Optimizing the Energy Efficiency of Laboratory Exhaust Stacks: Case Study of the California Institute of Technology Designing a New Home for the Center for Global Environmental Sciences (CGES)
Brad Cochran, CPP, Inc.
The California Institute of Technology (Caltech) is currently designing a new laboratory for the Center for Global Environmental Sciences (CGES). The center will be housed in the existing Robinson Laboratory, originally constructed in 1933, on the Caltech campus, in Pasadena, California. The new Linde + Robinson renovation will provide CGES with a state-of-the-art laboratory facility for geochemistry, microbiology, and atmospheric and oceanic science, while restoring the original elegance of the historic building. In addition, the design team is seeking a LEED® Platinum certification and the lowest-energy research lab in the United States.
To achieve these goals it was critical that the laboratory exhaust system be designed to operate in the most efficient manner technically available. This meant that the system should not only minimize the fan horsepower requirements, but it should also do so in a manner that would not adversely affect the air quality within the Linde + Robinson Laboratory or neighboring buildings.
Because of the complexity of the environment surrounding the Linde + Robinson Laboratory, in particular the nearby 146-foot-tall Millikan Tower, adequate dilution of the laboratory exhaust at surrounding receptor locations could not be obtained using the planned exhaust parameters. Therefore, alternate solutions were devised to meet the established maximum concentration re-entrainment criteria at surrounding receptor locations while maximizing energy savings.
In a traditional laboratory exhaust design, the stack heights and volume flow rates are designed to minimize the re-entrainment of the laboratory effluent during critical wind conditions, which is generally at or near the 1-percent wind speed for the site. In this case, a stack that operates safely under the high wind conditions will also operate at acceptable levels under lower wind conditions. In fact, lower wind speeds provide an opportunity to reduce the exit velocities, as discussed during previous Labs21 presentations.
For the Linde + Robinson Laboratory, the critical wind speeds for most wind directions follow this model; however, when the wind blows from the southwest, toward the Millikan Tower rooftop air handler units, the critical wind speeds are significantly lower. Therefore, in order to optimize the laboratory exhaust system, the system has to not only adjust the minimum acceptable volume flow rates based on the current wind speed, but also must take into account the current wind direction.
This presentation will discuss the methodology used to identify the most efficient operating parameters as a function of both the approaching wind speed and wind direction, as well as an indication of the projected energy savings that should be realized by implementing the design approach.
Biographies:
Brad Cochran 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, the University of California at Los Angeles and other University of California facilities, the National Institutes of Health, University of Texas Medical Center, Loyola University, and Genentech, to name a few. While employed at CPP, he has also been instrumental in the development of the U.S. Environmental Protection Agency (EPA)-accepted Equivalent Building Dimension concept for making generic dispersion models more site specific. He has also worked on the development of a new algorithm used to describe plume trajectories under sea breeze conditions. During the past several years, Mr. Cochran has focused on defining new design techniques to minimize the energy requirements for laboratory exhaust stacks. He has authored and presented several papers on the subject for ASHRAE, Labs21, R&D Magazine, and AWMA.