January 2011

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Alarms Lead to Reactive Operations
An alarm event indicates that a problem has already occurred.

Paul Ehrlich, Ira Goldschmidt & Angela Lewis
Building Intelligence Group

As published
Engineered Systems 

January Issue - Column

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Alarms are a common part of nearly any building automation system.  Building operators are expected to monitor and respond to alarms.  Although responding to alarms is an important part of building operations, it is generally a reactive process.  An alarm event indicates that a problem has already occurred.  For example, an alarm may be triggered if the static pressure across a filter within an air handling unit reached the threshold.  By the time this occurred, it is quite likely that indoor environmental quality has been negatively impacted for the last several weeks or months, not to mention an increase in fan energy consumption. 

As building operations practices transition from reactive to proactive, it is necessary to consider if responding to alarms is really the most efficient way to operate buildings, especially high performance buildings.  What if predictive algorithms could be imbedded within building automation systems to help operators proactively detect when an alarm event may be triggered in the future?  This could allow the operator to take action to prevent the alarm event from occurring to begin with. 

The concept of predictive algorithms is not that futuristic.  Predictive control algorithms, also called fault detection diagnostics (FDD), have been an area of research for many years and have been implemented within some packaged equipment, as well as within some standalone software programs.  Packaged equipment with FDD algorithms ranges from local chiller controllers to packaged rooftop controllers.  FDD algorithms within controllers could include, but are not limited to:

•    Identifying when a sensor, or actuator has failed
•    Auto-tuning of loops
•    Troubleshooting of equipment when improperly installed
•    Detecting and avoiding problem conditions. I.E. use of an alternate refrigerant circuit when coil frost is detected, or detecting a chiller surge condition and backing off the vane position.

[an error occurred while processing this directive]Uses of FDD algorithms within standalone software programs include, but are not limited to assisting with commissioning of HVAC systems and chiller plant optimization.

Although the use of FDD in rooftop units are estimated to help reduce energy consumption by 10 percent or more, the largest barrier to implementation is that FDD applications often require fault thresholds and statistical parameters for each unit to be determined on a case-by-case basis.  This can make implementation time consuming and expensive.  

Ideally fault detection algorithms could easily be incorporated as an integrated part of building automation systems.  The use of open protocols, factory integrated controls, and new software applications will help to make this a reality.  As FDD algorithms occasionally found today in packaged controllers are incorporated into BAS, more advanced predictive control strategies may be able to be successfully incorporated as well.  These strategies could include:

•    Predictive control using active and passive thermal storage
•    Weather forecast driven control strategies
•    Electric power load forecasting

As more building owners and facility managers seek to have high performance buildings and transition to proactive management practices, FDD and predictive control algorithms will become of higher interest.  However, in order for FDD and predictive control to become more than research concepts the market (engineers, building owners, facility managers and building operators) will need to ask for it.  

This month’s column is courtesy of our associate Angela Lewis.  She can be contacted at angela@buildingintelligengegroup.com


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