Performance improvement of solar photovoltaic/thermal heat pump system in winter by employing vapor injection cycle

Direct-expansion solar assisted heat pump (DX-SAHP) is a promising technology for saving energy. In this paper, vapor injection (VI) cycle system to DX-SAHP system is studied. Thermodynamic comparative analyses of ideal VI cycle and ideal conventional vapor compression cycle was carried out for verifying the advantages by applying VI cycle into DX-SAHP. Additionally, photovoltaic/thermal (PVT) modules were used in the system to harvest thermal energy and electric power. A PVT based solar heat pump system employing VI cycle (PVT-VISHP) was proposed, fabricated and investigated experimentally. Performance of the experimental prototype was subsequently evaluated for seven days in winter. The system's performance was evaluated based on the average ambient temperature of -1.13 degrees C and solar irradiation of 164.03 W/m(2). Results showed that the total generated electricity, heat, and consumed power of the system were 0.51 kWh, 23.68 kWh, and 7.24 kWh, respectively. Moreover, average heating coefficient of performance (COPth) and advanced coefficient of performance (COPPVT) of the PVT-VISHP system were 3.27 and 3.45, respectively. In the study, the ambient-evaporating temperature difference ranged from 9.2 degrees C to 17.1 degrees C. Furthermore, variations of injected vapor's pressure, mass flow rate, mass flow rate ratio, and subcooling effects were analyzed in detail. Performance of the PVT modules during a sunny day was tested. It was found that the PVT modules' average thermal collecting and PV efficiencies were 49.9% and 7.51%, respectively.