Downsizing motor that drive fans

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Discussion Overview

The discussion centers around the feasibility of downsizing the motor that drives a fan, specifically in the context of reducing power consumption while maintaining airflow control without the use of a damper. The scope includes theoretical considerations and practical implications related to motor selection and fan operation.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant questions whether downsizing the motor could allow for operation at a lower RPM, potentially eliminating the need for a damper to control airflow.
  • Another suggests using a Variable Frequency Drive (VFD) as an alternative approach.
  • A participant notes that RPM is not solely determined by motor size for most AC motors, indicating that typical RPM options are available for selection.
  • It is mentioned that if the fan is belt-driven, resizing the pulleys could be a viable method to adjust RPM.
  • One participant cautions that using a smaller motor does not automatically result in lower RPM, as it primarily reduces horsepower. They emphasize the need to determine the desired volumetric flow rate and consult the fan curve to identify the necessary motor horsepower.

Areas of Agreement / Disagreement

Participants express differing views on the implications of downsizing the motor, with no consensus reached on the best approach or the feasibility of eliminating the damper.

Contextual Notes

Participants highlight the importance of understanding the fan curve and the relationship between motor size, horsepower, and RPM, indicating that assumptions about performance may vary based on specific conditions.

Ming1992
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Hi, I am facing some problem

can i just downsize the motor that drive the fan as currently the fan is operated at full load but the flow rate is controlled by a damper.
my thought is that is it possible to downsize the motor so it will operate at lower rpm therefore we no longer need to use damper to control the airflow.

the implication to it is to lower down power consumption of the motor.
 
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Use a VFD?
 
Rpm isn't a function of size for most AC motors, but you can select from several typical RPMs.

If the fan is belt driven, you could also resize the pulleys.
 
Using a smaller motor won't necessarily mean a lower rpm: it means less horse power. If you want to use a smaller motor, you must first determine your desired volumetric flow rate, and then look at the fan curve for that particular fan to see what minimal motor horse power you need.
 

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