A new concept propane/supercritical CO_2 cascade system for heating has been suggested. In this system, propane is used as refrigerant in the heat pump side (the primary side) instead of HFC-410A and supercritical CO_2 is used as the heat transfer medium in the secondary loop. The efficiency of this system is estimated theoretically and is confirmed experimentally. Furthermore, a pressure-proof pump for supercritical CO_2 has been developed. The performance of the CO_2 pump is evaluated in the liquid and supercritical states. It is observed that the pump performance curve is independent of the circulating fluid state, even when it is liquid with a small degree of subcooling.
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