Effect of a superheating and sub-cooling heat exchanger to t(3)

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)

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