Abstract

Simple models of ventilation flows allow designers to anticipate the performance of buildings readily without the cost of heavy computation. Such a model is detailed here to examine the transient flows and stratification in a naturally ventilated enclosure containing both a localised and distributed source of buoyancy. Both sources of buoyancy are located at the base of the enclosure to represent a building where there is a distributed heat flux from the floor, for example from a sun patch, which has to compete with localised heat sources within the space. To investigate this problem, small-scale experiments were conducted and compared to both a `perfect-mixing’ and ‘zero-mixing’ model of the transients.

Providing the ratio of distributed to localised buoyancy flux $\Psi$ isn’t too large, a stable two-layer stratification is reached in steady state. How the stratification evolves in time, in particular how long it takes to reach steady state, is key to understanding what can be expected in real buildings. The transient evolution of the interior stratification is reported here and compared to the theoretical model.