Ceiling Space Return Air Plenum

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.

Ceiling space return air plenum. Ceiling plenum 0 03 in. Fire protection within a return plenum is very important to the integrity of the entire structure and. 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. Of thumb for sizing various return air transfer assem blies are shown in table 1.

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. 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. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum.

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. 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. Other common framing cavities used as return air pathways or plenums are air handler platforms open floor truss cavities and dropped ceilings.