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

In this paper, a direct-expansion heat pump water heater system integrated uninsulated micro-channel PV/T solar collector (UMC-PVT-SC) is proposed. This system can realize storage for both thermal energy and electricity, ensuring the supply of domestic hot water. The theoretical models of micro-channel PV/T solar collector, hot water storage tank, compressor and electronic expansion valve are established to investigate the performance of the micro-channel PV/T heat pump water heater system. R134a is used as refrigerant. The system performance is numerically simulated using MATLAB for different solar radiation intensity, ambient temperature and wind speed. The results show that solar radiation intensity has the largest influence on the system performance, followed by ambient temperature and wind speed. The coefficient of performance of the heat pump (COPHP) and the overall coefficient of performance (COPpvt) of the integrated system increase while the required operating time reduces, as solar radiation intensity and ambient temperature increase. The uninsulated micro-channel PV/T solar collector (evaporator) can absorb thermal energy from both ambient air and solar radiation and therefore achieve high COPHP, electric efficiency and COPpvt. Even under cold weather conditions, the proposed solar collector and heat pump heater demonstrate high efficiencies, heating and power generation capacities. When ambient temperature is -18.6 degrees C and solar irradiance is 322 W/m2, the collector efficiency and electric efficiency of UMC-PVT-SC are still at 0.718 and 0.244, respectively, and the COPHP and COPpvt of the heat pump heater are 3.5, 5.63, respectively. The present work is of potential value for delivering net zero.