Raised Floor Plenum : The space between the top of the finished floor and the underside of a raised floor where used to supply air to the occupied area, or to return or exhaust air from the occupied area
NFPA 90A Standard for the Installation of Air-Conditioning and Ventilating Systems, 2009 ed. http://catalog.nfpa.org/NFPA-90A-Standard-for-the- Installation-of-Air-Conditioning-and-Ventilating-S ystems-Prior-Years-P4155.aspx, (Std: Instll of AC & Vent Sys - Amer) {235 NFC}