Fume Dispersal: Is That Giant Flue Really Doing Its Job?

Andy Parker, BuroHappold Engineering
Aimee Smith, RWDI

Laboratory Buildings discharge various types of hazardous and odorous emissions through their exhaust systems. To provide a healthy and comfortable space, it is important to ensure that the laboratory exhausts do not re-enter the building air supply at undesirable concentrations. In addition to maintaining safety, it is imperative for the long term sustainability of these facilities to implement energy savings techniques; one of which is to reduce the speed of the rooftop extract fans.

This session will review the commonly used approaches that are used to define the fume dilution system and ultimately determine the actual fume dilution performance. In terms of guidance for exhaust stack design, a first level approach is to follow the general guidance provided by agencies like U.S. EPA, ASHRAE, ANSI/AIHA Z9.5, and in the United Kingdom, BS EN 14175. However, there is no guarantee that following this guidance will ensure safe levels at the building air intakes. A more thorough approach involves dispersion modelling of the exhaust to determine the levels achieved at the air intakes. However, developing a means of judging the acceptability of these levels is critical. There is some limited published guidance available regarding acceptable levels. However, a more robust approach is to investigate the details for the laboratory in question (i.e., chemical use, expected activities, etc.) to develop a site and laboratory specific emission scenario and acceptance criteria.

We will present a proposed procedure to successfully address the interactive issues of safety and fan energy savings through an assessment of the overall risk involved. With laboratory specific acceptance criteria, wind tunnel dispersion modeling can be conducted to identify potentially problematic wind conditions for fan turn-down. Using this data to perform an analysis of the frequency of occurrence of these winds allows for a rigorous assessment of the potential risk associated with the design. If the risk of unsafe levels occurring at the air intakes is considered to be unacceptable, mitigation options can be considered to implement the desired fan turn-down. The use of this procedure can minimize energy consumption, enhance aesthetics and maintain, or even improve safety levels.

The session will describe the procedure outlined above in detail and include a case study of the Imperial College London West Campus, demonstrating how this approach to evaluating the overall potential risk associated with fan turn-down was applied for a new Research Building in the United Kingdom.

Learning Objectives

  • The speakers will provide an overview of the fundamental objectives of fume dispersion, with reference to the limitations associated with available published guidance for laboratory stack design.
  • A detailed procedure will be described to estimate the emission levels from site and laboratory specific chemical use, and how this information can be used to generate a site specific acceptance criterion.
  • Participants will be provided with a detailed explanation of the preferred tools for exhaust dispersion modeling, and an overview of how climate data can be combined with dispersion modeling data and acceptance criteria to estimate the risk of undesirable conditions.
  • Through presentation and discussion of the Imperial College London case study, participants will gain insight to the benefit of considering site specific acceptance criteria, and the influence of local climate conditions to satisfy safety concerns while achieving fan energy savings.

Biographies:

Andy is the Global Director for BuroHappold Engineering's Science & Technology sector. His extensive project experience around the world ranges from research labs to GMP manufacturing facilities with private companies, universities and government institutions. His current interests are the use of modelling techniques to address the sustainability and effectiveness of labs. He is looking at reducing fume dispersal system energy and modelling of lab environments to optimise creativity.

Aimée is a Principal of RWDI, and the firm leader for the higher education, laboratory and health care sectors. Aimée is widely recognized among the design community for her deep knowledge of exhaust dispersion and air intake systems and her strong technical understanding of health & well-being of occupants, building energy use, and local microclimate factors including air quality, ventilation, acoustics and wind behavior. Aimee is a licensed Prof. Engineer (Ontario), an I2SL and SLCan member.

 

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