Top-down natural ventilation of multi-storey buildings.

We examine natural ventilation in buildings with multiple storeys, each storey linked to acommon chimney or atrium, and ventilated using 'top-down chimneys' to draw in relativelyunpolluted air from openings located high above street level. Two significant issues relatingto ventilation design and management are addressed. First, the common stack providesconnections between every storey and, consequently, the ventilation of each storey cannot becalculated in isolation, but must be calculated simultaneously for all storeys. Second, theintroduction of the top-down chimney results in frictional losses whose magnitude depends, inpart, on the chimney length and cross-sectional area. We develop a simple theoretical modelto quantify the effect each storey has on others, and to predict how ventilation openingsshould be resized in order to overcome the pressure losses associated with the top-downchimney. The model describes the thermal stratification and ventilation flow rate in eachstorey, and leads to design curves for the sizing of vents to achieve the required ventilation.We focus on steady-state displacement ventilation and compare our theoretical predictionswith paradigm small-scale laboratory experiments in a model two-storey building. Our studyindicates that, with careful design, top-down ventilation of multi-storey buildings is a realisticstrategy in urban environments.