Particles and displacement ventilation.

In displacement ventilation the airflow pattern in a room is mainly guided by the convection flows from the heat sources present in the room. This implies that the air in the breathing zone mostly comes from the lower parts of the room, where the air often is less polluted by pollutants originating from persons or electrical appliances present in the room. In earlier investigations by the author the transportation of tracer gas from thermally active and thermally passive sources into the convection flows has been studied. A resuspension of floor deposited particles caused by the influence of the supply air or people moving around may increase the number of particles in the convection flows rising around the heat sources. This transportation of particles, by the convection flows, from the floor level of the room up to the breathing zone has not yet been reported. In this paper will be presented some results from laboratory measurements of particle concentrations at different positions under steady state and transient conditions. Transient conditions in this case means that a person walking around has initiated a resuspension of particles and the decay of particles is then measured. The results indicate that there seem to be little risk of resuspension of particles, in the measured size interval, by the influence of the supply air. With a forced resuspension the particle concentrations in the convection current differs from concentration outside the convection current.