Validation of Energy Saving Laboratory Exhaust Design—Lethbridge Research Centre
Brad Cochran, CPP, Inc.
Energy saving strategies for laboratory exhaust systems has become a hot topic for the laboratory design community. The first Labs 21 presentation on the topic was conducted in 2004 and evaluated the opportunity to reduce exit velocities in a constant volume exhaust system to minimize horsepower requirements. In 2005, the first application of variable air volume (VAV) for a laboratory exhaust was presented as a case study of the Lethbridge Research Centre. Last year, there were half a dozen different talks on the subject.
Until now, all of these presentations described the design of the systems with theoretical energy-saving calculations. Finally, actual field measurements are available to indicate how well these energy-saving strategies are working and to validate the energy savings that are being realized by the owners of the facilities.
The Lethbridge Research Centre converted its laboratory exhaust systems to VAV in 2006. It has now been in operation for nearly four years, with no anomalies noted. In 2008, a monitoring study was conducted to measure the loads on the system to determine whether or not the projected energy savings are being realized.
The initial projections predicted that by applying VAV technology to the five 26,000-cubic-feet-per-minute (cfm) laboratory exhaust stacks the annual energy consumption could be reduced from 1,120 megawatt hours per year (MW hrs/year) to just over 550 MW hrs/yr for an annual savings of just over $57,000 per year. These projections were obtained assuming a minimum volume flow rate of 65,000 cfm and a daily peak volume flow rate of 120,000 cfm.
Results from the monitoring program indicated that the peak building loads were significantly less than those that were projected. The hourly average volume flow rates during working hours were just over 70,000 cfm, with a maximum hourly volume flow rate of only 85,000 cfm, indicating that the diversity factors assumed for the fume hoods were well below the actual operating environment. As a result, the actual annual energy consumption for 2008 was only 180 MW hrs/yr, a savings of nearly $96,000 for the year.
Biography:
Brad Cochran is a registered professional engineer in the State of Colorado and has nearly 20 years of experience conducting wind-tunnel and mathematical modeling studies related to laboratory exhaust design. Mr. Cochran has managed projects for such clients as Harvard University, the National Institutes of Health, University of Texas Medical Center, Loyola University, Genentech, and the University of California to name a few.
Mr. Cochran is active in ASHRAE and is currently serving as the lead author of Chapter 9, Exhaust Stack Design, in the upcoming latest edition of the ASHRAE Laboratory Design Guide.
Mr. Cochran also served on the Air Movement and Control Association International, Inc. (AMCA) Induced Flow Fan Certified Rating Program (CRP) Committee that developed AMCA Standard 260-07, "Laboratory Methods of Testing Induced Flow Fans for Rating."
During the past decade, Mr. Cochran has focused on defining new design techniques to minimize the energy requirements for laboratory exhaust stacks. In 2005, Mr. Cochran developed the first laboratory exhaust system that utilized local wind data to minimize exhaust fan horsepower requirements, and in 2008 introduced the concept of monitoring chemical constituents within the exhaust manifold to reduce volume flow rates when the exhaust is essentially "clean." Both of these techniques are either in use or under development in laboratories across the country.
He has authored and presented several papers on the subject of energy-efficient laboratory exhaust design for ASHRAE, Labs21, R&D Magazine, Lab Manager, LabWize, the International Facility Management Association (IFMA), AMCA, and the Air and Waste Management Association (AWMA).