TABLE OF CONTENTS The use of an underfloor plenum to deliver conditioned air directly into the occupied zone of the building is one of the key features that distinguish underfloor air distribution (UFAD) systems from conventional ducted overhead air distribution systems. In the design of underfloor air supply plenums, the primary objective is to ensure that supply air at the required quantity and conditions (temperature and humidity), and containing at least the minimum amount of ventilation air, is delivered wherever it is needed on the floor plate of the building. This process differs from fully ducted designs because as the air passes through the plenum, it can come in direct contact with thermally massive materials (concrete slab and floor panels) that will transfer heat to or from the supply air, depending on the temperature difference and flow rate. In some configurations, the amount of air reaching the desired locations may be influenced by plenum inlet conditions, plenum height, obstructions within the plenum, and leakage from the plenum. These and other design and performance considerations for underfloor plenums are discussed below.
An underfloor plenum is the open service distribution space between a structural concrete slab and the underside of a raised, or access, floor system (Figure 4.1a). As shown in the photo in Figure 4.1b, the raised floor platform is made up of 2 ft 2 ft (0.6 m 0.6 m) steel panels filled with concrete-like material (other compositions and finishes are available). The floor panels are attached and supported...
