Effect of mechanical ventilation on infiltration rate under stack effect in buildings with multilayer windows

Abstract

In order to prevent outdoor air pollutants from infiltrating indoors, a positive indoor air pressure (i.e., a zero air infiltration rate) should be maintained. ASHRAE requires a zero air infiltration rate in buildings when the mechanical ventilating system is operating. In fact, when the building is leaky or the rate of mechanical ventilation is low, the air infiltration rate of zero is hardly achieved. This contradiction causes the need for figuring out the required rate of mechanical ventilation in order to achieve a zero infiltration rate in a building. Previous studies have focused on this issue for single rooms or buildings with simple crack distributions on the envelope. There is not enough research on this issue for complex models such as buildings with multilayer windows. This study aims to investigate the effect of mechanical ventilation rate on infiltration rate under stack effect for buildings with multilayer windows. A method providing the mathematics relationship between the two rates is put forward. Then, tests are conducted in an actual large space building to validate the method. The validated method is used to calculate the minimum rate of mechanical ventilation required to achieve a zero infiltration rate for a building with multilayer windows. It is concluded that the minimum ratio between the rates of mechanical ventilation and initial air infiltration to achieve a zero infiltration rate depends on the window width-height ratio, the vertical spacing between windows, and the number of window layers. More regulations are summarized and analyzed to guide ventilation design.