Principle and performance optimization analysis of a frost-free control for electric vehicle heat pumps

To avoid the attenuation of the electric vehicle driving range caused by the performance degradation of the heat pump during frost, a frost-free control strategy was developed which enables frost-free operation without adding any additional dehumidifying and drying components. Simulation analyses of the frost-free control principle and performance characteristics are carried out. Thermodynamic and response characteristics of evaporation temperature to valve openings of different heat pumps are compared. The results show that excessive pressure drops in evaporators severely hinder the realization of frost-free operation. Then, the effect of evaporator designs on frost-free operation is further investigated. A new comprehensive evaluation parameter (η) that can unify pressure drop and heat transfer is proposed. When η is between 0 and −2, the heat exchanger meets the requirements of frost-free control. In addition, the upper humidity range for frost-free operation at different temperatures is calibrated. When the ambient temperature is 0/-5/-10/-15/-25 °C, the corresponding maximum humidity that can achieve frost-free operation is 87/86/85/84/82 %, respectively. In low temperature and high humidity regions, the frost-free operation can be guaranteed by increasing the evaporator airflow volume rate and reducing the supply air temperature.