Performance Enhancement of a Novel Compression/Ejection Trans-Critical CO₂ Heat Pump System Coupled with Composite Heat Sources

The efficient utilization of renewable heat sources is important for the performance enhancement of trans-critical CO₂ heat pump systems and for promoting the transformation of energy structures. A composite-heat-source matching ratio is introduced in this article to assess the impact of a high-temperature heat source and low-temperature heat source on the performance of a novel compression/ejection trans-critical CO₂ heat pump (CTHP) system coupled with the use of composite heat sources theoretically. The research results show that the maximum reduction in the optimum gas cooler outlet pressure (P_opt,out,gc) is 3.13% with the increase in evaporating temperature (T_e), and the maximum reduction is 1.67% with the rise in the composite-heat-source matching ratio, which means that the composite-heat-source matching ratio is equally significant on the optimum high-pressure side compared to the T_e. The correlations of optimum high pressure and other optimum cycle parameters for the CTHP system, considering the composite-heat-source matching ratio, were obtained, which provide useful guidelines for optimizing the system design and selecting the appropriate operating conditions. Overall, this article will be helpful for the further development and optimization of the CTHP system, which is of great importance for increasing the utilization rate of renewable heat sources such as geothermal or air-source for urban buildings and accelerating the electrification and low-carbon transformation of terminal energy consumption.