A constant RA method is a method in which the SA air volume (supplied air volume Fsa) is always constant (setting value) and the amount of supplied refrigerant etc. is controlled so that the RA temperature (return air temperature Tra) is always equal to the target value (setting value) regardless of the loads.

In the example illustrated in FIGS. 4A-4D, the temperature of the supplied air SA, the temperature of return air RA and the SA air volume (supplied air volume Fsa) are respectively set to 27° C., 37° C. and 7450 (m³/h) as the rated conditions in the case where the load factor is 100%. Note that, in the convention method, because the SA air volume is constant regardless of the loads, the SA air volume is 7450 (m³/h) even when the load factor is 25% or 50%. By contrast, in the present method, when for example the load factor is 50%, the SA air volume is 50% of 7450 (m³/h) in view of calculation.

Note that a load factor represents the load state (operation state) of a cooling target (server apparatus 2 etc.) and the state in which the server apparatuses 2 etc. are operating with their maximum capacity may be considered to be the load factor of 100%.

The average consumed power was obtained respectively for four load states, specifically a state with the load of 100 kW (load factor of 100%), a state with the load of 75 kW (load factor of 75%), a state with the load of 50 kW (load factor of 50%) and a state with the load of 25 kW (load factor of 25%).

FIG. 4A illustrates the average consumed power per one indirect outside air air-conditioning device. FIG. 4B illustrates a graph of this average consumed power.