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9th May 2014, 11:47 AM #16
I've just finished relocating the 6m flexxy so that it runs along the ceiling. The first half of the run is semi permanently held in place, and the last half of it is secured by three garden hose hangers into which the 5" hose is a nice snug fit and can be easily reconfigured to reach all the ports that it needs to. This isn't as convenient as blast gates, but there are other benefits:
- there is only one hose to hang down (and it can be put in a resting position out of the way)
- massive cost saving on running a complex 6" trunk with 5 or 6 ports
- no extra weight to support (and this would have been considerable - it's not the strongest structure up top)
However, the idea of a gable run to remove hot air and dust is still very appealing indeed. I will put those vents in the ends of the gables, but there is plenty of time for that (6 months).
So, this brings up what movements invisible dust will follow with air currents, particularly in summer when there are two distinct layers of air in the shed: the lower cooler layer up to about 1.5m from the floor, and the hot layer above it. These two layers will no doubt change with the extraction of the top layer (through the gable run) every 45 mins or so, but what I am wondering is how fine dust moves around between the cooler and hotter layers.
As near as I can understand it the dust will more or less behave like air, with the exception that the warming or cooling of the dust particles themselves won't very much affect dust movement - unlike air which will rise or fall because its density changes. I imagine that it would be more of a case of the dust being dragged along in whatever pocket of air it is in (so if that the air is given a shove by either the extraction or heating/cooling then presumably the majority of the fine dust within it will follow suit.
While the extractor is running it will take the very hottest air and then the air under that will obviously rise up to take the place of the previous air, etc etc for as long as I run the extractor (probably ~5 minutes)
Am I right in thinking that most of the dust will go along for the ride with the air that it is already in? And that therefore much of the dust will be sucked out and dust from the cooler layers will rise up to replace the previous, and also be then sucked out?
Sounds logical to me, but invisible dust seems to do some counter-intuitive things.....
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9th May 2014, 01:16 PM #17.
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If you run the DC for 5 minutes with a 4" duct (~400 cfm) that will remove ~ 400 x 5 - 2000 CF.
If your shed is 9 ft high x 15 ft long x 10 ft wide thats 1350 CF so running your DC for 5 minutes will give you ~1.5 room air changes.
This time is probably not enough to clean the shed
To fully vent a room really requires ~10 room air changes because the fresh air coming in mixes with air already in the shed and some of this fresh air will get vented out of the shed before some of the existing dirty air.
10 room air changes will required running your DC for ~35 minutes.
The long time required is a problem with using 4" ducting and a smallish.
Contrast that with a DC that can fully use 6" ducting (~1250 CFM) and its more that 3 times quicker and the time required will be under 10 minutes for that size shed.
This is why my time delay switch operates on the 0 to 12 minute range.
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9th May 2014, 03:05 PM #18
Yes, I see. Actually by 5 mins I meant for getting rid of hot air (and that would be variable with the ambient temp). Understood that dust removal would be longer.
How's my logic on the dust movement?
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9th May 2014, 04:54 PM #19.
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9th May 2014, 06:38 PM #20
You bewdy! Thanks very much for all your help Bob.
Shortly I'll be posting about the ducting upgrade from 40mm to 50mm pipe for the Festool vac system which has made a huge improvement. This allowed me to install a 36mm hose on the drop saw (which is significantly better than Festool's recommendation of 27mm). However, there is some dust left behind, and no doubt plenty of scatterable invisible dust.
A little while ago I did a trial with the 5" hose from the big DE sitting just behind the back of the cut (along with the CT Vac as normal) and voila - no dust. One would have to think that a goodly amount of the invisible went along with it. So tomorrow I'll jimmy up a jig to hold the big hose in place. The hose will have to stand away from the saw a little way to stop it fouling the movements of the saw, so I'll use a very short ducted rig and plug the hose into the top of that.
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12th May 2014, 01:35 PM #21
The next phase is shown here:
https://www.woodworkforums.com/f200/ducted-system-shop-vac-mk-ii-184635
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12th May 2014, 10:12 PM #22
Never seen any sawdust in Brett's shed!!!!
Never seen any sawdust in Brett's shed!!!!
It's always as clear as a hospital operating theater...........
I'd be trying to keep the heat in at Katoomba .... at 1000mtrs .......
and just the dust out...oh, you already trying to do that............
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13th May 2014, 09:52 AM #23... and this too shall pass away ...
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In a previous life I had an unlined 6M X 9 M tin shed. It got hotter than Hades in summer because the roof radiated heat into the shed. The quick and cheap fix was to put a series of sprinklers along the ridge line that were run occasionally to cool the roof. This made a big difference.
My roof was not lined, making it worse than yours. However, stopping the iron from getting too hot may be one component of a solution for you. The little black sprinklers are invisible unless you really look for them.
Have fun!
John
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13th May 2014, 10:40 AM #24
Good idea John, and one I have considered - just have to fix the leaks then
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