November 2014

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Control of Critical Environments

When designing controls for a critical environment it is imperative to start with a solid understanding of the operational parameters.

Paul Ehrlich, Ira Goldschmidt & Angela Lewis
Building Intelligence Group

As published
Engineered Systems 
November Issue - BAS Column

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Most commercial building system designs including controls and building automation are carefully constructed to balance between reliability, performance, efficiency, and budget.  On all projects the need to provide reliability, accuracy and safety need to be carefully considered as part of the overall design, but when we start looking at critical environments these requirements become paramount in the design process.

Critical environments refer to the areas or systems that are considered to be Mission Critical or in other words facilities or areas where loosing systems such as lights, power or HVAC would result in health, safety or major economic impacts.  Some examples of areas often considered as critical can include:  data centers (generally tier 2 or higher), laboratories, critical areas in hospitals (i.e. operating rooms, isolation rooms, labs), call centers, etc. 

Start by Defining Requirements:
When designing controls for a critical environment it is imperative to start with a solid understanding of the operational parameters.  What areas would be considered critical?  Does a certain range of temperatures and humidity levels need to be maintained?  Are there specific needs for pressure relationships, air changes or outdoor air? Do these requirements vary when the space is occupied or unoccupied?  Are there special emergency modes (such as a purge) required?  What are the requirements for uptime and the impact of a loss of power or space conditioning?  Documentation of the owner’s requirements can be used to drive and test the project design and implementation.

Special Design Considerations:
Design work should be driven from the owner’s requirements.  Much of this is fairly straightforward such as the system selections and specific sequences.  In addition, there are several areas of special requirements that are required for critical environment projects:

Careful consideration should be taken in selecting of both the controls product and contractor for critical environment projects.  Some designers elect to utilize industrial style controls (PLC and SCADA) instead of conventional BAS.  Others elect to only work with control contractors that have demonstrated experience in working in these critical areas.

In summary, controls for critical environments need to start with a good understanding of the requirements, and drive through the design process, contractor selection, installation, and commissioning. 

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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