Theoretical analysis of performance of a two-stage compression CO2 cycle with two different evaporating temperatures

• The performance of a two-stage CO2 system with two different evaporating temperatures was simulated with operating conditions.
• The system performance was analyzed under frost conditions.
• The system performance was very sensitive to the variation of 2nd-stage EEV opening.

The performance characteristics of a two-stage CO2 system with two different evaporating temperatures have been analyzed through simulation with such variables as outdoor air temperature, outdoor air velocity, and 2nd-stage EEV opening. The simulation of performance of the two-stage compression cycle indicated that the cooling COP decreased by 22.9, 16.1, 18.9, and 19.4%, respectively, for frostless cooling capacities of 0, −10, −20, and −30%, when the outdoor temperature was increased. The system had a maximum cooling COP for the frostless cooling capacity of −10%, or −20% when the 2nd-stage EEV opening was 56%. The maximum cooling COPs for the non-frost and the frostless cooling capacity of −30% were 1.45 and 1.003, respectively, when the 2nd-stage EEV opening was 52%. The system performance was very sensitive to the variation of 2nd-stage EEV opening.