Natural ventilation of a building with heating at multiple levels

This paper describes the theoretical and experimental modelling of a room with low and high level openings and distributed heating at multiple levels. By elevating a proportion of the heat load from the base, the temperature of the space will becomes stratified. Consequently, the height of neutral buoyancy is raised and is a function not only of the geometric areas of upper and lower openings but also of the ratio of heat fluxes and the heights over which they apply. If an intermediate opening is now introduced, air will flow outwards if the height of neutral buoyancy is below the opening and inwards if it is above. When the intermediate opening acts as an inflow vent, two regimes may occur. Firstly, if the magnitude of the elevated heat flux is sufficient to warm up the incoming cool air the space will remain stratified. However, if it is insufficient the incoming air will descend to the base and the whole space will become well mixed. Quantitative models have been developed to describe the conditions under which each regime occurs and each has been validated using small scale analogue experiments.