Both R1270 and R290 are the alternative refrigerants of great potential. The influence of refrigerant charge on the performances of heat pump water heater using R1270 and R290 respectively and the temperature distribution of the heat transfer fluids in the condenser were investigated experimentally under nominal operating conditions

and the feasibility of natural refrigerants replacing R22 was also studied. The results indicated that the refrigerant charge had apparent impact on the cycle performance and temperature distribution of the heat transfer fluids of both systems. At the same optimal charge (0.90 kg)

R1270 system and R290 system achieved the maximum COP of 4.443 and 4.317 respectively. Under different refrigerant charges

two heat transfer pinch points and two maximum heat transfer temperature differences appeared in the condensers of both systems

and the locations of the first narrow heat transfer point and the second maximum heat transfer temperature difference had similar migration with the change of refrigerant charge. Compared to R22 system

both R1270 system and R290 system at the optimal charge obtained markedly superior COP and discharge temperatures and relatively equivalent discharge pressures

and their heating capacities increased by 7.05% and decreased by 10.65%

respectively. Hence

both R1270 and R290 have marked advantages when replacing R22

especially the former.