Optimizing refrigerant charge in PHEV air conditioning system through genetic algorithm, COP, exergy analysis and condenser size adjustment

The air - conditioning of Plug-in Hybrid Electric Vehicle (PHEV) cools the cabin and battery. Refrigerant charge greatly affects the system’s COP. This paper explores battery heat dissipation’s impact on optimal refrigerant charge, which is corresponding to the maximum system COP, using genetic algorithm, COP, exergy analysis, and condenser size enlargement. Firstly, under each steady-state condition, the optimal refrigerant charge is estimated using the genetic algorithm, with the maximum COP as the response. The findings prove that the optimal refrigerant charge rises with the battery thermal load. Then, based on the exergy analysis results, increasing the condenser size leads to a significant improvement in the system COP, with a maximum increase of 35.3 %. Meanwhile, the optimal refrigerant charge rises in accordance with the increase in battery heat load, and these optimal refrigerant charges are all bigger than the original system values. Finally, after the condenser size is increased, steady-state tests with different battery heat dissipations show that a refrigerant charge of 685 g (optimal when battery heat dissipation is 0 W), leads to a COP decrease of up to 13.3 %. While, with a refrigerant charge of 1200 g (optimal at battery heat dissipation 4350 W), the COP decline relative to its peak value is just 1.9 %. The analysis indicates that, when determining the refrigerant charge, the battery thermal load should be relatively high to reduce the impact of the refrigerant charge on the system’s performance.