises thedesigndecisionmakinginrelationtoperformance[17].Similar totheevidence-baseddesign(EBD)approachthatemphasisesthe importanceofusingcredibledatainordertoinfluencethedesign processinhealthcarearchitecture,thePBDhasbecomea funda-mentalapproachtoevaluatetheenergyperformanceofbuildings inenvironmentalarchitecture.ExperiencewithconstructedNZEBs showsthat theirdesign processis basedonperformance-based decision makingthateffectively integrates,earlyon, allaspects ofpassivebuildingdesign,energyefficiency,daylightautonomy, comfortlevels,renewableenergyinstallations,HVACsolutions,in additiontoinnovativesolutionsandtechnologies[13,18,19].Thus, evaluatingdifferentdesigncombinationsandparametersbasedon theirperformancebecameanadditionalactivityduringtheearly design stages of NZEBs. To putthedesign process of NZEBs in perspective,designershavetomeetwithsuccessivelayering con-straintswithaperformance-basedobjective,where“formfollows performance”.Designershavetodefinetheirworkinasetof per-formancecriteria,ratherthanworkoutthedesigntraditionallyin aprescriptiveobjective.TheimplicationsoftheNZEBperformance baseddesignapproachonthedesignprocessarediscussedinthe nextparagraph.

ConceptualearlydesignstagesofNZEBs

TheprocessofNZEBsdesigncanbedescribedasasuccessive lay-eringofconstraintsonabuilding.Everynewaddeddecision,every deﬁnedparameters,isjustonemoreconstraintonthedesigner.At thestartoftheNZEBsdesignprocessthedesignerhasmany deci-sionsandarelativelyopensetofgoals.Bytheend,thebuilding

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Fig.4. Barriersofdecisionmakingduringearlydesignstages.

issharplydeﬁnedandheavilyconstrained.Forhighperformance buildingshighconstraintsareimposedduetoenvironmentaland energeticrequirements.Theconstraintsprovideusefulanchorfor ideas.ConceptualearlydesignstagesofNZEBscanbedividedinto ﬁvesub-stages:(1)specifyingperformancecriteria,(2)generating ideas,(3)zones-layoutdesign,(4)preliminaryconceptualdesign, and(5)detailedconceptualdesign.Sub-stages2–5donotalways followa sequentiallinear order.Thedesignprocess goesintoa cyclicprogressionbetweenthosesub-stagesinwhicheach sub-stageelaboratesuponpreviousconstraints.

BarrierstointegratingBPSduringearlydesignphases

Experience with post occupancy evaluation of constructed NZEBsshowsthatthedesignofhigh-performancebuildingsisnot intuitive,andthatBPStoolsareafundamentalpartofthedesign process.ThenatureoftheaggressivegoalsofNZEBsrequiresthe earlycreationofenergymodelsduringpre-conceptualand concep-tualdesignphases.Recentstudiesoncurrentbarriersthatfacethe integrationofBPStoolsintoNZEBsdesignaresummarisedbelow [13].Fig.4illustratesthebarriersofdecisionmakingduringthe earlydesignstagesofNZEBsdesign.

Geometryrepresentationinsimulationtools

Architects work in different ways through sketches, phys-ical models, 2D and 3D computer generated imagery, and analytically–andthushavedifferentrequirementsforrepresenting andcommunicatingtheirdesignform.

Fillinginput

Therepresentationofinputparametersinthelanguageof archi-tects is a challenge in many tools. There is a clear separation betweenarchitectsdesignlanguageandthebuildingphysics lan-guageofmosttools.Thisdifferenceisoftenaddressedbyusing reducedinputparametersorusingdefaultvalues.However,ﬁlling inthedesignparametersisanoverlookedissueamongBPStools developers.

Informativesupportduringthedecisionmaking

Designcannoteasilypredicttheimpactofdecisionson build-ingperformanceandcost.ThebuildingdeliveryprocessofNZEB requiresinstantaneousfeedbackandsupporttoinformthedecision makingforpassiveandactivedesignstrategies.Thedisadvantage ofmostexistingtoolsisthattheyoperateaspostdesignevaluation

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tools.Therefore,theinformativesupportshouldbecomprehensive enoughtoincludegeometryandenvelopeandsystems.

Evaluativeperformancecomparisons

Duringtheearlydesignstagesthebenchmarkingandthe pos-sibilitytocomparealternativesismoreimportantthanevaluating absolutevalues.Theideasgenerationphaseisiterativeand com-parative.Mostexistingtoolsdonotemulatethisprocessandfocus onpost-designevaluation.

Interpretationofresults

The representation of simulation output and its interpreta-tionisfrequentlyreportedasabarrieramongarchitects[10,14]. Analyticalresultspresented intables ofnumbersor graphsare oftentoocomplex anddetailed, providinganexcessiveamount ofinformation.Theoutputrepresentationoftenlacksvarietyand visualqualities.Analysisandsimulationresultsshouldbedisplayed withinthecontextofthe3Dgeometricmodel[20].

Informediteration

Themostimportantbarrierfacingarchitectsiscyclinginformed iterationsforconceptdevelopmentandoptimisation.Inthepast, architectsiteratedbackonthedesignforfunctionalandaesthetical optimisationpurposes.ForNZEBstheyhavetoiteratefor perfor-manceoptimisationpurposes.Thisrequiresanunderstandingof buildingphysicsandperformance. Architectsneed fundamental understandingofbasicbuildingphysicsthatallowsthemto inter-pretthesimulationfeedbackanddrivethemtoiteratebacktothe concept.

Simulationtoolsreview

Almost no current tool addresses the design of NZEBs for architectsduringearlydesignphases[21].NZEBsdesignstrategy addressesadesignduo:ﬁrstmaximumenergyefﬁciencyandthen thedeliveryofenergyrequiredfromrenewablesystems.Almostno toollistedinTable2helpstoanswerthis.Acriticallookatthe exist-ingtoolsinrelationtotheNZEBsdesignprocessshowsthatseveral barriersexistinintegratingthecurrentBPSatthisstage. There-fore,futuretoolsshouldallowbothstrategiesinordertodevelop NZEBsandsupplementtheintuitivenessofthedesignprocesswith analyticaltechniquesandsimulationmethods.

Overthelastfewdecades,alargenumberof BPStoolshave beendevelopedtohelpengineersduringlatedesignphases.Such toolsweredevelopedtoproducedataconcerningbuildings’ numer-icalmodelling,simulatingtheperformanceofrealbuildings.Those energyBPStoolsrequireacomplicatedrepresentationofthe build-ingalternativesthatrequirespeciﬁcandnumericalattributesofthe buildinganditscontext.Thosetoolscanbeclassiﬁedunderamain

groupnamed“evaluationtools”asshowninTable2.Theexamples inTable2aremeanttobeindicative,notexhaustive.

Evaluation tools include energy analysis computer tools. Although bybeing evaluativethey produceresults that do not actuallyprovideanydirectguidanceastohowtheNZEBdesign shouldbeimprovedortheperformanceobjectiveachieved.The useofevaluationtoolsinNZEBdesignisbasedonapost-decision trialand errorapproach,wherethesimulationresultsare com-paredto a desired value. Ifthe resultsare not satisfactorythe designismodiﬁedandtheprocessisrepeated.Thisapproachis cumbersome,tedious,andcostlyandforcesarchitectstorelyon simulationexpertsduringtheearlydesignstages.Recently,some plug-insweredevelopedtofacilitatethegeometryinputandlink architecturalformsofvisualisationand3Drepresentationwiththe evaluationtools.However,evaluativetoolsembedmostintegration barriersdiscussedinSection2.3.

However,duringthelastdecade, arangeofdesign toolshas beenavailabletohelparchitectsinthedesignofmoreenergy efﬁ-cientbuildings.Thosetoolsarelabelled “guidancetools”,which weredevelopedtofacilitatedecisionmakingpriortodesign.They rangefromquitesimplepre-decisionevaluationandanalysistools toparametricandoptimisationdecisiontoolsthataimtoinform the design and integrate BPS during the early design process. However,Table2showsthatmostdevelopedguidancetoolsare pre-decisionevaluativetools.Despitetheirremarkablecapabilities, mostthosetoolshavenotbeentransferredeffectivelytothe archi-tecturalcommunity,andinparticulararchitectsduringtheearly designstages.Theuptakeofmostthosetoolsamongarchitectsis verylow,anddoesnotallowcontinuitywiththedesignprocess [10,22–24].Whiletheyarequiteusefultolowerthe“input ﬁll-ing”barrier,theycouldnotlowerthe“informativesupportduring thedecisionmaking”barrier.Currently,fewnon-publictoolsexist thatsupportdesignpre-decisions,includingjEPlusandiDbuildthat allowparametricanalysisorBEoptthatallowsoptimisation analy-sis[25,26].Thepotentialofparametrictoolsisveryhightobridge the“informativesupport”barrierbecausetheycanprovide con-structivefeedbackwithverylittleiterations,andatthesametime allowawiderangeofsolutionspace.Incontrasttooptimisation toolsthatreducesthesolutionspacetoaminimum.

In order to address these shortcomings, we identiﬁed the requirementsofatoolthatcanbeusedforthedesignofNZEBs duringearlydesignprocesses.Theauthorconductedasurvey, com-parisonstudyandworkshopsontheuseofBPSbyarchitectsfor NZEBdesigninEgypt[27].Theguidelinesofthenewtoolcanbe summarisedasfollows:

• ProvidebetterguidancefordesigndecisionstodeliverNZEBin hotclimates

Table2

ClassiﬁcationofBPStoolsallowingdesignevaluationanddesignguidance.

Evaluative Informative

Support(Technique) Post-decisionEvaluative GeometryPlug-in Pre-decisionEvaluative(Para& Opt.)

Pre-decisionInformative (Parametric)

Pre-decisionInformative

Iterations High High Medium Low Low

Renewablesystems Energyefﬁciency EnergyPlusTRNSYS Esp-r IESVE OpenStudio IESVE-Ware SolarShoeBox Energy10 DesignBuilder jEPlus iDbuild BeOPT OptiPlus OptiMaison Vasari MITAdvisor BDA DesginInent HEED SolarHouse Sunrel

Daylighting&Facades SunTools COMFENNewFacadesLightsolve Diva

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• Enablesensitivityanalysistoinformdecisionmakingandallow avarietyofalternativestobecreatedinshorttime

• Thecomfortrangecriteriaanddesignstrategiescanbeadjusted torespondtolocaldeﬁnitionsofindoorcomfort,local construc-tionsystemsandlocalcoderequirements

• Improveaccessibilitytodecisiontoolsforsmallpractices • Integrate thenew tool withsufﬁciently established, accurate

tools

• Matchthecyclicdesigniterationsandextendthescopeoftools totheconceptualphasesofthedesignprocess

• Allowconnectivitywithestablishedtoolsusedbydifferent dis-ciplinesandinlaterdesignstages.

• Veryeasytouseandtolearn,andadaptablefortheless experi-encedwithminimuminput

Inorder tosupportdecisionmaking duringtheearlydesign phasesitisimportanttoincludeaninformativetoolfortheearly design phasesthatcanmodel thecomplexityof thedesign.An energysimulationtool,ZEBO,wasdevelopedtohelparchitects dis-coverparametersthatwouldachieveazeroenergybuildingand informthemaboutthesensitivityofeachparameter.Theinterface forZEBOwasbuiltontheabovementionedguidelines.Howthe proposedtoolintendstoachieve thesegoalsisexplainedinthe followingsections.

Tooldescription

In response to the barriers, requirements, and expectations identiﬁedinSection2,aprototypeoftheproposeddecision sup-porttoolwasdeveloped.Thetoolisaconceptualmodelforsoftware underdevelopmentcalled“ZEBO”thataimstoaddressthese short-comingsandtestthevalidityofthemethodproposedinSection 2[28].Thetool allowsfor sensitivityanalysisofpossible varia-tionsof NZEBdesign parametersandelementsduringtheearly designphasesinhotclimates.Itsaddedvalueresidesinits abil-itytoinformthedecisionpriortothedecisionmakingforNZEBs design.Thetooliscontextualandisbasedonanembedded bench-markmodelanddatabaseforEgyptianresidentialbuildings,which includeslocalmaterialsandconstructionandallowsthegeneration ofcodecomplyingdesignalternatives(seeFig.6).

TheinitialtargetaudienceofZEBOisarchitectsand architec-turalstudentswithlittleexperienceinbuildingenergyefﬁciency. Thetoolcanbeusedbyarchitectstolowerthebarriertodesign NZEBsduringtheearlyconceptualphases.Typically,architects pro-duceseveraldesignalternativesintheconceptualdesignphases. Thusthisisthemomentwherethetoolshouldbeappliedtoassess theenergyperformanceandenergygenerationpotentialforeach designsolutionbystudyingtheeffectofthevariationofdifferent designparametersranges.ZEBOalsoallowsforcomparativeenergy evaluations.

Simulationbenchmarkanddatabase

Oneofthechallengestodevelopingthetoolwastoimplementa representativebenchmarkorreferencebuildingfordwellings.The benchmarkshouldrepresentEgyptianﬂatapartmentsinnarrow fronthousingblocks.Forthisstudyweselectedabenchmarkbased onarecentresearch,conductedbytheauthor[29,30],todevelop abenchmarkmodelsfortheEgyptianresidentialbuildingssector. Thebenchmarkrepresentsdifferentsettingsofapartmentsthatcan beconstructedinadetached,semidetached,orattachedform.It wasassumedtorepresentapartmentsinhighurbandensitiesof Egyptiancities,incorporatingsurroundingbuildingsand streets. The benchmark developed by Attia et al. describes the energy useproﬁlesforair-conditioners,lighting,domestichotwaterand

appliances inrespect tobuildings layout and construction.The benchmarksimulationmodelswereveriﬁedagainsttheutilitybills andﬁeldsurveydatafor1500apartmentsinAlexandria,Cairoand Asyut.

ForZEBOasimplemulti-dimensionalrectangularzonewas cre-atedtorepresentmechanicallycooledapartmentunits.Despitethe limitationofthisreductionorabstractionoftheunderlyingmodel, thetoolcoupledthemodeltotheEgyptianclimaticandurban con-text.TheselectedmodelisshowninFig.8andallowsmaximum designﬂexibilityforarangeofarchitecturalearlydesign parame-ters,includingthesites’urbandensityandclimaticconditions.The inputparametersandoutputoptionsarediscussedinSection3.5. Moreover,ZEBOisbasedonaknowledgebasesystemthatembeds therecommendationsoftheEgyptianResidentialEnergyStandard ECP306-2005I[31,32].Theprescriptiverecommendationsofthe standardsaretranslatedintoinputdefault valuesdependingon theselectedsitelocationandcode.Alsoaself-developedmaterials libraryisembeddedthatallowsthecombinationofthemost com-monmaterialconstructionsinEgypt,includingglazing,insulation, andwallandroofconstruction.

Thermalcomfortinhotclimates

DesigningNZEBsdependontheexpectedthermalcomfortlevel. InEgyptcomfortisadaptiveandmechanicalequipmentsuchas ceilingfansareusedmainlyforoccupancysatisfaction.Itisknown thatairmovementaffectsbothconvectiveandevaporativeheat lossesfromthehumanbody,andthusinﬂuencethethermal com-fortandconsequentlyinﬂuencethe‘netzero’objective.ForZEBO wechoseGivoni’scomfortmethod[33]thatallowsadaptive com-fort boundariesin relationto theincrease of air movementby turningonfanoropeningwindows.AsshowninFig.8,a psychro-metricchartallowsthevisualisationofoutdoororindoordrybulb temperatureand relative humidityareatemperature.The chart canbeusedpriorto,orafter,designtoestimatethenecessityof installinganacclimatisationsystem.Thechartcanalsoestimate theimpactofmechanicallyassistedventilationusing,e.g.,ceiling fansinrelationtoforcedwindspeedsrangingfrom0.5to2m/s asadesirablestrategyforunconditionedbuildingsinhotclimates. Thisleadsthedesignertostart thinkingabouttheeffectiveness ofhisorherpassivedesignstrategiesinrelationtoactivecooling system.Thechartcanvisualiseimpactofanyparameterchange onthermal comfortopposite tomany simulationtools thatare unabletoadequatelysimulatehumanthermalcomfortaswellas theacclimatizationmechanicalequipmentssuchasceilingfansin hotclimates.

Renewablesystems

Lessonslearnedfrompracticeshowtheimportanceof inform-ingarchitectswithactivesystemrequirementstointegratethemin theenvelopeandbecomeabasicpartoftheNZEBdesignconcept. Therefore,anextraintegralmoduleofZEBOallowstheestimation oftheenergygenerationandrequiredphotovoltaicandsolarwater heaterpanelarea.Thesolaractivetoolmoduleisbasedonearlier researchbytheauthor[28]andinformsthedecisionmakingon thephysicalintegrationwithinthebuildingenvelope,addressing thepanels’area,mountingposition,rowspacingandinclination. Theideaofthismoduleistoinformthedesignerasearlyas pos-sibleonthespatialandphysicalimplicationoftheNZEBobjective. Therenewablesystemmoduleisanimplementationofsimulation resultsthatestimatetheaverageperformanceofaPVsystemin dif-ferentlocationsandpositionsinEgypt.Thesimulation-generated datawasmatchedwithrealmeasurementsobtainedfromthe lit-erature.

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Fig.5. Toolworkﬂowscheme.

Toidentifytheinputparameters5 mandatoryquestions are askedontwosuccessivescreensshowninFig.6.Ontheﬁrstscreen usersareaskedtoselectacity,moduletypeandmounting posi-tion.Thesecondscreenasksforinputregardingpanelorientation (azimuthangle)andinclination.Therearetwoadditionalelective questionsonscreentwothatallowuserstoinputvaluesregarding

thepanelefﬁciencyand/ornominalpeakpower.Foreveryquestion, theuserhastochoosebetweendifferentanswers,corresponding tothevarious simulatedcases.Insteadofcommunicatingthose resultsintheformoftextual/numericaldataagraphical interac-tiveinterfaceisdevelopedtoconveythedesignguidelinesinan visualway.Theresultsarethencompiledintoperformancegraphs asshowninFig.6.

Decisionsupportlogicandsensitivityanalysis

Theuseofsensitivityanalysispriortothedecisionmaking rep-resentsaninformativeapproachfortherobustnessofthedesign decision in relationtoenergy consumption and comfort. Based onthefeedbackobtainedfromthesensitivityanalysisresults,the designdecisionissupportedinrelationtothepossibilitiesofthe parameterrange.Therefore,thesensitivityanalysisisamethod thatenablesdesignerstotakeenergyandcomfortconscious deci-sionstoreachtheﬁnalperformance goal.Forthetool, aglobal sensitivityanalysiswasundertakentoinvestigatethemostearly designparametersandtheirranges[34,35].Fig.5illustratesthe methodusedforthedevelopmentofthetool.Thedesigners inves-tigatesthesensitivityofasingleparameteranditsconsequences onenergysaving,energy generationorcomfort. Thesensitivity analysisresultshowsthewholeparameterrangeandprovidesa pre-decisionoverviewoftheparameterrangeandintervals.The designermakes decisionsbasedonthis overview,and speciﬁes aperturbation.Based onthecompliancewiththerules set,the designercanthenrepeattheprocesswithotherparametersbefore combiningallperturbationsandrunningacompleteevaluation.

ZEBO allows sensitivity analysis to illustratehow variations inbuildingdesignparameterscanaffectthecomfortandenergy performance.Infact,sensitivitydesignenvironmentsprovidean opportunity toinform thedecision making.Therefore, the tool depends on the parametricpre-processor, a recent additionto EnergyPlusutilitiesthatallowstheaccomplishmentofsensitivity analysis.TheparametricobjectsofEnergyPluscanbeusedina sin-glefileasanalternativetomaintainingagroupoffileswithsmall differences.Theusereffectuatesaseriesofsimulationscloningthe sameIDFfilebutincludingalldiscreteintervalsofapredefined parameterrange,justbyclickingthesensitivityanalysisbutton. TheRunBatchwillrundifferentsimulationsusingtheIDFinputfile.

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Theuseristhenprovidedwithagraphthatshowsthevariationin annualenergyperformanceinrelationtotheparameterintervals’ range,inawayitcanbecomeanimmediateyetcomprehensive supporttomakeinformeddesigndecisions.

Implementation,Interface,input,outputanddesignﬂowand designcontinuation

ZEBOcanacceptinputdatarequiredbythelaterphasetool Ener-gyPlusv6andrunasimulationwithitsengine[36].EnergyPlusisa whole-buildingenergyperformancesimulationtooldevelopedby theUSDepartmentofEnergy.EnergyPlusisthenextgenerationof BPStoolthatisunderconstantdevelopmentandoffersadvanced simulationcapabilities.Thesoftwareisafreeopensourcetoolthat allowsthird-partygraphicaluserinterfaces(GUIs).Therefore, Ener-gyPluswasselectedbecauseitcanbeusedinacyclicalprocessthat allowscontinuitywiththedesignprocessusingthesameinputfiles. Thetoolisbasedonaonepageinterfacethatcommunicateswith EnergyPlusviatheinputandoutputformatthatareinASCIIformat. ZEBOcreatesanIDFinputfileandthesimulationrunsthe Energy-Plusenginethrougha“RUN”batch-file.Thesimulationresultsare thengeneratedindifferentformats,mainlyHTMLandCSVfiles. ThetoolusesEnergyPlus’sIDFformatthatallowsconnectivitywith establishedtoolsusedbydifferentdisciplinesandinlaterdesign stages.ZEBOextractstherequiredoutputandpresentsthem graph-icallyonthesamepage.Theprogramminglanguagewaswrittenin VisualBasic2008.

ToaddresstheNZEBobjective,theinterfacefirstaddressesthe passivedesignstrategiesandthentheactivedesignstrategies.The overallconceptualflowchartisillustratedinFig.6.Uponclicking theexecutionfile,ZEBOopensthemainpageoftheinterfaceas showninFig.8.Inputoptionsarecategorisedontheupperleft oftheGUI,andarelistedinFig.7.Inputcategoriesaredividedinto eightgroups:weatherfile,orientation,zonedimensions,northand southwindowwidthandtype,shadingdevicesanddimensions, walltype,wallinsulationtypeandthickness,androofinsulation typeand thickness.Theweatherfileis selectedbyapull down menu.ThefileisanEPWfiletypeforelevenEgyptiancities down-loadedfromtheDOEEnergyPlusweatherfilelibrary[36].Oncethe weatherfileisselected,thestandardrequirementsofthechosen locationareautomaticallysetasdefaultvalues,allowingthe cre-ationofthebaselinecase[30].Theuseristhenallowedtochange theparameterinputwithout exceedingtheminimum standard requirement.

Themainpurposeofthepassivedesigninterventionistoreduce thecoolingdemand.Forexample,thebuildingcanberotatedinto eightdirectionsevery45◦.Threehorizontalscrollbarsallowthe modificationoftheheight,lengthanddepthofthehousingoroffice unit.Designerscandefinewindows.Theycancheckthewindow optionandmodifythewindowwidthandtype.Elevendifferent windowtypescanbechosenrepresentingarrangementsof typ-icalEgyptianwindowtypesinadditiontomoreenergyefficient types.Itispossibletodefinethehorizontalshadingoptionsand determiningtheshadingdevicelocationsanddimensionsabove thewindows.Alsothewallsectioncanbeselected,includingthe walltype,insulationmaterialandinsulationthickness.Attheend ofthisprocess,andpriortopressingtheEnergyPlusbutton,thetool willupdatetheEnergyPlusinputfilewiththeinputparameters.

Theactivedesigninterventioncanbedoneasalaststepasit dependsonthetotalenergyconsumed(seeSection3.3).Thesolar activemoduleallowstheselectionofdifferentparameters includ-ingthePVpaneltype,paneltilt,panelorientation,panelefﬁciency andmountingtooptimisetheelectricalyield.Oncethesimulation hasbeenrun,theoutputgraphicsaredisplayeduponclickingon anyofthe11outputbuttonsillustratedinFig.8.Graphsare gen-eratedbyreadingtheCSVoutputﬁleusingExcelmacros.Fig.8

illustratesanexampleoftheoutputgraphics.Foreachcase,the ZEBOoutputscreendisplaystheresultsinthreedifferentgraphs: theoutdoortemperaturesgraphlocatedintheupperrightcorner ofthescreen,themonthlyendusegraphinthebottomrightside, andtheenergyconsumptionbreakdowngraphonthebottomleft sideofthescreen.

Casestudy

Inordertotestthevalidityandusabilityofthetoolwetooktwo measures.Firstuseacasestudyasanexamplehowahypothetical designconceptwouldbedevelopedandtodiscusshowtheresults generatedbythetoolaresufﬁcientlyaccuratefortheNZEBdesign. Seconduseausabilitytestingstudy.

Casestudy

TotestthevalidityoftheproposedtoolofZEBO,wepresent ahypotheticaldesignexampleforanapartmentinnarrowfront housingblockin Cairo.Thefirst stepis tocreate a basecasein ZEBO. Theuserselects abuildingtype,and theweatherfilefor Cairo, a TypicalMeteorological Year (TMY2)weather file. Then theuserhastoselectthetargetedstandardforminimum perfor-mance.Thechoiceofstandard determinesmanyofthedefaults andassumptionsthatgointothesimulationmodel.Thetoolis cur-rentlylimitedtotheResidentialEnergyStandardECP306-2005-I. ForthiscasetheEgyptianstandardwaschosen.Thetoolthen auto-maticallyloadsacompleteEnergyPlusinputfileforasinglezone withcompletegeometrydescriptionthatcomplieswiththe Egyp-tianbuildingenergyandthermalindoorenvironmentstandard.The usercanchangethebuildinggeometry,includingtheheight,floor plandimensionsandnumberoffloorsinthebuilding,inaddition totheotherinputparametersmentionedearlier.However,forthis casestudywechosenottomakeanychangesandrunthedefault filetocreateabasecaseaccordingtoTable3.

Thesecondstep,afterviewingthesimulation resultsfor the basecase(Fig.8),isperformingsensitivityanalysis.Thedesigneris encouragedtorunsensitivityanalysisforanyselectedparameter. Thisstepintroducesdesignerstotheimpactofvaryingthe param-etervaluespriortothedecisionmaking.Thesensitivityanalysis resultsformthebasisforinformeddecisionmaking.Oppositeto theclassicaldesignapproach,wheresimulationisusedasa post-decisionevaluativetool,thedesignerisinformedontheimpactof hisorherdecisionpriortothedecisionmaking(Fig.9).

Inthiscasestudywechosetoexaminethewallconstruction type.UponselectingthePAcheckboxnexttotheWallConstruction Typeanewwindowpopsuptoaskingtheusertoconfirmhischoice, whichwillrequiretherunningof8filesforatleast2min.Upon con-firmation,theresultsaregeneratedbyEnergyPlusandtheoutput ispresentedasshowninFig.10.Basedonthesensitivityanalysis results,thedesignerisencouragedtoselectthemostenergysaving wallconstructiontype.Basedonthetwosensitivityanalysisgraphs inFig.10,theusercanseetheimpactofthedifferentconstruction types,andhencewillprobablyselectthewallconstructiontype (7)withthelowestenergyconsumption(Uvalue=0.4W/m2_K_for

basecasewall).Oncetheoutputisdisplayed,theusercanmove ontothephotovoltaictoolmodule.Thisstepisdoneasalaststep whereﬁveinputs(location,PVtype,paneltilt,panelorientation, panelefﬁciency)arerequestedtooptimisetheelectricalyield[36]. ThusZEBOallowsthedesignerstoexplorefurtherparameter variationswhileindicatingtheoptimalvalueinrelationtoenergy consumption.Thedesignerthenmakesaninformeddesign deci-sionand enters thedecision asan inputand reruns thewhole simulation. On the same screen the total energy consumption canbecomparedtothereferencecaseresultsFig.11.ZEBOalso

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Fig.7.Referencemodelandoutputplots.

Fig.8. InterfaceforZEBOandreferencemodelandoutputplots.

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Fig.10.Referencemodelandoutputplotsincludingsensitivityanalysisresults.

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Table3

Referencemodelandoutputplots.

Buildingdescription Basecase1 Parametricrange Orientation 0◦ ₀◦_,₄₅◦_,₉₀◦_,₁₃₅◦_,₁₈₀◦_, 225◦_,₂₇₀◦_,₃₁₅◦ Shape Rectangular (12m×10m) 12×10,12×11, 12×12,10×10 Floorheight 3mheight 3,4

Numberofﬂoors 1 1,2,3,4,5,6,7,8

Volume 360m3 _NA

Externalwallarea 72m2 _NA

Overhang None 0.0,0.5,1,1.5,2 Fin None 0.0,0.3,0.5,0.8,1.0,1.5

Roofarea 120m2 _NA

Floorarea 120m2 _NA

Windowsarea 28m2 _NA

WindowwallratioWWR 45% 50,45,40,35,30,25, 20,15

ExteriorwallU-value W/m2_K _2,_1.8,_1.6,_1.4,_1.2,_1,

0.8,0.6,0.4 RoofU-value 1.4W/m2_K _1,4,_1.2,_1,_0,8,_0.6

FloorU-value W/m2_K _1.4,_1.2,₁

Singleclearglazing Tv=0.9 1,0.9,0.8,0.7,0.6,0.5, 0.4,0.3

SHGC 0.75 1,0.75,0.5,0.25 Peopledensity 0.033people/m2 _NA

Lightingpowerdensity 6W/m2 _NA

Plugloads 7W/m2 _NA

Outsideair 20(m3_/h_per_person) _NA

Inﬁltration 0.7ach NA HVACtype On-Split+separate NA CoolingCOP ventilation NA Thermalcomfortmodel 2.00 NA Coolingsetpoint(◦_C) _Givoni _NA

Relativehumidity(%) 24 NA Fanefﬁciency(%) 60 NA Waterheater(%) 70 NA PVtype Amorph,mchrist,

pchrist

NA

PVsurface 0–100 NA

Cellefﬁciency 6–14% NA Inverterefﬁciency None NA

allowsthearchitecttoeasilymakemultipleinformeddecisionsat onceandrunthesimulationbutton.EnergyPlusactuatesthelatest changesandtheresultispresented.

Resultsvalidity

Byexaminingtheresultsofthebasecasesimulationthe con-sumptionwas19.85/kWh/m2_/year_(U_value₌_1.78_W/m2_K_for_wall construction1).BasedonthesensitivityresultsshowninFig.10 thewallconstructionwiththelowestenergy consumptionwas selected.Accordinglytheenergyconsumptionwasreducedaround 16%toreach16.61/kWh/m2_/year_(U_value₌_0.421_W/m2_K_for_wall

construction7).Comparedtothe8wallconstructionsthewall con-struction7,comprisinga125mmdoublewallwith50mmglass woolinsulation,hadthebestenergyperformance.Thisresultis consistentwiththeﬁndingsof[29]forlowenergydesign.Thecase resultsshowsthatthetooldecisionsupportbringsigniﬁcant sav-ingswithoutanytimefordesigniterations.Thishelpstoextend theapplicationofsensitivityanalysistoguidethedecisionmaking beforethebuildingisdesignedusingappropriateenergyprinciples. Usabilitytesting

Themainobjectivefromthetestingandevaluationwastoassess theusabilityoftheinterfaceandtheabilityofdecisionmakingby performingusabilitytestsonthedifferentprototypeversions.Two mainiterationsofusabilitytestinghavebeencarriedoutduring thedevelopmentofprototype1and2ofZEBO.Thiswasdoneto achievefeedbackfromdesignersandpotentialusers.Eachusability

Fig.12.Meantimepertask.

iterationincludedtwotesttypes.Thefirstwasasatisfactionsimple paper-basedusabilityquestionnaire.SystemUsabilityScale(SUS), asdefinedbythestandard,wasusedtoenhanceandvalidatethe tool[37].Toguaranteetheinternalvalidityofthetestasetof10 ordinary(pre-defined)SUSquestionswereused.Theanalysisofthe responseswasbasedonthereportingframework[38].Thesecond wasausabilitymetrictesting,measuringthetasksuccess.Theaim wastomeasurehoweffectivelyusersareabletocompleteagiven setoftasks.Twodifferenttypesoftasksuccesswereused:binary successandlevelsofsuccessasshowninFigs.12and13.

TheusabilityiterationforZEBOprototype1tookplaceinAugust 2010with27userscomprisingarchitects,architecturalengineers andarchitecturalstudents.Theresultswerepublishedina previ-ouspublicationandareshowninFig.14[28].Apaperbasedsurvey wasconductedusingLikertscale.Usershaveexpressedtheir agree-mentwiththequestionnairequestionsonascalerangingfrom1to 5(1=’stronglydisagree’–5=stronglyagree’).Scoreswereadded andthetotalwasmultipliedby2.5.Ameanscorewascomputed outofthechosenresponseswitharangebetween0and100.The highestthescorethemoreusablethewebsiteis.Anyvaluearound 60andaboveisconsideredasgoodusability.AsshowninFig.14, theﬁrstprototypescoredagoodusabilityforninequestions, how-everforthelastquestion,participantsindicatedthattheyneeded tounderstandhowtheZEBOworkedinordertogetgoing. Addi-tionally,everyparticipantwasinterviewedafterconductingthe

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Fig.14. UsabilitytestingofZEBOprototype1usingsystemusabilityscale.

Fig.15. UsabilitytestingofZEBOprototype2usingsystemusabilityscale.

usabilitytestingtofollowupandgetavaluableunderstandingof thetools’limitations.ThefeedbackwasincorporatedintheZEBO prototype2andfollowedbyasecondusabilitytesting.

Thesecond usability testing roundwasachieved duringthe organizationoffourdesignworkshopsofZeroEnergyBuildingsin CairoconductedinJanuary2011.Fourusers’focusgroupstested thetool.Threetestinggroupscomprisingarchitects,architectural engineersandarchitecturalstudents(62users)werehandedalist oftasksshowingtherequiredactions.AfterinstallingZEBO,every userwasshown a shorttutorialvideo [39] illustratingthe ele-mentsoftheinterfaceandtheirmeaning.Fig.15illustratesthe users’feedbackaftercompilingthe62responses.Ingeneral,the prototypeusabilitywasimprovedwhencompared toprototype 1.Participantsseemedmoreconﬁdenttousethetool,85percent comparedto72percent,afteraddingthesensitivityanalysis fea-ture.ThisresultedinparticipantsscoringhigherfortheuseofZEBO moreregularly(75percentcomparedto62percent).Alsothetool complexitywasreducedbyalmost10percentwhichresultedin easierofuse(78percentcomparedto68percent).Alsotheneedto understandhowthetoolworkedwasimprovedexceedingthe60 percentthresholdofgooduse.

Fromtheanalysissomemainstrengthsandlimitationswere revealed.Overall,thereactionswereparticularpositiveonthetools effectiveness.Fromtheanalysisitemergedthatthereisa great potentialfortheinterface.Fromtheopenquestionsandpost test-inginterviewsusersappreciatedtheembeddedbenchmarkandthe abilitytosizeandsimulatetherenewablesystem.Respondents werealsoparticularlyenthusiasticaboutthesensitivityanalysis featurethatsupportsthedecisionmakingintuitivelyandreduce thenumberofdesigniterationsforeachparameterandtotaldesign. Havingcomfortevaluationexpressedthroughthepsychrometric chartforforcedwindspeeds(rangingfrom0.5to2m/s)seemed extremelyhelpfultoeasilyinterprettheweatherandtheyfound great value in connecting comfort with weather and desirable

passivedeignstrategy.However,thepostusabilitytesting inter-views revealed other limitations. For example, many users indicatedtheirunfamiliaritywiththetool’sassumptionsandwere uncertainaboutcommunicatingthetoolresultswiththeirclients. Someusersfoundthebenchmarkveryusefulbutpreferredtouse other more comprehensivetools beside ZEBO. Othersuggested usingthetoolasaneducationaltool.Alsouserssuggestedabetter guidanceonthetooluse.Manyuserssuggestedusingthetoolwith anexpertguidanceorasaneducationaltool.Anothermain reser-vationmanyusershadwasthedifficultytointerpretandexplain theoutputresults.Thishadadirectinfluenceonrespondents’ con-fidencein theresultsand thereliability of thetool’s resultsto communicatethemwiththeclient.Theresultsofthisusability test-ingwillbeembeddedinnextprototypeandexpandedtoamore formalcasestudydesigninthenearfuture.

Discussionandconclusion

Summaryofmainﬁndings

Thesimulation-baseddesign supporttoolwasfoundto pro-moteinformeddecisionmakingforzeroenergy buildingdesign duringearlydesignstages.Itincreasedtheknowledgeaboutthe zeroenergybuildingdesignlessenedtheuncertaintyofdecision making. Participants who used ZEBO reported a high level of knowledgeandoperatedtheirdesignfromaninformative deci-sionsupportapproach ratherthan anevaluativetrialand error approach.Thiscongruencebetweendecision makinganddesign objective in thecontext of higher knowledgeaccords withour deﬁnitionofinformeddecisionmakingofZEBdesign. However, basedontheinterfaceusabilitytestingthecurrentprototypehas notreachedausabilitylevelthatsatisﬁedtheneedsofdesigners. Assuch,thetoolisastartingpointforthedevelopmentofwidely usabletool.

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Strengthandlimitations

Thisistheﬁrstsimulationbaseddecisionsupporttoolforearly stagesofzeroenergybuildingdesigninEgypt.Thetools’strengthis itscapacitytoinformdesignpriortodecisionmaking,while man-aginglargesensitivitysimulationsand presentingcomplexdata in easilycomprehensible, fastand comparativeformats. Basing thetoolsonarepresentativebenchmarkforEgyptianresidential buildingand localbuildingcomponentsand systemlinked toa detailedsimulationenginelikeEnergyPlusisreinforcingthetools resultvalidityandcertaintyindecisionmaking.Thetooliseasy touse,withaninterfacestructurethatisbasedonmatchingthe passiveandactivedesignstrategiesforthenetzeroobjectives.The toolcanhelpachievetheenergyperformancegoalwhileexploring differentrangesofathermalcomfortinhotclimatestoachieve theperformance objective.ZEBO’s strengthis in itscapacity to reducedecisionconﬂictandtheneedfortediousdesigniterations toachievetheperformanceobjective,whilecreatingavarietyof alternativesinashorttime,whichmatchtheearlydesigncyclic explorationsanditerations.Betterinformeddecisions,especially attheearliestconceptualdesignphases,willimprovethedesignof NZEBs.Itishopedthatseveraldesigntrials,currentlyinprogress usingthetool,willallowagreaterimpactonarchitects’decision makingandactualdesignoutcomes,andenableintegrationofBPS toolstoproceedfurtherthanthedecisionsupportlevelreachedin thisstudy.

However,thetoolinitscurrentstatecanhardlyattractlarge enoughnumbersofusers.Theusabilitytestingresultsrevealedthat thetoolseemsmoreusefulifusedwiththesupportofanexpertto useZEBOorinthehandsofaneducatorfordesignexploration.Also thedecisionmakingsupportofcurrentprototypecanonlyhandle energyissueswhilemanyusersexpectotherenvironmentaland economicalindices.Oneofthemainlimitationsidentiﬁedduring theworkshopswasthegeometryandnon-geometricinput.Users suggestedlinkstoGoogleSketchUpforgeometryinputanduser interfaceimprovementstoinsertinputvisually(notnumericalor textual).Similarlythetoolislimitedtoitsownlibraryofageneric rectangularsingle-zonetemplatewithfewalternativesforbuilding componentsandsystems.

Comparisonwithexistingtools

Thisdiscussionbuildsonearliersoftwarereview(Section2.4) thathasprovidedasnapshotonthecurrentlyavailableBPStools. Accordingtotheliterature,therearefewtoolsthatinformdesign priortothedecisionmakingforearlydesignstages,[24,26]and inthesametimeaddressesthezeroenergyobjective,combining passiveandactivedesignstrategies.Thesuggestedtoolisa para-metrictoolthatcanprovidesupportdecision makingwithvery littleiterationswhileaddressingthezero-energyobjective.

Arecentpublicationbytheauthorprovesthatmostexisting informativetoolsareexclusivelylocalservingcertaincountries’ context [21]. In fact, most BPS tools are developed in heat-ing dominated countries. They cater for developed countries withhigh energy consumption patterns and different expecta-tions for comfort. The main barriers in using those tools are relatedtotheavailabilityandcompatibilityofinputdataincluding weather,comfort models, buildingbenchmarks,renewable sys-tems,andoperationalcharacteristics.Noneofthesetools,however, addressedthezero-energytargetinacontextofhotclimate devel-opingcountryasinourtool.

Futureresearch

ZEBOisastartingpointtoprovidebetterguidancefordesign decisions to deliver NZEBs in hot climates. The tool in its

current state hassigniﬁcantlimitations and designerswill still requiremoreinformationinordertomakeinformeddecision.For betterusability, the tool can include a fully visualinput inter-faceandallowinguserstoaddnewbuildingtemplatesfornew buildingtypesorcasestudies.ItcanhaveT-shape, H-Shape, U-shapeandcourtyardshapedtemplates,orevenbetterintegratean OpenGLmodeller.Alsotheinterfacecanbeexpandedtoinclude morebuildingsystemsandcomponents,especiallydifferent enve-lopetypesandcoolingsystemsatdifferentcitiesinEgyptusing suitableCOPs(coefﬁcientofperformance).Alsothescopeofthe toolcanbeextendedfurthertoachievethenetzeroobjectivefor existingbuildingsoronalargerscale(clusterorneighbourhood).

Concerningtheusabilitytestingthestudywilladdressthetool efﬁciency and effectiveness as a complementarytesting tothe satisfactiontesting.Onthelevelofdecisionsupportfurther devel-opmentsofthetoolcanincorporateeconomicindicestoachieve netzeroenergycosteffectively.Thetoolcanbelinkedto optimi-sationalgorithmstoo.Thiscancreatemoreviablealternativesand allowstheexplorationofawidersearchspaceforcomplexdesigns. Thisdevelopmentcanincludeeconomyandcost,whichmaybe ofinterestfordesigners,researchers,energylegislatorsandpolicy makers.

Acknowledgements

Thispaperisanupdateandexpansionoftwopapersauthored byShadyAttiaetal.entitled“Decisiondesigntoolforzeroenergy buildings”presentedatthePLEAconferencein2011and“Sizing photovoltaicsystemsduringearlydesignadecisiontoolfor archi-tects”presentedatASES2010.

TheauthorwouldliketoacknowledgeArchitectureetClimat and in particular Cédric Hermand and Stéphanie Salawa. Also AurélieLeNoirefromthetheUniversitédelaRéunion,France.The authorsthankMohamedHamdy(AaltoUniversity)forcomments onearlierversionsofthisarticle.Thispaperispartofanongoing PhDresearchfundedbytheUniversitécatholiquedeLouvain.

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