1.2.9 Underfloor Air Distribution
Reduce energy use, increase thermal comfort and increase indoor air quality by providing conditioned air from floor registers.
A supply air plenum beneath a raised floor with diffusers to provide air to the occupied space.
Conditioned air is provided through in-floor diffusers from a supply air plenum under the floor. Diffusers are often adjustable, providing greater occupant control as compared to a conventional ceiling system. Air is supplied directly to the occupied zone in the direction of the thermodynamic air stream, rather than supplying air above the occupied zone. The resulting temperature stratification (accumulation of hot air in unoccupied space near the ceiling) reduces heating/cooling/air loads by allowing air to be supplied at a higher temperature and a lower velocity.
The first cost for UFAD systems can be about 5% greater than for a conventional air distribution system. However, if a raised floor is required for other reasons, such as flexible network distribution, then the cost differential will decrease. UFAD can also lower the required floor to floor height, reducing structural costs and potentially adding leasable area.
Greater occupant comfort due to occupant control, greater energy efficiency due to reduced fan speeds and increased supply air temperature. Reduced cross-contamination and increased removal of particles from the occupied space. Potential indoor air quality problems due to dust and debris in the plenum are minimized with a low velocity system; the air travels over the settled dust and debris and does not carry it in to the occupied space.
Under floor air supply distribution (UFAD) works most effectively for in large, consecutive floor areas, i.e. larger single-tenant floor areas. Structure-born sound from foot traffic can be of concern to some users. UFAD should be avoided for cellular offices due to acoustical bridging under wall partitions and poor temperature stratification: Limited and unsteady occupant and equipment loads of cellular offices hinder thermodynamic mixing and the space will be experienced as thermally uncomfortable. The placement of floor diffusers in cellular offices is problematic due to space planning constraints. The technology requires a coordinated team approach from the outset of the project to achieve the optimal results. Early coordination of floor heights, plenum and duct heights, duct run lengths, plenum design for air-tightness, etc. are required. See also 1.2.5 Stack Ventilation.
1.2.3 Task Ambient Conditioning
1.7.10 Radiant Heating and Cooling