Best Energy-Saving Opportunities for Motors
Motors are major consumers of energy in industrial and commercial facilities. Equipment such as pumps, chillers and compressors all have motors performing a mechanical function. Mark Farrell, program manager and energy coach, draws on his many years of experience to provide some insights into the best opportunities for reducing motor energy use.
1. Turn motors off when not in use
The biggest energy-saving opportunity for motors is to turn them off where they’re not being used. There’s a perception that it costs a lot of extra energy to turn a motor on, so they’re often left on during breaks. There’s a slight bump in energy use when you turn a motor on, but it’s a lot smaller than most people think.
Starting and stopping motors isn’t just an energy issue, it’s also a wear and tear issue. There are guidelines that tell you the number of starts and stops in a motor, which takes into consideration the wear and tear. For example, a 50 horsepower (hp) motor will have fewer starts and stops allowable over a one-minute period than a 3 or 5 hp unit. Those guidelines are spelled out in NEMA Standard MG 10 and they’re set up to cover wear and tear issues.
If a motor is going to potentially be off for five minutes or more, that’s an energy-saving opportunity. If it’s a smaller (two or three hp) motor, there’s an opportunity to shut it down that’s often overlooked.
For example, a single 10 hp motor operating 25% of the time at idle would consume roughly 1.0 kWh per day at idle. That would be around 200 kWh per year, which at an electric rate of 0.08/kWh would cost about $16 annually. If the motor operated at partial load, such as running an empty conveyor belt, that number could be ten times larger or $160 per year.
2. Right-size your motors
Make sure your motor is sized appropriately. Often, you’ll see motors that are oversized. That’s a good opportunity; the motors are wasting a lot of energy because they’re not operating in their most efficient zone.
For more information about determining if your motors are oversized and the potential savings from downsizing, see the U.S. Department of Energy fact sheet Replacing an Oversized or Underloaded Motor.
3. Add variable frequency drives
Another very common opportunity is to look at the motor load. If you have a varying load in the production process, such as a fan or a pump, that may be a good opportunity to add a variable frequency drive (VFD).
For more information about the energy-saving potential of VFDs in your facility, see Adjustable Speed Drive Part-Load Efficiency from the U.S. Department of Energy.
In the end, you want to be sure that the amount of energy being consumed fits with the application.