Air Valves Versus VAV Boxes in the Lab Environment: Lessons Learned From Commissioning Agents in the Field

Chris Schmidt, B2Q Associates
Brad Newell, B2Q Associates

When designing, constructing or renovating a laboratory facility, owners and/or design teams often choose to use more traditional variable air volume (VAV) boxes for airflow control for all or part of the labs as opposed to more precise, but more costly, air valves or precision control devices. This presentation explores the various impacts that these decisions have on the building operation, performance, energy use, and maintenance, as well as health and safety. We further explore the financial, operational, and safety tradeoffs that result from these decisions over the lifetime of the building.

Utilizing VAVs rather than pressure-independent air valves can save money during construction but can have lasting impacts. VAVs are inherently less-precise airflow control devices, and therefore can result in a multitude of issues in laboratory control. A primary impact is inaccurate pressure balances and inaccurate ventilation rates, which not only impact health and safety, but also energy consumption. Additionally, VAVs can be hard to control to an exact setpoint, particularly when coupled with fast-acting actuators, and therefore suffer from rapid, fluctuations in airflow, also known as hunting. This hunting impacts the control of the labs, and can result in annoyances to staff, and often results in the premature failure of the actuators. Failed actuators often go unnoticed for extended periods, during which the labs are not under safe or efficient control.

In addition to the impact on controllability, the choice of using VAV's often results in turndown limitations. With constantly changing laboratory ventilation standards, there is a significant opportunity to lower occupied and unoccupied ventilation and reduce energy dramatically. However, unlike most air valves that can turn down to 10%-20%, VAVs typically have limited turndown, often only being able to turndown accurately and reliably to 25%-40% flow. This inability to turndown is further exacerbated by oversizing the VAVs. As a result, laboratories with VAVs often cannot reach the lower occupied/unoccupied ventilation rates, resulting in permanent excess ventilation, unnecessary energy use, and poor performance and comfort in the labs.

Alternatively, pressure-independent airflow control devices or air valves, solve many of these issues, and while more expensive initially, if designed and setup properly the use of air valves can result in significant energy and maintenance savings over their lifetime, as well as improved laboratory safety, performance and comfort.

Learning Objectives

  • Become familiar with basic laboratory ventilation terms, concepts, and requirements for laboratory ventilation
  • Identify the different types of airflow control devices for lab environment and their differences
  • Better understand the impacts of airflow control devices on ventilation system performance
  • Review design consideration impacts on initial costs versus long-term operating costs, safety, occupant comfort and research

Biographies:

Chris is a Vice President with B2Q Associates and is a mechanical engineer with a Masters of Science in Engineering from the University of Dayton, with a focus in commercial and industrial building energy efficiency. He has over 17 years experience working in building efficiency, HVAC mechanical and controls systems optimization, re-commissioning, and project management and he co-teaches the Association of Energy Engineers Existing Buildings Commissioning course.

Brad is a Project Manager with B2Q Associates and is a mechanical engineer with a Master of Science in Engineering from the University of Massachusetts, with a focus in industrial building energy efficiency. He has over 4 years of experience working in energy efficiency, controls systems, project oversight, implementation and commissioning.

 

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