Using Local Site Winds to Save Exhaust Fan Energy
Chet Wisner, Ambient Air Technologies, LLC
As efforts to reduce laboratory air change rates progress, the exhaust flow coming from laboratory buildings is being dramatically decreased. This presents a challenge in exhaust system design, as well as an opportunity to implement an equally dramatic decrease in exhaust flow from the stacks. The challenge is to do so while preserving the health and safety of building occupants and neighbors.
Local winds around a laboratory building drive the exhaust and intake system designs. As the requirement to reduce exhaust fan energy intensifies, the commonly used assumptions regarding the wind environment must be reexamined. The onsite winds are commonly taken to be adequately represented by nearby airport meteorological stations, and the design wind speed is taken as the 99th percentile fastest wind speed regardless of wind direction, time of day, or season. In some cases, these approaches can be challenged to produce significantly greater fan energy savings with the same level of system complexity and cost.
Where analysis of the wind climatology shows systematic variation in winds as a function of time of day or season, simple changes to exhaust fan operating sequences can be triggered by the system clock with no added equipment required. This approach can sometimes achieve a large portion of the energy savings potentially available with the installation of onsite anemometers and real-time, wind-responsive control systems.
In some cases, the local onsite winds at a laboratory building are significantly different than those at nearby airport meteorological stations. The Stanford University campus is a strong case in point. Winds on campus are about half of the wind speed at nearby long-term airport stations due to a protective eddy caused by the nearby coastal mountains. Stanford University has benefited from an on-site meteorological station, which now has accumulated approximately five years of data. Ambient Air Technologies, LLC used this record in conjunction with long-term airport and offshore buoy stations to develop a 20-year pseudo climatology for the campus, which has served as the basis for exhaust design and air quality permits. Wind directions and speeds on campus are both dramatically different than those at nearby locations. Accounting for the local wind characteristics has allowed significant savings in exhaust fan energy for new laboratory designs and for energy retrofits of existing laboratories.
This presentation will review the acquisition and utilization of onsite winds (real-time and non-real-time) to allow greater exhaust fan energy savings for laboratory buildings. The speaker will present cases that include wind tunnel video clips to show the impact of exhaust flows in the various wind regimes.
Chet Wisner has more than 40 years experience in conducting both laboratory and field studies for air quality and dispersion modeling. As the president of Ambient Air Technologies, LLC, which specializes in wind tunnel studies for laboratory and healthcare facilities, Mr. Wisner is the principal-in-charge of all studies dealing with air quality and dispersion modeling. Mr. Wisner holds a Bachelor of Science in engineering physics from University of California, Berkeley, a Masters of Science in meteorology from the South Dakota School of Mines, and a Masters of Business Administration in management strategy and policy/marketing from the University of California, Los Angeles. Mr. Wisner has published and presented numerous project reports and research articles including presentations at each of the Labs21 2004 to 2011 Annual Conferences and is a member of several professional organizations, including ASHRAE, the Air and Waste Management Association, The American Meteorological Society, and others.