Design criteria for outdoor air intakes and exhaust air outlets located on an external wall

Abstract

Optimal placement of outdoor air intakes and exhaust outlets is a source control measure to avoid the degradation of air quality at the air intakes. Re-entrainment is an occasional air pollution instance that happens if pollutants in the exhaust air stream, after being discharged to outdoors, are transferred back to outdoor air intake location due to unfavorable meteorological conditions and inadequate positioning of the air intakes and exhaust outlets. In engineering practice, it is impractical to always conduct detailed dispersion modeling due to the complexity of airflow phenomena in the urban environments, and therefore, engineers rely on prescriptive design guidelines or simplified empirical models published in technical literature and regulation documents. Commonly, the design guidelines to avoid the re-entrainment phenomenon are for buildings with rooftop exhaust stacks, but the exhaust outlets might also be situated on the building façade. The objective of this paper is to overview the existing design guidelines for the placement of horizontal air intakes and exhaust outlets. Technical engineering literature, including international standards, codes, and guidebooks is reviewed to extract both qualitative and quantitative design guidelines relevant to the placement of air intakes and exhausts on an external wall.