Thermal stratification performance of underfloor air distribution (UFAD) systems

Tests were conducted to determine the impact of room airflow and supply air temperature (SAT) on the thermal stratification in interior spaces, and the effect of blinds in perimeter spaces for UFAD systems. Room airflow was varied over the range of 0.7-5.1 (L/s)/m^2 (0.3-1.0 cfm/ft^2) and SATs over 15-19°C (60-67°F) for constant nominal interior heat input of 55-59 W/m^2 (5.2-5.5 W/ft^2). Results show that spaces can be highly stratified when the airflow is reduced for a given load. When SAT is varied, the shape of the temperature profile does not change; it only moves to higher or lower temperatures. Perimeter space tests conducted at a heat load of 116 W/m2 (10.7 W/ft^2) and constant room airflow of 5.1 (L/s)/m^2 (1.0 cfm/ft^2) with blinds opened or closed showed that room load is reduced when blinds are closed due to bypassing of window gains directly to the ceiling return via a convective plume