Anatomy of a Raised Floor
A raised floor is generally constructed on a grounded framework, with a load surface of two-foot square tiles (also called panels). The space beneath the floor is called the plenum. Feeding conditioned air directly from the HVAC units into the plenum is simple, and gives the flexibility to channel air, in varying degrees, to the locations where it is needed. The plenum is also generally used to route cables and mount electrical outlets that feed right up to the racks. This plan keeps the cabling out of the way, eliminating the possibility of people tripping over them, or accidently unplugging a vital system.
The height of the floor depends on the purpose of the room. Height should be based on air conditioner ...