An ejector-assisted integrated thermal management of electric vehicles switchable between heating and cooling (reversible AC/HP)

Abstract

Electric vehicles have become increasingly widespread in recent years due to environmental issues and limited natural resources, and the related thermal management strategies are receiving growing notice. A heat pump air conditioning system for cabin and battery pack thermal regulation (both heating and cooling) is proposed and studied under different operating conditions. The attention of the present study is more directed towards the heating mode of operation; cabin air conditioning in winter and electric aircraft application. Due to environmental considerations and restrictive laws, environmentally friendly refrigerants are also considered as alternatives for R134a. To improve the system's performance, an ejector is placed before the compressor and the refrigerant temperatures in the evaporator and chiller are set to be different. The performance of the proposed system is studied for both heating and cooling modes to compare with the basic system (without ejector). An exergy analysis is also carried out to further analyze the thermodynamic characteristics of the system. The results indicate that the proposed system's COP is improved for both cooling and heating modes under all operating conditions. For the heating mode, the highest COP was equal to 4.36 for R600a, and the COP improvement was between 8 and 47 % based on the different operating conditions. For the cooling mode, the highest COPs were equal to 5.20 and 5.17 for R600a and R1234ze(E) atTevap=Tchil=5°C respectively. The COP improvement for R600a was equal to 14 % atTevap=Tchil=−25°C, and it increases as the chiller temperature is raised. The exergy analysis also indicate that the highest exergy destruction occurs in the compressor and throttling valves. Moreover, R600a and R1234ze(E) show a better overall performance compared to other refrigerants. R600a and R1234ze(E) resulted in the least total exergy destruction of approximately 41 kW for the cooling mode and 51 kW for the heating mode. The exergy efficiency for R600a and R1234ze(E) was equal to 64 and 63 % respectively for both the cooling and heating modes.