Air velocity in a room

Velocity matters

The velocity of the air influences the efficiency of heat exchange between the air and its surroundings. This means that the heat balance for a person in a room is influenced by the speed of the air. At low air velocity, <=0.1 m/s, the effect of air movement in the room is negligible. At low air speed, the updraught of air from the body’s heat emanation will dominate the air velocity. Increased air velocity may cause dissatisfaction with the thermal climate due to cooling of parts of the body. This type of drought problem is one of the more common causes of dissatisfaction with the thermal climate.

The problem of draughts mainly affects people in sedentary jobs, who may be affected by cooling of parts of the body for extended periods of time. Not only air velocity, but also turbulence intensity disturbs the perception of comfort.

Temperature is also a factor to consider

To what extent and in what way air velocity affects the perception of the thermal climate depends on the temperature. Someone sensitive to cold will percieve draughts as more uncomfortable than someone sensitive to excessive heat. Increased air spead increases heat exchange with the air. Since the human body normally is warmer than the ambient air, increased air velocity will have a cooling effect. This is the reason why fans tend to provide a more comfortable thermal climate in hot climates.