Buoyancy-driven displacement natural ventilation in a single-zone building with three-level openings

Theoretical solutions for thermal stratification and airflow rates are obtained for buoyancy-driven displacement ventilation in a single-zone building with three-level openings. Three displacement natural ventilation modes are identified: (I) the middle opening (MO) is below the stratification interface; (II) MO is above the stratification interface with inflow through MO; (III) MO is above the stratification interface with outflow through MO. It was found that for a wide range of building geometries, the ventilation mode is uniquely determined by the building geometry and the type of buoyancy sources. However, there are certain ranges of building geometry for which displacement ventilation may occur with either mode (I) or mode (II) depending on initial conditions. The significance of this finding is that numerical simulation packages for predicting displacement natural ventilation of buildings need to have the ability to cope with multiple solutions. It was also found that for a given ventilation mode, the location of the stratification interface is a function of the geometrical parameters only and independent of the strength of buoyancy sources. Some general guidelines for optimising natural ventilation in a building with three-level openings are provided