1.2.2 Displacement Ventilation
Increase air quality and thermal comfort by moving air through the use of thermodynamics. As opposed to overhead air mixing systems, a displacement ventilation system extracts the stale, heated air from openings in the ceiling, curtain wall or roof and allows fresh air to enter through lower openings to replace it.
Envelope: air-inlets, placed apart from and below air-outlets.
Floor: under floor air distribution within a raised floor.
Ceiling/ Wall: mechanical, ducted air extract.
Interior components: air-outlets can be located at columns / pedestal bases in fixed casework (in spaces such as retail atria).
Air rises as it warms up, moving to a high point where it is exhausted. Cooler make-up air will take its place, supplied at a lower level and drawn upward by the negative pressure caused by the exhaust air flow. Air is stratified, not mixed, focusing comfort zone at the lower six feet of a room.
Lower operational cost due to higher supply temperature, lower supply pressure, and higher ventilation effectiveness due to same direction of air flow and thermal uplift. Unoccupied ceiling spaces can be designed for higher temperature, requiring less cooling volume per floor area.
Reduced energy consumption; cleaner supply air due to minimal air-borne particle content; mold-free due to limited condensation by means of higher supply temperature; silent mechanical system, due to duct-less lower air supply pressures; maximum comfort, due to individual control over ventilation rates; higher staff performance, less absenteeism.
Under floor air distribution (UFAD) works most effectively 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.
1.2.5 Stack Ventilation
1.2.9 Under Floor Air Distribution
5.1.2 Air Flow Modeling