Experimental determination of the optimum intermediate and gas-cooler pressures of a commercial transcritical CO2 refrigeration plant with parallel compression

Abstract

CO2 systems used in refrigeration are becoming more complex with the aim of improving their energy performance. Parallel compression is one of the implemented solutions to enhance the performance of the plants. However, an optimization process is required to operate this system at high performance and its operation is subjected to physical limitations in real plants. This work presents the experimental optimization of a transcritical CO2 plant working with parallel compression. The plant is tested at different discharge pressures and different secondary compressor speeds in order to optimize the COP of the plant and determine the optimal conditions for three gas-cooler exit temperatures 27.5ºC, 32.5ºC and 37.5ºC and three evaporation levels: -15.0ºC, -10.0ºC and -5.0ºC. The optimal working conditions that can be achieved in a real plant have been determined, obtaining COP from 1.71 to 2.63 for -5.0ºC, from 1.50 to 2.22 for -10.0ºC and from 1.25 to 1.84 for -15.0ºC. Cooling capacity ranges from 8.94 kW to 11.34 for -5.0ºC, from 7.71 kW to 9.47 kW for -10.0ºC and from 6.22 kW to 7.76 kW for -15.0ºC. The trends observed in theoretical results have been corroborated and the optimum gas-cooler and intermediate pressures have been determined and discussed.