| Air flow in buildings is one of the major factors that governs the interaction of the building structure with the mechanical system, climate and occupants. If the air flow at any point within a building or building assembly can be determined or predicted, the temperature and moisture (hygrothermal or psychometric) conditions can also be determined or predicted. If the hygrothermal conditions of the building or building assembly are known, the performance of materials can also be determined or predicted.
This paper shows that air flow in buildings is complex, time dependent and multi-directional. The understanding of air flow through and within buildings has been based on the requirement for continuity of mass and momentum caused by wind forces, thermal effects (stack action) and forces associated with the operation of mechanical cooling, heating, exhaust and other ventilation s ystems.
Interstitial air flow and interstitial air pressure fields are not often considered. Building analysis typically develops the building pressure field from the air flow field. In doing so exterior and interior walls, floors, and roof assemblies are either considered as monolithic or having openings resulting in flow across the specific assemblies.
This paper shows that many problems associated with pollutant transfer, smoke and fire spread cannot be explained by cross assembly (one-dimensional) air flow as well as such moisture effects as microbial contamination, corrosion and biological decay. Even the analysis of energy consumption and comfort within buildings needs to be considered in terms of multi-directional air flow. This paper shows that buildings typically comprise multi-layer envelope assemblies with numerous air gaps or void spaces that are often connected to service chases. Complex three dimensional flow paths and intricate air pressure relationships must be co nsidered.
This paper also introduces an alternative pattern of analysis: developing the flow field, the leakage areas and the flow relationships from the measured building pressure field ¡ª the air pressure regime within and surrounding the building. This approach accounts for interstitial air pressure fields and resulting interstitial air flows. It provides a powerful diagnostic tool for solving many of the problems related to direct and indirect effects of air flows. | 