PURPOSE: To save an energy by a method wherein a heat pump type airconditioner is operatively connected to, throygh valves, a solar heat accumulating tank to which a water feeding pipe and a hot water feeding pipe are connected.

CONSTITUTION: The system is constructed such that a solar energy collected at the solar heat collector 12 is accumulated as hot water in the solar heat accumulator 1 through a circulation piping system provided with a pump 13. Within this heat accumulation tank 1 is immersed a heat excanger 5 which is connected through a circuit 30 including valves 3, 3' after and before the heat exchanger 24 of an airconditioner 2 composed of a heat pump which is assembled with the closed circuit wherein a compressor 22, four-way valve 21, in-door radiator 23 and out-door radiator 24 etc. are connected with each other. And, the circuit lines 30 are connected to after and before the radiator 23 in said airconditioner 2 through circuit lines 40 having valves 4, 4' therein. Thereby, each of the valves 3, 3' and 4, 4' is operated to be changed over, a relative efficient utilization of the solar energy between the heat accumulation tank 1 and the airconditioner 2 may be made.