JPS6311575B

PURPOSE:To permit the most efficient operation by a method wherein a plurality of pumps are provided in a pipe connecting a heat accumulating tank and a heat collector and either one of series, parallel or single operation is adopted in accordance with the employing purpose of the pump. CONSTITUTION:Upon the initial period of heat collecting operation, each bypass pipes 21, 22 are closed by three-way switching valves 19, 20 to connect the first and second pumps 17, 18 in series and operate both pumps 17, 18. According to this connection, a high lift capacity is obtained and water in the heat accumulating tank 11 is supplied to the heat collector 12. Next, when the heat collecting operation is stabilized, the pump 18 is stopped under the circuit connecting condition same as described above and the operation is carried out by only the pump 17. Upon the hot-water supplying operation, the three-way switching valves 19, 20 are switched to open the pipes 21, 22 and connect both pumps 17, 18 in parallel, thereafter, both pumps 17, 18 are operated. According to this method, a supplying pressure may be restrained while the flow amount of supplying hot- water may be increased.