【正文】 intain a high level of performance even in colder climates.The ground heat exchanger used in conjunction with a closedandconnectedtoaheatpumpthroughwhichwater/antifreezeiscirculated. For the groundloop heat exchangers, verticalheat sink in cooling mode operation. In the heating mode, aGSHP absorbs heat from the ground and uses it to heat thesystems consist of a sealed loop of pipe, buried in the groundthe design, simulation and testing of GSHP systems. 2020 Elsevier . All rights reserved.Keywords: Building。 Exergy。 Geothermal energy。 Renewable energy1. IntroductionGroundcoupled heat pump systems are increasinglydeployed for heating and airconditioning in mercial andinstitutional buildings as well as in residential ones. TheseGSHP systems are inherently higher than that of air source heatpumps because the ground maintains a relatively stable source/sink temperature [1,2].The use of ground source heat pumps (GSHPs) inmercial and residential buildings is a tremendous example.product/%%.ItisexpectedthatthemodelpresentedherewouldbebeneficialtoeveryonedealingwithModeling and performance(geothermal) heatOnder OzgeneraaSolar Energy Institute, Ege UniversitybDepartment of Mechanical EngineeringEge University, 35100Received 6 December 2020。 accepted 30 April 2020source heat pump (GSHP) systems for the system analysis anda solar assisted vertical GSHP and horizontal GSHP. The performancesratio, relative irreversibility, productivity lack and exergeticin terms of energetic and exergetic aspects. The values for COPHP66–75O. Ozgener, A. Hepbasli/Energy andNomenclatureC specific heat (kJ/kg K)COP heating coefficient of performance (dimensionless)˙E energy rate (kW)˙Ex exergy rate (kW)f exergetic factor (%)F exergy rate of fuel (kW)h specific enthalpy (kJ/kg)˙I irreversibility (exergy destruction) rate (kW)˙m mass flow rate (kg/s)P pressure (kPa)˙P exergy rate of the product (kW)˙Q heat rejection rate (kW)R ideal gas constant (kJ/kg K)s specific entropy (kJ/kg K)˙S entropy rate (kJ/K)T temperature (K or 8C)˙V volumetric flow rate (m3/s)˙W rate of work or power (kW)Greek lettersd fuel depletion rate (dimensionless)e exergy (second law) efficiency (dimensionless)w humidity (dimensionless)j productivity lack (dimensionless)r density (kg/m3)x relative irreversibility (dimensionless)c specific exergy (kJ/kg)v specific humidity ratio (kgwater/kgair)Indices0 reference (dead) statea, air aircol collectorp pressorcond condenserdest destroyedevap evaporatorfc fancoilgen generationgrh groundheat exchangerHP heat pumpi isentropicin input, inletm mechanicalout outputp constant pressurepump pumpr residentre relativeref refrigerant (R22)s isentropic process, surfacesl space heating loadsys systemTot total% of the worldwide capacity and use. The installedcapacityis15,384 MWtandtheannualenergyuseis87,503 TJ/year, with a capacity factor of (in the heating mode).Almost all of the installations occur in North America andEurope, increasing from 26 countries in 2020 to the present 33countries. The equivalent number of installed 12 kW units(typical of US and Western European homes) is approximately million, over double the number of units reported for 2020.The size of individual units, however, ranges from kW forresidential use to large units of over 150 kW for mercialand institutional installations.During the last decade, a number of investigations have beenconducted by some researchers (. [4,6–13]) in the design,modelling and testing of GSHPs and solar assisted heat pumpsystems. The study reported here includes: (i) The performanceexperimentalevaluationofaverticalsolarassistedgroundsourceheat pump system with R22 as the refrigerant in the heatingmode. A flattype solar collector was directly installed into thegroundcoupled loop, is constructed and tested for the first timeonthebasisofauniversitystudyperformedinthecountry[8–10].(ii)ThetheoreticalperformanceevaluationofahorizontalGSHPwith R22 designed. Although many installations of GSHPsystems worldwide have been realized, the exergetic evaluationstudiesofthesesystemsareverylimited(.[8,11]).This studyalsodescribesaneasytofollowprocedureforexergyanalysisofsolar assisted vertical and horizontal GSHP systems and how toapplythisproceduretoassesstheheatingsystemperformancebycalculating the exergy destructions.2. Description of the systems studiedThe university studies on GSHPs at the Turkish universitiescan be classified into two categories: theoretically andexperimentally. These studies have been reviewed by theauthors in more detail elsewhere [12].. Ground source heat pump system IA schematic diagramof the constructedexperimental systemis illustrated in Fig. 1. This system mainly consists of threeseparate circuits as follows: (i) the ground coupling circuit withsolarcollector(brinecircuitorwater–antifreezesolutioncircuit),Buildings 39 (2020) 66–75 67u usefulv water vaporvalve expansion valvewa water–antifreeze solution(ii) the refrigerant circuit (or a reversible vapour pressioncycle)and(iii)thefancoilcircuitforheating(watercircuit).Themain characteristics of the elements of the solar assisted groundsourceheatpumpsystemaregiveninTable1,wherethenumbers.Conversion from the heating cycle to the cooling cycle isobtained by means of a fourway valve. To avoid freezing thewater under theworking condition and during thewinter, a 10%O. Ozgener, A. Hepbasli/Energy and Buildings 39 (2020) 66–7568groundethyl glycol mixture by weight was prepared. The refrigerantcircuit was built on the closed loop copper tubing. The workingFig. 1. Schematic of the solar assistedstudied was installed at Solar Energy Institute of Ege University(latitude 388240N, longitude 278500E), Izmir, Turkey.Table 1Measured