Performance experiments of R290/CO2 cascade refrigeration system were conducted. The performance of a cascade refrigeration system having a high temperature cycle using R290 as refrigerant and a CO2 based low temperature cycle was compared with that of a cascade refrigeration system having a high temperature cycle using R22 as refrigerant and a CO2 based low temperature cycle. The results show that the optimum mass flow rate ratio and the maximum COP of the R290/CO2 cascade refrigeration system increase with the increase of evaporation temperature and with the decrease of condensation temperature. Moreover

the power consumption of the R290 compressor is slightly higher than that of the R22 compressor and the COPh of the R290 cycle is higher than that of the R22 cycle at the higher compressor inlet temperatures.