BA-92-02-1 -- Correlation of Residual Velocity with Throw and Terminal Velocity from a Louvre-Faced Unidirectional Diffuser PDF

The central thesis is the stated importance of predicting the residual air velocity in the microenvironment of an occupant served by a ceiling-mounted air diffuser obtaining horizontal air flow along the ceiling. Experimental data are presented for a unidirectional, louvre-faced, ceiling-mounted diffuser supplying air to a room under isothermal test conditions. Test data correlating residual air velocity with terminal air velocity are given for five different arrangements of furnishings in the zone of occupancy that correspond to typical conditions encountered in practice. The correlation of residual air velocity with terminal air velocity corresponds with a new definition of throw. Throw is defined as the horizontal distance from the ceiling diffuser to a wall that intercepts the air trajectory, wherein the terminal air velocity is measured at the wall 5 feet (1.52m) above the floor. At any specified value of residual velocity in the zone of occupancy, it is demonstrated that the corresponding value of terminal velocity is a variable with respect to the throw of the diffuser. For a relatively short throw, such as 5ft (1.52m), the allowable terminal velocity is in excess of 100 fpm (0.51 m/s) and approaches 200 fpm (1.02 m/s), depending upon the arrangement of furnishings in the room. At throw values in excess of 20 ft (6.1m), the allowable terminal velocity is only marginally greater than the specified value of residual velocity in the zone of occupancy. Should diffuser throw versus terminal velocity on the wall be available, the data presented would enable a designer of room air distribution systems to quantify residual air motion in the occupied zone. A predictable residual air velocity could enhance the purging of bioemissions and control of the temperature field in the microenvironment. In a variable-air-volume system, the lower limit of air supply could, effectively, be specified.

KEYWORDS: diffusers, ceilings, rooms, air flow, air, speed, measuring, zones, unit air conditioners, ventilation, air movement, occupancy, calculating, variable volume air conditioning, air supply, air distribution