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Laboratory Offset Air - The Overlooked Constant Volume Exhaust System

Lee Tapper, Holabird & Root

This presentation looks at a specific way in which the design of a building, rather than a specific indoor component, influences air quality, safety, and energy use. This presentation calls for engineers to take a fresh look at constant volume exhaust systems, which may not be new or flashy, but do offer huge potential to building designers. This approach considers the building as a whole, rather than as a collection of different equipment.

In order to achieve the required cascading pressure control between laboratory and non-laboratory spaces, it is necessary to incorporate offset air into the design for the heating, ventilation, and air-conditioning system (HVAC). The offset air is an intentional differential between the quantity of air supplied into a laboratory and the quantity being exhausted from the laboratory. In order to make the laboratories consistently negative with respect to the surrounding non-laboratory spaces there is more exhaust from the space than supply to the space. However, in order to control the overall building pressurization, this offset must be introduced into the building as make up air. The offset air for the facility operates like a 24/7 constant volume hood.

This presentation will examine the multitude of items that affect the sizing of the offset air and how designers can positively affect the quantity of offset air required to safely and effectively operate a laboratory building. This presents a tremendous opportunity to reduce the overall facility energy consumption, which is often overlooked or not understood.


Lee Tapper, as the lead mechanical system designer (both HVAC and plumbing) on numerous multidiscipline science and research facilities, has designed mechanical systems for a variety of laboratory types and conditions. The laboratory types include instructional, research, and production laboratory facilities for chemistry, physics, biology, biomedical, psychology, neurology, and genetics. These types of projects require developing an assortment of energy conservation strategies for containment and the operational character of the building fabric to address personnel safety, research flexibility, operational consistency, and energy stewardship. This necessitates development of testing and modeling methods to verify appropriateness of the design solutions.

Lee is a mechanical engineer, certified indoor air quality professional, and LEED®-Accredited Professional. He currently serves as a member of the ASHRAE Steering Committee, Rochester Section. He has spoken at Labs21 in the past, as well as conferences for the Iowa Department of Natural Resources, the American Energy Engineers, and the World Energy Engineering Conference, among others.

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