VERTICAL DISTRIBUTION OF OCCUPANT-GENERATED PARTICLES IN A ROOM WITH DISPLACEMENT VENTILATION

摘要

The vertical distribution of airborne particles in a room ventilated according to the displacement principle was measured using a vertically conveyed particle counter. The supply air was absolute-filtered and the particles generated through office-like activity of people. In general, particle concentrations increased with height, indicating a displacement effect. This effect improved with ventilation rate. A threshold-size of the particles could be discerned, above which the displacement effect started declining. The measured threshold-size agreed well with calculations based on the settling velocity of the particles and the hypothetical vertical piston-flow velocity of the room air (ventilation rate divided by floor area). At the ventilation rates tested (normal to high), the threshold-size was in the range 5-10 μm. Slightly negative concentration gradients were observed for large particles at the lowest ventilation rate. Hence, if hazardous substances are known to be associated with fairly large particles, the use of displacement ventilation is questionable.