Return Air
 Warm, more polluted air is removed from the room near ceiling level (typically through return grilles located in a suspended ceiling, or through high side-wall grilles if no ceiling plenum is present) for optimal operation of the UFAD system.  This supports an overall floor-to-ceiling air flow pattern that takes advantage of the natural buoyancy produced by heat sources in the office and more efficiently removes heat loads and contaminants from the space.

A certain portion of return air is mixed with primary air from the AHU to achieve desired air temperatures and humidity, and enable reduced energy costs. In many climates to achieve proper humidity control, conventional cooling coil temperatures must be used (producing a coil leaving temperature of 55°F (12.8°C)). In this situation, a return air bypass control strategy can be employed in which a portion of the return air is bypassed around the cooling coil and then mixed with the air leaving the coil to produce the desired warmer supply air temperature (63-68°F [17-20°C]).

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