March 2015

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Lab Hood Control

Ideally the more data that can come back into the BAS, the better the facility operations team can work with the lab staff to make sure that things are being operated efficiently. 

Paul Ehrlich, Ira Goldschmidt & Angela Lewis
Building Intelligence Group

As published
Engineered Systems 
March Issue - BAS Column

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The use of chemical and biological agents often requires a laboratory fume hood for conducting experiments and storage of dangerous materials.  You will find these hoods in facilities ranging from research centers, and hospitals to schools.  Controlling these laboratory areas is a challenge, since proper control needs to focus on protecting the lab occupants as well as those in adjacent spaces.  Labs may also have specific requirements for temperature and humidity that need to be maintained.  While all of this is challenging, it is even more complicated to do it in a manner that is reliable and as energy efficient as possible. 

The basic concept for labs is to utilize exhaust to safely remove contaminants from the occupants and away from the space.  Exhaust is usually provided at the fume hood, but can also be provided in other areas including general and bench exhaust.  The lab space needs to be provided with adequate make up air to balance the exhaust and should remain slightly negative to adjacent spaces.  Of course at the same time, temperature (and optionally humidity) conditions need to be maintained as well.

Hood Control:
Fume hoods generally consist of an enclosed bench with a movable sash.  The sash is generally opened to set up and access work on the bench and should be kept closed (or near to closed) the rest of the time.  Hoods are usually provided with an integrated controller that measures the sash position and air velocity and can then adjust an air valve to vary the flow rate from the hood.  The sash controller also provides indication for the lab occupants of air velocity (or differential pressure) and may also include an alarm if the sash is left open.  Most hood controllers can be integrated into a BAS using open protocols such as BACnet or LonTalk.

Room Control:
The control of the room air includes both temperature control as well as pressurization control.  While there are several ways to do this, ideally lab pressure should be controlled in relation to adjacent spaces so that the lab can maintain an overall slight negative pressure.

The challenge with labs is that they need to be designed for safe removal of contaminants which is energy intense.  In reality though, the usage of lab spaces varies greatly.  At times there may be a lot of experiments or materials present.  At other times, there may be little activity going on in the lab.  This requires both careful design to make sure that systems are able to react appropriately to changes in key factors such as hood mode and sash position.  It also requires ongoing coordination with the lab users so that they understand the systems and how to operate them in a safe and efficient manner.  For example practices such as closing sashes at night can have a large impact on the efficiency of a lab environment.  Ideally the more data that can come back into the BAS, the better the facility operations team can work with the lab staff to make sure that things are being operated efficiently. 

About the Authors
Paul and IraPaul and Ira first worked together on a series of ASHRAE projects including the BACnet committee and Guideline 13 – Specifying DDC Controls. The formation of Building Intelligence Group provided them the ability to work together professionally providing assistance to owners with the planning, design and development of Intelligent Building Systems. Building Intelligence Group provides services for clients worldwide including leading Universities, Corporations, and Developers. More information can be found at  We also invite you to contact us directly at or


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