Effect of a superheating and sub-cooling heat exchanger to the performance

Energy44(2012)996e1004

ContentslistsavailableatSciVerseScienceDirect

Energy

journalhomepage:/lo

cate/energy

Effectofasuperheatingandsub-coolingheatexchangertotheperformanceofagroundsourceheatpumpsystem

KadirBakirci*,DeryaColak1

DepartmentofMechanicalEngineering,AtatürkUniversity,25240Erzurum,Turkey

articleinfo

Articlehistory:

Received15November2011Receivedinrevisedform13April2012

Accepted20April2012

Availableonline7June2012Keywords:

GroundsourceheatpumpGroundheatexchangerColdclimateHeating

SuperheatingSub-cooling

abstract

Theaimofthisstudyistoevaluatetheeffectofasuperheatingandsub-coolingheatexchanger(SHCHE)totheperformanceofgroundsourceheatpumpsystemforclimaticconditionofErzurumhavingcoldclimateinTurkey.Forthispurpose,anexperimentalset-upwasconstructed.Theexperimentalapparatusconsistsofaseriesgroundheatexchanger(GHE),aliquid-to-liquidvaporcompressionheatpump,watercirculatingpumpsandothermeasurementequipments.Inthisstudy,theperformanceofthesystemswithandwithoutSHCHEwasexperimentallyinvestigated.Theexperimentswereperformedin2010forJanuaryandFebruarywhicharethecoldestmonthsoftheheatingseason.Theexperimentallyobtainedresultswereusedtocalculatethepowervaluesofthemainsystemequipments,thecoef cientofperformanceoftheheatpump(COP)andtheoverallsystem(COPS)forsystemswithandwithoutSHCHE.

Ó2012ElsevierLtd.Allrightsreserved.

1.Introduction

Turkey’sdemandforenergyandelectricityisincreasingrapidly.Turkeyisheavilydependentonexpensiveimportedenergyresourcesthatplaceabigburdenontheeconomy.Aswouldbeexpected,therapidexpansionofenergyproductionandconsumptionhasbroughtwithitawiderangeofenvironmentalissuesatthelocal,regional,andgloballevels.Withrespecttoglobalenvironmentalissues,Turkey’scarbondioxide(CO2)emissionshavegrownalongwithitsenergyconsumption.Stateshaveplayedaleadingroleinprotectingtheenvironmentbyreducingemissionsofgreenhousegases.Inthisregard,renewableenergyresourcesappeartobeoneofthemostef cientandeffectivesolutionsforcleanandsustainableenergydevelopmentinTurkey.Turkey’sgeographicallocationhasseveraladvantagesforextensiveuseofmostoftheserenewableenergysources[1].

Infuturetheworld’senergysupplymustbecomemoresustainable.Thiscanbeachievedbothbyamoreef cientuseofenergyandbyrelyingonrenewablesourcesofenergy,particularlywind,hydropower,solarandgeothermalenergy[2].Turkeyisan

*Correspondingauthor.Fax:þ904422360957.E-mailaddress:abakirci@atauni.edu.tr(K.Bakirci).1

Presentaddress:Directoryofthe12thRegionofHighways,25080Erzurum,

Turkey.

0360-5442/$eseefrontmatterÓ2012ElsevierLtd.Allrightsreserved.doi:10.1016/j.energy.2012.04.049

energyimportingnationwithmorethanhalfofourenergyrequirementsmetbyimportedfuels.Airpollutionisbecomingasigni cantenvironmentalconcerninthecountry.Achievingsolutionstoenvironmentalproblemsthatwefacetodayrequireslong-termpotentialactionsforsustainabledevelopment.Forthegovernmentsorsocietiestoattainsustainabledevelopment,muchefforthastobedevotedtoutilizingsustainableenergyresourcesintermsofrenewableenergies[3,4].

TheGSHP(groundsourceheatpump)isoneoftheef cientandsustainablemethodstoprovidespaceheatingandhotwaterforvariouskindsofbuildings.TheGSHP,worksbymeansofthevaporcompressioncycle,whichcoolsacirculating uidthat owsthroughasystemofclosedloops.Theseloopsareburiedwithinthegroundeitherhorizontally,iflandspacepermits,orverticallybymeansofboreholes.Thedirectionofheat owisfromthegroundtothecooler uidandthisheatisupgradedtoahighertemperaturethroughthevaporcompressioncyclefordeliverytothebuilding[5].Thegroundsourceheatpumpsprovideanewandcleanwayofheatingbuildingsintheworld.Theymakeuseofrenewableenergystoredintheground,providingoneofthemostenergy-ef cientwaysofheating.Theyaresuitableforawidevarietyofbuildingtypesandareparticularlyappropriateforlowenvironmentalimpactprojects[6].

Intheliterature,anumberofinvestigationshavebeencon-ductedbysomeresearchersinthedesign,modelingandtestingoftheGSHPsystems[7e18].HealyandUgursal[8]haveinvestigated

K.Bakirci,D.Colak/Energy44(2012)996e1004997

theeffectofvarioussystemparametersontheGSHPperformanceusingacomputermodel.TheyhavealsocarriedoutacomparativeeconomicevaluationtoassessthefeasibilityofusingaGSHPinplaceofconventionalheating/coolingsystemsandanairsourceheatpump.Floridesetal.[9]carriedoutastudyonthegeothermalcharacteristicsofthegroundandthepotentialofusinggroundcoupledheatpumpsinCyprus.Yuetal.[11]designedaconstanttemperatureandhumiditysystemdrivenbyagroundcoupledheatpumpandconstructedinanarchivesbuildingofShanghai.TheexperimentalresultsunderweatherconditioninShanghaiwereanalyzedand,theinvestigationoftheexperimentinayearwaspresented.Pulatetal.[15]haveinvestigatedtheperformanceofthehorizontalclosed-loopwater-to-airgroundsourceheatpumpsystemincludingtheeffectofvariousparameterssuchasleavingtemperatureofgroundheatexchangerunitandoutdoortemper-atureforwinterclimaticconditionofBursa,Turkey.Blumetal.[16]determinedandassessedtheeconomicandtechnicalfactorsthatin uencethedesignandperformanceoftheGSHPsystemsinprivatehouseholds.

Xietal.[19]presentedexperimentalstudiesonasolar-assistedgroundcoupledheatpumpsystemforspaceheating.Fouropera-tionmodesofthesystemwereinvestigatedthroughoutthecoldestperiodinwinter.Theheatpumpperformance,theboreholetemperaturedistributionsandthesolarcolletingcharacteristicsofthesystemwereanalyzed.Jeonetal.[20]analyzedtheperformanceofahybridcoolingsystemthatcombinesascrewwaterchillerwithagroundsourceheatpumpatvariouscoolingloads.

TheSHCHEisusedtosuperheatandsub-cooltherefrigerantinoutletofthecondenserandevaporatorofthevaporcompressionheatpumpsystem,respectively.Thesuperheatingandsub-coolingproceduresareappliedforimprovingthesystemef ciency.Intheliterature,availablestudiesonsub-coolingandsuperheatingeffectsofvaporcompressionrefrigerationcyclesareverylimited.Selbasetal.[21]obtainedoptimumheatexchangerareasandoptimumsub-coolingandsuperheatingtemperaturesundervariousoper-atingconditionsofvaporcompressionrefrigerationsystem.Theapplicationwasconsistedofdeterminingtheoptimumheatexchangerareaswiththecorrespondingoptimumsub-coolingandsuperheatingtemperatures.

Variousstudieshavebeencarriedoutbyresearchersinorderto

analyzetheperformanceoftheGSHPsystemsaroundtheworld.Theyperformedtheoreticalandexperimentalstudiesonthegroundsourceheatpumpsystemswithagroundheatexchangerandconcludedthatusingheatpumpsystemsarefeasible.

ThisstudyincludestheperformanceevaluationofthegroundsourceheatpumpsystemwithandwithoutSHCHEfortheclimaticconditionofErzurumhavingcoldclimateinTurkey.Anexperimentalset-up,describedinthenextsection,isconstructedandtestedonthebasisofauniversitystudy.Thecoef cientofperformanceoftheheatpumpandtheoverallsystemiscomputedfromthemeasurementsand,theenergyconsumptionofthegroundsourceheatpumpsysteminheatingseasoniscalculated.

2.Experimentalprocedureandmeasurement

ThegroundsourceheatpumpsystempresentedhereisatErzurum,Turkey,latitude:39.55 N;longitude:41.16 E;placedontheEastAnatolianRegionofTurkey.Table1givestheclimaticdataforErzurum.AschematicoverviewofthesystemisillustratedinFig.1.

Thecompressor(4)usedfortheheatpumpsystemisahermeticscrolltype,whichisdrivenbya2610Wattelectricalmotor.Theheatpumphasanevaporator(12)andcondenser(5);bothofwhicharewatercooledplatetypeheatexchanger.Theseequipmentshavebeeninsulatedentirelywith25mmthickrubberfoamagainstheatloss.

AsshowninFig.1,thesystemconsistsofaverticalgroundheatexchanger(3)locatedtothedepthof2Â53m,aheatpumpwithwater-to-refrigerantheatexchanger,watercirculatingpumps(1)andotherconventionalequipments.Inthesystem,theheattransfer uid(antifreeze-watermixtureof50%)whichcomesfromtheundergroundgoestothewater-sourceevaporatoroftheheatpumpwhereitreleasessomeenergy,andthen,itissenttothegroundheatexchangersbyawatercirculatingpump.However,duringtheday,theheattransferring uidthatcomesfromtheevaporatoroftheheatpumpissenttotheground.Refrigerant134awasusedasworking uid.Theverticalgroundheatexchanger(GHE)unitisasingleU-tubeplacedintwoverticalboreholesatthedepthof53m.ThepipesconnectingtheGHEtotheevaporatorwereinsulatedandburiedatthedepthof2mtominimizetheheatloss.

Inthepresentstudy,thetemperatures, owrates,pressuredrops,voltagesandcurrentsweremeasuredbyappropriateinstrumentsgiveninTable2.Thetestswereconductedon

the

Table1

ClimaticconditionofErzurumforlong-termaveragevalues.Climaticvalues

MonthsinheatingseasonNov.

Dec.Jan.Feb.Mar.Apr.AverageoutdoorÀ0.5À7.2À10.8À10.1À3.75.2temperature( C)MinimumoutdoorÀ6.8À12.6À16.9À16.7À9.8À0.9temperature( C)Maximumoutdoor6.9À1.6À4.4À3.12.611.8temperature( C)Averagerelative82.081.377.573.175.056.7humidity(%)Averagewind2.22.22.32.42.83.3velocity(m/s)Averagesunshine4.32.33.03.84.45.9duration(h)Averagesolar

8.8

7.0

8.9

12.6

16.0

17.0

radiation(MJ/m2.day)

998K.Bakirci,D.Colak/Energy44(2012)996e1004

7.Receiver8.Dryer

9. Sight glass 10. Solenoid valve 11. Expansion valve

18.Electroniccounter19.Controlpanel

20. NTC temperature indicator 21. Data acquisition card22. Computer and monitor

a

bc

Fig.1.a)Aschematicrepresentationofthesystem(withoutSHCHE)b)AschematicrepresentationoftheheatpumpwithSHCHEandc)Outsideviewsoftheheatpump.

groundsourceheatpumpsystemintheheatingperiodof2010.Themeasurementsweretakenfrom8.00a.m.to18.00p.m.withanintervalof30min.Thetemperaturesmeasuredbythethermo-couplesweremonitoredinacomputerandrecordedbyadata-acquisitioncardineachsecond,whichwaslaterusedforanalysis.

Theelectroniccounter(digitalpowermeter)wasusedtomeasurethepowerconsumptionofthecompressorand,thepowerconsumptionsofthepumpsweremeasuredbyawatt-meter.Allthemeasuringprocessesofthetemperaturesweremonitoredandcontrolledbyapersonalcomputer-baseddata-acquisitionsystem.

2.1.Uncertaintyanalysis

Experimentalerrorsanduncertaintiescanresultfrominstru-mentselection,instrumentcondition,instrumentcalibration,environment,observationandreadingandtestplanning.Theuncertaintyanalysisisneededtoprovetheaccuracyoftheexper-iments[22].AnuncertaintyanalysiswasperformedusingamethoddescribedbyHolman[23].

ThetotaluncertaintiesofthemeasurementsareestimatedtobeÆ1.01%forthewaterandtheantifreeze-watersolutiontempera-tures,Æ2.05%forpressures,Æ1.00%forpowerinputstothe

K.Bakirci,D.Colak/Energy44(2012)996e1004

999

Table2

Instrumentsusedinthesystemformeasurements.InstrumentMeasurement

Rotameter

Themass owratesoftheantifreeze-watersolution(approximately50%)

Copper-constantanThetemperatureoftheantifreeze-waterthermocouples

solutionenteringandleavingthegroundheatexchanger,theinletwater

temperaturetoandexitwatertemperaturefromheatingunit

Bourdon-typemanometersThepressuresofthecondenserandevaporator

MeteorologicalstationTheoutdoorairtemperaturesandhumidityWattmeterTheelectricalpowerinputtothecirculatingpump

Electroniccounter

Instantaneouspowerconsumptionsofthecompressor

NTC(negative

Thegroundtemperatureatthedepthof53m

temperaturecoef cient)sensor

compressorandÆ3.00%forthecirculatingpumps.TheuncertaintyinreadingvaluesofthetableisassumedtobeÆ0.20%.Thetotaluncertaintiesassociatedwithmass owrateofthewaterandantifreeze-watersolutionareestimatedtobeÆ7.15%.ThetotaluncertaintiesassociatedwithenergyreceivedfromtheðQ_conÞandwithheatextractedfromthegroundðQ_condenser

groÞareÆ7.23%.

ThetotaluncertaintiesassociatedwiththeCOPandCOPSareÆ7.30andÆ7.28%,respectively.

3.Climatepropertiesandenvironment3.1.Weatherdata

Theexperimentalgroundsourceheatpumpsystemwasestab-lishedandtestedinErzurumprovincehavinganaltitudeof1869mandthecoldestclimateinTurkey.TheclimaticconditionsofErzurumforlong-termaveragevalues(monthlyaverageminimum,maximumandmeanoutdoortemperature,themonthlyaveragesofrelativehumidity,windvelocity,solarradiationandsunshinedurationsfortheheatingseason)aregiveninTable1.TheannualheatingandcoolingdegreedaysforErzurumwithabasetemper-atureof18 Carefoundtobe4870[24].

ThehoursofthesmallesttemperaturebinofÀ19.5 C(À21 C/À18 C)observedforErzurumintheEastAnatoliaRegionofTurkeyare17inJanuaryandFebruary.Also,thehoursofthetemperaturebinfromÀ21 Cto18 CforErzurumare7498intheaverageof1995e2005.Thisprocedurecanaccountforthepart-loadperfor-manceofheating,ventilatingandair-conditioningequipmentaswellasforthevaryingperformanceofheatpumpsystemsandprimaryHVACequipment[25].

3.2.Soilcharacteristics

Erzurumisanintermountainsedimentarybasinwith

aMiocene-Quaternaryvolcanicbasement,andesiticebasalticlava owsand ssureeruptionslava.ThegroundstructureinthecitycentreofErzurumispredominantlyalluvialstructureuntilthethicknessof1kmfromsurface.Also,thegroundstructureofthecitycentreisgravel,sandandalittleclay.ThelocalityofPalandoken(inthesouthoftheCentre)isthevolcanicrockpiecesconsistingofbasalt.ThelocalityofSanayi(inthewestoftheCentre)issand,thingravelandalittleclaysometimesand,thelocalityofDadaskent(intheeastoftheCentre)isthinsandandclay[18].

3.3.Environment

Ingeneral,CO2emissionsarehighasfossilfuelsareusedinourcountry.Theheatpumpsconsumelessprimaryenergythanconventionalheatingsystemsand,theyareanimportanttech-nologyforreducingemissionsofgasesthatharmtheenviron-ment[5].Theheatpumpsystemsarethemostef cientformofelectricheating,providingtwotothreetimesmoreheatingthantheequivalentamountofenergytheyconsumeinelectricity.Signi cantemissionreductionsareavailablethroughtheapplicationoftheheatpumpsystem(HPS)inbothresidentialandcommercialbuildings[26].Residentialfossilfuelheatingsystemsproducedanywherefrom1.2to36timestheequivalentCO2emissionsoftheHPS.TheCO2emissionreductionsfrom15%to77%wereachievedthroughtheuseoftheHPS[27].Itisknownthattheheatpumpssigni cantlyreducetheCO2emis-sionseverydaywhilsttheyprovidecentralanddomestichotwaterheating[28].Theheatpumpsofferthemostenergy-ef cientwaytoprovideheatingandcoolinginmanyapplica-tions,astheycanuserenewableheatsourcesinoursurround-ings[29].

4.Energyanalysis

Themeasuredvaluessuchasthetemperaturechangesofthewaterandtheantifreeze-watersolution,the owratesandtheelectricalpowerinputwereusedtodeterminetheperformancethesystem.TheusefulheatobtainedfromthecondenserQ_of

conis

calculatedas,

Q_con¼m

_wcwðTcwoÀTcwiÞ(1)

Theextractedheatfromthegroundisgivenbythefollowingequation;

Q_gro¼m

_awcawðTeaiÀTeaoÞ(2)

wherem

_wandm_awarethe owrateofthewaterinthecondenserandtheantifreeze-watersolutionintheevaporator,respectively.TheCOP(theheatpump)iscalculatedas;

COP¼

Q_W

con(3)

comTheCOPS(theoverallsystem)iscalculatedas;

COPS¼

Q_W

con

comþW(4)

pThepowerinputtoacirculatingpumpW

_piscomputedfromthefollowingequation;

W

_Vp¼IppcosðfÞ(5)

whereIpisthecurrentofthepump,Vpisthevoltageofthepumpandcos(f)isthepowerfactor.

1000

Table3

Technicaldetailsoftheexperimentalset-up.

Location:Erzurum,Turkey(lat.39.55 N;long.41.16 E)Weatherinformation(yearlyaveragevalues)Averageoutdoortemperature( C)Minimumoutdoortemperature( C)Maximumoutdoortemperature( C)Averagerelativehumidity,(%)Averagesunshineduration(h)

Averagesolarradiation(MJ/m2.day)Averagewindvelocity(m/s)

GroundheatexchangerinformationType

Diameter(mm)Deep(m)

HeatpumpinformationCapacity(kW)CompressortypeEvaporatortypeCondensertype

Compressorpowerinput(kW)Capacityofcooling(kW)

Maximumdischargepressure(bar)Compressordisplacement(m3/h)Refrigeranttype

K.Bakirci,D.Colak/Energy44(2012)996e1004

4.7À2.812.264.66.415.62.7Vertical32

2Â53

7

HermeticscrollPlatePlate

2.61(3.5HP)5.7299.4R-134a

5.Resultsanddiscussions

Inthisstudy,theperformanceofthegroundsourceheatpumpsystemwithverticalgroundheatexchangerwas

experimentallyanalyzedinErzurum,Turkey.Theexperimentalresultswereobtainedintheheatingseasonof2010.JanuaryandFebruaryarethecoolestmonthsoftheheatingseasonintheregion.Therefore,theexperimentaldataweregivenonlyforthesemonths.

Thetechnicaldetailsoftheexperimentalset-uparegiveninTable3.Fig.2showsthevariationsintheinlet-outlettempera-turesoftheheattransfer uidstotheevaporatorandthecondenserwithtimeofdayforthesystemswithandwithoutSHCHE.AsseeninFig.2,whilethetemperatureofthecondenseroutlet(Tcwo)forJanuaryvariesinthebandof49.6e61.0 C,itvariesinthebandof47.9e51.4 CforFebruaryduringtheexper-imentscarriedoutwithSHCHE.ThesametemperatureforJanuaryandFebruaryvariesinthebandof47.7e53.0 Cand47.2e50.2 C,respectively,duringtheexperimentscarriedoutwithoutSHCHE.Fig.2showsalsothehourlyvariationsoftheinlettemperaturesoftheevaporator.Theinlettemperaturesoftheevaporatorhavethemaximumvalueinlocaltimeof08:00foralltheexperimentalconditions.

Fig.3showsthevariationsinthecondenserpower,theGHE(evaporator)powerandthecompressorpowerwiththetimeofdayforthesystemswithandwithoutSHCHE.Fig.4showsthedailyvariationsofthegroundtemperatureatthedepthof53mforthesystemswithandwithoutSHCHE.AsseeninFig.4,theaveragegroundtemperaturesforthesystemswithandwithoutSHCHEare6.6and6.5 CforJanuary,respectively.ThesetemperaturesforthesystemswithandwithoutSHCHEare5.7and5.8 CforFebruary,respectively.

a

Temperature (°C)

20151050-5-1008:00

2015

Temperature (°C)

16:00

18:00

1050-5

10:0012:0014:00

b

Time of day

7060

-1008:00

7060Temperature (°C)

5040302008:00

10:0012:0014:0016:0018:00

Time of day

Temperature (°C)

5040302008:00

10:0012:0014:0016:0018:00

Time of day

10:0012:0014:0016:0018:00

Time of day

With (Jan. 20) and without (Jan. 23) SHCHE With (Feb. 05) and without (Feb. 03) SHCHE

Fig.2.Variationsininlet-outlettemperatureswithtimeofdayforthesystemswithandwithoutSHCHE,fora)Evaporatorandb)Condenser.

K.Bakirci,D.Colak/Energy44(2012)996e10041001

a

Condenser power (kW)

8

8

Condenser power (kW)

66

44

2

2

008:00

10:0012:0014:0016:0018:00

008:00

10:0012:0014:0016:0018:00

b

GHE (evaporator) power (kW)

Time of day

8

Time of day

8GHE (evaporator) power (kW)

66

44

22

008:00

10:0012:0014:0016:0018:00

008:00

10:0012:0014:0016:0018:00

Time of day

Time of day

c

Compressor power (kW)

88Compressor power (kW)

66

44

22

008:00

10:0012:0014:0016:0018:00

008:00

10:0012:0014:0016:0018:00

Time of dayTime of day

With (Jan. 20) and without (Jan. 23) SHCHE With (Feb. 05) and without (Feb. 03) SHCHE

Fig.3.DailypowervaluesofthesystemswithandwithoutSHCHE,for(a)Condenserpower,(b)GHE(evaporator)powerand(c)Compressorpower.

14

14Ground temperature (°C)

12Ground temperature (°C)

108642008:00

12108642008:00

10:0012:0014:0016:0018:00

10:00

Time of day

12:0014:00Time of day

16:0018:00

With (Jan. 20) and without (Jan. 23) SHCHEWith (Feb. 05) and without (Feb. 03) SHCHE

Fig.4.Dailyvariationsofthegroundtemperatureatthedepthof53mforthesystemswithandwithoutSHCHE.

1002K.Bakirci,D.Colak/Energy44(2012)996e1004

a

654COP

321008:00

654COP

321008:00

10:00

12:0014:00Time of day

16:0018:0010:00

12:0014:00Time of day

16:0018:00

b

654COPS

COPS

6

54321008:00

321008:00

10:00

12:0014:00Time of day

16:0018:0010:00

12:0014:00Time of day

16:0018:00

With (Jan. 20) and without (Jan. 23) SHCHE With (Feb. 05) and without (Feb. 03) SHCHE

Fig.5.Performancecoef cientsversustimeofdayforthesystemswithandwithoutSHCHE,fora)Heatpumpandb)Overallsystem.

Fig.5showsthevaluesoftheperformancecoef cientoftheheatpump(COP)andoverallsystem(COPS)versustimeofdayforthesystemswithandwithoutSHCHE.AsshowninFig.5,thevaluesoftheCOPforthesystemswithandwithoutSHCHEvaryfrom2.1to2.7andfrom2.4to2.6inJanuary,whiletheychangefrom2.6to3.3andfrom2.7to3.3inFebruary,respectively.Additionally,thevaluesoftheCOPSforthesystemswithandwithoutSHCHEvaryfrom1.9to2.5andfrom2.1to2.3inJanuary,whiletheychangefrom2.4to3.1andfrom2.5to3.1inFebruary,respectively.TheaveragevaluesoftheCOPforthesystemswithandwithoutSHCHEarecalculatedtobe2.31and2.47inJanuary,whiletheyarecalculatedtobe2.73and2.81inFebruary,respectively.TheaveragevaluesoftheCOPSforthesystemswithandwithoutSHCHEarealsocalculatedtobe2.07and2.19inJanuary,whiletheyarecalculatedtobe2.55and2.62inFebruary,respectively.Thevariationsintheinlet-outlettemperaturedifferences(TeaiÀTeao)oftheantifreeze-watersolutiontotheGHEunitwithtimeofdayforthesystemswithandwithoutSHCHEaregiveninFig.6.

ThedailyaveragevaluesofthemeasureddataandcalculatedresultsaregiveninTable4.Thesevaluesconsistoftheaveragevaluesofthemeasurementsof21recordedfrom8.00a.m.to18.00p.m.withanintervalof30min.AsseeninTable4,thecondensationpressuresinaverageareabout15barand,thisvalueisveryreasonablebecausethemaximumdischargepressurelimitofthecompressoris29bar.

8

8

6Teai-Teao (°C)

6Teai-Teao (°C)

44

2

2

008:00

10:00

12:0014:00Time of day

16:0018:00

008:00

10:0012:0014:0016:0018:00

Time of day

With(Jan. 20)andwithout (Jan. 23)SHCHEWith(Feb. 05)andwithout(Feb. 03)SHCHE

Fig.6.Variationsininlet-outlettemperaturedifferences(TeaiÀTeao)oftheantifreeze-watersolutiontotheGHEunitwithtimeofdayforthesystemswithandwithoutSHCHE.

K.Bakirci,D.Colak/Energy44(2012)996e1004

1003

Table4

MeasuredandcalculatedparametersinaverageforthesystemwithoutSHCHE(January23,2010andFebruary03,2010).Item

Jan.23,Feb.03,Unit

Total

2010

2010

uncertainty(%)MeasuredparametersEvaporationpressure2.642.59BarÆ2.05Condensationpressure14.7714.69BarÆ2.05Temperatureofrefrigerant2.351.52 C

Æ1.01atthecompressorinletTemperatureofrefrigerant81.2781.31

CÆ1.01atthecondenserinletTemperatureofrefrigerant48.4347.73

CÆ1.01atthecondenseroutletTemperatureofrefrigerantÀ7.83À8.24

C

Æ1.01attheevaporatorinletCondensingtemperature54.6054.38

CÆ1.01EvaporatingtemperatureÀ2.95À3.46

CÆ1.01Flowrateofantifreeze-water0.2880.333kgsÀ1

Æ7.15solutionintheevaporatorFlowrateofwaterinthe0.267

0.324

kgsÀ1

Æ7.15

heatingunitorthecondenser

Indoorairtemperature

11.749.73

CÆ1.01Currentofcirculatingpump0.600.60AÆ1.00attheGHE

Currentofcirculatingpump0.690.69AÆ1.00attheheatingunitTwo-phasevoltage220.0220.0VÆ1.00Temperatureof

1.74

1.11

C

Æ1.01

antifreeze-watersolutionattheevaporatorinletTemperatureof

À2.30À2.65

CÆ1.01

antifreeze-watersolutionattheevaporatoroutletSupplywatertemperature49.5648.41

CÆ1.01oftheheatingunit

Returnwatertemperature45.1144.68

C

Æ1.01oftheheatingunit

Powerinputtothecompressor2.001.85kWÆ1.00Calculatedparameters

Powerinputtothecirculating0.1190.119kWÆ3.00pumpattheGHE

Powerinputtothecirculating0.1370.137kWÆ3.00pumpattheheatingunitHeatingloadofthecondenser4.9555.207kWÆ7.23Coolingloadoftheevaporator3.6023.907kWÆ7.23HeatingCOP(theheatpump)

2.4702.809eÆ7.30HeatingCOPS(theoverallsystem)

2.190

2.621

e

Æ7.28

6.Conclusions

Theperformanceofaverticalgroundsourceheatpumpsystemwasinvestigatedexperimentally.Inthestudy,theexperimentalresultsweregivenforthemonthsofJanuaryandFebruaryintheheatingseasonof2010.TheexperimentalresultsindicatethattheaveragevaluesoftheCOPandtheCOPSareapproximately2.31and2.07withSHCHEand2.47and2.19withoutSHCHEinJanuary,whiletheyareapproximately2.73and2.55withSHCHEand2.81and2.62withoutSHCHEinFebruary,respectively.Additionally,theresultsshowthatthesystemswithandwithoutSHCHEarenotverydifferentintermsofthecoef cientofperformancebutthesystemwithSHCHEcanbepreferredforhighercondenseroutlettemperature.

Theheatpumpsystemsareenvironmentallyfriendly.Theinitialcostsoftheheatpumpsystemsarehigher,buttheyhavelowoperating,maintenance,andlifecyclecostsandalongerlifeexpectancythanmostconventionalsystems.Also,theheatpumpsystemsprovideheating,coolingandhotwaterinmanyapplications.Thegroundsourceheatpumpsystemspresent

tremendousenvironmentalbene tswhencomparedtotheconventionalsystems.Therefore,thesesystemscanbeusedtominimizeenvironmentalimpactsandairemission.

Acknowledgment

TheauthorsthanktheAtatürkUniversityResearchFund(ProjectNo:2005/25)andTheScienti candTechnologicalResearchCouncilofTurkey(TUBITAK,ProjectNo:106M068)duetotheir nancialsupportforthisresearch.

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