Performance-Based Approach to Laboratory Exhaust Systems

ASHRAE Journal, September 2020

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    Laboratory facilities serve as a critical nexus for innovation and discovery, but they often come with the potential for high operational cost (HVAC energy consumption) and high risk (air quality performance). A prescriptive approach to designing laboratory exhaust stacks has been common. It will likely have a place in the future based on the need for broadly applicable minimum design criteria that can be enforced consistently through code adoption and inspectors. However, achieving superior energy performance and acceptable air quality requires a performance-based approach to laboratory exhaust stack design.

    Examples of Prescriptive Design Criteria

    A performance approach begins with an understanding of the origins and limitations of prescriptive design criteria. Local code and recognized industry standards often serve as the basis of prescriptive criteria a designer would use to design a laboratory exhaust stack. Let us examine the California Mechanical Code, California Energy Code and the American National Standards Institute/ American Industrial Hygiene Association Standard for Laboratory Ventilation (ANSI/AIHA Z9.5) as examples.

    2019 California Mechanical Code

    “502.2.2 Product Conveying Ducts. Ducts conveying explosive or flammable vapors, fumes or dusts shall terminate not less than 30 ft (9 m) from a property line, 10 ft (3 m) from openings into the building, 6 ft (2 m) from exterior walls or roofs, 30 ft (9 m) from combustible walls or openings into the building that are in the direction of the exhaust discharge and 10 ft (3 m) above adjoining grade. (Emphasis is the author’s.) Other product-conveying outlets shall terminate not less than 10 ft (3 m) from a property line, 3 ft (914 mm) from exterior walls or roofs, 10 ft (3 m) from openings into the building and 10 ft (3 m) above adjoining grade.”(Emphasis is the author’s.)

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