What are the other factors to consider when choosing an Energy Efficient Motor?

Answer by Hugh Falkner (Atkins)

Apart from the saving of energy, money and carbon, energy efficient motors have other indirect impacts that can make them more, or less, attractive:

  • Energy efficient motors have less energy losses, and so produce less heat.  This is particularly important in cooling applications where extra work has to be done to remove this heat.
  • The lower losses mean that it can be possible to use a smaller fan, making the motor quieter.  This is particularly important in hospitals and other residential applications.
  • In order to comply with IEC dimensional standards, the distance from the mounting holes to the front face, and the height and diameter of the shaft, will always remain the same.  It is therefore the length from the Non Drive End (usually fitted with a fan) to the motor mounting holes that will increase as efficiency is increased.  This should be checked for fit, as it might be a problem in compact packaged machinery.  The use of Copper rotor motors allows for a smaller and more compact package.
  • Higher efficiencies are most commonly achieved by the use of additional active material (steel and wire), which means greater motor weight.  This may be a problem where the supporting structure has limited strength.
  • Energy efficient motors will have a lower slip, and so will run slightly faster, providing more power to the load. In some uncontrolled applications this will reduce the energy saving.  This disadvantage can be overcome by the use of improved controls or slight re-specification of the transmission or driven load.
  • During start up, the motor current will be much greater than during normal operation.  In frequent cycling operations, the higher inertia of the heavier motor means that these start up losses will last for longer, and so the overall energy saving benefit will be reduced.
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