Indoor Air Flow and Pollutant Removal in a Room with Task Ventilation

In an experimental facility, we studied the performance of a task ventilation system designed for use in office buildings. With this system, occupants can adjust the flow rate and direction of air supplied to their work space through four floor-mounted supply grills. Air typically exits the ventilated space through ceiling-mounted return grills. To study indoor air flow patterns, we measured the age of air at multiple indoor locations using the tracer gas step-up procedure. To study the intra-room transport of tobacco smoke particles, cigarettes were smoked mechanically in one workstation and particle concentrations were measured at multiple indoor locations. Test variables included the furnishing of the chamber, the location(s) of air supply, supply flow rates, temperatures, and directions, and internal heat loads. Our major findings were as follows: (1) In most tests, deviations from a uniform age of air, and a uniform particle concentration, were less than 30 percent. (2) Some supply air short circuits to the return grill when the air is directed toward the return grill with a high velocity. (3) Low supply velocities resulted in a floor-to-ceiling displacement ventilation flow pattern. (4) Directing the supply air toward the occupant, or away from the center of the four supply grills, typically yielded an age of air at the occupant's breathing level that was 15 to 25 percent lower than the age at other breathing-level locations. (5) With low supply velocities and air directed toward the occupants, tobacco smoke particle concentrations in a ventilated non­smoking workstation were 50 percent of the chamber-average concentration.