Roof Plenum Units
Air distribution systems for commercial and industrial buildings sometimes require variable amounts of outside air for ventilation purposes to be mixed with return air from conditioned spaces within the structure. A roof-mounted insulated plenum to which distribution supply and return air ducts may be connected through a roof opening is required for such an installation. Outside air dampers are designed to adjust from closed to full open and may be manually controlled by a multiposition remote potentiometer. When full open, the dampers will permit the introduction of a maximum of 80 percent outside air for ventilation purposes.
The Janitrol roof plenum unit shown in Figure 7-24 is located next to the control box to which it is connected by means of a flex- ible conduit. The construction of the roof base and curb is illus- trated in Figure 7-25. Roof plenum units that do not provide for the addition of outside air to the system are also available.
