Towards integrated design strategies for implementing BIPV systems into urban renewal processes : preliminare case study in Neuchâtel (Switzerland)

 TOWARDSINTEGRATEDDESIGNSTRATEGIESFORIMPLEMENTINGBIPV SYSTEMSINTOURBANRENEWALPROCESSES:PRELIMINARYCASESTUDYIN NEUCHÂTEL(SWITZERLAND)  SergiAguacilLaboratoryofArchitectureandSustainableTechnologies (LAST) ÉcolepolytechniquefédéraledeLausanne(EPFL) [email protected] SophieLufkinLAST‐EPFL[email protected] EmmanuelReyLAST‐EPFL[email protected]   Fig1:Diagramoftheproposedresearchmethodology WHICHAREYOURARCHITECTURAL(R)SOLUTIONSTOTHESOCIAL,ENVIRONMENTALANDECONOMIC CHALLENGESOFTODAY? Researchsummary Europeanenergydirectivesdefinehighly‐demandingperformancestandards,fromzero‐energy buildingstopositive‐energybuildings.InSwitzerland,oneofthespecificobjectivesofthenew“Energy strategy2050”istoinstallPVsystemsonexistingbuildingsurfacesinordertocover1/3oftheannual Swissdemandforelectricity.Inviewoftheconsiderableimportanceofurbanrenewalprocesses, building‐integratedphotovoltaic(BIPV)systemsthereforeprovideacrucialresponsetothechallenges oftheenergyturnaround.However,inspiteoftechnologicprogressandeconomicevolution,diverse typesofobstacleslimitalarge‐scaleadvancedPVintegrationintourbanrenewalprocesses. Inthiscontext,urbanandarchitecturaldesigntowardsincreasedintegration–andthereforeincreased acceptance–providesanessentialsolutiontoovercomethesebarriers.Itrepresentsakeyelement towardsestablishingasystematiclinkbetweenBIPVandthenecessaryrenewaloftheconsiderable existingbuildingstock.Towardsthisaim,thepresentpaperproposesafirstapproachtodefineaholistic multi‐criteriaassessmentmethodologyforBIPV‐adaptedsolutionsinurbanrenewaldesignprocesses intheSwisscontext.Thisdocumentpresentsthefirststepstowardsthevalidationoftheproposed methodologythroughapreliminarycasestudyinNeuchâtel(Switzerland). Keywords:building‐integratedphotovoltaics,energyefficiency,renewableenergy,sustainable architecturaldesign,urbanrenewal,renovationstrategy,multi‐criteriaassessment.  1.Introduction  OneofthetopprioritiesofEuropeancountries istoreduceenergyconsumptionand greenhouseeffectinthebuiltenvironment. Towardsthisaim,sincethecityoftomorrowis largelyalreadybuilt,manystrategiesstressthe importanceofurbanrenewalprocesses towardsmoresustainabilityintermsof economic,socialandenvironmentalimpacts. Indeed,therearestillhugepotentialenergy savingstobemadeinEuropeancountriesin general,andinSwitzerlandinparticular.Most residentialbuildingswerebuiltbefore1985and requirelargeamountsofenergytoensurethe minimumindoorthermalcomfort(OFS,2014). Inresponse,recentresearchworkshavestarted consideringthelargeexistingbuildingstock, bringingtolighttheconsiderableimportanceof urbanrenewalstrategiesforthesustainability ofthebuiltenvironmentinthenextdecades (Riera,Rey,2013). Inparallel,oneoftheobjectivesofthe“Energy strategy2050”istoinstallPVsystemson approximately30%ofexistingbuildingsurfaces inordertocover1/3oftheannualSwiss demandforelectricity(IEA,2002).Buildingintegratedphotovoltaic(BIPV)systems thereforeprovideacrucialresponsetothe challengesoftheenergyturnaround(SFOE, 2014). BIPVisagrowinganddiverseareaofresearch. Inparticular,itincludesresearchonthe developmentofnewproducts,modelling, simulation,assessmentoftheirintegration, electricalandthermalperformancesof mountedmodules(Frontinietal.,2012).   2.Researchobjectives  Despiteallthistechnologicalprogress,onlya smallpartoftheavailablelocalpotentialfor BIPVisvalorisedinurbanareas(integrationinto roofandfaçadeselements).Diversetypesof obstacleslimitalarge‐scaleadvancedPV integrationintourbanrenewalprocesses.Most barriersarerelatedtothelimitedmotivationof architecturaldesigners,arestrictedknowledge oftheBIPVpotentialandaninsufficiencyof aesthetically‐convincingexemplarybuildings (Heinstein,Ballif,Perret‐Aebi,2013). Toaddressthischallenge,urbanand architecturaldesigntowardsincreased integration–andthereforeincreased acceptance–couldpotentiallyprovidea decisivesolution.Althoughitremainslargely disconnectedfromsolarrenewableenergy issues(Nault,Andersen,Rey,2013),it representsakeyelementtowardsestablishing asystematiclinkbetweenBIPVandthe necessaryrenewaloftheconsiderableexisting buildingstock. Therefore,insteadofconsideringBIPVasa technicalconstraintfordesigners,weproposea newapproachbasedontheintegrationofBIPV solutionsasanew“rawmaterial”for architecturalrenewalprojects(Aiulfi,Rey,2010; Rey,2014).Byprioritizingarchitecturalquality anddialoguewiththebuiltenvironment,itaims atidentifyingwhichconstructionelementscan besubstitutedbythemostappropriatePV components.Thelatterwillnotonlyprovide answerstothesamerequirementsasother partsofthebuildingenvelope(waterandair tightness,mechanicalresistance,etc.),butalso generateelectricityonsitefromarenewable energysource. Towardsthisaim,anambitiousresearchproject entitledACTIVEINTERFACESiscurrentlybeing developedinordertostudyinastructuredand in‐depthmannerthetechnological,spatial, legalandsocio‐economicparametersrelatedto thedevelopmentofnewadaptedsolutions, takingintoaccountdiversecriteria(energy, comfort,LCA,costs,aesthetics,costsof  electricityandgridconnection).Crossingover thelimitsofcurrentpractices,thisongoing projectaimsatdesigningandassessingBIPV‐ adaptedscenariosembodyingdifferenturban renewalstrategiesintheSwisscontextthrough amulti‐criteriaassessmentmethodology. Thepresentpaperisthefirstmilestoneonthe roadtowardstheseintegrateddesignstrategies forimplementingBIPVsystemsintourban renewaldesignprocesses.Itpresentsthe resultsfromthepreliminarycasestudyin Neuchâtel(Switzerland),basedonthe simplifiedanalysisandcomparisonofdifferent urbanrenewalscenarios.Theintermediary objectiveistotest,validateandfindwaysto improvetheproposedmethodology.   3.Proposedmethodology  Themethodologyinvolvesfourmainphases:1) preselectionofanarchetypalbuilding;2)study ofthecurrentstateofthebuildingandofthe thermalenvelope’sconstructiondetails;3) developmentofthreearchitecturalrenewal scenariosembodyingdifferentlevelsof intervention;4)multi‐criteriaassessmentofthe designscenarios.  3.1Preselectionofanarchetypalbuilding Theprocessofidentificationofthefirstcase studystartswithananalysisofthecityaturban scale.Firstlybasedonatypologicalstudy includingparameterssuchastheconstruction periodandtype,itusesdifferentsourcessuch asthecurrentmasterplan,aerialimages, informationfromregistrationofthepropriety andstatisticaldatafromtheconstruction sector. Subsequently,toselectarepresentative buildingwithineacharchetypaltype,five selectioncriteriaaredefined,relatedtothe opportunitytoimplementBIPVelements.They arelistedbelowonaprioritybasis: 1. Contextandurbanmorphology 2. Solaraccess(roof/façades) 3. Averageheritageprotection 4. Stakeholdersintherenovationprocess (typeofownership) 5. Accesstoinformationonthebuilding  3.2Descriptionofthecasestudy Thebuildingchosenforthefirsttestofthe methodologyisanurbanresidentialbuilding typicalofthe70’s:afour‐storeycommunal property,consistingof18apartmentsand1,287 m 2 oflivingfloorarea.Thisbuildinghasbeen recentlyrenovatedwithoutconsideringthe integrationofBIPV(Baueretal.,2013),beinga publicpropertybuilding,theenergysavingdata havebeenpublishedanditwillbeusedto validateoursresultsusingtheproposed methodology. Intermsofactivesystems,thebuildingis connectedtothedistrictheat2ing(DH)ofthe citytocoverheatinganddomestichotwater (DHW)needs(Fig2).   Fig2:Buildingimagebeforerenovation(Google)  Accordingtothearchitecturalapproachbased onarenovationdesignprocess,astudyofthe thermalenvelope’sconstructiondetailsis crucialtoidentifyopportunitiestoimplement photovoltaicelements.Theexistingbuilding  presentsaconcretesandwichpanelfaçade, composedbyaninteriorplaster,concrete, insulationandexternalconcretefacing.The doublesloperoofiscomposedbyreinforced concrete,insulationwoodenplateandceramic tile(Fig3).  3.3Descriptionoftherenewalscenarios Forthepurposeofthispaper,threesimplified architecturalrenewalscenariosembodying differentlevelsofinterventionareproposed:A) Currentstate(referencecase):representsthe currentsituationofthebuildingwithoutany renovationstrategy;B)Currentlegal requirements:groupofmeasuresthatensure compliancewiththeminimumlevelof performanceaccordingtoSIA380/1:2009 (currentSwissbuildingperformancestandard). C)BIPVrenovation:groupofstrategiesthat ensurecompliancewiththelevelof performanceaccordingtoSIA380/1:2009 (currentSwissbuildingperformancestandard) withtheintegrationofPVelementsintothe roofrenovationprocess(Table1).Inorderto focusonthedevelopmentofthemethodology, BIPVonfacadesisbeingdeliberately overlooked.  Fig3:Envelopedetailsforinsulationstrategy   Elements A BC Facades ‐∆Insulation Roof ‐∆Insulation ∆Insulation+BIPV Windows ‐Replacement+shadingsystem Table1:Improvementstrategiesforeachscenario  3.4Definitionofassessmentindicators Tocarryoutamulti‐criteriaevaluationofthe designscenarios,sevenindicatorsaredefined. Theyassessandcomparetheirperformancesin termsofenergy,economicandenvironmental aspects(Table2).Thispreliminarydefinitionwill providethebasisforthemorein‐depth assessmentinthefuturestepsoftheresearch project.  Energyconsumption ‐PrimaryenergyconsumptionkWhPE/m2.yea r ‐EquivalentGHGemissionsCO2EQ/m2.yea r Photovoltaicinstallation ‐Annualproduction kWhFE/m2.yea r ‐Ratioelectricitycovered% Costsandpayback ‐Renovationcost CHF ‐Payback years ‐Impactonrent CHF/ m2.yea r Table2:Assessmentindicators    4.Simulation  Thetoolusedtoestimatetheassessment criteriarelatedtoenergyconsumption, emissionsandphotovoltaicproductionis DesignBuilderv.4(basedontheEnergyPlus simulationengine.www.designbuilder.co.uk). Foreconomiccriteria,thecalculationhasbeen donewiththeEPIQRtool(F.Flourentzouetal., 2000),developedfortestingdifferentrenewal scenariosandidentifyingthemostperforming one(s).    4.1Inputdataforenergyconsumption Themeanvaluesforthecorresponding constructionperiod(1960‐1970)intheSwiss contextareusedtodefinetheinputdataofthe currentstatus(A)(Giebeleretal.,2011).For scenariosBandC,theU‐valuescorrespondto SIA380/1:2009requirements(Table3).  ScenarioABC Exteriorwalls W/m²K 0.70.20.2 Roof1.30.2 0.2 Internalfloor1.10.2 0.2 Window2.61.3 1.3 Glazin g  2.81.0 1.0 Windowsframe1.61.3 1.3 Vent.+Infiltr. r/h1.00.50.5 Table3:Inputdataforthedifferentscenarios  4.2Inputdataforphotovoltaicinstallation ThechoiceoftheBIPVcomponenttobeusedin scenarioCrespondstothewillofcarryingouta rehabilitationwhichpreservesthearchitectural qualityofthebuilding,whilecompromisingas littleaspossiblethelevelofelectricityproduced (Swisspearl,2015).TheSwisspearlINTEGRAL2® PVmodule(Fig.4)waschosentosubstitutethe existingtilesintheretrofittingprocessofthe roofinsulation.Basedonthemonocrystalline (sc‐Si)technologyofPVcells,anefficiencyof 14%isestimated(Cerón,Caamaño‐Martín, Neila,2013).   Fig4:RoofBIPVcomponent(www.swisspearls.ch) Accordingtothetechnicalspecifications,the installedpowercanbeestimatedat1kWp=7m2 ofPV.Priceisaround3,000CHF/kWp,including inverters,wiring,accessoriesandconnectors. Weproposetocovertheentireroofofthe building(360m2)usingBIPVelements, substitutingtheactualtilesduringthe improvementprocessoftheroofinsulation.  4.3Inputdataforcostsandpayback OneofthemainconcernsaboutBIPV installationsisrelatedtotheeconomicand financialaspects.Therefore,theprecise evaluationofthecostsisanessentialaspectof theproposedmethodology.Theestimationof thepaybackperiodforeachsituationis calculatedbycountingthenumberofyearsit willtaketorecoverthecashinvestedina project,usingenergycostsavingsandextra revenuesfromthesaleofPVenergyproduced. Thismethodisrecommendedbythecostoptimalmethodologyappliedtorenewal processes(BPIE,2011),consideringmedium‐or long‐terminvestmentscenarios.Forthiscase,a horizonof40years(3%ofinterestrate)has beenconsidered.Apartfromenergysavings, wealsotookintoaccounttherepercussionof theinvestmentcostonpriceofthemonthly rent;3differentthresholdsareanalysed:3%for minimumprofitability,4.5%foraverage profitabilityand6%forsignificantprofitability (Table6).   5.Results  5.1Energyconsumption ThetargetsetbytheSIA380/1:2009for housing,consideringAth=1,764m2and AE=1,587m2is45kWh/m2peryear (renovations).Thetargetisachievedfor scenariosBandC(Fig5),correspondingto56% savingsonheatingenergydemand.Intermsof  finalenergyconsumption,scenariosBandC achieve58%savings(accordingtotheHOLISTIC report),relateddirectlytoconsumptioncosts. Withtheaimofanalysingtheinfluenceofan architecturalrenovationbasedonpassive strategiestoreduceenergydemand,noactive improvementstrategiesareproposedtoreduce energyconsumptionofDHWandelectricity(Fig 6). Thevaluesobtainedforthecurrentsituation (scenarioA)farexceedthetargetvaluessetby SIA380/1.Theyshowthechangesneededto achievethegoalssetbythe“EnergyStrategy 2050”andhighlighttheimportanceof strategiestopromoteurbanrenewalprocesses.   Fig5:Heatingneeds  (kWh/m2.year)   Fig6:Finalenergyconsumption(kWh/m2.year)   Fig7:Netenergyconsumptionandemissions Comparingtheresultsintermsofprimary energyisessentialtotakeintoaccountthe originofeachenergysource.Inthiscase,we havenotproposedanychangeofenergysource (DH)tohighlighttheinfluenceofthe photovoltaicinstallation(Fig8). Toobtaintheresultsofthenetprimaryenergy consumptionandCO2equivalentemissions,it isnecessarytousecoefficientstoconvertfrom finaltoprimaryenergy.IntheSwisscontext, thesecoefficientsareprovidedbySIA380/1 (Table4).  ElectricityDH k g CO2e q /kWh 0.1620.162 kWhEP/kWhEF 2.9700.810 Table4:Conversioncoefficients   5.2Photovoltaicinstallation ConcerningtheBIPVstrategyimplementedin scenarioC,theestimatedproductionofthe installationis49,262kWhperyear(50kWp), correspondingto39.2kWh/m 2 peryear(116.4 kWh/m 2 peryearintermsofprimaryenergy savings)(Fig.7),or177%ofdomesticelectricity consumption.Thecostoftheinstallationis approximately150,000CHF.  5.3Costsandpayback TheglobalcostsofrenewalscenariosBandC correspondto236,400CHFand386,400CHF respectively.ThedifferenceliesintheBIPV installation,whichrepresentsanadditionalcostof 63%comparedtoscenarioB.  Profitability threshold Rentincrease(CHF/m2peryear) ABC 3.0% ‐ +5.5+9.0 4.5% ‐ +8.3+13.5 6.0% ‐ +11.0+18.0 Table5:Rentincreaseforeachscenario   Inthiscasewehavechosen3%ofprofitability thresholdstotakeintoaccountthe repercussionoftheinvestmentcostontherent 78 44.2 44.2 0 15 30 45 60 75 90 ABC Heatingneed(kWh/m2.year) 91.7 52.9 52.9 24.8 24.8 24.8 22.1 22.1 22.1 0 25 50 75 100 125 150 175 ABC Heating DHW Electricity 160 128.5 12.1 25.9 20.8 2 0 25 50 75 100 125 150 175 ABC Primaryenergyconsumption(kWh/m².year) EquivalentGHGemissions(CO2/m².year) DHW EL HDHW EL H BIPV prod.  (Table5),ascomparedwiththeaveragevalue oftherentintheregionofNeuchâtel,estimated at220CHF/m2peryear(OFS,2015). Inthisregard,itisimportanttojointlyrepresent thethreedifferentscenariostocomparetheir performancesandhighlighttheeffectivenessof eachstrategy(Fig9). IntheSwisscontext,thesaleandpurchaseprice ofelectricityisapprox.0.2CHF/kWh,tax included.Financialaidtotackletheinvestment cost(correspondingtoaround1,000CHFper kWpinstalled)areobtainedonlyifthe installationislessthan30kWp(Swissgrid, 2015).Usingthesedata,thepaybackis24years forscenarioBand16yearsforscenarioC.The BIPVstrategythusrepresentsapaybacktime 30%shorterthankstotheextrarevenue generatedbythesaleoftheenergyproduced.   Fig8:Costevolutionofenergyconsumptionand paybackestimation   6.Conclusions  Basedontheresultsoftheevaluation,itseems clearthatenergyrenovationprojectswithout integrationofrenewalenergyingeneraland BIPVinparticulararenolongeranoptionifwe wanttoachievetheobjectivesofthe“Energy strategy2050”.Today,renovationprojects improvingthebuildingenvelopewithavery highlevelofthermalenergyperformanceare necessary,butnotsufficient.Compensating buildings’energyconsumptionbyproducing electricityon‐sitehasbecomenumberone priority.Inthissense,byproposingnew adaptedBIPVsolutionsforurbanrenewal processes,theresearchcontributesto advancingarchitecturalandconstructiondesign practicesinthisdirection. Atanearlystageoftheresearch,theresultsof thispreliminaryapplicationcasestudyhighlight severalinterestingelements,suchasthe shorterpaybackperiodoftheBIPVscenario, justtakingintoaccountasimplestpassive strategy(insulation)40%savingofheatingare achieved.Itseemseasilyarriveto80%oftotal savingswithintroducingofmixstrategies (passive,activeandrenewalenergysystems). Economicaspects,inparticular,appearaskey elementstounderstandobstaclesandfindways ofgettingaroundthem.Inthissense,thetype offinancingisanessentialissueandwillrequire specificattentioninthefuturephasesofthe project.Thedistributionofeconomicbenefits generatedbytheBIPVelectricityproduction amongtheinvolvedstakeholders(ownerand tenant)isanotherkeyaspect. Thispreliminarystudyalsoallowsafirst validationoftheproposedmethodologyand opensupperspectivesfortheupcoming processoffinalisationandrefinement. First,inordertosupportamoreholistic approach,implicitintheconceptofsustainable development,itisessentialtoincreasethe numberofindicators.Themulti‐criteria assessmentneedsnotonlytotakeinto considerationquantitativeandqualitative parameters,butalsotoincludecriteriafromall threepillarsofsustainability(i.e.notonly environmentalandeconomicindicators,but alsosocioculturalones).Amongothers,wewill includeindoorcomfortandLCAassessmentof 0 200000 400000 600000 800000 1000000 0 5 10 15 20 25 30 35 40 CHF Years Scenario_A Scenario_B Scenario_C  theentirerenovationproject.Theintegrationof theseadditionalindicatorswillrequireusing newsimulationtoolsspecificallydesigned assessretrofittingprojectswithBIPV. Furthermore,theamountofscenarioswillalso needtobeincreasedinordertodefineand evaluateabroadernumberofBIPVretrofitting options.BIPVproductswillbeintroducedto substitutenotonlyroofelements,butalso façadecomponents.Differentlevelsof interventionwillthusbedistinguishedwith moresubtlety,frombasicsanitationto substitution,includingrenovationand transformationstrategies.Finally,afterthese variousrefinementswillhavebeencarriedout, furtherphasesoftheresearchwillconsistin applyingthemethodologytootherarchetypal buildings.Theseupcomingcasestudieswill ensurethevalidationofthefinalised methodologyandenabletheextrapolationof themostperformingBIPVrenovationstrategies aturbanscale.Moreover,thesecasestudies willprovidearchitects,installersandpublic authoritieswithacatalogueofinnovativeand adapted“bestpractice”solutionsforalargescaleadvancedBIPVintegrationintourban renewalprocesses.   7.Acknowledgments  ThisworkwassupportedbytheSwissNational ScienceFoundation(SNSF)–NationalResearch ProgramNRP70“EnergyTurnaround”andthe EcolePolytechniqueFédéraledeLausanne (EPFL).  8.References  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