PURPOSE: To obtain the constant temperature constant humidity device whose energy consumption is small by a method wherein the air temperature of outlet of a cooling coil is controlled by a micro-computer based on an indoor relative humidity to minimize the cooling of the air.

CONSTITUTION: The cooling temperature of air is controlled by a microcomputer in accordance with the relative humidity in a room. When an atmospheric temperature and the relative humidity of the atmosphere is lower than those in the room, the absolute humidity is low also, the absolute humidity in the room is not increased by mixing the atmosphere and dehumidifying is not necessitated so much when the generation of moisture in the room is small, accordingly, the outlet air temperature of the coil C may be set between 4 and 5 in the diagram. Therefore, it is set at the temperature 4". The air temperature 4" at the outlet of the coil is controlled by changing the amount of refrigerant of the cooling coil or the amount of cooling water in the same coil by a general electric or electronic control in accordance with the change of set cooling temperature. When the relative humidity in % is high, the air temperature 4" is reduced to a low temperature side or to the left and when the relative humidity in percentage is increased, the temperature is made close to the right or point 5 as closely as possible to prevent useless cooling. The blow-off air temperature 5 may be controlled by controlling a heating coil E by a temperature sensor T in accordance with the change of the room temperature.