Research PaperNumerical study of the effects of injection-port design on the heating performance of an R134a heat pump with vapor injection used in electric vehicles

•A simulation model for an EV heat pump with vapor injection is developed and validated.•Geometries of the injection port are analyzed according to angle of the injection port.•Design of the injection port is determined to optimize COP and isentropic efficiency.•Performance of dual-injection ports is compared to that of the non-injection heat pump.

Heat pumps, which enable the cooling and heating of vehicular cabins, consume a significant portion of the total energy consumption in electric vehicles (EVs). The efficiency of the heat pump is typically degraded owing to cold-weather conditions, so the refrigerant-injection technique has been proposed for improving the system performance and compressor reliability. In this study, a simulation model for an R134a heat pump with vapor injection is developed and validated by performing thermodynamic analyses with geometrical information. The effects of the injection-port design are investigated using the developed numerical model. Single-injection and dual-injection ports are considered to optimize the coefficient of performance (COP) and isentropic efficiency by controlling the injection mass flow rate. The optimal angles of the single- and dual-injection ports are determined to be 440° and 535°/355° (for pocket A/B), respectively, while the corresponding COPs are improved by 7.5% and 9.8%, respectively, compared to the non-injection heat pump at an outdoor temperature of −10 °C.