Energy and exergy analyses and thermoeconomic optimization of geothermal heat pump for domestic water heating

Abstract

Energy and exergy analyses and thermo-economic optimization of a geothermal (ground source) heat pump for domestic water heating are performed in this study. The modeling and optimization of the geothermal heat pump with closed horizontal ground heat exchanger are conducted by applying EES program. The effect of water temperature at the inlet of evaporator is investigated on the coefficient of performance (COP) for several types of refrigerants. The results show that R507a has the highest COP in comparison with the other refrigerants. In the optimization process, the total annual cost (TAC) is selected as objective function, and optimum design parameters are calculated for minimizing the defined objective function. Moreover, variations of TAC values with heating capacity, and overall heat transfer coefficient of soil for various refrigerants for three climatic regions of Iran are discussed. The results show that by changing the temperature of water entering the evaporator, R507a has the lowest TAC value. Also, the greatest share of the system cost is corresponded to ground heat exchanger which is 34 % of total cost. In addition, the compressor has the maximum irreversibility of the system about 53%. Also, variations of TAC value at low temperatures of inlet water are almost equal and with smooth slope for three cities of Tehran, Yazd and Rasht. However, at high temperatures, the slope variation in Yazd is lower in comparison with Tehran and Rasht. Additionally, at optimum conditions, the saturation temperatures for evaporator and condenser are estimated −1.5 and 51.89°C, respectively.