The performance of four CO2 cycle options was measured for three different evaporating temperatures, 7.2, -6.7, and -23.3°C under the ARI Standard 520 for condensing units. The four cycle options were the baseline cycle, the cycle with suction line heat exchanger, the cycle with intercooler, and two-stage split cycle. The cycle operation at the low evaporating temperature was limited by the high discharge temperature for most cycle options except the two-stage split cycle. The compressor used in the testing was a hermetic, rotary type two-stage compressor.

The effect of cycles and individual cycle components on system capacity and performance was investigated. Cycle optimization was conducted by using mass flow rate ratio, intermediate pressure coefficient and power ratio.

Modeling of these four cycles by EES showed similar results with the test data and provided information on sizing the system components for different system capacities for maximum performance.