Heat pump air-conditioning systems play an important role in meeting the winter heating needs of electric vehicles. In this study

the new refrigerant R1234yf

which has a low GWP value

was used for the working medium. The low-temperature heating performance of the electric vehicle heat pump air-conditioning system was tested at ?20 ℃ to 7 ℃. The winter heat load of the electric vehicle was calibrated. The refrigerant charge amount

heating performance

COP

and discharge temperature of the system were studied and compared with those of refrigerant R134a. Exergy loss of system components was analyzed

and the system was also optimized. The results show that the optimal refrigerant charge amount of the system was 1551 g

and the heating capacity and COP reached greater than 2 kW and 1.8

respectively

under most working conditions

which could meet the needs of heating at low temperatures. When directly substituted

the heating capacity and COP of the system were 7.1% and 6.6% lower than that of the R134a system. The discharge temperature of the R1234yf heat pump system is 5.3 ℃lower than that of R134a

which could make the system more stable and reliable. The exergy loss of the inner condenser and compressor accounts for more than 80% of the total exergy loss of the system

which is the key optimization parameter for heat pump air conditioning. Increasing the heat transfer area of the inner condenser

increasing the air volume

and improving the compressor speed can significantly improve the heating performance of the system

making it basically equal to or even better than the R134a system.