Experimental study of the integrated vapor injection R1234yf electric vehicle heat pump system in cold conditions

The heat pump system of pure electric vehicles (EVs) urgently requires more environmentally friendly refrigerants and a modular design. R1234yf offers similar thermal performance to R134a and serves as its primary alternative refrigerant. To address these challenges, this study proposes a novel integrated vapor injection (VPI) module, which is installed in a heat pump system using R1234yf refrigerant for experimental research. The innovation of the module lies in the integration of key components and the elimination of complex piping designs, thereby achieving a modular structure and effectively reducing system weight. Experimental results indicate that, under the condition of meeting the same VPI mass flow rate, the module can reduce the intermediate pressure by 34.3 % compared to typical VPI systems, while lowering the optimal refrigerant charge by 15.2 % to 37.1 %. Exergy analysis reveals that at 0 degrees C, opening the VPI improves exergy efficiency by 5.3 %-12.5 %, and even at -5 degrees C, the efficiency remains higher than that observed without VPI at 0 degrees C. Furthermore, the study investigates the combined effects of increasing compressor speed and opening VPI on system performance at various speeds, and preliminarily proposes a control strategy to achieve a synergistic effect between the two methods, thereby optimizing system operation under different working conditions.