Natural ventilation of multiple storey buildings: The use of stacks for secondary ventilation

The natural ventilation of buildings may be enhanced by the use of stacks. As well as increasing the buoyancy pressure available to drive a flow, the stacks may also be used to drive ventilation in floors where there is little heat load. This is achieved by connecting the floor with a relatively low heat load to a floor with a higher heat load through a common stack. The warm air expelled from the warmer space into the stack thereby drives a flow through the floor with no heat load. This principle of ventilation has been adopted in the basement archive library of the new SSEES building at UCL. In this paper a series of laboratory experiments and supporting quantitative models are used to investigate such secondary ventilation of a low level floor driven by a heat source in a higher level floor. The magnitude of the secondary ventilation within the lower floor is shown to increase with the ratio of the size of the openings on the lower to the upper floor and also the height of the stack. The results also indicate that the secondary ventilation leads to a reduction in the magnitude of the ventilation through the upper floor, especially if the lower floor has a large inlet area.