How to Troubleshoot Fan Performance Issues

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Industrial fan troubleshooting can seem complex, but in a way, it’s pretty simple. Know what to look for and/or who to call for help.
AirPro Sales Manager / Senior Application Engineer Chet White walks you through a detailed fan troubleshooting exercise in this in-depth whiteboard video.
Full Transcript:
We’re going to look at troubleshooting fan issues.
Disclaimer: This is based on 11 years of experience of one fan engineer. It does not necessarily cover all possible fan problems, nor does it represent all possible solutions.
It starts with a system problem. A producer of products or materials with a system - or an original equipment manufacturer of a system - that requires a fan to operate, and the system is not working properly or at all. You’re not getting the output that you need from the system. We’re starting with the assumption that you consider the fan to be the problem and you need a solution. We need to look at what we need from you in order to troubleshoot properly.
First, we’re going to ask you to verify a couple of things that may seem very basic, but you’d be surprised how many issues this catches.
Rotation and Speed:
Rotation: In a centrifugal fan, you’ve got an inlet and an outlet. The outlet always indicates how the wheel needs to spin. Check to ensure the fan moves the air in the correct direction from the inlet to the outlet. If you’re not getting the pressure you need, consider reversing the rotation to determine if that might be the problem
Speed: We ask to verify speed because you’re probably getting your speed reading off of digital output. Most of the time, it’s correct. In order to be sure, we ask you to go find the shaft that’s driving the fan wheel and put a tachometer (tach) on it. Put the guard back on. There should be a hole in the guard so you can read the tach with a laser to verify the operating speed and make sure there’s not a connection issue in your electrical readout.
Measurements & Info: We, as fan engineers, want to help you solve this problem. These are the measurements and information most commonly needed:
Horsepower: The horsepower being consumed by the motor doesn’t lie. We use a calculation to figure out what your motor horsepower is and relate it to the fan curve. To do that, we ask you for:
Voltage, Amperage, and Photo of motor nameplate.
Temperature: We need to verify the gas temperature at the fan inlet. The reason we’re only asking for temperature is because we’re assuming it’s only air. If you’re working with a gas that is not just air, we also need you to calculate and send us the density of the gas or give us all the properties of the gas and let us calculate it.
Static Pressure: This is fairly easy to read in the field using a gauge through a hole at the inlet and the outlet. Give us those two numbers so we can look at the differential.
Volumetric Flow: This is extremely difficult to measure accurately. We can use the other information provided to calculate it.
Solution: Start by creating the ideal fan curve at your actual conditions. This may vary from the fan curve provided by the manufacturer because conditions make a difference.
A fan engineer plots your fan curve with calculations using the above information, with the volume on the horizontal x-axis and the static pressure on the vertical y-axis. As volume grows, static pressure drops. We also plot a horsepower curve on the same grid and cross the fan curve at a certain point.
Find your specific horsepower on the calculated horsepower curve with your given conditions. Draw a vertical line from the point on the horsepower curve to find the point where it crosses the ideal fan curve to determine the related static pressure. Now see if those points on the ideal fan curve match your actual calculations. It might. It might be related to system effects like duct length, constraints, or 90-degree turn if it doesn't.
Pictures: We need photos of your installation to compare the ideal to the actual. That can help us identify the source of the issue if it’s truly related to the fan.
Investigation: If things still don’t make sense based on your curve calculations and comparisons, there might be something else going on or other actions you can take.
Possible faulty fan design that must be corrected. This is unlikely if you’re working with a reputable fan manufacturer, but not impossible.
Check the system thoroughly for things like leaks bringing unwanted air in
Bring in a fan engineer to investigate fully and identify the appropriate solution. There’s nothing wrong with starting here - they might get to the solution faster.
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