Energy utilization of CO2 thermal management system for electric vehicles in cold climate: Assessment of different heat source modes

To further improve the heating energy efficiency at low temperatures, this study analyzes the feasibility of a CO₂ electric vehicle (EV) utilizing different heat source (air source, waste heat-only, and dual-source) modes under low-temperature conditions. Initially, the difference in heating energy efficiency between air source and waste heat-only modes was compared at different supply air temperatures of -10°C. Concurrently, the dual heat source mode was evaluated at -20°C, emphasizing the impact of the electronic expansion valve 3 (EEV3) opening on heating performance at different constant coolant temperatures. This study presents an evaluation method for heating performance, and the temperature rise characteristics of a real vehicle in air source mode at -20°C are validated through environmental chamber experiments. The results indicate that the inner gas cooler outlet refrigerant temperature strongly correlates with the maximum heating capacity. When the supply air temperature is set to 50°C, the compressor power consumption in the waste heat-only mode decreases by 12.9 % compared with the air source mode, and the COP increases by 13.5 %. As the supply air temperature rises, the efficiency improvements of the COP gradually decrease. Compared with the air source mode, the heating capacity of the dual heat source mode increased by 6.4 %-19.2 %, the COP improved by 4.5 %-5.7 %, and the driving range improved by 9.4 %-15.6 %. This study demonstrates that the thermal management system can meet the temperature rise characteristics, and the maximum outlet air temperature of the air source mode reaches 56.83°C at -20°C.