Experimental determination of the optimum working conditions of a commercial transcritical CO2 refrigeration plant with a R-152a dedicated mechanical subcooling.

Abstract

Abstract Transcritical CO2 plants combined with subcooling systems are the focus of several researches in the last years with the objective of improving their performance. Among the subcooling systems, the Dedicated Mechanical Subcooling system (DMS) is one of the most interesting because it greatly improves the overall COP and the cooling capacity of the system. This work presents the experimental study of a transcritical CO2 plant working with an R-152a DMS. The plant was tested at different pressure and subcooling conditions in order to determine the working conditions where the COP of the plant is maximum. The optimal operation conditions are determined for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and three cold sink temperatures (-1.3 °C, 3.8 °C and 10.0 °C). The measured values go from 6.5 kW to 7.3 kW for glycol inlet temperature -1.3 °C, from 7.6 kW to 8.4 kW for 3.8 °C and from 8.8 kW to 9.8 kW for 10.0 °C. Optimum COP goes from 1.51 to 1.95 for -1.3 °C, from 1.69 to 2.21 for 3.8 °C and from 1.86 to 2.52 for 10.0 °C. Optimum gas-cooler pressure has a higher dependence on the heat rejection level, being higher when higher the heat rejection level is, but it slightly depends on the evaporation level. Optimum subcooling degree is both dependent on the water inlet temperature and on the glycol inlet temperature. Two correlations are proposed to determine the optimal pressure and subcooling degree for the CO2 plants working with DMS as a function of the gas-cooler outlet temperature and the evaporation level.