Experimental evaluation of a CO2 transcritical refrigeration plant with dedicated mechanical subcooling

• A CO2 transcritical refrigeration plant with dedicated mechanical subcooling is evaluated experimentally.
• Overall COP increment ranges from 10.9% to 26.1% at evaporation of 0 °C and from 6.9% to 30.3% at evaporation of −10 °C.
• Cooling capacity increases from 23.1% to 39.4% at evaporation of 0 °C and from 24.2% to 55.7% at evaporation of −10 °C.
• The improvements are higher at high dissipation temperatures and high evaporation levels.
• Use of dedicated mechanical subcooling is very recommended for hot climates.

CO2 transcritical refrigeration cycles require optimization to reach the performance of conventional solutions at high ambient temperatures. Theoretical studies demonstrated that the combination of a transcritical cycle with a mechanical subcooling cycle improves its performance; however, any experimentation with CO2 has been found. This work presents the energy improvements of the use of a mechanical subcooling cycle in combination with a CO2 transcritical refrigeration plant, experimentally. It tested the combination of a R1234yf single-stage refrigeration cycle with a semihermetic compressor for the mechanical subcooling cycle, with a single-stage CO2 transcritical refrigeration plant with a semihermetic compressor. The combination is evaluated at two evaporating levels of the CO2 cycle (0 and −10 °C) and three heat rejection temperatures (24, 30 and 40 °C). The optimum operating conditions and capacity and COP improvements are analysed with maximum increments on capacity of 55.7% and 30.3% on COP.