Fab Lab Exhaust Fan

Digging into the requirements for exhaust on the lasers. The current fab lab exhaust fan is stated as 2500 CFM. That’s huge.
It’s doubtful it’s moving that much air. The fan pictured in the machine manual is smaller.

In considering the proper size for the exhaust fan some items to consider:

  1. What goes out, must come in. Every exhaust fan needs make up air. We can run an inlet duct to bring in make up air or rely on normal hive leakage to replace what goes out the exhaust.

In the current fab lab, that make up air comes from the main room of the HIVE. That is warmed or cooled by the main equipment. The annex is much more heat deprived.
2) Noise levels. Big fans are noisy.

Given 8 inch ducting 30 feet or less the air flow of 200 to 300 CFM is around 6 mph.
A couple of repurposed computer fans in a sheet metal box can do this amount of air, fairly quietly.

Truly moving that amount of air should clear either laser of smoke. I’m far from expert at sizing duct work, so anyone out there want to throw in on this?

There are a few important parameters for getting a certain amount of airflow from a blower. the rated CFM is typically with either no ducting, or a very short duct in the test.

In practice, in a long duct, you will have much higher pressure loss, and thus lower airflow.

Could you find the rated static or stagnation pressure? With either of those values and the duct length/config I could approximate what airflow we are actually getting.

The current fan is way back against the outer wall above the fab lab. Specs may be on the fan, I haven’t been up there. It’s otherwise an unknown.
Perhaps we should just move it. The new duct run will be much less distance and fewer bends.
Probably also ought to run makeup air. Perhaps from the inside hallway.

“Make up air”

If you look at the top of the wall on the hallway side of the annex, you’ll note that there is no shortage of venting.

That being said, a hose or duct bringing outside air IN, and going right to the machines would reduce the loss of heated or air conditioned air in the room.

Nancy

I should have posted this, but I have worked out solutions to this.

  1. Current duct is obstructed. We would have fixed this if I weren’t only told about it ‎after deciding to move the laser. The obstruction would require taking apart the ducts. The fact that the current fan ducked a t-shirt deep into the duct is proof that it did have significant pressure…

  2. Flex duct is so lossy. We should use as little as possible.

  3. I have some bilge blowers from boats that I use for powerful air scrubber with activated carbon. They’re cheap, and, since they are designed to withstand salt water and bilge, we could place outside for a boost. Outside, the sound would not be an issue.

4 We need constant air replacement and filtration in annex. I use box fans with merv filters at home. It may be worth getting a surplus industrial pace or oki ‎scrubber from ebay. Dust and VOC’s are a big part of the problem with current FabLab failures.

  1. What about rigging a filter input on laser so air coming in has low resistance AND is dust free.


From: Dave Velzy
Sent: Saturday, June 16, 2018 11:57 PM
To: Hive13 Hackerspace
Reply To: cincihackerspace@googlegroups.com
Subject: [CHP] Re: Fab Lab Exhaust Fan

The current fan is way back against the outer wall above the fab lab. Specs may be on the fan, I haven’t been up there. It’s otherwise an unknown.
Perhaps we should just move it. The new duct run will be much less distance and fewer bends.
Probably also ought to run makeup air. Perhaps from the inside hallway.

The current FabLab fan is pictured below. The wiki states it’s 2500 cfm though that doesn’t appear anywhere on a visible label. The stack of foam on the top closes one side of the squirrel cage.
Once the elegant foam stack is removed you can see the motor. We haven’t found the t-shirt reportedly sucked into the duct work.

Rather than move this assembly to the new location, I’ll be investigating replacements capable of 500 to 1000 cfm and the potential of running a small duct for make up air.

Given the partial wall of the annex, air quality is an open subject. Pardon the pun. Filters and scrubbers must remain future projects.

Second things first… it wasn’t a t-shirt as far as I recall. It was one of those blue paper shop towels. It may well have been beaten into dust and blown outside over the last couple years.

On the hardware front… do we need to purchase anything today? Particularly a vent fan? We do have some leftover duct tubing from the dust collector project. IIRC some funds remain in the move budget, and I might argue that the fablab and lounge warden budgets are also applicable.

If we need a parts run, let’s try to tackle that earlier in the day.

  • Ry

I would also add that when we first installed that fan, it ran smooth & had a lot of suction. I remember that when I stopped down after the shop towel got sucked it, it had a pretty solid vibration. I am not sure if that vibration is still present, but if it is, then I would guess the shop towel is still in there.

With the proposed arrangement of lasers in the fab lab near the AC window we can minimize exhaust duct runs and have full access to the equipment for maintenance.

Fyi - progress supply, across the street, probably has all those duct parts in stock.