Optimising a multi-storey atrium building for stack ventilation

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Session 18 Paper 3, University College London, 16-17 April 2015

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Atria, solar chimneys and similar architectural features that span multiple floors have the potential to enhance buoyancy driven (stack) ventilation by providing a tall vertical space within which buoyant air can accumulate. However, whilst an atrium can assist ventilation, there are also scenarios in which it can restrict ventilation, particularly through the top floor of a building. Using a simple mathematical analysis, we identify the scenarios in which an atrium assists flows – and optimise its performance in these cases – and in which it restricts flows. We quantify the ventilation performance of the atrium in terms of an 'enhancement ratio' which compares the theoretical ventilation flow rate through a given storey with and without an atrium.

We identify an optimum enhancement at which the control of ventilating flows is evenly shared between vents, undesirable flow patterns are avoided and adequate ventilation is delivered to all building occupants. The optimum enhancement varies from building to building and is increased both by increasing the extension of the atrium above the top storey, and by increasing the heat gains within the atrium (due to solar gains, for example). However, for short, unheated atria, better ventilation through the top storey can be achieved without an atrium. In this case it is beneficial to disconnect the top storey from the atrium. This work is intended to provide simple preliminary guidance for designers of naturally ventilated multi-storey buildings.