Potential assessment of transcritical CO2 secondary loop heat pump for electric vehicles

The excellent heating performance and environmental advantages of the transcritical CO2 heat pump system make it a great fit for the electric vehicles (EVs). However, the high operating pressure leads to the possibility of excessive CO2 concentration in the cabin. To ensure the safety of passengers, a secondary loop (SL) system is proposed. In this study, we make a comparison between the traditional direct (TD) system and the SL system for an EV. The results show that the optimal coolant flow rate, with a range of 0.56 to 1.36 L/min in heating mode and 5.60 to 8.80 L/min in cooling mode, can increase the COP of the SL system in all working situations. In the heating mode, the COP of the SL system is 13.98% to 21.96% lower than that of the TD system, and the cruising range of the EV is reduced by 1.4 km ∼ 10.0 km. In cooling mode, the COP of the SL system is 16.95% to 22.45% lower than that of the TD system, and the cruising range has a reduction of 7.7 km ∼ 20.9 km. Results demonstrate that running the SL system in cooling mode rather than heating mode is more detrimental to EVs.