Ventilation Apparatus.
—Fig. 172 illustrates the form of apparatus used for ventilating buildings where no attempt is made at washing or humidifying the air. Enclosed in a sheet-iron case C is a fan which is driven by the electric motor M. The capacity of the fan, for the delivery of air, is made to suit the requirements of the building. In this case the fan is secured to an extension of the armature shaft of the motor. Connecting with the case which encloses the fan is another sheet-iron box H, containg coils of heating pipe. The heating apparatus is designed to change the temperature of the entering air to suit the requirements of the building.
This represents the draw-through or induced-draft type of ventilation apparatus. The air delivered by the fan induces a flow of outside air which is drawn through the heating coils and discharged through the opening E. At this point it enters the main ventilation duct from which it is distributed by branch conduits throughout the building.
The temperature of the air sent out from the fan is regulated by the steam valves of the heater coils to suit the prevailing conditions. Under some installations of this character the ventilating air is made to furnish the heat necessary to warm the building as well as to provide its air supply. As ordinarily used, however, the temperature of the ventilating air is the same as that of the room.
The method of conveying air to the various apartments depends entirely on local conditions. The conduits may be made of sheet iron, placed to suit the existing conditions; but when a building is constructed with a ventilating plant in view as a part of the building equipment, it is customary to make the ducts part of the partitions. In brick buildings the ducts are constructed, so far as it is practicable, in the walls. These ducts are made in size and arrangement to suit the amount of air required for each room. When the plant is put into operation each duct is tested with an anemometer which indicates the velocity of the entering air. The calculated amount of air, determined by the velocity and area of the entering column, when compared with the necessary quantity demanded for good ventilation, gives the efficiency of the system.