Using Shrouds and Other Rooftop Structures to Reduce Exhaust Fan Energy
Chet Wisner, Ambient Air Technologies, LLC
Shrouds, tall parapets, and other rooftop structures can be effectively used to enhance dispersion of exhaust plumes from stacks within the structures. Such structures have generally been considered impediments to good dispersion because they can potentially inhibit the plume rise, which the exhaust would otherwise experience. However, it is possible, using careful wind tunnel modeling, to take advantage of the turbulence and eddy circulations these structures create in the wind to obtain considerable, near-immediate mixing of fresh air with the exhaust plume and to reduce the maximum concentrations produced nearby to acceptable levels. This approach often requires that these structures or the roof itself be subject to restricted access because of the high concentrations that can occur within the structures. But assuming these restrictions are acceptable to the building owner, significant reductions in the required exhaust fan energy and/or stack height can be achieved. The approaches to successfully implementing this technique will be described, and examples from exhaust design for research laboratories and hospital facilities will be presented.
Biography:
Chet Wisner is the president of Ambient Air Technologies, LLC, a Colorado-based firm specializing in wind-tunnel modeling of laboratory and healthcare facilities. He has played an active role in the air quality portion of the environmental industry for more than 35 years. Applying his experience and expertise in meteorology, engineering, and physics to physical modeling using scale models in a boundary-layer wind tunnel, he has developed systems and tools to assist architects, mechanical engineers, and facilities planners with safe and efficient design. In addition to personally directing and managing wind-tunnel testing projects througout the country, he has also been involved with developing methodologies for providing clients with substantial energy reduction and sustainable design, which are currently being implemented.