Energy Saving Strategies for Laboratory Exhaust Fans

Brad Cochran, CPP Wind Engineering, Inc.
Jim Meats, Loren Cook Company

With labs consuming 30-100 kilowatt-hours of electricity per square foot per year (2 to 7 times the average office space), energy saving strategies are more important than ever. . Over the years, the primary focus on reducing energy consumption in the laboratories is to address methods to either reduce the air flow requirements or reduce the thermal conditioning requirements. However, the exhaust fans are often left untouched because rules of thumb associated with prescriptive designs limit the minimum volume flow rates and exit velocities out of the exhaust stacks. As a result, as the ventilation requirements within the laboratory are reduced, the amount of air flow through bypass dampers on the exhaust manifold are increasing, in order to maintain minimum acceptable exit velocities. More recently it has become possible to employ variable air volume (VAV) lab exhaust strategies that maintain performance and safety while reducing energy consumption. Primarily, these strategies focus on the ability to reduce the exit velocities out of the top of the stack and the volume flow rates through the bypass dampers, when either wind conditions or chemical concentration within the manifold meet certain criteria. These VAV control strategies may work adequately in some situations, however, depending upon the complexity of the site and the chemical usage within the laboratories, these strategies may not be the most energy efficient approach because the opportunity to reduce the exit velocity out of the top of the stack may be limited.

This presentation will evaluate several of the VAV exhaust strategies, calculate energy savings potential, and identify keys to successful implementation. Strategies to be examined and compared will include modified N+1, decoupling lab air from plume and dilution air (secondary fan), in-situ monitoring, wind responsive control, and simple turndown control strategies. In addition, tactics will be evaluated for particularly difficult installations including alternative exhaust fan or fresh intake placement, extended stack heights and the like.

The audience will learn key elements necessary to implement each strategy, how to quantify the energy savings, differences in plume rise calculations and how they affect proper fan selection, what data is needed for each strategy, and when to employ a wind tunnel-based or numerical-based exhaust dispersion study.

Learning Objectives

  • Key elements necessary to implement energy saving lab exhaust strategies;
  • How to quantify the energy savings;
  • differences in plume rise calculation and how the affect proper fan selection; and
  • What data is needed for each strategy and when to employ a wind tunnel-based or numerical-based exhaust dispersion study.

Biographies:

BRAD COCHRAN, PE PRINCIPAL/DIR - AIR QUALITY SERVICES CPP WIND ENGINEERING, INC. Brad has over 25 years of experience in wind-tunnel, analytical, and CFD modeling of airflow in and around structures. He has a BS and MS in Mech Eng, an MBA, and a is a PE.He has designed VAV lab exhaust control systems for more than 100 labs in the US, Canada, and the UK.He authored Ch. 9 'Exhaust Stack Design' in ASHRAE's Laboratory Design Guide; serves on the ASSE Z9.5 committee and is Chair of ASHRAE TC9.10

JIM MEATS, PE VP/MARKETING LOREN COOK COMPANY In the industry since '82, Jim holds a BS in Eng from Kansas State Univ and is a PE (MO). Jim started his career designing mechanical and electrical systems for commercial and industrial projects. He has been in HVAC mfg since 87 with both air moving and control companies. Jim serves on the AMCA Board of Directors and has been active on AMCA technical committees in air movement, air control and sound control.

 

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