Improvement of the Seasonal Performance Factor of Variable Compression Heat Pump System for Cold Regions

　The values of the SPF (Seasonal Performance Factor) for the cold regions in Japan were estimated for three types of heating systems: a heating system with a conventional constant-compression heat pump and a sub-heater, a variable compression heat pump system, and a variable-compression heat pump system with a two-phase flow screw expander for power recovery. The result showed that the SPF of a variable-compression heat pump system was about twice as high as that of a conventional constant-heat pump system. By incorporating the two-phase flow screw expander, the SPF value increased by more than 20 per cent. And with a five-degree decrease in the temperature difference at the evaporator, SPF value increased by twenty per cent.