Performance comparison between R22 and R744 solar-geothermal hybrid heat pumps according to heat source conditions

Solar heat and geothermal energy are widely used renewable energy which is one of important issue for future. Besides, R744 as environmental friendly refrigerant has advantage to apply into heat pump system. In this study, the performance the R22 and R744 solar-geothermal hybrid heat pumps was investigated numerically according to heat pump operating temperature, solar radiation, indoor design temperature and evaporator inlet temperature from ground. As a result, as the heat pump operating temperature increased from 40 °C to 48 °C, the coefficients of performance (COPs) of the R22 and R744 heat pump systems decreased by 20.1% and 19.0%, respectively. Additionally, as the evaporator inlet temperature from ground increased from 11 °C to 19 °C, the COPs for the R22 and R744 heat pumps increased by 17% and 29%, respectively. Under basic operational conditions, the heat COP of the R22 heat pump showed a 28.8% higher value compared to that of the R744 heat pump. The efficiency of solar collector in R744 solar-geothermal hybrid heat pump is 4.1% higher than that in R22 one. In addition, the heating capacity of the R22 heat pump was 10% higher than that of the R744 heat pump. The solar collector system was more effective in the R744 hybrid heat pump compared to the R22 hybrid heat pump.