Overhead Sweep Fans
The slow, high displacement, fans are used quite extensively in tropical regions where the humidity is high and air movement sluggish.
The gentle movement of any breeze would cool the skin as the capillaries offer up their moisture.
The sweep fans in the tropics were placed halfway down from the high ceiling and avoided drawing the warm air uppermost to the region below and moved ever so slowly due to high displacement.
Today’s’ overhead fans are some thing quite different in that their location is quite close to the ceiling, drawing the warmer volume into play and their displacement capacity somewhat lacking at slow speed.
Using high speed results in a dehydrating effect, particularly on sensitive skin, when exposed for prolonged periods of time.
Initially the capillaries secrete token moisture imparting a cooling effect however when the skin is no longer able to surrender any more moisture the skin becomes dry and dehydrates.
This is evident when left on with sleeping children who become thirsty midway through their sleep cycle and women complain of dry skin on their faces and arms.
The overhead sweep fans need to be used prudently as they do not improve the quality of the air.
Their use as an alternative to ventilation is based on presumption if not wishful thinking.
The reverse motion used to reintegrate warm air with cooler during the winter months is a better use of these fans.
The circulatory function is suited more to outdoor use rather than indoor as natural currents that arise from moment to moment assist in the ventilation through displacement.
The preferred momentum of air movement in the tropics is from side to side and not top to bottom which is why oscillating fans at low speed and located to one side of a room are more beneficial, although the dehydration factor is still present. The faster the flow the quicker the dehydration.
Slow movement with positive displacement is the most efficient method.