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Are more fan choices a good thing?

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Are more fan choices a good thing?

Dec 8, 2015

Of course there is an ongoing shift toward direct driven fan assemblies.   Consider the choices available and this discussion is worth some attention.

There is no ‘one size fits all’ answer to these options.

Some facts to consider:

OPTION 1: Belt Driven Fan Any Size Fan

This fan has to be maintained regularly, including replacing belts, pulley alignment.  On the other hand, the ability to control the fan curve and evaluate sound is far easier.

Option 2 Direct Driven Fan Induction Motor

The motor is just as efficient as the belt drive.  A variable frequency drive is required and generally installed remotely.  Attention is required to address the FLA of the motor and drive.  Shaft grounding still an issue in this configuration.

Option 3 Direct Driven Fan EC Motor Single phase up to 2HP

This is a great option for small fans.  Maintenance goes away, no remote drive required, good controllability options for integration to DDC.  Saves money compared to a split capacitor motor.  Probably not a great option for coordinating electrical once the MHP exceeds 3/4HP.

Option 4 Direct Driven Fan Permanent Magnet Motor Three phase up to 30HP

A new option is now available through Loren Cook incorporating permanent magnet motors (PM).  PM motors are more efficient than induction motors, particularly under part load.  (Yes, that’s true.)  No remote drive required.  Easy integration for DDC control.  Warranties on the motor/drive control assembly are longer than traditional.  Prices are coming down.  The motor controls can be limited to reduce the full load amps at the motor.

Summary:

Of course, these options are not limited to PRVs. Just about any fan is a candidate.

Any downside? Of course… Notes below apply to direct drive, EC and PM options:

  • PM motors are more expensive than a direct drive induction assembly plus remote drive, but the gap is quickly shrinking.
  • 860 rpm motors get to be larger, so they may not fit in a small motor compartment.
  • 860 rpm motors are more expensive than their 1140 and 1725 rpm counterparts.
  • FLA needs to be reconciled on the project, or the motors could be significantly larger than BHP
  • Low static fans that require low rpm may be tougher fits for direct drive
  • Often, higher rpm of direct driven fans increase the sound output

The good news is we can evaluate ALL these options.  LOREN COOK’S Compute-A-Fan software will be upgraded soon to allow engineers to select 3-phase direct drive fans, but in the meantime the folks at Air Flow would enjoy the opportunity to look at these fans for you.

Please take a moment to view the full post and check out how Air Flow can help you select the best fan for your needs.

Thanks!

Tom
414.351.7744

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