Transient analysis of an electric vehicle air-conditioning system using CO₂ for start-up and cabin pull-down operations

The energy consumption during the start-up and cabin pull-down operation of an air-conditioning system (A/C) for electric cars was studied in this work. An entire system model consisting of a CO₂ vapor compression system (VCS), air handling unit (AHU), and the cabin was established utilizing an acausal, object-oriented, and equation-based modeling platform. A previously validated model was adopted for the VCS. AHU and cabin models were established by paying attention to the latent heat load, humidity, and dehumidification. The models were validated against the data from three different studies. A set of transient simulations was carried out for the start-up and cabin pull-down operation periods. It is found that the initial temperature of the cabin significantly influences the energy consumption and pull-down time. When the cabin target temperature decreases from 25 °C to 21 °C, the compressor consumes 58% more energy, and the pull-down time increases by 23%. Increasing the initial temperature 35 °C to 55 °C leads to 150% longer pull-down time, and 289% more energy consumption. The initial RH of the cabin air has a negligible impact on the pull-down time, but affects energy consumption. Increasing the RH from 33% to 66% results in 9% energy consumption.