Humidifying Plants.
—Mechanical ventilation plants that are intended for washing the air may be made up of parts similar to that of Fig. 173, but in addition to the apparatus shown provision is made for the air to pass through a chamber filled with a spray of water. The air in passing through this spray is washed free of dust and at the same time absorbs water necessary for its desired humidity.
The humidity of air may be increased by the addition of moisture or decreased (dehumidified) by raising its temperature, thereby increasing its capacity for containing moisture. Suppose that air at 50° is saturated with moisture; it will contain practically 4 grains of water per cubic foot. If now the temperature of the air is raised to 70°, the same amount of air is capable of containing 8 grains of water and is, therefore, only 50 per cent. saturated.
Humidification is accomplished in air-conditioning plants through one of two general methods: by the evaporation type of apparatus, in which the passing air absorbs moisture from contact with a large area of water; or the spray method, in which the water is broken into a very fine spray by a specially devised nozzle and thus rendered easy of absorption by the air to be moistened. A third method is sometimes employed, in which steam is introduced into the air supply. Steam is already vaporized water and immediately becomes a part of the air without further change. The steam type of humidifying plant possesses features that limit its application, in that the steam in some cases may possess objectionable odor or includes the vapor of grease, either of which would materially effect its use. Further, the heat of vaporization liberated by the condensing steam is also a factor that influences the temperature of the air and in case of direct humidification must receive special attention.