Ceiling Space Return Air Plenum

If this is an area used as a return it is normally referenced as a return plenum.

Ceiling space return air plenum.

Dropped ceilings or suspended ceilings are often installed so that the space between them and the floor above or the roof deck can be used as a return air plenum. The word plenum in the nec is used to describe both an air space and also various types of wiring methods that are specifically designed and tested for installation within these areas. Ceiling plenum 0 03 in. A plenum space is a part of a building that can facilitate air circulation for heating and air conditioning systems by providing pathways for either heated conditioned or return airflows usually at greater than atmospheric pressure.

Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. Section 300 22 a of the nec provides information on the installation and uses of electrical wiring and equipment in ducts that are used to transport dust. However some drop ceiling designs create a. From reading 8 15 1 it seems vague on whether the plenum needs ductwork to the ceiling or leaving a portion s of the ceiling open to allow a return air unit to pull from the environmental space and thus pull from the occupied space.

Normally the space above the ceiling and the deck above is used to return air from the conditioned spaces below the ceiling to the air handling equipment. This is most common in commercial buildings schools hospitals or libraries. In humid climates a cavity space used as a return air pathway will pull humid air into the cavity space possibly encouraging mold growth or the deterioration of building materials. Maintaining a low pressure drop return air path from conditioned spaces to the air handler can be a challenge using architectural plenums when spaces are divided by figure 1 figure 2typical pressures.