Diffuser Location
Supply air from the underfloor plenum is emitted into the workspace through diffusers, usually located in the floor. Partition-and desk-mounted types are also available. Compared to standard overhead systems, UFAD systems have a larger number of supply diffusers, many in close proximity to the building occupants, with each delivering a smaller amount of air than typical ceiling diffusers. In most applications, diffusers placed near permanent work locations allow individuals to have some amount of control over their local environment, without adversely affecting that of other nearby occupants.Often referred to as task/ambient conditioning (TAC), depending on the type of diffuser used, this system configuration enables occupants to adjust the volume and direction, and in some cases the temperature, of the incoming air supply, much like the dashboard of a car.

Floor-based Diffusers
Floor-based diffusers can be positioned anywhere within an office plan, as all models are designed to be installed in a single raised access floor panel, typically 0.6 m (24 in.) square. This configuration allows maximum flexibility in placing a floor diffuser, provided the location of any underfloor HVAC components are taken into account.

swirl diffusers

constant velocity floor diffuser

linear floor grills

Several different diffuser designs are currently on the market. Swirl floor diffusers are the most commonly installed type of diffuser in UFAD systems, other options include square-grill diffusers.  Within each diffuser type (i.e. round swirl/constant velocity/linear floor) a number of different models are available, varying in design according to the particular manufacturer. Swirl diffusers are generally installed as passive diffusers, requiring a pressurized underfloor plenum.  Other passive diffusers include a recently introduced constant velocity floor diffuser and standard linear floor grills.

Linear grills are typically used only in perimeter zones, as shown in the image at left, and often incorporate finned-tube heating elements for winter heating periods.
For more information on the role of diffusers in the overall pattern of air distribution within the workspace, see our typical office section and accompanying text.

All passive diffusers can also be installed as active (fan-driven) diffusers.  Other fan-driven diffusers include a floor supply module, desktop air supply pedestal, underdesk grill, and partition-based grill.  For more information on diffuser types see 'Applying the Technology' for our design guidelines.

Furniture-based Diffusers
Diffusers that are more frequently associated with TAC systems - as they provide a high degree of individual control- are typically installed above the floor, as part of the furniture or partitions.  Air is delivered to these TAC diffusers through flexible ductwork or other passageways that are either integrated into the furniture or immediately adjacent to it.

Occupant Control

Within a standard office space, under the uniform well-mixed temperatures of a conventional ceiling based system there will be some occupants who are too cool, others too warm.  As an example, a person walking around continuously in an office will experience an effective temperature of the environment approximately 3 to 5F (2 to 3C) warmer than that of a person sitting quietly at their desk, depending on their respective clothing levels.  User-controlled diffusers enable occupants to fine tune conditions in their workstation, thereby accommodating the significant variations in individual comfort levels that may occur due to differences in clothing, activity and personal preferences. 

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