Air Movement

In this section of the Air Movement module, the fundamentals of air movement are described.  The driving forces including wind, natural stack action, and mechanical ventilation that lead to air movement are introduced.  Using conservation of energy methods, Bernoulli’s Equation for orifice flow is derived. The volumetric flow rates of air through both sharp-edged and smooth-edged orifices are considered and the flows quantified using illustrative induced pressure differences. Worked sample problems are presented to highlight the fundamental principles governing air flow at sharp-edged leakage openings.

In this section of the Air Movement module, air movement in and around buildings is presented.  Wind, stack action and mechanical ventilation all lead to pressure differences that drive air flow.  The pressure differences created by these individual driving forces are quantified and the resulting air flows studied. Next, the combined effects of wind, stack action, and mechanical ventilation are examined.  Flow through small sharp-edged openings in the building envelope due to the combined effects of wind, stack action and mechanical ventilation is quantified using the orifice flow equation. Methods of estimating the air tightness of whole buildings are then examined together with means of field testing the air tightness of buildings. Students are shown how to analyze air tightness test data using a power law form to find the functional relationship between air flows through the building envelope and induced air pressure differences.  As each concept is examined in this section, a series of illustrative worked problems are presented to assist students with understanding of air movement in buildings.