Performance of CO2 Cycles with a Two-Stage Compressor

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 the condensing units . Four cycle options were a basic cycle, a cycle with a suction line heat exchanger, a cycle with an intercooler, and a two -stage split cycle. The compressor used in testing was a hermetic, rotary type two-stage compressor. The results show that the cycle with a suction line heat exchanger worked better when the suction temperature was higher. The cycle with a suction line heat exchanger, the cycle with an intercooler and the twostage split cycle improved the COP by 18, 22, and 35% over the basic CO2 cycle at 7.2°C evaporating temperature. At -6.7°C evaporating temperature, the cycle with intercooler and two-stage split cycle improved the COP by 10 and 40% over the basis CO2 cycle. The cycle operation at low evaporating temperatures was limited by the excessively high discharge temperature for most cycle options except the two-stage split cycle. Measured volumetric efficiencies and compressor efficiencies were 0.80 to 0.95 and 0.55 to 0.70, respectively.