Navigating Exhaust and Intake Design Challenges with Urban Laboratories: The Issues and How to Solve Them

Michael Craig, RWDI Inc.

Many university, healthcare, and private laboratory facilities are located in high density urban centers. As existing building infrastructure ages and laboratory programming changes, there is a need to either retrofit or construct new urban laboratory facilities.

Urban settings provide interesting challenges in the mechanical design of such retrofits or new buildings in terms of maintaining acceptable air quality within the facilities. These laboratories are often sandwiched between existing taller structures, which can significantly influence the local wind climate and dispersion performance of exhausts (such as fume hoods, vivarium and standby generators). This can result in re-entrainment of hazardous and odorous exhaust at nearby building air intakes. It can also cause concerns at operable windows and terraces should the neighboring buildings be residential, which is common in an urban setting. Mitigating these issues in urban areas can be challenging because of local building effects on dispersion, and some of the options typically used for lab buildings (such as increased stack height) may be of little benefit. Often there is a need to find the balance between reducing ventilation rates for energy savings, maintaining a safe air quality environment, and providing flexibility in chemical use to the user.

Wind tunnel dispersion modeling is the best tool for understanding dispersion and wind flow characteristics in an urban setting and determining their influence on dispersion. This tool can be used to confirm potential re-entrainment issues and examine potential mitigation strategies for proposed exhausts and intakes.

This presentation covers many common exhaust re-entrainment issues associated with urban laboratory designs to help designers identify potential issues at an early stage. It will examine several wind tunnel dispersion case studies to provide concrete examples of these issues and options for reducing the risk of re-entrainment.

Learning Objectives

  • Gain an understanding of common building situations causing potential air quality issues for urban laboratories to help designers identify potential issues early.
  • Gain an understanding of the best approach for confirming re-entrainment issues and evaluating mitigation options through wind tunnel dispersion modeling.
  • Gain an understanding of exhaust re-entrainment solution options that work and do not work for consideration on future urban lab building design projects.
  • Learn about possible operational protocols that can be used to help reduce the risk of re-entrainment when design options do not work.


Michael Craig has a B.Sc. (Eng) in Environmental Engineering from the University of Guelph. Mr. Craig is a project Engineer in the exhaust re-entrainment division at Rowan Williams Davies & Irwin Inc. (RWDI). His current focus includes consulting on exhaust re-entrainment issues at laboratory and healthcare facilities. He has also performed numerous air quality studies for industrial sectors including landfills, waste water treatment, and manufacturing.


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