Refrigerants selection for a direct expansion solar assisted heat pump for domestic hot water

An important step during a project of a heat pump system is choosing a more suitable refrigerant. This paper presents a comparative study among refrigerants for a small direct expansion solar assisted heat pump (DX-SAHP). The mathematical model used in this study is presented in detail and validated from an experimental setup. The R134a is the reference and the refrigerants with low GWP are R290, R600a, R744 and R1234yf. The results show that R290 has better COP than others refrigerants for solar radiation between 300 W/m(2) and 700 W/m(2), as well as for environment temperature between 10 degrees C and 35 degrees C. On the other hand, for solar radiation less than 50 W/m(2), the R134a has better COP than R290. TEWI (Total Equivalent Warming Impact) analysis indicates that the indirect emission is the most important effect, and then, the TEWI results almost followed the COP outcome. A parametric analysis was conducted to evaluate the influence of the CO2 emission factor for producing electricity. In countries with higher emission factor, the refrigerant with the best COP has the best TEWI. The influence of wind speed and ambient temperature in COP of a DX-SAHP using R290 were more relevant in low solar radiation.