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Silence of the Fans

By April 26, 2016December 26th, 2021Briefs

Hannibal: Then something woke you, didn’t it? Was it a dream? What was it?

Clarice: I heard a strange noise.

Hannibal: What was it?

Clarice: It was…screaming. Some kind of screaming, like…

Rarely does a building speak when something’s wrong, but sometimes it does. Among the multitude of equipment in a building, fan motors are one, in particular, that tend to “scream”.

Screams and Squeals

When a fan is humming away, there is nothing to fear as it is operating as it should. However, if it starts to make odd noises or “scream”, it’s a sign that something is amiss. Older, dry bearings or loose belts at high speed can cause a screaming/squealing noise and reduce the efficiency of the motor operating the fan. Larger fan wheels driven by three horsepower motors and larger can also have resonant frequencies (speeds) that can cause excessive vibration and noise. Variable frequency drives can be used to keep fan speeds away from these noise-making frequencies.


Other times, personnel may hear a whistling noise coming from the mechanical room. It’s not the boogeyman, but rather an air handler blowing air through a small hole or gap in the casing. Making sure the air handler is properly sealed is important to get the conditioned air where it is needed and eliminate waste. While it is easy to make the hole or gap larger so the whistling stops, it doesn’t fix the problem.

Nighttime Roaring

For larger air handling units, it’s normal for the fans to be quite loud and almost “roar” in the mechanical room during normal operation. However, the fans don’t need to be roaring all the time and consuming large amounts of energy – especially at night! This is very common and can go unchecked for months until somebody stumbles into the mechanical room at night to notice it. Maintaining and verifying proper scheduling can have definite and immediate energy savings. This can even be taken one step further by reducing the fan speed during occupied hours through demand controlled ventilation controls.

In general, it’s always a good idea to keep up on maintenance and periodically walkthrough the building during both “occupied” and “unoccupied” periods because it’s a great opportunity to see and hear how everything is functioning. However, at night the building should be relatively quiet…

Michaels Energy

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