![]() ![]() ![]() They are often, but not always, driven by fan forces coupled with duct leakage. The interstitial air pressure fields often vary with time with complex daily, weekly, seasonal and sometimes random cycles. In this manner, continuity of mass and momentum holds across the volume of the assembly or element. To account for the presence of interstitial air pressure fields air flow must be added or subtracted within an assembly, chase or void space. With air pressure fields connecting non-contiguous spaces illustrated (right)Īs a result of these interstitial air pressure fields, direct cross assembly (one-dimensional) air flow does not always hold. These interstitial air pressure fields within building assemblies and their linkage to chases and service cavities can lead to lateral flow paths or more intricate three dimensional flow paths that may or may not connect to the interior or exterior spaces that the building assemblies separate.įigure 1: Three dimensional multi-layer multi-cell analogue (left) Typical buildings also contain numerous service chases that provide complex three-dimensional linkage among the exterior wall, roof, interior floor and interior wall/partition assembly cavities and void spaces. Air flow has been assumed to occur across these assemblies, from one side to the other based on the air pressure difference across them, typically through simple leakage areas resulting in one dimensional air flow.Īctually, exterior wall, roof, interior floor and interior wall/partition assemblies are often hollow or multi-layered with numerous air gaps or void spaces and can operate under air pressure regimes (fields) that are largely independent of the air pressures on either side of them. Under this view, the wall assemblies, roof assemblies, interior floors and demising walls/partitions are treated either as monolithic or having through-the-assembly openings. In principle, this view is correct, though often too simplistic. The understanding of air flow through and within buildings has assumed that wind forces, thermal effects (stack action), and air movement associated with mechanical cooling, heating and exhaust and other ventilation systems are the dominant factors relating to air pressure relationships and air pressure related building performance. ![]() Complex three dimensional flow paths and intricate air pressure relationships must be considered.Īir flow in buildings is complex, time dependent and multi-directional. Even the analysis of energy consumption and comfort within buildings needs to be considered in terms of multi-directional air flow.īuildings typically comprise multi-layer envelope assemblies with numerous air gaps or void spaces that are often connected to service chases. 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. 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. Building analysis typically develops the building pressure field from the air flow field. Interstitial air flow and interstitial air pressure fields are not often considered. 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 systems. ![]() Air flow in buildings is complex, time dependent and multi-directional. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |