Operation strategy and performance of thermal management system with dual-evaporation temperature for electric vehicles

The high thermal management energy consumption is a crucial reason for the severe driving range degradation of electric vehicles (EVs) at low temperatures. Currently, heat pumps and waste heat recovery technology have been widely used to improve the energy efficiency of thermal management systems and alleviate the driving range degradation of EVs in low-temperature environments. However, the conventional waste heat recovery heat pump, with the ambient air and waste heat as heat sources, operates at a single evaporation temperature, resulting in poor performance of the heat pump at low temperatures because the low-energy-grade ambient air source limits the recovery efficiency of the high-energy-grade waste heat. To address the issues, in this study, a thermal management system with dual-evaporation temperature for EVs, which can switch between the single-evaporation temperature and the dual-evaporation temperature modes to match the energy grade of the ambient air and waste heat sources, is proposed. A simulation model of the proposed system is established and validated. The appropriate compressor volume ratio, the heating performance under different operation modes, the energy-saving operation strategy adapted to different operating conditions, and the energy-saving and range extension effect of the proposed system are investigated. The results indicate that the heating energy consumption in dual-evaporation temperature mode can be reduced by 25.2 % and 9.5 % compared to that in single-air source mode and single-evaporation temperature mode, respectively, at −10 °C with waste heat of 1500 W. In Beijing, the proposed system and operation strategy can achieve an average heating energy saving of 14.2 % and an average driving range extension of 12.4 % under HWFET, compared with the conventional thermal management system without waste heat recovery.