Natural ventilation of a room with vents at multiple levels

Abstract

The natural ventilation of a room with a source of heating at the base and with vents at multiple heights is investigated both theoretically and experimentally. The key to the analysis is determination of the position of neutral buoyancy, where the pressure in the room equals that in the exterior. Air flows in through vents below the position of neutral buoyancy and exits from vents above it. When a room is heated by a distributed source the room heats up to a uniform state and the position of neutral buoyancy depends solely on the ratio of the upper and lower vent areas. When a room is heated by a point source or series of point sources, a vertically stratified environment develops and the neutral buoyancy surface is higher. Depending on the nature of the heat source, the mixing of air flowing in through an intermediate opening leads to different types of stratification in the interior. For a distributed heat source, the interior remains well mixed whereas for a point source, a two-layer stratification develops. The flow produced by both distributed and point sources of heating are compared; the point source leads to a lower ventilation flow, although in both cases the ventilation flow can be raised by increasing the heat flux, the separation of the upper and lower vents, the total vent area or the distance of the intermediate level vents from the height of neutral buoyancy.