Coupled effect of operation conditions and refrigerant charge on the performance of a transcritical CO2 automotive air conditioning system

Refrigerant charge is one of the most important factors affecting the performance of the transcritical CO₂ automotive air conditioning system. In the presented study, a transcritical CO₂ automotive air conditioning system test bench was set up, and the effect of normalized charge on the temperature, pressure and system performance were studied. A novel standard for judging the appropriate normalized charge was proposed. Meanwhile, the pressure-enthalpy diagrams under different charge was shown. Moreover, the influence of the ambient temperature and the compressor frequency on the charge characteristic were also experimentally studied and analyzed. Results revealed that the discharge temperature, the suction temperature and the temperature before the EXV were the optimal parameters to judge the charge characteristic. As the ambient temperature and compressor speed increased, the required charge amount decreased. It was concluded that the optimal normalized charge range of the transcritical CO₂ air-conditioning system was recommended to be set between 0.111 and 0.321. The results provide good guides in charge of automobile air conditioning system.