Influencing Factors of Optimal Discharge Pressure of Transcritical CO₂ Heat Pumps under Heating Conditions

Optimal discharge pressure is the most important factor affecting the performance of a transcritical CO₂ heat pump. In this study, the reasons for the optimal discharge pressure were theoretically analyzed based on the heat transfer pinch point. The factors influencing the optimal discharge pressure and their influence mechanism were determined by constructing a transcritical CO₂ heat pump simulation model using the AMESim software. The model took into consideration the internal heat transfer pinch point of the gas cooler. Under inlet water temperature of 10 ℃-40 ℃, outlet water temperature of 60 ℃-90 ℃, and ambient temperature-30 ℃-25 ℃, the influence of inlet temperature, outlet temperature, ambient temperature, and heat recovery rate on the optimal discharge pressure was studied quantitatively. The results showed that the lower the inlet, outlet, and ambient temperatures, the lower the optimal discharge pressure of the system. Moreover, the optimal discharge pressure could be reduced by using an internal heat exchanger. The influence mechanism of each factor on the optimal discharge pressure was found to be closely related to the heat transfer pinch point and the physical properties of CO₂ near the critical point and supercritical zone. The research results can provide a reference for the design and performance optimization of CO₂ heat pump systems.