How System Requirements & System Effect Can Fail the Fan
When the operation or efficiency of a fan is off, people often jump to the conclusion that the fan isn’t working. We get it. The fan is an easy and obvious target. It’s big, with moving mechanical components. It needs power and makes noise. It blows a lot of hot air. But don’t be too quick to judge this essential component of your system. Often, the problem is not the fan, but rather the fan’s design capability doesn’t match the system requirements, or there’s a negative system effect.
Making the Call
Don’t get us wrong – we love hearing from our customers. No matter what the reason is for poor fan performance, we are here to help you solve it. We want you up and running, productive and efficient. But the fact is that when we get a call about a fan not working, often the fan is functioning exactly as intended.
So what’s the problem? Remember, a fan is a basic machine. It simply moves air in response to three primary components. They are wheel size, speed/RPM, and the pressure or resistance that it’s trying to move the air through. In diagnosing the cause of poor fan performance, we recommend looking in two key areas before spending time on maintenance:
- Test System Requirements – air volume, pressure, temperature, etc.
- Check for System Effect – fan installation, ductwork, etc.
Back to Basics: Take System Measurements and Compare Findings with Fan Design
First, let’s look at the original fan design specifications compared to the actual system requirements. Do they match? It could be as simple as a fan specified for a pressure of 10,000 cfm at 20 inches w.g., but the application is actually 30 inches w.g.. Now, the pressure could be off for multiple reasons, and system troubleshooting may resolve the issue. However, the fan will simply respond to what the system tells it to do.
You need to verify the original specifications when your fan was selected – air volume, fan static pressure, and temperature. You can do this with some simple field measurements.
- Measure the air flow & pressure at the fan inlet and outlet (different inst./drill hole in duct/best reading with laminar flow/long section of duct/talk to our engineers for recommendations)
- Take a temperature reading at the fan inlet
Don’t panic if your system measurements don’t match your original fan specification. System troubleshooting may reveal a few things causing the problem that are simple to address. If you find the system really does need more than originally calculated, a few tweaks to the fan in the field may be all you need. if you do find that you’ve specified incorrectly, see if you can make adjustments in the fan system to bring it in line with the fan you have already selected and installed.
The Environment: Fan System Effect
Now you have confirmed that your fan design matches your actual system requirements. Next, it’s time to check the broader fan system effect. You need to look at both the inlet and the outlet of the fan, and the ductwork that carries the air to and from the fan.
Watch for things like twists and turns where there should be straight ductwork. These are often due to space constraints. Though not ideal, there are solutions like an inlet box to adjust for necessary angles.
Once you’ve identified a fan system effect, you have a great starting point for a conversation with an application engineer. The fan manufacturer can identify these issues in the design phase, and may also be able to help with resolution if necessary.
Hear it from the Application Engineer
Senior Application Engineer Fred Besasie provides a brief overview and demonstration of some do’s and don’ts in fan specification, fan system design and problem diagnosis in this 2⅓-minute video.
When you’re ready to start your project, reach out and connect with one of our application engineers to discuss the details of your specification.
Related Content on Industrial Fan Applications
If this article raises additional questions, you might find answers in several other articles on our site. Here are a few that might be of interest:
- Fan Selection: How to tell us what you need
- Inlet Box: Do You Need One in Your Industrial Fan Application?
- Inlet Air Density Calculations for Centrifugal Fan Applications
- Understanding Fan Static Pressure
- How to Avoid Problems with Your Industrial Exhaust Fans
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