Numerical analysis on the design of an evaporator for a PV/microchannel direct-expansion CO2 heat pump

Typically, a photovoltaic (PV) panel converts 10% to 20% of incident solar radiation into electricity. The remaining absorbed radiation converts to heat, raising the panel's temperature and reducing its electrical efficiency. A photovoltaic thermal (PVT) system, which integrates the PV panel with a thermal absorber, allows the system to utilize the insolation converted to heat. Making the thermal absorber an evaporator in a heat pump (PVT-DXHP) system improves the thermal output. Utilizing microchannels in the evaporator enhances the heat transfer by increasing the surface area-to-volume ratio which results in improving the coefficient of performance (COP). In this study, a numerical model of the photovoltaic (PV) panel with the integrated microchannel evaporator coupled to a model of the rest of the heat pump is used. This model simulates the combined operation of the heat pump and PV panel, allowing for a detailed analysis of thermal and electrical performance under varying conditions. The analysis on how variations in evaporator design, e.g. microchannel spacing, influence the key metrics such as the system's COP, the temperature distribution of the PV panel, and water outlet temperature. The results show that increasing the microchannel spacing results in a reduction in COP, though this effect becomes negligible as the channel diameter increases. Additionally, the evaporator tilt angle and flow direction play a significant role in modifying the system's COP, particularly under low ambient conditions (273K). The results show evaporator design can be altered to improve system performance.