A set of waste heat recovery series-type CO2 heat pump systems is designed for electric vehicles

and the effects of different operating parameters on the low-temperature heating performance of the system are experimentally studied by using a standard enthalpy difference test facility. The results show that the performance of the dual heat source system is better than that of the single source system. The dual heat source mode can optimize the system parameters

increase the heating capacity of the system

and expand the low-temperature working range of the heat pump system. When the ambient temperature is ?20 ℃

the heating capacity and COP of the waste heat recovery mode are increased by 18.9% and 5.9%

respectively. The performance characteristics of the system are analyzed by changing the temperature conditions. The dual heat source mode exhibits more significant advantages in low-temperature environments; as the ambient temperature decreases from ?5 to -20 ℃

the increase ratio of the heating capacity improves from 4.3% to 18.9%

and the increase ratio of COP improves from 4.3% to 5.9%. Thus

it is the best temperature range for using the waste heat mode when the ambient temperature is lower than ?5 ℃. These results guide the practical applications of CO2 vehicle heat-pump systems.