Must cold air downdraughts be compensated when using highly insulating windows?

Rooms with high windows are likely to have comfort problems caused by cold airdowndraught, which are usually solved by placing heating appliances underneath thewindows. In the city of Zug, Switzerland, a highly insulated educational building with aconcrete core system for heating and cooling is planned. The purpose of our investigation wasto find out whether any measures are necessary in this building to compensate the effects ofdowndraught in the occupied zone. Special attention has been paid to the effect of passivemeasures like air flow obstacles or openings in the window sill. Experiments were carried outin a room climate laboratory on 1:1 scale to measure the downdraught and the thermalcomfort in the occupied zone. Several configurations of window sizes, insulating standardsand outside temperatures were investigated. In addition the results were compared to valuesobtained from analytical calculations and from literature.