Experimental study on an electric vehicle heat pump system with multi-level waste heat recovery using a vapor injection technique at low ambient temperatures

Abstract

This study suggests multi-level waste heat recovery utilizing the vapor-injection technique. Conventionally, waste heat from electric devices is recovered at low temperatures. However, considering the thermal requirements of the energy storage system, the temperature level should be subdivided into multiple levels to maintain the energy storage system at an appropriate operating temperature. The vapor injection technique enables the utilization of waste heat from an energy storage system at an intermediate temperature level. The refrigerant absorbs waste heat, resulting in a higher heating capacity provided to the cabin and proper thermal management of the energy storage system. Experiments were conducted in three modes: non-waste heat recovery, conventional waste heat recovery, and multi-level waste heat recovery. The performance of each mode was investigated under different operating conditions, including the ambient air temperature, compressor speed, and amount of waste heat. Results show that multi-level waste heat recovery augments heating capacity up to 72.5% in the coldest condition of −20 °C while maintaining the temperature of the energy storage system within an appropriate operating range. In addition, it is shown that a multi-level waste heat recovery system can utilize ambient air sources under any operating condition. In contrast, the conventional waste heat recovery system conditionally absorbs heat from the ambient air.