Engineering Notes Index

Minnesota/Wisconsin Engineering Notes
Fall 1998

Reducing Fan Noise from Grain Systems

Bill Wilcke, Minnesota Extension Engineer

Noise from grain drying and storage fans is a frequent concern for people who own, operate, and/or live near grain handling facilities. Axial-flow fans, the noisiest type of fan, are the most common type used at many grain drying and storage facilities. These fans have a barrel-shaped housing with the motor and a propeller-like impeller mounted inside the housing. Air enters one end of the housing and moves straight through the impeller, over the motor, and out the other end of the housing. They are usually the cheapest type of fan and often the most efficient type for grain drying and storage applications, but they are by far the noisiest type. Here are some possible approaches for dealing with noise generated by axial-flow fans and for making life more pleasant for workers, owners, and neighbors.

• Experiment with homemade sound barriers. The side of the barrier closest to the fan should be made of some kind of porous material like fiberglass, or perhaps hay or straw. The barrier should be placed as close to the fan as possible, without restricting airflow. Try to maintain a separation distance of at least one fan diameter. For example, place the barrier at least 24 in. away from a 24-in. diameter fan.
• Try repositioning fans so that they point away from offices or homes, and away from surfaces like metal bins or buildings that reflect sound waves.
• Consider installing commercially available silencers on fans. Contact dealers that handle grain drying and storage equipment to see if they can get silencers that would work on your fans. If you have trouble finding silencers locally, try contacting Alanco, a company in Falls City NE ((800) 500-9777) that manufacturers a variety of specialty grain drying and storage equipment, including silencers.
• Consider replacing axial-flow fans with conventional centrifugal or in-line centrifugal fans. A centrifugal fan has a wheel-type impeller (sometimes called a squirrel cage impeller) that pulls air in through the side of the wheel and forces it out at a tangent to the wheel. The main difference between conventional centrifugal fans and in-line centrifugal fans is the way the impeller and motor are mounted relative to the housing. For conventional centrifugal fans, the shape of the housing matches the shape of the impeller and the motor is mounted outside of the housing. From the outside, in-line centrifugal fans look like axial flow fans; the impeller and the motor are both mounted inside a barrel-shaped housing.

Both types of centrifugal fans are much quieter than axial-flow fans, but unfortunately, they are also more expensive. The performance characteristics of centrifugal fans can be quite different from those of axial-flow fans that have the same horsepower rating. So if you decide to replace axial-flow fans with centrifugal fans, examine the costs carefully and make sure that the new fans provide the airflow needed. The FANS computer program (available from our department’s WorldWideWeb site at www.bae.umn.edu/extens/harvest.html) can be used to help select the proper size and type of fan.

This page is part of the Biosystems and Agricultural Engineering Department web at http://www.bae.umn.edu/