PURPOSE: To save energy consumption by branching off the cooling water, passing through the reheater of an air-conditioner installed in a computer room or the like, into a heat exchanger on the unused side of an air-conditioner of heat recovering type for the use of general office room or the like.

CONSTITUTION: The air in a computer room is sucked into an air-conditioner from an intake 2, passing through an air passage 4 and a coolar 5, where it is cooled and dehumidified, and then is reheated by a reheater 6, and is blown off into an under-floor air passage 16 from a blow-off port 3, where it conditions the air in the computer room. On the other hand, the cooling water in a cooling tower 9 on the circuit side heats the air which is cooled by the cooler 5, passing through a water feed passage 12, a three-way automatic water feeding valve 17, a condenser 7 and a reheater 6. The cooling water flowing out of the reheater 6 is branched off into a cooling tower 9 and into a heat exchanger 11 on the unused side of an air-conditioner 10 of heat recovering type by the three-way automatic feeding valve 17. With such a constitution, the discharged heat after conditioned the air in a computer room can be utilized for conditioning of the air in a general office room, and in such a manner, energy consumption can be saved in the air-conditioner.