Navigating Exhaust Stack Design Codes/Standards/Guidelines While Achieving Exhaust Fan Energy Savings

Aimee Smith, RWDI

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Laboratory buildings discharge various types of hazardous and odorous emissions through their exhaust systems. For many years, it has been well understood that these exhausts need to be dispersed away from the building and the neighbors to maintain a safe environment. It is now paramount to ensure that in addition to maintaining safety, that the long-term sustainability of these facilities is addressed by implementing energy savings techniques; one of which is to reduce the speed of the rooftop exhaust fans.

One of the increasing challenges with balancing safety and energy savings techniques for laboratory exhaust design is the confusion that can arise from the number of guidelines and standards that exist for the design of these exhaust stacks (and new ones that continue to emerge). These guidelines and standards are intended to aid designers in their quest to balance safety and energy for laboratories but can often be misinterpreted and misapplied in practice.

This session will review several of the commonly referenced standards, guidelines and codes (including U.S. EPA, ASHRAE, ANSI/AIHA Z9.5, California Title 24, NFPA, and in the United Kingdom, BS EN 14175) to demonstrate the challenges with interpretation and application of these guidelines. In addition, many institutions have their own guidelines which must be followed. These are often driven through the real estate office in the form of design standards, or by the Environmental Health and Safety (EH&S) departments. This creates another layer of expectations that must be managed. How can designers meet these expectations while still driving to reduce the energy impact of the HVAC systems? Will the steps required to satisfy all the requirements result in overly complex designs and/or operating systems? The good news is that there are methods that can be applied that can address the expectations without overly complicated solutions. Uing specific examples, the session will demonstrate an approach that can be used to ensure a design that satisfies even the most complex set of expectations, while balancing this with reduced energy use of the laboratory exhaust system.

Learning Objectives

  • Gain an appreciation for the potential benefits and limitations associated with available published guidance for laboratory stack design and this can affect successful smart laboratory ventilation;
  • Describe a detailed procedure to estimate the emission levels from site and laboratory specific chemical use, and how this information can be used to satisfy the intent behind many of the published codes and standards;
  • Identify the preferred tools for exhaust dispersion modeling, and how a site specific emissions understanding can be combined with dispersion modeling to meet requirements and reduce energy use; and
  • Identify the range of solution techniques that exist to successfully balance the requirements with energy use, and the specific scenarios where more complex solutions may be beneficial.


Aimee is a Principal of RWDI, and the firm Director of Technical Excellence. Aimee is widely recognized among the laboratory and healthcare design community for her deep knowledge of exhaust dispersion and air intake systems and her strong technical understanding of health and well-being of occupants, building energy use, and local microclimate factors including air quality, ventilation, acoustics and wind behavior. Aimee is a licensed Professional Engineer (Ontario) and is a member of SCUP and I2SL.


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