The performance comparison of the direct-expansion solar assisted heat pumps with three different PV evaporators

Abstract

Aiming to analyze the optimal structure of evaporator, three direct-expansion solar assisted heat pumps with Fresnel PV evaporator (FPV-SAHP), hybrid Fresnel PV plus TEG evaporator (FPV/TEG-SAHP) and traditional PV evaporator (PV-SAHP) are compared and discussed in this paper. It is known for us that the solar heat stored on PV causes a rise of the PV temperature as well as a reduction of the electrical efficiency for the negative correlation. In addition, the evaporators in direct-expansion solar assisted heat pumps(DX-SAHP) own a low temperature for the refrigerant absorbs heat directly. Inserting thermoelectric generator (TEG) between PV and evaporator can convert the heat conducted from PV to evaporator into electrical energy. Although TEG generates electrical energy, it increases thermal resistance between PV and evaporator, which hinders the cooling of PV cells. Considering the coupling relationship between the electricity generated by TEG and the loss caused by blocking PV heat dissipation, it is valuable to discuss whether the performance of the system has been improved after TEG is added and whether direct-expansion solar assisted heat pumps with concentrated PV evaporators perform better than that with traditional PV evaporators. As a result, the comparison among the three systems under different solar irradiation is made. It is found that FPV-SAHP shows the best performance in electrical efficiency, COPPVT, total efficiency and the exergy efficiency, meanwhile, the two novel FPV-SAHP system and FPV/TEG-SAHP system are all superior than traditional PV-SAHP system. Besides, the impact of ambient temperature and water temperature in the tank on the optimal system FPV-SAHP system is also predicted and discussed.