Thread: Dusty install - outlet questions

The issue with those kind of vents is although they are 150mm i wouldn't be surprised if thats outer diameter and secondly the grates cause turbulance/restrictions that reduce efficiency.

The idea of having such a large outlet is to reduce back pressure as much as possible, think what comes in must come out. I believe I read that BobL did some testing a while back and even at 4 times the size there was still some back pressure. So with a 2hp DC you want to have as much flow as you possibly can at the get go.

Also if you have a fan/ventillation or something blowing from the other side of the roller door the dust shouldn't come back in

If you mount multiple of those vents, you're going to have to penetrate the wall 'x' times anyway.

Why not make up a small louvre window, that will give you the dimensions you require? Say two or three brick courses high and 2 or 3 bricks lengths wide? (It's also way easier to make wide holes in brickwork than small ones. )

If you make it wider you should look at either including centre stiles every 1.5 - 2 bricks or, better still, add a lintel to support the upper bricks.

The end result would look professional without having the... "tacked on bits of plastic" look.

I like the window idea, I know you touched on this subject, but keep in mind that the volume of air that the DC sucks in from the shed has to come into the shed from outside, be careful with a roller door or unsealed roof joins near the DC outlet, (I had the same problem) try and put a big shed intake somewhere away from the DC exhaust location to stop recirculating that fine dust.

The 4 times ducting area recommendation is for S or Z shaped baffles and/or vents with hard (90º) entrances and exits

This where a pair of Bell Mouth hoods (one on the inside and one on the outside of the enclosure joined by 6" duct) will come in really handy as a vent.
My testing shows that at full flow a 6" BMH on one end of a duct improves the flow by 10% compared to a naked duct, and using a second BMH on the same duct will further improve the flow but it won't quite be another 10%

If you used a pair of these double BMH ended vents you should get close to the same resistance to flow to 4 naked ended ducts.

BTW I've done some testing on dryer ducting and found that (unless you use really e.g. 12: diameter) it's not good for any DC system. It's too floppy and it vibrates and sets up turbulence. I would use straight PVC pipe.

I agree with others about watching out for roller doors. Can you put a large 2m high screen between the roller door and then vents? The air that exits from a DC is usually warmer that ambient air and will rise so if you put any sort of barrier in the way this will give the air (and dust) exiting a vent to rise up out of the way before it has time to go back around to the leaks around the roller door. Not a perfect solution but better than nothing

Thanks all for your feedback. Some good ideas there, thanks for the tip the air coming into the shed from somewhere, didn't really consider that too much. Upside on that is that I have a personal door on the opposite side which I can open, which should help eliminate draw back from around the roller door area. I like the double BMH vents could work ok with a shroud (for rain). I like the window idea but it might not work too well, and am not sure if people will complain. I need your PVC BMH's Bobl they look great! and would work well through the wall. I have to make my own out of MDF, and with a router and while they are fine, they might not fair so well in the weather (even with a shroud), but let me think on that for a bit. Thanks all for the tips.