Impact of System Effects on the Centrifugal Fan Performance Curve

Wondering why your fan is underperforming? If your application system effects were not calculated into your original fan specification, you might be experiencing performance below the expected centrifugal fan performance curve from the manufacturer.

What are System Effects?

System effects are anything that makes your application different from the “ideal” conditions assumed when developing the centrifugal fan performance curve during the design and testing phases if not specified otherwise.

As described in the article Mitigating System Effect to Optimize Fan Performance and Efficiency ( by Mike Humann in the 2020 edition of the Air Movement and Control Association International (AMCA) inmotion magazine, “System effect refers to losses in air-system performance caused by adverse flow conditions (excess turbulence or swirl) at or near the fan. System effect can occur at a fan’s inlet or outlet or both. Often, it results from changes to system design—commonly involving the length, width, and/or transition points of ductwork—made during the fan-installation process.”

There are many elements of fan applications and installations that can affect the centrifugal fan performance curve, for example:

  • Inlet boxes
  • 90-degree elbows in front of the inlet of the fan
  • 90-degree elbows off the outlet of the fan, especially in directions unnatural to the rotational flow of the air
  • Rapid changes in gas velocity close to the inlet or outlet

In the video above, you can see a detailed example of how unintended system effects can impact the centrifugal fan performance curve.

5 Ways to Reduce the Impact of System Effects on the Centrifugal Fan Performance Curve

Once you know how the surrounding ductwork and fan installation can affect the system, there are several things you can do to help reduce the impact.

1. Know your application and include known system effects in your original fan specification

Application engineers can make recommendations and accommodations in the design phase to help minimize the losses in air system performance after installation.

2. Follow the Installation and Operations Manual (IOM)

Your fan always comes with an IOM. If you follow the instructions during installation and operation, you have a much better chance of achieving the specified centrifugal fan performance curve.

3, Involve an Application Engineer During Installation

An application engineer from the fan manufacturer or your local rep can help you avoid costly mistakes during installation. Don’t be afraid to ask for help!

4. Increase Fan Speed to Get Closer to the Curve

If your fan is already installed and experiencing unplanned system effects, you can add speed (if you have the amperage available) to increase performance, but be sure to keep it within the max safe speed, and remember this will add energy consumption and cost.

5. Adjust the Surrounding Ductwork and/or Accessories

Just as you would during installation, you can consult with an application engineer to help you identify opportunities to adjust your system to mitigate negative effects.

Hear it from an Application Engineer

Chet White, Senior Application Engineer / Sales Manager runs through a detailed demo of system effects on the centrifugal fan performance curve in this 2½-minute video. To ask questions, get more details, or discuss your application, reach out and connect with one of our application engineers.

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