Natural ventilation of buildings is the flow generated by temperature differences and by the wind. The governing feature of this flow is the exchange between an interior space and the external ambient. Although the wind may often appear to be the dominant driving mechanism, in many circumstances temperature variations play a controlling feature on the ventilation since the directional buoyancy force has a large influence on the flow patterns within the space and on the nature of the exchange with the outside. Two forms of ventilation are discussed: mixing ventilation, in which the interior is at an approximately uniform temperature, and displacement ventilation, where there is strong internal stratification. The dynamics of these buoyancy-driven flows are considered, and the effects of wind on them are examined. The aim behind this work is to give designers rules and intuition on how air moves within a building; the research reveals a fascinating branch of fluid mechanics.

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The fluid mechanics of natural ventilation

This paper describes experiments and theoretical modelling of a naturally ventilated enclosure containing two point sources of buoyancy. Previous work on the flow and stratification that develop in a space owing to the presence of a single source of buoyancy has been extended to cover two sources of positive or negative buoyancy in an attempt to produce more realistic models of practical problems. Examples include naturally ventilated buildings, and industrial or medical processes involving dispersal of contaminants by air currents. The experimental technique involves the use of a water-filled enclosure with salt solution injected at two points. These sources of negative buoyancy form turbulent plumes within the enclosure. Two sources of unequal strength are found to produce a vertical density profile consisting of three distinct, fully mixed layers. The paper describes a theoretical model that successfully predicts the depths and densities of these layers. The positions of the interfaces between the three layers were found to be a function only of the effective area A* of the enclosure openings, the height of the enclosure H and the ratio of the strengths of the two sources of buoyancy B1/B2. The behaviour of a system with one source of positive buoyancy at the lower boundary and one of negative buoyancy at the upper boundary of the enclosure is also examined. This case has particular relevance to the prediction of thermal stratification in rooms with both cold and warm surfaces present. Again the height of the interfaces is dependent only on the geometry of the enclosure and the source strength ratio. Three distinct types of flow pattern are predicted and observed.

Natural ventilation of an enclosure containing two buoyancy sources

The expansion of modern cities has increased the popularity of large space buildings. However, without appropriate building designs and efficient heating, ventilation, and air-conditioning systems, large space buildings exhibit poor thermal comfort and high energy consumption. In this study, the thermal non-uniformity and energy migration in large space buildings were analysed. Considering the complex influential factors and large-span structure, zonal modelling as an intermediate approach between the nodal model and computational fluid dynamics (CFD) can provide a rough and quick estimation of the airflow and temperature distributions in large spaces. The literature was reviewed comprehensively and in depth with a focus on the evolvement, principles, characteristics, validation, and applications of various zonal models over the past three decades. Recent zonal models have gradually overcome the initial imperfections and improve reliability by establishing simplified momentum equations. These models have exhibited remarkable superiority in computational efficiency, and the simulation accuracy is comparable to actual conditions and CFD. Moreover, the zonal model is promising for coupling with the multizone model and the building energy model, particularly in the dynamic, long-term analysis of large space buildings. Hence, its development and application should be promoted further.

Zonal modelling for thermal and energy performance of large space buildings: A review

On the calculation of heat migration in thermally stratified environment of large space building with sidewall nozzle air-supply

Design configuration for a higher efficiency air conditioning system in large space building

Determination of temperature profiles and loads in a thermally stratified, air-conditioned system. II: Program description and comparison of computed and measured results

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Determination of temperature profiles and loads in a thermally stratified, air-conditioned system. II: Program description and comparison of computed and measured results