Performance evaluation of an electric vehicle vapor injection heat pump system during cold and hot start-up using dynamic system modeling

Electric vehicles (EVs) typically utilize heat pumps to provide both cooling and heating to the cabin. However, heat pump performance significantly deteriorates under extreme ambient conditions. To combat system performance degradation, vapor injection compression has been developed and used. This study presents a comprehensive system-level analysis of a vapor injection heat pump system for EVs under dynamic start-up conditions. A detailed model was developed using the Modelon Impact environment which was validated against experimental data. Using this validated model, the heat pump performance was analyzed under both cold and hot ambient conditions and compared against a conventional non-injection system to evaluate performance enhancements. The results highlight significant performance improvements with vapor injection compared to the non-injection heat pump. In cooling mode, the vapor injection system reduced cabin cooling time by 22.2–29.6% and improved the coefficient of performance (COP) by 8.6–12.1%. In heating mode, vapor injection reduced cabin heating time by 27.5–36.5% and achieved COP improvements of 5.1–9.4%. Moreover, the performance of an R1234yf heat pump cycle was compared to that of the R134a with and without vapor injection. Results indicate that with the application of vapor injection, significant performance improvement is achieved in the R1234yf heat pump system, which exceeds that of the R134a system. The work reported here not only provides design guidelines for implementing vapor injection compression in EV heat pumps, it develops dynamic system modeling methodologies that can be extended to various energy applications.