Refined Design Criteria for Laboratory Exhaust Plume Dispersion
Chester Wisner, Ambient Air Technologies, LLC
Laboratory exhaust systems are designed to protect personnel and research animals from harmful exposures to exhaust plumes containing fume hood effluent and other hazardous airborne pollutants from laboratory activities. Currently, the design criteria typically consist of a single number specifying the minimum dilution required to render the plume safe or acceptable. The criteria do not vary from one location to another. That is, the criteria will be the same on a rarely inhabited roof as the criteria at the outside air intakes serving the building or at the elementary school next door. No account is explicitly taken of the probability that an exposure will actually take place or of the relative vulnerability of the person or animal that may be exposed. Although these factors are sometimes taken into account through professional judgment in the application of the design criteria, they are not dealt with quantitatively in a consistent manner. There is often a built-in tendency to err on the conservative (safe) side of the energy versus safety tradeoffs, which, in the absence of a readily defensible analysis, will produce less energy-efficient designs.
During this presentation, the speaker will report on the development of a refined, risk-based approach to establishing design criteria that explicitly and quantitatively accounts for these factors. The speaker will present this methodology, along with examples of its impact on laboratory exhaust system design projects that are striving to reduce exhaust fan energy while maintaining a safe laboratory and environs. The speaker will use wind tunnel simulations to demonstrate the impact of the refined design criteria methodology on the reduction of exhaust fan energy usage.
The design criteria are often the most critical element in determining the energy savings available as a result of reducing exhaust flows or exit velocities for laboratory exhaust. If the design criteria are too conservative, more fan energy will be used than is necessary. If the design criteria are not conservative enough, the safety of building occupants will be jeopardized. As more attention is being paid to reducing the fan energy on new designs and energy retrofits, it is becoming critical that the design criteria are correct in order to allow for the most informed decision regarding design tradeoffs between safety margins and energy savings.
Biography:
Chester Wisner is the president of Ambient Air Technologies, LLC, a Colorado firm specializing in wind tunnel modeling of laboratory and healthcare facilities. Mr. Wisner has played an active role in the air quality portion of the environmental industry for more than 35 years. In several recent cutting-edge studies, some of which have been reported at past Labs21 sessions, Mr. Wisner has used the wind tunnel to produce data supporting energy-reduction initiatives that are already producing results. Initiatives include a wind-responsive system being installed on a major laboratory at the University of California (UC), Irvine, where a reduction in exhaust fan energy of approximately 75 percent is expected, and another system at the University of Wisconsin–Madison where the wind responsive system is expected to achieve a 90 percent energy reduction. Mr. Wisner's educational background includes a Masters of Business Administration from the University of California, Los Angeles (UCLA), a Masters of Science in meteorology from the South Dakota School of Mines and Technology, and a Bachelor of Science in engineering physics from UC Berkeley.