Center for the Built Environment

Air movement from fans is an effective way to deliver thermal comfort in warm air temperatures. We measured air speeds in a shared office at 15 siteswhere an occupant would typically be located. The fan speed and direction were changed to operate in either the upwards or downwards direction. Mean airspeeds in the occupied zone were higher when fans were blowing downwards, but the spatial distribution across the space was less uniform. When fans areblowing upwards, thermal comfort estimates using SET indicate less risk of discomfort from high airspeed locations directly under the fans compared withthe downward case. Vertical air speed gradients showed higher air speeds at head height and lower air speeds at ankle height in the upwards direction, butthe opposite profile for fans blowing in the downward direction. The positive vertical gradient in the upwards direction is favorable to reduce the potential fordraft at the ankles. These results suggest that despite lower air speeds, fans blowing upwards can provide more spatially uniform thermal comfort underelevated air movement, requiring less consideration of occupant and furniture placement relative to the fan.