Study on performance of direct-expansion heat pump water heater integrating uninsulated micro-channel PV/T solar collector

Abstract

In this paper, a direct-expansion heat pump water heater system integrating uninsulated micro-channel PV/T solar collector is proposed. This system can realize storage for both thermal energy and electricity and complementary grade, ensuring the supply of domestic hot water. Based on the performance of the micro-channel PV/T heat pump water heater system, the theoretical models of micro-channel PV/T solar collector, hot water storage tank, compressor and electronic expansion valve are established where R134a is used as refrigerant. Theoretical simulation and analysis of system performance under different solar radiation intensities, ambient temperatures and different outdoor wind speeds are carried out with MATLAB. The results show that solar radiation intensity has the greatest influence on the system performance, followed by ambient temperature and wind speed. The basic-thermal system performance coefficient (COP) and the advanced system performance coefficient (COPpvt) will be enhanced, while the required operating time will be reduced, as solar radiation intensity and ambient temperature increase. This system removes the thermal insulation for the micro-channel PV/T solar collector that the convection heat transfer on the micro-channel evaporator is enhanced. Therefore, the system can absorb the thermal energy from the ambient air according to different solar radiation intensities, and maintain a high coefficient of performance, electric efficiency, thermal efficiency and overall energy efficiency. Even when the solar irradiation is 322 W/m2 and the ambient temperature is −18.6 °C, the thermal efficiency, electric efficiency and overall energy efficiency of UMC-PVT-SC and COPpvt can still remain at 0.718, 0.2442, 1.341 and 5.63, ensuring the heating capacity and high grade power output capacity.