Pseudo-optimal discharge pressure analysis of different CO2 electric vehicle heat pumps based on cabin thermal model

摘要

The discharge pressure of electric vehicle heat pumps, aiming for peak COP values, is termed the pseudo-optimal discharge pressure for dynamic regulation, distinguishing it from the optimal discharge pressure at a constant compressor speed. A theoretical model was presented to analyze the impacts of operational parameters considering the variation of cabin loads with operating conditions. Based on simulation results, the effects of ambient temperature, cabin temperature, drive speed, and supply air flow rate on the pseudo-optimal discharge pressure were investigated for single-stage and two-stage compression systems, respectively. Among them, the ambient temperature had the highest degree of influence, more than 45 % in different systems. Heat recovery in electrical systems introduced slight variations, less than 1 bar, to the pseudo-optimal discharge pressure by affecting the evaporation temperature. While the trend remains consistent across the different systems, the values of pseudo-optimal discharge pressure are higher for the two-stage compression. At -10/20 degrees C, two-stage compression provides a 49.42 % higher COP compared to single-stage while maintaining a safe discharge temperature. In addition, the heating efficiency under the improved prediction can be increased by 18.49 % compared to the existing research. Predictions for the pseudo-optimal discharge pressure provide a basis for effective and cleaner control of electric vehicle heat pumps.

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