LBNL Report Number
A laboratory-based study of the performance of a floor-based task ventilation system designed for use in office buildings has been completed. With the task ventilation system, occupants can adjust the flow rate and direction of air supplied to their work space through floor-mounted supply grilles. Air exits the ventilated space through a ceiling-mounted return grille. To study indoor airflow patterns, the age of air at multiple indoor locations was measured 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 supply flow rates, temperatures, supply directions, and internal heat loads. Multiple floor supply units were in operation simultaneously. During all tests, the ventilation system supplied 100% outside air. Our major findings are as follows. (1) Deviations from a uniform age of air, and a uniform particle concentration, were generally less than 30%. (2) With two floor-supply units operating and supply air directed toward the occupant, the age of air in the breathing zone was about 20–40% less than the age of air that would occur in the room if the air was perfectly mixed. (3) With two floor-supply units operating, the air appears to travel from the floor to the ceiling in a piston-like flow pattern. (4) With three floor-supply units operating, a two-zone flow pattern, with a piston-like flow in the lower region of the room and mixing in the upper region, was evident at some operating conditions. (5) A strong (r2 = 0.81) correlation was found between the rate of change in the average age of air with height and two factors hypothesized to be determinants of the indoor airflow pattern. (6) Workstations without a cigarette smoking machine and with an operating task ventilation system were not significantly protected from tobacco smoke in an adjacent workstation.