Effects of Intermittent Air Velocity on Thermal and Draught Perception – A Field Study in a School Environment

Air movement in an indoor space may be experienced in very different ways. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movement may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. One possible way to use air movement as a method to improve thermal comfort, without resultant draught problems, could be to use intermittent air velocity instead of constant velocity. This new cooling method was implemented in a high school in Sweden and evaluated during spring (April) and autumn (September). The present paper reports results from two field experiments where subjects were exposed to velocity variations. The analysis shows significant effects of velocity condition on thermal comfort and air quality. In summary, people exposed to velocity variation perceived the air as cooler and fresher compared with those exposed to constant low velocity and very few classified the air movement as draught. A further conclusion is that even the pupils who were exposed to velocity variation wanted slightly more air movement.