Influence of Heat Exchanger Structure on System Performance in Trans-Critical CO₂ Heat Pump Air Conditioning Systems for Trains

To further study the influence of heat exchanger structures on system performance and overall power consumption in transcritical CO₂ heat pump air conditioning systems for high-speed trains to improve performance and reduce power consumption, this study builds a numerical simulation model based on the AMEsim simulation platform. The simulation results show that, in the high-speed train heat pump air conditioning system, the influence of the gas cooler structure on system performance is greater than that of the evaporator structure. In terms of the selection of heat exchanger structure, the optimal structure is that during refrigeration, the outdoor heat exchanger adopts the countercurrent arrangement and the indoor heat exchanger adopts the concurrent arrangement (vice versa for heating). At the rated cooling condition of 35 ℃ ambient temperature, the COP is increased by 20.38% compared to the concurrent arrangement in outdoor heat exchangers, and at a rated heating condition of 7 ℃ ambient temperature, the COP is increased by 68.04% compared to the concurrent arrangement of indoor heat exchangers. Considering both the degree of backflow and fan power consumption, in the "fully heat exchange state", system COP increases with backflow degree, while system COP decreases with backflow degree when the air flow rate is insufficient.