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附录附录A外文资料RetrofittingDomesticHotWaterHeatersforSolarWaterHeatingSystemsinSingle-FamilyHousesinaColdClimate:ATheoreticalAnalysisAbstract:Oneofthebiggestobstaclestoeconomicprofitabilityofsolarwaterheatingsystemsistheinvestmentcost.Retrofittingexistingdomestichotwaterheaterswhenanewsolarhotwatersystemisinstalledcanreduceboththeinstallationandmaterialcosts.Inthisstudy,retrofittingexistingwaterheatersforsolarwaterheatingsystemsinSwedishsingle-familyhouseswastheoreticallyinvestigatedusingtheTRNSYSsoftware.Simulationmodelsusingforcedcirculationflowwithdifferentsystemconfigurationsandcontrolstrategiesweresimulatedandanalysedinthestudy.Acomparisonwithastandardsolarthermalsystemwasalsopresentedbasedontheannualsolarfraction.Thesimulationresultsindicatethattheretrofittingconfigurationachievingthehighestannualperformanceconsistsofasystemwheretheexistingtankisusedasstorageforthesolarheatandasmallertankwithaheaterisaddedinseriestomakesurethattherequiredoutlettemperaturecanbemet.Anexternalheatexchangerisusedbetweenthecollectorcircuitandtheexistingtank.Forthisretrofittedsystemanannualsolarfractionof50.5%wasachieved.Aconventionalsolarthermalsystemusingastandardsolartankachievesacomparableperformanceforthesametotalstoragevolume,collectorareaandreferenceconditions.Keywords:solarthermalstoragetankwaterheaterretrofitdomes1.IntroductionOneofthebiggestobstaclestotheeconomicprofitabilityofdomesticsolarwaterheating(SWH)systemsistheinvestmentcost.Theinstallationcostofforcedcirculationsystemsusedincoldclimatescanrepresentupto50%ofthetotalinvestmentcostdependingonthesizeandtypeofsystem.Also,thesolarstorageisoneofthemostexpensivecomponentsinasolarwaterheatingsystem.RetrofittingexistingdomesticwaterheaterswhennewSWHsystemsareinstalledcanreducethetotalinvestmentcostbydecreasingboththeinstallationandmaterialcosts.InSwedentherearemorethanhalfamillionelectricallyheatedsinglefamilyhousesthatuseconventionalwaterheatersfordomestichotwaterproduction.SuchretrofittingneedstobecarriedoutwithconsiderationofthecoldSwedishclimate.Insuchregionsthesolarstorageisplacedindoorsandafreezeprotectionmediumrunsinsidethecollectorcircuit.Sinceexistingwaterheatersarenotprovidedwithaheatexchanger,anexternaloneshouldbeused.Therearetwomaintypesofsystemsdesignedwithanexternalheatexchangeroutsidethestorage:thermosyphonandforcedflowcirculation.CruickshankandHarrison,in2004and2006,investigatedthistypeofthermosyphonsystemsintheCanadiancoldclimate.In2011,thesameauthorsstudiedtheperformanceofseriesandparallelconnectedthermosyphonstorages.ThermosyphonsystemsbecamepopularinseveralpartsoftheworldsuchasEasternAsiaandAustralia,mainlyduetotheirsimplicityandreliability.Thethermosyphondrivingforcedependsonthepressuredifferenceandfrictionallossesbetweentheheatexchangerside-armandthetank.Hence,thegeneratedflowwillbeacomplexfunctionofthestateofchargeofthetank,thetemperatureprofilealongtheheatexchangerandpipes,theheightdifferencebetweenthetopoftheheatexchangerandthetopofthetankandthepressuredropintheheatexchanger,pipingandconnections.Suchdependenceontheheatexchangerpressuredropandtankcharacteristicslimitshowtheretrofitiscarriedout,wheretheheatexchangershouldbeplacedandwhichstoragetankscanbeused.Moreover,whenproperlydesigned,forcedcirculationsystemscansignificantlyachievehigherperformancescomparedwithnaturalconvectiondrivensystems.Thisismai...