CLICK PID Tutorial Videos Bonus 1 - How to size an exhaust fan from AutomationDirect

The enclosure we are using in this series of PID videos is rated for 250 degrees max, so it’s really important we choose the right exhaust fan size. But how do we know what size fan to use to keep the enclosure at a reasonable temperature? Well, I know room temperature is around here, and I want to operate the enclosure at 110 degrees. I also know that this enclosure is rated for 250 degrees max and that the 500-watt heater trips it’s thermal safety at around 225 degrees. So, we need a fan that will keep the enclosure below maybe 180 to 190 degrees, just so we have some margin. That will give PID plenty of headroom, so it can shoot for a very high temperature to heat things up rapidly, but then back off at the last minute at the temperature we want. The more headroom you have, the more responsive your system will be. It’s just like accelerating a car. It sure is nice to have the horse power to do 120 miles per hour just so you can get to 60 miles per hour quickly – right? Same thing. But how do we know what size fan will keep the box from overheating, but still give us plenty of headroom for a responsive PID system? Easy. Just go to the Stego website and click on cooling. My room temperature is going to average around 72 degrees. We want the internal box temperature to be around 190 degrees max and I have a 500-watt heater in the box. I’m in Atlanta Georgia, which is around 350 meters above sea level. Altitude is important because thinner air has fewer hot molecules for the fan to move, so at a higher altitude, a fan won’t be able to move as much heat per minute. Hit calculate and it tells me I need a fan with around 15 cubic feet per minute of air flow. That was for an ideal system of course, and it depends heavily on things like how the air flows through the box, enclosure materials, etc. But, it gives us a really good starting point. AutomationDirect has tons of enclosure fans that are designed specifically for this purpose and it looks like it even has one with an airflow rating near what we need when used without the filter. But, it is physically too large to use on this small enclosure, so I looked at replacement fans for variable frequency drives, soft starters, etc., to see if any would do the job. Looks like this replacement fan for a GS3 Drive is pretty close and it is nice and compact! It will move more air than we need, which will reduce our headroom some, but it should be good enough, so that’s the one I installed here to pull air through the box. I drilled some holes in the top of the box to allow that airflow to happen. To see how well it worked, I turned the heater on full power and let it run until the enclosure temperature leveled off. And sure enough, the temperature settled out just under 170 degrees. Which is about what we expected because we designed for 190 degrees but ended up using a larger fan than was required which kept the box cooler. But since we want to keep the box around 110 degrees, PID still has plenty of headroom to operate so we are in good shape. Click here to see the rest of the videos in this series. Click here to learn about AutomationDirect’s FREE support options and click here to subscribe to our YouTube channel so you will be notified when we publish new videos.