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Last edited 22 Sep 2016
Plenum ventilation in buildings
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Plenums are air compartments or chambers that are sometimes found in buildings, either above suspended ceilings, in the gap between the ceiling and the floor slab, or below raised floors in the gap between the raised floor and the floor slab. They form part of the ventilation system for the building.
They may be supply or return plenum, and may serve either an entire building, or a specific zone in a building. Supply plenum supply ventilation air to the occupied space, whilst return air is generally extracted through ductwork. Conversely, in return plenum the air is generally ducted to the space, whilst the return air is extracted through the plenum.
Underfloor air distribution (UFAD) uses the underfloor plenum beneath a raised floor to provide ventilation air through floor diffusers directly to the occupied zone. The air spreads across the floor forming a reservoir of fresh, cool air. Any sources of heat (such as people or computers) generate a thermal plume lifting contaminated air to high level where it can be removed from the space. See Underfloor air distribution for more information.
Plenum can give good flexibility for the layout of buildings. However, they can provide a space within which fire can spread, particularly because of the air supply they offer, and so they may be required to include fire and smoke detection, and potentially combustible material (such as cables) may be controlled. They can also create a pathway for the transmission of sound between separate spaces.
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