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Part 3: Motors: Impact on Energy Efficiency
By James Piper, P.E.
March 2012 -
Commercial and institutional facilities typically have many more motors operating in their HVAC systems than most managers realize. Because these motors use so much energy, they offer great opportunities to make a significant impact on facility energy use.
By far the leading cause of energy inefficiency with HVAC system motors is a mismatch between the motor's rated horsepower and the load it is driving. Most HVAC system motors are induction motors.
While these motors are efficient and reliable, their efficiency, like building chillers, drops off significantly when they operate under part-load conditions. By properly matching motor horsepower to system load requirements, managers can achieve major energy savings.
Achieving this goal requires that managers conduct a survey on HVAC system motors to identify those that are significantly oversized for the application. The goal of the process is to develop a comprehensive list of applications that use motors, including information on the motor horsepower, the load it is driving, and the age and rated efficiency of the motor.
The focus should be on motors that are oversized or have exceeded their operating life expectancies.
Replacing older, oversized motors with properly sized ones offers two benefits. First, matching the motor horsepower to the actual load improves the operating efficiency of the system.
Second, changes in motor design have resulted in a generation of motors that have operating efficiencies 2-8 percent higher than older, standard motors. Coupled with the improved operating efficiency that comes from matching the motor horsepower to the load, the improvement in efficiency can provide a relatively quick payback for managers and facilities.
A building automation system (BAS) serves as a central nervous systems for building HVAC systems. These systems not only help identify locations in the facility in which energy is used and when it is used. They also give maintenance and engineering managers the tools they need to minimize system energy use while improving comfort.
For a BAS to operate effectively, operating and maintenance personnel must constantly monitor it. Too often, managers simply set up a BAS allow it to run — sometimes for years — without much attention.
But buildings and facilities are not static. Changes to operations are constant. To keep HVAC systems properly matched to building operations while maintaining high operating efficiency, operating and maintenance personnel must constantly review and adjust the BAS operation in order to match those changes within the facility.
James Piper, P.E., is a national facilities management consultant based in Bowie, Md. He has more than 25 years of experience with facilities maintenance and engineering issues.
Part 1: HVAC Energy Efficiency Strategies
Part 2: Boilers: The Biggest Users of Fuel