Exhaust Stack Location as a Tool in Designing Energy-Efficient Laboratory Exhaust Systems

Chet Wisner, Ambient Air Technologies, LLC

While often overlooked, proper selection of the location for an exhaust stack can have as much, and often more, impact on the exhaust fan energy requirements than many other parameters of the design. This is especially true for complex buildings, complex built environments or complex terrain. While one location on a roof might present a very challenging plume dispersion environment, another location not too far away can be quite benign. Large scale eddies and other external flow features, such as areas of enhanced turbulence, can make one location dramatically better for exhaust plume dispersion than another. Selecting the proper stack location to take advantage of these features can save large amounts of exhaust fan energy. This presentation will show examples from recent laboratory building design efforts using videos of wind tunnel smoke visualization runs and quantitative dilution measurement results. Configurations and conditions which should flag for architects and engineers will be discussed and demonstrated.

Learning Objectives

  • Recognize situations in which nearby terrain and/or buildings can create obstacles to good exhaust dispersion from a newly designed or renovated laboratory exhaust system.
  • Understand the general features of typical airflow patterns affecting laboratory exhaust plume dispersion.
  • Avoid energy penalties involved in resolving exhaust dispersion issues late in the design process.
  • Understand how advanced techniques such as wind-responsive exhaust system controls can resolve problems with exhaust dispersion as a result of exhaust stack placement.


Chet Wisner is the President of Ambient Air Technologies, a Colorado firm specializing in wind tunnel modeling of laboratory and healthcare facilities. In several recent cutting-edge studies, AAT has produced data supporting energy reduction initiatives which are reaping significant energy savings for numerous clients. He has a BS from UC Berkeley in Eng Physics, an MS in Meteorology from the SD School of Mines, and an MBA from UCLA. He is a frequent presenter and member of ASHRAE, A&WMA and AMS.


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