Ducting is an approach to air management that uses a series of metal or plastic pipse to carry heated or cooled air from one place to another. A duct system is often referred to as ductwork.
There are two types of ducts: active and passive. Ducts are naturally passive because they have no moving parts. Active ducts use fans to help move the air. In the data center, air cooled by a computer room air conditioner (CRAC) can be carried through ducts into the raised floor and forced into the data center's IT space through perforations in the raised floor panels. The duct moves heated or cooled air around (such as above ceiling spaces) without spilling the air into other areas. Ducting is used in hot and cold aisle containment, which improves data center reliability and energy efficiency. It can be used to exhaust hot air from IT equipment into a dropped ceiling, which then acts as its own duct to move air back to the CRAC. Ducts can also direct cold outside air into data centers, with proper filtration for contaminants and accommodation for humidity control.
Typically, the air pressure differential produced by CRAC activity pushes the heated air upwards as the cooled air is forced into the space below it, helping to complete the cooling loop. Return ducts are typically located above server racks or at the raised exhaust point within a containment enclosure where heated air (which is less dense than cool air) rises and can be exhausted more easily. Fans are generally only used with a simple ventilating duct (not a CRAC) or if there is a specific need to enhance airflow.
Ducting can also refer to a cable and wiring strategy in which a run of cables are organized in duct pipes near a high-traffic area of the data center or above data center cabinets. Adding cable ducts eliminates the need to run cables underneath flooring.