Comparison between variable displacement and variable speed compressors for electric vehicle heat pumps

Abstract

Recent developments in electric vehicles have heightened the need for high-efficiency heat pump technology to improve cruising range and cabinet thermal comfort. As the key component for a heat pump system, compressor has a significant impact on heat pump system performance. In this work, a numerical model of a heat pump system consisting of a variable displacement compressor (VDC) model, a variable speed compressor (VSC) model, and a heat exchanger model is presented to compare the two major types of compressor. The simulation is executed across a diverse array of conditions to assess the performance disparity between two variants of compressors, particularly in challenging environments. The proposed model is validated based on the experimental data from a heat pump test rig which compressor section can be replaced with a prototype VDC or VSC based on validation demands. Overall, the modeling results demonstrate a favorable alignment with the measurements. The simulated power input of VDC under heat and cooling mode has a mean absolute percentage error (MPAE) of 4.4% and 6.0%, respectively, while the MAPEs for VSC under heating and cooling modes are 3.2%, and 4.5%. The modelling results indicate that the VDC system shows superior performance in specific mass flow rate, compressor power input, and system efficiency, especially at part load conditions.