June 2011
Column
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How Far We’ve Come
you can see readily observe the “state of the art” from the 1970’s and 1980’s in many existing buildings

Paul Ehrlich, Ira Goldschmidt & Angela Lewis
Building Intelligence Group

As published
Engineered Systems 
June Issue - Column

 

Often many of us (including the authors of this column) lament on the sad state of affairs of controls. Why are designing controls so hard?  Why don’t systems work the without continued commissioning?  How come the industry isn’t delivering better projects?  But it is sometimes valuable to step back and look at the incredible progress we have made as an industry over the last 20 years.  To go back in time you don’t need a time machine, or even a good recollection for history, you can see readily observe the “state of the art” from the 1970’s and 1980’s in many existing buildings which are continuing to operate, stopped in time, in the same method that they were installed so many years ago.  Here are a few key areas where we have made significant progress over the last 20 years:

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VAV Box Control:
The accurate control of a variable air volume (VAV) terminal requires proper measurement of both zone temperature and the ability to use it to reset airflow.  Early VAV box controls often did not provide the ability to measure airflow and provided pressure dependent control.  These systems result in variations in airflow as the system static pressure varies and rarely result in either good comfort or consistent ventilation.  A step up from pressure dependent control was the mechanical volume regulator, followed closely by the pneumatic and analog electronic volume regulator.  Both concepts can work, if rigorously maintained, but in reality are rarely operating properly providing improper airflow.  These early devices also do not provide the ability to have multiple flow minimums or to provide any feedback to the operator.  The end result of these old solutions is challenges with comfort, ventilation, and energy efficiency.  DDC controls are able to solve all of these problems and to readily support optimization concepts including zone based scheduling and static pressure reset, which is not possible with other technologies. 

Fan Control:
Attempting to control air handler capacity with the use of inlet guide vanes, cones, or discharge dampers is an effective method to reduce duct static pressure.  However it has little impact on reducing fan energy usage, and we are finding cases were this fan energy is causing significant heating during low airflow.  Today the use of variable frequency drives provides a cost effective solution for fan (and pump) modulation which is both more effective and also results in significant energy savings.  Drives provide added benefits including the ability to meter energy usage of key equipment for just the cost of integration. 

CatNet Systems Economizer Control:
On older buildings we frequently find that economizers are not utilized.  When they are used, it is at best, a dry bulb changeover.  While this is a good strategy it tends to run the economizer for fewer hours then may be applicable, resulting in wasted energy.  Deploying and enthalpy or wet bulb economizer is available for little cost with most DDC systems, resulting in improved efficiency and performance. 

These three examples are just a few of the many improvements, which are available for control systems.  The good news is that all of these are readily achievable today, using the current generation of BAS and provide attractive opportunities for upgrade.  Moving to more efficient control provides benefits both in terms of more energy efficient operations as well as improved ventilation, comfort, and operational efficiency. 


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 www.buildingintelligencegroup.com  We also invite you to contact us directly at Paul@buildingintelligencegroup.com or ira@buildingintelligencegroup.com






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