Perceived and measured indoor climate with dilution versus displacement ventilation: an intervention study in a sewing plant.

Mechanical ventilation of workrooms was formerly based mainly on the dilution principle. In recent years, however, 50% of new investments in industrial ventilation in Scandinavia have been spent on displacement ventilation. Very little data exist from industrial settings on the relative performance of displacement ventilation versus dilution ventilation as regards air quality and thermal comfort. The present study collected data on the indoor climate in a sewing plant before and after the ventilation was changed from dilution to displacement. The indoor climate was evaluated by hygienic measurements of air pollution, temperature, air velocity, etc., and 40 employees were interviewed about perceived thermal comfort, air quality, and irritative symptoms. Changing the ventilation from dilution to displacement induced a slightly higher air change in the occupied zone of the plant and entailed higher temperature gradients. In spite of these findings, complaints of draught decreased significantly, and temperature was perceived to be more pleasant after the change. The air was perceived as less heavy and less dry, especially when humidification was added to the supply air. The improvements in the workers' reports on the environment could not be attributed to placebo effects. Generally, the hygienic measurements were improved or unchanged after the change in ventilation system. Thus, displacement ventilation improved environmental conditions in this study. When adding humidification, this improvement was further sustained.