VAV Laboratory Exhaust Control Systems: The Sequence of Operation, What Works and Why From the Real World Perspective to Save Energy and Achieve Compliance With ANSI Z9.5 2012 and the New California Title 24 Requirements

Richard Yardley, Newmatic Engineering
Roger Gedminas, Spira-Loc

Laboratory exhausts systems for VAV labs need to maintain design parameters (typically 3000 feet per minute discharge velocity) in a dynamic system. The system curve is not static, since terminal devices are constantly re-positioning. The plenum most operate in a stable fashion in this pressure-independent environment.

A bypass air is typically added to allow outside air into the plenum to maintain a discharge velocity from the fan(s). If the fan is sized properly (or the multi-fan plenum is operated properly), savings can be safely maximized by minimizing the use of outside air.

Parallel blade dampers should be used for isolation dampers, opposed-blade dampers (OBDs) for bypass-air dampers. Dampers must be sized to have proper damper authority.

Mechanical configuration options include a bypass damper with fan airflow measurement, or a bypass damper without fan airflow measurement.

Spending time on developing a proper sequence of operation is time well spent! Fan staging, maximizing the use of VFDs (and minimizing the use of bypass dampers) should be considered. Prevent pressure loss or over-pressurization of the plenum while staging fans, calculate what combination of fans and speed control is optimal for which operating conditions, and program/commission your system to actually work that way.

Learning Objectives

  • Understanding the economic impact of laboratory VAV exhaust air systems.
  • Understanding VAV lab exhaust design fundamentals.
  • Understanding stack height / discharge velocity and how they affect energy consumption.
  • Operational efficiencies in VAV Laboratory facilities


Richard Yardley is a professional engineer in mechanical engineering and supplies mechanical systems that require sophisticated application engineering. He works on designs, understands system operation, and does startup and commissioning. His goal is to deliver unprecedented operational efficiency to his customers for their high-energy-use mechanical systems.

Roger Gedminas is a professional engineer in mechanical engineering and a certified balancer. He is typically retained by his customers to analyze their systems and to deliver the efficiency that was promised to them in a conceptual design. Understanding both the engineering and the real-world application of technology, he is able to deliver exceptional process control and energy efficiency to his customers.


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