CFD simulation of cold air downdraughts from windows

During cold winter days it is likely that people in buildings with older windows or high glass facades experience thermal discomfort due to cold air down draughts. Earlier work has been aimed at finding analytical methods to predict the speed of the airflow in a room and in practice heating appliances are often placed beneath the windows to reduce the draught along the floor. In a study from 2012 Mohammad Parchami developed a method for estimating the required heating power to counteract the downdraught with such heating appliances. In this study, Computational Fluid Dynamics (CFD) was used to evaluate the usefulness of Parchami’s method and also to examine the potential of adapting the depth of the inward window sill as a means of decreasing the down draught. The result suggested that Parchami’s method is in need of certain modifications and further CFD-simulations can be a useful tool to make the method more acceptable to the building profession. Further, it was also shown that an adapted sill depth could considerably reduce the airflow speed in the room and the result indicated that there is an “effective sill depth” at which the airflow speed from the downdraught reaches a minimum. It is likely that this effective sill depth in large part depends on the boundary layer thickness at the window, in which case the constructors are given the alternative to determine the window sill depth by an easy estimation of the boundary layer thickness