Performance improvement of heat pump system during cold climate operation for electric vehicle application

Abstract

Battery-powered electric vehicles(EVs) need an efficient electric heating system for extending the driving mileage. An air-source heat pump system offers an economical alternative for electric vehicles because it consumes less energy than a heating system using Joule heat and it can use the same components as an air conditioning system for cooling. However, its performance degradation is inevitable at very low ambient temperature (cold climate condition). Although EV applies the heat pump system, it needs additional electric heater like high voltage positive temperature coefficient (PTC) heater. It does raise cost a lot, but also makes the vehicle package more complex. Therefore the heating performance improvement of heat pump during cold climate is very important theme. This has been studied a lot in the residential or industrial heat pump, but the cold climate heat pump (CCHP) for EV application is quite limited. In this study, we tried to investigate the cold climate heat pmp for electric vehicle application. The configuration of a vapor injection heat pump, which was well known as a good technology to overcome this problem in residential heat pump systems, was introduced and the performance characteristics were studied using a scroll compressor geometry-based thermodynamic analysis. And three types of cold climate heat pump (CCHP) were proposed to improve the heat pump performance in cold climate, and were experimentally evaluated for electric vehicle application. These experiments were system-level tests. To validate the real electric vehicle heating performance considering transient performance, in other words, the cabin thermal load change during soak and warm-up process, we installed the cold climate heat pump (CCHP), which was chosen as an best solution by system-level experiences. And vehicle tests were done for the cabin warm-up performance and power consumption comparison, in the real electric vehicle. Finally we could find out the possibilities for developing the cold climate heat pump (CCHP) for future electric vehicle without high cost and high capacity additional heater.