Mixing and displacement ventilation compared in classrooms; distribution of particles, cat allergen and CO2

Mixing ventilation and displacement ventilation were compared in an intervention study inclassrooms. Particles, cat allergen and CO2, were measured in classroom air at different levelsabove the floor, during regular lessons. With mixing ventilation, the particle concentrationtended to decrease with height, with a stronger gradient occurring for larger particles. Withdisplacement ventilation, the particle concentration increased with height, except for particles>25 m. The displacement system thus tended to have a slight upward displacement effect onmost of the particles. Significant correlations were found between concentrations of catallergen and particles in the size fraction 110 m. The particle and cat allergen concentrationat breathing height did not, however, differ significantly between the two ventilation systems.CO2 was about 10% lower with displacement ventilation. A fairly high level of physicalactivity of the pupils is believed to have had significant dispersing effect on the airbornecontaminants.