TABLE OF CONTENTS The installation of a raised floor system and the many advantages that it produces in terms of improved cable management, flexibility, and life-cycle cost savings will, in many cases, be the main driver in justifying the use of underfloor air distribution. Once an underfloor air supply plenum is included in the design, there are three basic approaches to configuring it: (1) pressurized plenum with a central air handler delivering air through the plenum and into the space through passive grilles/diffusers; (2) zero-pressure, or neutral, plenum with air delivered into the conditioned space through local fan-powered (active) supply outlets in combination with the central air handler; and (3) in some cases, ducted air supply through the plenum to terminal devices and supply outlets. In practice, although not a requirement, the final designs often end up as hybrid solutions including some combination of the above components. For example, a common pressurized plenum design uses passive diffusers in the interior zone, active fan-driven diffusers in the perimeter or special zones with rapid load changes, and some amount of distribution ductwork in the underfloor plenum.
The largest dimension of ductwork and other non-movable system components that can reasonably fit between underfloor pedestals is 22 in. (560 mm). For components such as fan coils and terminals whose relocation or removal (for maintenance considerations) is foreseen, this maximum dimension should be limited to 19 in. (480 mm). The removal of any component larger than 19 in. between pedestals...
