Self-enhanced enthalpy heat pump system based on the performance of CO2 whole-vehicle thermal management below −20 °C

The automotive industry has begun to shift to new energy electric vehicles due to the challenges of oil and environmental resources. However, heating in low-temperature environments results in poor endurance of electric vehicles in winter, which has always hindered the development of electric vehicles. The main reason is that the commonly used heating method, Positive Temperature Coefficient Heating (PTC), has a lower efficiency, while traditional heat pumps lack heat absorption and heat exchanger frosting, resulting in heat pumps not being able to be used well in low-temperature environments. This article proposes a transcritical CO2 self-enhanced enthalpy heat pump system suitable for low-temperature environmental applications to address this issue. The system can be divided into self-enhanced enthalpy heat pump (SEHP) mode, self-enhanced enthalpy waste heat hybrid heat pump (SEWHHP) mode, and waste heat recovery heat pump (WHHP) mode based on no waste heat, low waste heat to high waste heat. A mathematical analysis was conducted on the operating characteristics of CO2 in three modes using the AMESIM platform. The heat from the condenser in the system can be distributed by the cooling water circuit to the cabin and evaporator for heat absorption, and the waste heat from the battery motor can also be well utilized by the evaporator. This article focuses on analyzing the efficiency of three modes under different ambient temperatures, target temperatures, and residual heat. When the ambient temperature is −20℃, the mode switches from the SEHP to the SEWHHP mode and then to the WHHP mode, with the efficiency increasing from 0.89 to 1.31 and 1.77, respectively. COP increases with increasing ambient temperature in all modes, with the WHHP mode increasing from 1.46 to 1.67 when the ambient temperature increases from 50 °C to 20 °C. The efficiency is much greater than that of PTC, and this study provides new ideas for the thermal management of electric vehicles in low-temperature environments.