Thermodynamic analysis of a transcritical CO₂ heat pump for heating applications

An experimental transcritical CO₂ heat pump system was deployed in Harbin, China, and a thermodynamic model based on experimental data was developed. COP_h (Coefficient of Performance of heat pump) and heating load, influenced by regenerator efficiency, high pressure, low pressure, outlet temperature of gas cooler, and evaporator superheat, were thoroughly examined. Sensitivity analysis and Response Surface Methodology were employed to evaluate the influences and derive new predictive correlations of COP_h and heating load. The results indicated that as the regenerator efficiency increased from 0 to 0.8, COP_h rosed from 1.6 to 2.5, while the heating load increased from 7.8 to 15.2 kW. When the high pressure climbed from 8 to 12 MPa, COP_h increased from 2.0 to 2.9 and the heating load varied from 8.1 to 23.0 kW. When the low pressure increased from 3 to 7 MPa, COP_h increased from 1.9 to 3.2, while the heating load decreased from 23.7 kW to 8.7 kW. When the outlet temperature of gas cooler increased from 40 to 80 °C, COP_h and the heating load decreased from 5.2 to 1.8 and 27.9 to 11.9 kW, respectively. The evaporator superheat exerted a minimal impact on COP_h and the heating load. For COP_h, the influence hierarchy is as follows: outlet temperature of gas cooler > low pressure > high pressure. Conversely, for the heating load: high pressure > low pressure > outlet temperature of gas cooler.