Experimental investigation on the heating characteristics of a transcritical CO2 heat pump

Abstract

Inadequately configured operating parameters can have a detrimental effect on the performance of a transcritical CO2 heat pump due to the unique thermophysical properties of CO2 . This study investigates the heat transfer characteristics of the gas cooler (GC) and the effects of three operating parameters on the heating process of the system. The results showed that: The temperature distribution of CO2 and water in the GC exhibited typical “two-region” and “three-zone” patterns; and the increase in discharge pressure enhanced the thermal quality of the GC CO2 side, thereby improving the heat output temperature. Nevertheless, higher thermal quality on the GC CO2 side can exacerbate the heat capacity mismatch between the two fluids, thereby reducing the system coefficient of performance (COP). Furthermore, increasing compressor speed (ncom) mitigated the mismatch in heat capacity caused by elevated thermal quality. Taken together, ncom resulted in a 14.7°C increase in heating temperature within the experimental range, accompanied by an 18.4% decrease in COP, showing the best performance among the three parameters studied. This study offers a critical reference for both the theoretical analysis and the control strategy of transcritical CO2 heat pumps, directly supporting the pursuit of efficient heating.