Operation strategy and performance investigation of a high-efficiency multifunctional two-stage vapor compression heat pump air conditioning system for electric vehicles in severe cold regions

Cooling and heating are indispensable for electric vehicles (EVs) in severe cold regions due to the hot summer caused by global warming. A multifunctional two-stage vapor compression (MTSC) heat pump air conditioning system (HPAC) with its operation strategies is proposed, which can operate in not only single-stage vapor compression (SSC) cooling and heating mode, but also two-stage vapor compression (TSC) heating mode under ambient temperatures as low as -35 degrees C. Then a simulation model is developed, and comparative analyses among the MTSC HPACs with different refrigerants, and between MTSC HPACs and SSC HPACs are conducted. The influences of intermediate pressure and pressure drop on performance are discussed. Besides, exergy analysis and second law performance are presented. It is found that the MTSC HPAC attains a 6% to 30% higher coefficient of performance (COP) than the SSC HPAC when the evaporating temperature changes from -10 degrees C to -20 degrees C, and 156% to 85% higher energy efficiency than the positive temperature coefficient (PTC) heaters when the evaporating temperature varies from -25 degrees C to -45 degrees C. The COP of R290 is slightly higher than that of R410A, R32 and R454C. Furthermore, the main exergy destruction appears in compressors, accounting for 40% to 45%.