The Journey to VAV Laboratory Exhaust Stack Control at UC Davis

Brad Cochran, CPP, Inc.
Justin Lewis, UC Davis

The University of California at Davis has recently begun a project to convert many of their laboratory exhaust systems from constant volume control to variable air volume (VAV) control. Prior to undertaking this project, the University underwent a due diligence assessment to determine the economic and safety implications associated with VAV exhaust strategies. This presentation will provide insight into the steps that the University undertook to during their decision making process. This involved discussions with building safety officers, the environmental health & safety department, campus design engineers, and facility maintenance personnel. Special attention was paid to developing and fully understanding an appropriate concentration design criterion for the laboratory exhausts, based on the types and quantities of chemicals expected to be used within the laboratory's fume hoods.

Once the due diligence assessment was completed, the decision was made to move forward with a pilot project at the Plant and Environmental Sciences (PES) laboratory. The first step involved dispersion modeling to determine the minimum volume flow rates through each of the exhaust systems that would provide adequate plume rise, as a function of wind speed and wind direction, in order to maintain acceptable air quality at all nearby air intake, operable windows, roof top worker locations, and pedestrian plaza locations. The dispersion modeling results, along with operational data of the exhaust fan performance, were combined to develop an updated sequence of operation. The University's in-house controls engineers were used to convert the sequence of operation into control code for each the laboratory exhaust systems. Additional hardware included variable frequency drives on each of the fan motors and a sonic anemometer to measure the local wind speed and wind direction.

In addition to providing insight into to the decision and implementation processes, the presentation will also provide a post-facto assessment of the process along with actual measurement of the realized energy savings.

Learning Objectives

  • Understand the process that UC Davis went through to determine whether it was appropriate or not to implement VAV laboratory exhaust strategies on their campus. How they identified who were the stake holders and how they were brought on board in that decision making process.
  • Learn the process of how a normalized concentration design criterion is developed for a laboratory exhaust system and how the development of this criterion can impact the current and future chemical usage within the laboratory fume hoods.
  • Understand the implications of employing a VAV laboratory exhaust system and that special care should be taken, via dispersion modeling, to ensure a safe working environment. Learn why, rules of thumb, i.e., 3000 fpm exit velocities should not be used as the design basis for reducing flow rates.
  • Learn about the significant energy savings that can be obtained by converting existing constant volume laboratory exhaust systems to VAV control.

Biographies:

Brad Cochran is a registered PE in the State of Colorado and has over 20 years of experience designing laboratory exhaust systems.

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 wind responsive exhaust system to minimize fan horsepower requirements. Since then he has been involved in the design and implementation of several dozen VAV laboratory exhaust systems.

Justin Lewis, PE, LEED, Sr Energy Project Manager at UC Davis. Mr. Lewis oversees the Energy Projects & Commissioning team which develops and implements numerous energy projects across the campus, including projects under the Statewide Energy Partnership (SEP) program. His team is leading efforts to improve energy efficiency across the campus through HVAC system upgrades and improved monitoring and control systems. Prior to starting at Davis, Mr. Lewis helped save 14 data centers around the country

 

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