Parametric evaluation and performance comparison of a modified CO2 transcritical refrigeration cycle in air-conditioning applications

Nowadays, the main two issues of heating ventilation and air conditioning (HVAC) are refrigerant alternative and system efficiency improvement. As a safe and environmental protective refrigerant, CO2 has drawn a lot of attention these years. The improvement on its transcritical cycle efficiency has always been the study hotspot. On the basis of the traditional cycle system, this paper adds the internal heat exchangers (IHE) and pressure control devices into the system and optimizes the CO2 transcritical system with the dual throttling device. Engineering equation solver is used to build each module in the system as an object-oriented model. The effects of the IHE and bypass valve on system performance are investigated. The performance and configuration of four CO2 transcritical refrigeration cycles are analyzed and compared. Numerical studies also propose the formula expressing the relationship of the optimum high pressure, the gas-cooler CO2 outlet temperature and the evaporation temperature under specific operating conditions. In addition, the modified system can significantly improve the performance of the system under the operating conditions below the optimum high pressure. This research has played an effective guiding and facilitating role for CO2 transcritical refrigeration system development, optimization and improvement.