Belt- vs. Direct-Drive
Belt driven tube axial duct fans have the motor mounted outside the airstream. This is ideal in applications where the air moving through the duct fan is contaminated, high humidity or filled with hazardous gases or dust. In a belt drive configuration, the motor shaft drives a belt-driven pulley which is connected to a second pulley attached to a propeller shaft. Belt driven duct fans offer multiple ranges of RPM speed because of the many sizes of pulley combinations available, which results in a greater range of CFM. Belt driven tube axial duct fans are a great option when noise is a concern. The belt driven fan is generally much quieter because the fan RPM is typically slower. Furthermore, the belts and pulleys cause more friction when in motion, therefore leading to more maintenance and higher energy costs.
Direct driven tube axial duct fans have the motor mounted directly in the air stream. This is ideal for moving air that is clean and dry. On a direct drive duct fan, the motor shaft is connected directly to the fan propeller. Therefore, the fan propeller will rotate at the same RPM as the motor. Direct drive duct fans offer greater efficiency and are nearly maintenance free. The only way to alter the CFM on a direct driven fan would be to change the motor to a different RPM or to use a variable speed control (VFD).
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