daylighting control performance of a thin-film cer

Daylightingcontrolperformanceofathin-filmceramicelectrochromicwindow:FieldstudyresultsE.S.Lee*,D.L.DiBartolomeo,S.E.SelkowitzBuildingTechnologiesProgram,EnvironmentalEnergyTechnologiesDivision,LawrenceBerkeleyNationalLaboratory,Mailstop90-3111,1CyclotronRoad,Berkeley,CA94720,USAReceived16May2004;receivedinrevisedform26January2005;accepted15February2005AbstractControlsystemdevelopmentandlightingenergymonitoringofceramicthin-filmelectrochromic(EC)windowswereinitiatedatthenewfull-scalewindowsystemstestbedfacilityattheLawrenceBerkeleyNationalLaboratory(LBNL)inBerkeley,CA.Thenewfacilityconsistsofthreeidenticallyconfiguredside-by-sideprivateofficeswithlarge-areawindowsthatfaceduesouth.Inoneroom,anarrayofECwindowswithacenter-of-glassvisibletransmittanceTvrangeof0.05–0.60wasinstalled.Inthetwootherrooms,unshadedwindowswithaTv=0.50or0.15wereusedasreference.Thesamedimmablefluorescentlightingsystemwasusedinallthreerooms.ThisstudyexplainsthedesignandcommissioningofanintegratedECwindow-lightingcontrolsystem,andthenillustratesitsperformanceinthetestbedunderclear,partlycloudy,andovercastskyconditionsduringtheequinoxperiod.TheperformanceofanearlyprototypeECwindowcontrollerisalsoanalyzed.Lightingenergysavingsdataarepresented.Dailylightingenergysavingswere44–59%comparedtothereferencewindowofTv=0.15and8–23%comparedtothereferencewindowofTv=0.50.Theintegratedwindow-lightingcontrolsystemmaintainedinteriorilluminancelevelstowithin
10%ofthesetpointrangeof510–700lxfor89–99%oftheday.Furtherworkisplannedtorefinethecontrolalgorithmsandmonitorcoolingload,visualcomfort,andhumanfactorimpactsofthisemergingtechnology.PublishedbyElsevierB.V.Keywords:Buildingenergy-efficiency;Electrochromicwindows;Daylighting;Controlsystems1.IntroductionElectrochromic(EC)glazingsofferdynamicandresponsivecontrolofthethermalandopticalpropertiesofthebuildingfac¸ade.Thisfunctionalitycanbeusedtomaximizeoccupantcomfortandperformancewhilemini-mizingannualenergyuseandpeakelectricdemand.Theyareexpectedtoyieldgreatestbenefitsincoolingloaddominatedbuildings,suchascommercialbuildingslocatedintemperateandhotclimates,inhomesinthesunbeltandinpartsofthenation,whereelectricloadmanagementisofcriticalconcern.ECwindowsmayalsobeofbenefitforoffsettingtheneedforheatingincoldclimatesifcontrolledtoadmitsolarheatgains.Whileelectrochromicglazingshavebeenthesubjectofcomputersimulationstudiesformanyyears,ithasonlybeeninthelastfewyearsthatfull-sizeproductshavebeenevaluatedintestroomsorbuildings.In1999,electrochromicresidentialskylightsweretestedinoutdoortestroomsandshowed50%reductionsincoolingloadscomparedtospectrallyselectiveglazings[1].In2000,LawrenceBerkeleyNationalLaboratory(LBNL)completedthefirstfull-scalefielddemonstrationintheU.S.oflarge-areaelectrochromicwindowsinanofficebuilding[2].TheprojectdemonstratedthatmultipleECwindowscouldbesmoothlyswitchedacrosstheirdynamicrangeandcouldbefullyintegratedintoacompletedaylight,glare,andenergycontrolsystem.Althoughthisprojectreinforcedthepotentialimportanceandvalueofthistechnology,atthesametimeithighlightedaseriesofcomplexinteractionsthatarenotwellunderstoodbymanufacturers,researchersorspecifiers.Forexample,darkeninganelectrochromicwindowtocontrolglareandimprovevisualperformanceinsomeconditionswillincreaselightingenergyuse.Thesestudiesshowedthepotentialforelectrochromics,but(2006)30–44*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](E.S.Lee).0378-7788/$–seefrontmatter.PublishedbyElsevierB.V.doi:10.1016/j.enbuild.2005.02.009underscoredtheextenttowhichnumerousbuildingintegrationandsystemsengineeringissuesneedtobestudiedandresolvedifelectrochromicproductsaretobesuccessfulinmeetingallmarketneeds.ParallelworkintheEUSWIFTprogram[3]andtheInternationalEnergyAgencyTask27[4]isbeingconductedworldwide.Thismulti-yearproject,supportedbytheCaliforniaEnergyCommissionthroughitsPublicInterestEnergyResearchProgramandbytheU.S.DepartmentofEnergy,isintendedtoexpandandaccelerateawiderangeoffieldengineering,demonstration,andevaluationstudiestohelpmovetheelectrochromicwindowtechnologyfromthelaboratorytoproductssuitableforbuildingapplications.Thisinitialstudybeginstoaddresstwokeyoverallchallengesthatarefacedbymanynewtechnologiesandspecificallybycomplexdynamicsystemssuchaselectro-chromicwindows:(1)Asanactivelycontrollabledynamicsystem,ECwindowsfacemanyintegrationchallengesthatarenotaddressedbymostconventionalwindowsystems.IntegrationofthedynamicECwindowwithinthebuildingenvelopeandwithotherbuildingsystemsiscriticaltoobtainingaflexibleandreliablewholebuildingsolutionthatwillmeetenergysavings,activeloadmanagement,andoccupantobjectives.Integratedenvelope-lightingcontrolalgorithmsandcommission-inganddiagnostictoolsneedtobedeveloped,tested,andevaluatedtodeterminetheimpactsonarchitecturaldesign,energyperformance,occupantacceptance,andreliability.(2)Limitedperformancedataareavailabletothepublic,tobuildingowners,andtodesignprofessionalstounder-standandassesstheoverallbenefitsandrisksofthistechnologyinrealistic