From Underfloor Air Distribution (UFAD) Design Guide


Because the air is supplied directly into the occupied zone and close to occupants, supply air temperatures must be warmer than that used for conventional overhead system design. For cooling applications, supply air temperatures entering the plenum should be maintained in the range of 61 65 F (16 18 C) with 63 65 F (17 18 C) as a good target for supply air temperatures at the diffusers to avoid overcooling nearby occupants. By comparison, overhead systems typically deliver 55 F (13 C) air at ceiling level. This supply temperature can be reset even higher under partial-load conditions. In temperate climates, where high humidity is not a problem, these warmer supply air temperatures increase the potential for economizer use and allow higher cooling coil temperatures to be set, if desired. See Section 12.10 for further discussion of humidity control.

Mixed air temperature after the cooling coil, or plenum inlet temperature, must be determined by taking into account temperature increase as the air flows through the underfloor plenum. Under most conditions, heat will be transferred to the plenum air from the slab (heat conducted from the return air plenum of the floor below) and from the raised floor panels (heat conducted from the room). Current estimates for typical air flow rates in an underfloor plenum with a slab that is 5 F (3 C) warmer than the plenum inlet air temperature call for a 2 F (1 C) increase for every 33 ft (10 m) of distance traveled through the plenum. Some manufacturers also...

Products & Services
Compressed Air and Vortex Cooling Tubes
Compressed air and vortex cooling tubes are used for spot heating or cooling applications.
Air Handlers
Air handlers are a system-like device used in ventilating systems. They typically consist of a blower, heat exchange medium for heat or air conditioning, and housing.
Fans and Blowers (industrial)

Industrial fans and blowers are move air and ganular media in industrial and commercial settings. Typical applications include air circulation for personnel, exhaust, or material handling.

Variable Air Volume (VAV) Units
Variable air volume (VAV) units are manufactured assemblies of air valves and dampers contained in a single enclosure. As HVAC system components, they regulate airflow to a room or zone in response to a thermostat or other signaling device.
Laboratory Freezers
Laboratory freezers are designed for storing critical materials that demand a constant temperature and security.

Topics of Interest

12.8 SELECT AND LOCATE DIFFUSERS Floor diffusers are most commonly used and offer the widest selection of products to the designer. Due to growing interest in UFAD systems in the U.S., several new...

12.9 DETERMINE RETURN AIR CONFIGURATION For optimal cooling operation of a UFAD system, it is important to locate return grilles at ceiling level or, at a minimum, above the occupied zone (1.8 m [6...

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...

The control and optimization of temperatures in the occupied zone and the amount of thermal stratification (during cooling operation) is crucial to system design and sizing, energy-efficient...

12.10 SELECT AND SIZE PRIMARY HVAC EQUIPMENT Due to the reduction in supply ductwork and to the low operational static pressures in pressurized underfloor air supply plenums (typical pressures are...