PURPOSE: To reduce the temperature of a generator through the increase of refrigerant density of the generator and perform effective utilization of the exhaust gas heat of a prime mover required for vaporization of a refrigerant in the generator by a method wherein vapor from a vaporizer is compressed in an absorber by means of an intermediate mechanical compressor, and the absorber is operated by means of the pressures of the generator and the vaporizer.

CONSTITUTION: Concentrated ammonia liquid is fed from an absorber 4 to a generator 1 through a heat-exchanger 5 with the aid of a circulating pump 6 and vaporized by means of an exhaust heat, and the vaporized ammonia liquid is guided to a condenser 2 and condensed by a cooler 102. Vapor generated from a vaporizer 3 by means of a main compressor 20 is guided to the condenser 2 with the aid of a prime mover 30, heat is removed by the vaporizer 3 and a heat of condensation is removed by means of the condenser 2. Exhaust heat used for drive of a mechanical compressor has heat which is reduced through the feed of it to the generator 1 by means of a line 33. Meanwhile, in cooling water of the prime mover, since ammonia concentration is increased by the intermediate condenser 2 and thus a vaporizing temperature is low, heat is sufficiently received by a low temperature heating source and a quantity of heat can be effectively utilized.