Mixing VS.displacement ventilation in terms of air diffusion effectiveness.

In occupational hygiene the common practice is to use dilution ventilation (MIXVENT) which ideally requires perfect mixing. Increasingly, however, displacement ventilation (DISPVENT) is being applied; ideally this involves fresh air displacing contaminated air without mixing. Keeping MIXVENT as a reference the approach of intervention was used to estimate the potential of DISPVENT for improving environmental conditions in a garment sewing plant. Air exchange efficiency of MIXVENT came to 49%. DISPVENT improved the efficiency to a level of 57%. In terms of local mean age of air DISPVENT improved conditions by a factorof 1.3. From the air diffusion effectiveness MIXVENT improved air diffusion effectiveness by a factor of 1.7, and no short-circuiting was observed. It is concluded that DISPVENT has potential for improving environmental conditions in industry.