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# Belt driven Fans - Fan vs. Motor Speed

## Fan vs. motor speed in belt driven fans.

Belt driven fans are used in heating, ventilation, air-conditioning and cooling (HVAC) systems.

The speed of a fan wheel versus the speed of the motor with a belt drive can be calculated as

df nf = dm nm                          (1)

where

df = pulley diameter fan (inch, mm)

nf = speed of fan (rpm - rounds per minute)

dm = pulley diameter motor (inch, mm)

nm = speed of motor (rpm - rounds per minute)

### Example - Speed of Fan

A synchronous electrical motor rotates with speed 1000 rpm. The motor pulley diameter is 76.5 mm and the fan pulley diameter is 205.5 mm. The speed of the fan can be calculated by modifying (1) to

nf = dm nm / df

- or with values:

nf = (76.5 mm) (1000 rpm) / (205.5 mm)

= 372 rpm

## Related Topics

• ### Ventilation

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• ### Fans - Troubleshooting

Guide to troubleshooting fan problems.
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Pulley (Sheave) selection charts for motors ranging 850 - 3450 rpm.
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Pulleys, blocks and tackles.

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## Citation

• The Engineering ToolBox (2005). Belt driven Fans - Fan vs. Motor Speed. [online] Available at: https://www.engineeringtoolbox.com/belt-fan-motor-d_871.html [Accessed Day Month Year].

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