An air compartment or chamber to which one or more ducts are connected and that forms part of an air distribution system. NOTE: The definition of plenum is not intended to apply to the space above a suspended ceiling that is used for environmental air referred to in NFPA 70-2002 300.22(C).
The ceiling plenum is the volume defined by the area above the back of the ceiling tile, and below the bottom of the structural slab above. Within this plenum is usually found a combination of HVAC ducts, electrical and electronic conduits, water pipes, traditional masking sound speakers, etc.
In modern buildings, the ducts carrying the heat return are not metal ducts but are actually part of the ceiling. This is called plenum ceiling. If you run cabling through a plenum ceiling, you are not to use cabling sheathed in PVC (polyvinyl chloride). When it burns, PVC emits a toxic smoke. Plenum cable is low smoking so that if there is a fire in your building it won't be a hazard. Plenum cable is often made of Teflon, so it is typically more expensive than normal cabling.
The space between the ceiling of one floor and the surface of the floor above. HVAC ducts, VAV boxes, pipes, lighting fixtures and other building equipment is generally located in the plenum space. HVAC systems with air distribution can use the plenum for returning air to the fan system.
The area between the access floor panels and the concrete slab. Typically used as an air duct and a cableway for the data center. Can also refer the area above the suspended ceiling and the concrete slab above.
The air handling space between the walls, under structural floors, and above drop ceilings used to circulate and otherwise handle air in a building. Such spaces are considered plenums only if they are used for air handling. Work spaces are generally not considered plenums.
A space between the aquarium bottom and substrate, created by supporting the substrate above the bottom using UGF plates or some other support structure. Used to keep Nitrate levels low in a saltwater aquarium. Water and organic waste diffuses down into the plenum where the wastes concentrate. Nitrifying bacteria in the upper levels of the substrate use the oxygen and produce nitrate in the water as it moves down into the space. Denitrifying bacteria living in the oxygen-poor lower levels of the substrate slowly convert Nitrate into harmless nitrogen gas.
In some buildings, the entire space above the drop ceiling is used as a return air pathway instead of a set of ducts. Therefore air circulated within that space gets distributed throughout the floor, or the building. If a cable located in an open air plenum has a PVC jacket and catches fire, the toxic fumes would spread throughout the entire floor via the open plenum, thereby suffocating or at least impairing people's ability to get out of the building. To overcome this, some cables are coated with Teflon to prevent the spread of flame and toxic fumes. Individual states and provinces regulate what types of cables are acceptable as a minimum standard. Extreme care must be taken by the installer and designer to ensure the proper cables are specified and installed
A designated area used for transport of environmental air as part of the air distribution system. Because it is part of the air distribution system, cables installed in this space require a higher fire rating.
A type of network cable used thorough air ducts. The sheathing surrounding the cable is made from polymers that do not give off toxic or carcinogenic fumes when burned. Plenum-rated cable is intended to prevent the spread of hazardous fumes, not to prevent the spread of a fire itself. Plenum cable costs about 4 times that of regular CAT5 cable.