PROBLEM TO BE SOLVED: To miniaturize a compressor and also to obtain a high-temperature output in a heat pump which uses as a refrigerant a substance being in a liquid phase at normal temperatures and pressures, such as water.;SOLUTION: In the heat pump 20 using water as the refrigerant, a refrigerant circulation passage 21 is provided sequentially with a refrigerant pressure reducing valve 22, an evaporator 23, the compressor 24, a condenser 25 and a gas- liquid separator 26. The upper part of the gas-liquid separator 26 is filled with air (non-condensable gas). An injection path 27 extends from the upper part of the separator 26 and communicates with the lower part (one end part) of the evaporator 23. A gas pressure reducing valve 28 is provided on this injection path 27. The valve travel of the pressure reducing valve 28 is adjusted according to a set value of an output temperature of the condenser 25. By driving the compressor 24, the air in the upper part of the gas-liquid separator 26 is subjected to pressure reduction by the pressure reducing valve 28 and then injected into the water of the evaporator 23. The air becomes bubbles therein and rises up and further it is sucked into the compressor 24 and discharged. The water of the evaporator 23 is vaporized not only from the surface thereof, but also into the bubbles in the course of rising through the water.;COPYRIGHT: (C)2003,JPO
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