Imagine you have a regular light switch and a dimmer switch for a light bulb. A regular switch only has “on” and “off,” while a dimmer lets you control how bright the light is. A VFD is like a dimmer switch for a fan motor – it lets you control the fan’s speed. Changing the fan’s speed with a VFD also changes the motor’s horsepower (its ability to do work) and torque (its turning power). Let’s break it down for centrifugal fans (the most common type).
Fan Speed Adjustment
Why and How to Vary Speed in an Industrial Centrifugal Fan
A variable-speed fan is just what it sounds like. In this case, we’re talking about an industrial centrifugal fan that is capable of operating at more than one speed. That means it can run above or below the constant motor speed specified. There are several reasons why you would need a variable-speed fan, several ways to do it, and a few things to be careful to avoid when operating at varied speeds.
How to Control Fan Speed
Controlling fan speed for optimal efficiency and performance is as easy as having the right equipment and making a few simple calculations. The ability to control fan speed rests on your motor drive. On direct-driven fan applications, the most common way to change speeds is with a variable frequency drive (VFD). On belt-driven fan applications, a VFD is also useful for simple speed changes. In the absence of a VFD, simple sheave ratio modifications should do the trick. And of course, you need to know the input frequency of the motor and a few simple ratios.