外文翻译改造在寒冷气候下单户家庭房屋的太阳能热水器的生活热水的分析.docx
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外文翻译改造在寒冷气候下单户家庭房屋的太阳能热水器的生活热水的分析.docx
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外文翻译改造在寒冷气候下单户家庭房屋的太阳能热水器的生活热水的分析
中文2987字
附录
附录A外文资料
RetrofittingDomesticHotWaterHeatersforSolarWaterHeatingSystemsinSingle-FamilyHousesinaColdClimate:
ATheoreticalAnalysis
Abstract:
Oneofthebiggestobstaclestoeconomicprofitabilityofsolarwaterheatingsystemsistheinvestmentcost.Retrofittingexistingdomestichotwaterheaterswhenanewsolarhotwatersystemisinstalledcanreduceboththeinstallationandmaterialcosts.Inthisstudy,retrofittingexistingwaterheatersforsolarwaterheatingsystemsinSwedishsingle-familyhouseswastheoreticallyinvestigatedusingtheTRNSYSsoftware.Simulationmodelsusingforcedcirculationflowwithdifferentsystemconfigurationsandcontrolstrategiesweresimulatedandanalysedinthestudy.Acomparisonwithastandardsolarthermalsystemwasalsopresentedbasedontheannualsolarfraction.Thesimulationresultsindicatethattheretrofittingconfigurationachievingthehighestannualperformanceconsistsofasystemwheretheexistingtankisusedasstorageforthesolarheatandasmallertankwithaheaterisaddedinseriestomakesurethattherequiredoutlettemperaturecanbemet.Anexternalheatexchangerisusedbetweenthecollectorcircuitandtheexistingtank.Forthisretrofittedsystemanannualsolarfractionof50.5%wasachieved.Aconventionalsolarthermalsystemusingastandardsolartankachievesacomparableperformanceforthesametotalstoragevolume,collectorareaandreferenceconditions.
Keywords:
solarthermalstoragetankwaterheaterretrofitdomes
1.Introduction
Oneofthebiggestobstaclestotheeconomicprofitabilityofdomesticsolarwaterheating(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.Thisismainlyexplainedbytheincreaseinenergytransferrateatalowenergydrivingcost.Forexample,a40Wpumpcangenerateadrivingforce45timeshigherthantheoneachievedbynaturalconvectionsystems.Inaddition,lowenergypumpsarenowavailableatalowercost.Thedisadvantagesofforcedcirculatingsystemsarestatedtobeahigherdegreeofcomplexityandthedemandforelectricitytorunthepumpsandcontrols.
Fewerstudiesarefocusedonforcedcirculationsystemsspeciallydesignedforcoldregions.WongsuwanandKumarconcludedthatTRNSYSsoftwarepredictsaccuratelytheperformanceofforcedcirculationsystems.BucklesandKleinusedTRNSYSsoftwaretotheoreticallyinvestigatedifferentsystemconfigurations,andconcludedthatheatexchangers,withthesamecapacity,havesimilarperformancewhetherplacedinsideoroutsidethestorage.In2009,HobbiandSiddiquiusedTRNSYStotheoreticallyoptimizethedesignofaforcedcirculationhotwatersystemforcoldclimates.Asinotherstudies,theannualsolarfractionwasusedasdesignparametertobeoptimized.Ofspecificinterestisthefactthatthereisalackofstudiesinvestigatingtheretrofittingofexistingwaterheatersinsingle-familyhousesforsolarhotwaterapplicationincoldregions.
Retrofittingsolardomestichotwatersystemstodaycommonlyconsistsonseriesconnectingtheexistingsystemwithanewsolarstorageupstreamandusingtheexistinghotwaterboilerasabackupheater.Someretrofittedsystemsmakeuseofthermosyphoningandarethereforedependentonanewwellperformingstorageforthatpurpose.Existinginstallationsareoftenoversizedinvolumesincelargedesignloadshavebeenusedbeforeandbecausedomestichotwaterconsumptionhasbeendecreasing.Combinedwithlowlevelsofinsulation,suchoversizingcauseslargesystemheatlosses.Whenusingtheexistingstoragesassolarhotwaterstoragethethermallossesinthesystemcanbedecreasedsincethesolarwatertemperatureislowerthanthebackuptemperature.Incaseswhereitispossibletoknowwhentheexistingboilerisclosetotheendofitslifetime,itcanbeadvantageoustochangetheexistingstorage.
Inthisresearch,retrofittingofconventionaldomesticwaterheatersusingforcedcirculationSWHsystemsforsingle-familyhousesintheSwedishclimatewastheoreticallyinvestigated.Thiswascarriedoutbymeansoftwopumps,oneinthetankloopandtheotherinthesolarcollectorloopwithaheatexchangerinbetween.FourdifferentsystemconfigurationsweresimulatedinTRNSYSsoftwareandcomparedbasedontheannualsolarfraction.Sinceforcedcirculationisused,almostanykindofstoragetankcanberetrofittedwhenanewsolarthermalsystemisinstalled.Also,thedegreeofcomplexityofforcedcirculationsystemsmaybereducedwithsucharetrofit.Forabetterunderstandingoftheresearchcontributiontothefieldandtoincreasethereadabilityofthepaper,themainobjectivesofthestudyarestatedbelow.
TotheoreticallyinvestigatedifferentsystemconfigurationsandcontrolstrategiesinretrofittingconventionaldomesticwaterheatersforSWHsystemsinsingle-familyhousesintheSwedishclimate.
Tocomparetheperformanceoftheretrofittedsystemswiththeperformanceofastandardsolarthermalsystemforthesamereferenceconditions.
Thisstudyprovidesnecessaryinformationtofurtherinvestigatesuchsystemsinpractice.Itisthennecessarytovalidatethetheoreticalmodelsandcarryoutalifecyclecostassessmenttocomparethedifferentsystems.Suchassessmentisbasedonmanyfactorsthatvaryfromcountrytocountryandcanleadtodifferentconclusions.Outsidecoldregionsfreefromfreezing,ananti-freezesolutionandanexternalheatexchangerarenotrequired.Thiswillalterthesystemconfiguration,itsperformanceandfinalcosts.Othervariablefactorsarecostoftheauxiliaryenergy,itspredictedtrendduringthesystemlifetime,theinvestmentcostoftherequiredequipment,theinstallationcost,maintenancecosts,operationcosts,replacementcosts,subsidies,taxesoneventualloans,inflation,chosendiscountrateandresidualvalueattheendofthesystem’slifetime.Also,itisdifficulttoquantifyhowmuchtheindustrialdevelopmentontheintegrationofallretrofittingcomponentsintooneadd-onunitwoulddecreasethecost.Inaddition,thespaceoccupiedbytheintroductionoftheextraretrofittingmaterialsuchaspumps,controlsandheatexchangerisaqualitativecomparisonparameterbetweenthesystemsvalueddifferentlybytheconsumer.Theseassessmentsareoutsidethescopeofthisworkandwillbedealtwithinafurtherstageoftheinvestigation.
2.Methodology
DifferentsystemconfigurationswereanalysedusingTRNSYSsoftwareinordertodeterminetheannualsolarfraction.Firstly,thecharacteristicsofexistingdomesticwatertanksinSwedenweredetermined.Secondly,adomestichotwaterloadprofilerepresentativeofSwedishsingle-familyhouseswascreated.Lastly,theenergymodelofeachsystemconfigurationandsensitivityanalysiswasdescribed.
2.1.ExistingDomesticHotWaterHeatersinSwedishSingle-FamilyHouses
ThemainboundaryofthisinvestigationwastoretrofitthemostcommontypeofexistingdomestichotwaterheatersinsinglefamilyhousesinSweden.Tothebestofourknowledge,thereisnoofficialdataconcerningthemostcommontanksizeinsuchhouses.AccordingtotheSwedishdomesticwaterheatermanufacturers,installersandresearchersinthefield,themostcommonSwedishsingle-familyhousetanksizeis200–300litres,dependingonthefamilysize.Thetrendisthathigherloadscorrespondtohigheravailablestoragevolumes.Asensitivityanalysisshowedthatretrofittinga300litretankwouldgiveahigherannualsolarfractionthanusinga200litretankforthesameload.Hen
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