Effect of window bay on the downdraught from a well insulated window.

As the climate in the Nordic countries is cold for several months a year, windows are crucial parts of building envelopes. The current trend to reduce the heat losses by building- components has resulted in many modifications of the design work of windows in order to improve the thermal performance and the indoor climate. The improvements of window constructions have resulted in a higher surface temperature on the inner pane and considerably lower downdraught, which in turn has created an opportunity to introduce unconventional design of the heating and ventilation systems. The objectives of the present study are to investigate and improve the integration of windows in the indoor air climate and to make a survey of the general perception of windows. The unconventional system used in the present study is a well-insulated triple-glazing window with a U-value of about 1.0 W/m2K in combination with displacement ventilation and a floor heating system. The impetus of this paper is to investigate experimentally the flow and thermal behaviour of the downdraught from the window with different widths of the window bay. The experiments are carried out for several cases in full scale and are performed in a well-insulated room specially designed for this purpose. Velocity and temperature are measured by hot wire anemometer and thermocouples, respectively. The airflow pattern of the downdraught, mean velocity and temperature profiles as well as turbulence intensities with consideration to the width of window bay are reported.