Being Smart about "Smart" Laboratory Exhaust Systems

Brad Cochran, CPP, Inc.

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Modern laboratories with fume hood, biosafety cabinet and/or vivarium exhaust systems are often equipped with variable air volume control systems to minimize the energy consumption while maintaining acceptable concentrations of the effluent downwind of the exhaust stack. This design strategy has become so prevalent that it is now required for systems over 10,000 cfm in the new California Energy Code, Title 24.

There are several different control strategies that can be implemented, one of which is a monitor system, often described as a "smart" system. These control systems continuously monitor the constituents in the exhaust and adjust the volume flow rate accordingly. But how "smart" are these systems and how "smart" does the user need to be about these systems to make sure they avoid adverse air quality at critical locations downwind of the stacks? This presentation will go through how these systems work and what their limitations are. It will also discuss how to go about making sure that downwind concentration do not exceed published health limits and/or odor threshold values for those chemicals that can be detected with the sensors included in these systems and for those chemicals that cannot be detected with these systems.

Learning Objectives

  • Inform the audience on how monitored laboratory exhaust systems operate;
  • Provide insight on what chemicals can and cannot be detected by these monitored systems and which chemicals cannot be detected at concentrations below health and odor limits;
  • Describe how dispersion modeling can be used to define safe minimum volume flow rates when the monitored system does and does not detect chemicals in the exhaust stream; and
  • Review the process on defining the minimum allowable release rates for specific chemicals used within laboratories serviced by monitored exhaust systems.


Brad Cochran has over 25 years of experience conducting wind-tunnel, analytical, and computational fluid dynamics (CFD) modeling studies of air flow in and around man-made structures. He holds a BS and MS in Mechanical Engineering, an MBA, and a PE license. Over the last 15 years, he has develop new design techniques to minimize the energy requirements for laboratory exhaust stacks through the application of VAV technologies. Brad is also a currently on the I2SL Board and Chairman of ASHRAE's TC9.10 - Laboratory Systems.


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