Air velocities inside domestic environments: An important parameter in the study of indoor air quality and climate

Abstract

Very low air velocities were measured in six occupied homes and one unoccupied house particularly when forced-air air-conditioning systems (i.e., HVAC) were turned off. Segregating the velocity data by monitoring site, median velocities of 4.2, 4.3, 10.2, and 12.4 cm/s were found in the master bedroom, basement, and kitchen of the six occupied homes and the dining/living room of the unoccupied house, respectively. In the occupied homes, the comparatively high velocities in the kitchens correlated with increased occupant activities and the use of ceiling and/or exhaust fans. Segregating the data by use of forced-air HVAC systems, the median velocities increased from 5.8 to 6.2, 3.2 to 5.7, 1.5 to 8.1, and 4.4 to 15.5. cm/s with HVAC operation in three occupied houses and one unoccupied house, respectively. The lowest median velocity of 1.1 cm/s was found in a parent's bedroom, where occupant activities were purposely limited and the HVAC was off. These low air velocities raise concern that air movement may sometimes be inadequate for quantitative passive monitoring of pollutant vapors. Ten and 50% reductions in sampling rates are reported in the literature for passive monitors at air velocities ranging from <0.7 to 25 cm/s and from <0.7 to 2 cm/s, respectively. In addition, low velocities may limit off-gassing from evaporatively controlled emitters and decrease the thermal comfort of inhabitants under warm and humid conditions.