The fluid mechanics of the natural ventilation of a narrow-cavity double-skin facade

Abstract

This paper investigates the natural ventilation of a double-skin facade connected to a room in a multi-storey building. The room and the facade are connected to the exterior through vents at different levels. The room contains a horizontally distributed heat source analogous to occupants in an open-plan office or an underfloor heating system. The facade cavity contains a vertically distributed heat source analogous to a shading blind/louvers heated by solar radiation. These two sources of heat combine to provide buoyancy driving the ventilation. Two basic modes of facade operation are proposed and investigated. These two modes of operation should be alternated according to exterior climatic conditions. In colder seasons, the room draws air from the portion of the facade which extends one floor below the room, and solar radiation on the facade preheats supply air into the room. In warmer seasons, the room vents to the exterior through the portion of the facade which extends one floor above the room, and solar radiation on the facade enhances the ventilation and prevents overheating in the system. A quantitative model is developed to describe the fluid mechanics of the ventilation in these two modes of operation. The model is successfully tested with laboratory experiments. It shows how the height of the facade and the size of the openings can be adjusted to maximise the preheating of the room in colder seasons, and to prevent overheating in the room and the facade in warmer seasons. The model is used to explore the principles for design and control in different climatic and occupancy conditions.