Comparative study on the performance and exergy efficiency of a solar hybrid heat pump using R22 and R744

• Analyses of the performances and exergy losses of the R22 and R744 solar-hybrid heat pump systems were carried out.
• COP values of the R22 and R744 heat pumps were approximately 3.21 and 2.75 during the cloudy day.
• Exergy loss of the solar collector during the cloudy day increased 13.5% compared with that the sunny day.
• The second law efficiency of the entire R22 heat pump was 6.2% higher than that of the R744 one.

Solar energy has tremendous advantages including its low cost, cleanliness, and limitless supply. Specifically, the solar-hybrid heat pump system is a very safe system using the environment-friendly and harmless refrigerant R744. In this study, the analyses of the performances and exergy losses of the R22 and R744 solar-hybrid heat pump systems were carried out using experimental tests during a sunny and a cloudy day. As a result, the COP (coefficient of performance) values of the R22 and R744 heat pumps were approximately 3.21 and 2.75 during the cloudy day, respectively. On an average, these COP values increased by 20.2% compared with those elicited during the sunny day, whereas the efficiency of the solar collector decreased on average by 14.2%. In addition, the exergy loss of the solar collector during the cloudy day also increased 13.5% compared with that elicited during the sunny day. The second law efficiency of the entire R22 heat pump was 6.2% higher than that of the R744 because the irreversibility of the R744 heat pump was significantly higher and the cycle performance is very sensitive to the operating conditions compared with the subcritical cycles.