Center for the Built Environment

Underfloor air distribution systems use the underfloor plenum beneath a raised floor to provide conditioned air through floor diffusers that creates a vertical thermal stratification. Thermal stratification affects energy, indoor air quality and thermal comfort.

The purpose of this study was to characterize the influence of linear bar grilles and VAV directional diffusers on thermal stratification in perimeter zones by developing theoretically and empirically based models. Forty seven laboratory experiments were carried out in a climatic chamber equipped with a solar simulator.

Linear bar grilles tend to produce less stratification than VAV directional diffusers and, in some cases with high airflow rates, may generate reverse stratification. Models to predict temperature stratification for the two tested diffusers have been developed.