In this paper

the effects of a refrigerant charge on the system performance of a heat pump water heater and the regulating characteristics of the electronic expansion valve were studied experimentally. The system performance under different regulation modes of electronic expansion valve was also quantitatively analyzed. The experimental results show that 1.1 kg is the best refrigerant charge when the valve opening is 16% and the superheat temperature is 10 ℃. The corresponding maximum coefficient of performance (COPa) was 3.05 and 3.68

respectively. Excessive refrigerant charge reduces the system performance and the adjustment range of electronic expansion valve. To avoid the liquid suction of compressor

the adjustment of superheated temperature is better than that of valve opening. The system performances of the two regulating modes are compared under the optimum refrigerant charge

and the results show that the superheat regulation method is the best.