The Influence of Building Airtightness on Airflow |in Stairwells

Airflow into stairwells due to stack effect is a concern affecting fire safety, energy performance, and indoor air quality. Stack effect in tall buildings can create significant pressure differentials in vertical shafts when differences in outdoor and indoor temperature exist. The pressure differentials drive air through openings or gaps in walls and floors. Vertical shafts, consisting of stairs and elevators, may transport significant volumes of air. During heating season, this results in the infiltration of cold air at lower floors and the exhaust of warm air on the upper floors. Correspondingly, it results in the spread of air and potential contaminants within the building. Stack effect driven airflow will change according to size and distribution of leakage paths. The size of leakage areas can be approximated by a cross-sectional area of an orifice that would allow equivalent flow. This leakage area is dependent on construction material, workmanship, and even operation, as openings from windows and doors equate to large orifices. A building’s composition of these leakage areas can greatly impact the effective area and airflow. The effect of openings from stairwell doors can change the Neutral Pressure Plane location (NPP), altering airflow patterns within a building. This paper investigates the influence of effective area on airflow within stairwells for multi-unit residential buildings (MURB) due to stack effect. A range of parameters reflective of industry standards are evaluated using network modeling and computational fluid dynamics (CFD). Parametric analysis is used to determine the sensitivity to which they affect airflow between building and stairwells. The effect of airflow within vertical shafts has consequences on indoor air quality (IAQ) and smoke spread, energy efficiency, and thermal comfort. The benefit of reducing leakage in buildings can be understood by comparing the quantity and patterns in airflow in and out of stairwells. Improving air tightness of the building envelope or vertical shafts can have a significant impact on airflow.

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