Experimental assessment of different extraction points for the integrated mechanical subcooling system of a CO2 transcritical plant

Subcooling systems are positioned in recent years as one of the best solutions to improve the efficiency of transcritical CO2 cycles. Specifically, the integrated mechanical subcooling cycle allows the improvement of these systems only using CO2 as a refrigerant. This integrated cycle can be designed with three different architectures: extracting the CO2 from the gas-cooler outlet, from the subcooler outlet or from the liquid tank. In this work, the three configurations are experimentally analysed and the main differences between them are studied. An experimental plant has been tested at three heat rejection levels (25.0, 30.4 and 35.1 °C) and a fixed temperature of the secondary fluid at the evaporator inlet of 3.8 °C. The results show that from an energy efficiency point of view, all the configurations have practically the same COP, with certain variations in the cooling capacity and the greatest differences in the cycles are found in the subcooler.