Thread: Shed Ventilation

That looks to be very similar to the fan out of a ducted heating furnace. Our furnace was replaced so I grabbed the fan and put it in the wall of my garage. You need to have the wiring sorted by a sparkie.

Originally Posted by Chesand

That looks to be very similar to the fan out of a ducted heating furnace. Our furnace was replaced so I grabbed the fan and put it in the wall of my garage. You need to have the wiring sorted by a sparkie.

Is that because yours has a variable speed? - the Hydroponic ones look like they only have one speed.

So an exhaust fan is for three reasons: clearing dusty air, clearing hot air and clearing the noise outside. Ok, maybe two reasons.

In the case do I presume that it is best mount it as high as possible? (assuming that the hotter air will carry the dust with it - you have previously described invisible dust as behaving like a fart - farts rise - for a while at least).

Originally Posted by FenceFurniture

So an exhaust fan is for three reasons: clearing dusty air, clearing hot air and clearing the noise outside. Ok, maybe two reasons.

I quote the noise levels for persons working inside the shed.
A ventilation fan would usually be run for some time after dust making activity in place of using an externally vented dusty (2 -3 HP versus 1/3rd HP) so using something that is quiet and lop power had some benefit.

In the case do I presume that it is best mount it as high as possible? (assuming that the hotter air will carry the dust with it - you have previously described invisible dust as behaving like a fart - farts rise - for a while at least).

Correct.

Many thanks for your advice Bob, if no one has taken you up on the testing offer, I may just do that when I get back onto the job in November!

As an aside, for those who have noise issues (my dustie will be 2.4 metres from my neighbour's kitchen window and the fan(s) will be pointing directly at their house...), silencer kits can be had for these fans as well. They work a bit like car mufflers, presumably at some slight cost to performance. Realistically 50 db should be no worse than a pool pump or airconditioner.

I hope.

Cheers

P

Bob, is there a reason why I couldn't use 2 x 6" fans side by side instead of one 10"?

Since I have to cut a hole in the brickwork, I can get 2 x 6" gravity vents for a fair bet less than a proper weather proof 10" one, and I can use PVC for the little bit of ducting I need instead of making a plenum from MDF so I just thought....

Cheers,

P

Originally Posted by bitingmidge

Bob, is there a reason why I couldn't use 2 x 6" fans side by side instead of one 10"?

Since I have to cut a hole in the brickwork, I can get 2 x 6" gravity vents for a fair bet less than a proper weather proof 10" one, and I can use PVC for the little bit of ducting I need instead of making a plenum from MDF so I just thought....

Should be OK.

Thanks... getting the ducks in a row for when I get back in November!

P

Thanks Again BobL for sharing your expertise.

Do you have any thoughts on how many changes of air per hour would be required to get rid of most residual dust after the dusty is turned off?

Originally Posted by MikeJ

Thanks Again BobL for sharing your expertise.

Do you have any thoughts on how many changes of air per hour would be required to get rid of most residual dust after the dusty is turned off?

Good question but it is also a bit like that "length of a piece of string".
Lets ignore time for the moment.

It depends on the efficiency of your dust extraction at source, the ventilator arrangement, the size of the shed and length and nature of the activity.

For example turning in a small shed with a mediocre dust extractor for a few hours might send the dust levels up to over 100 ppm i.e. 100 times above OHS.

1 room change at best drops the levels by 50% (50 ppm), the next room change drops it by half (25 ppm), next room change 12.5 ppm, 6.25, 3.125, 1.56, Bingo!
So that is 7 room air changes.

In practice you need something more like 10 to 12 room changes as quickly as possible.

Bear in mind that during this time you are exposed to greater dust levels than is deemed unhealthy and some of that dust will have settled out on surfaces i.e. it is not vented as the ventilator will not pick up that dust - next time you walk through the shed or disturb those surfaces it fluffs up again. This is where the time comes into play as it takes about 25 minutes for half the fine dust to settle out so ideally it would be best to get those 10-12 room air changes happening in the first 25 minutes or so.

say 10 room air changes in about 30 minutes or 20 room changes per hour.
For a ~100 cubic metre shed ( 5 x 7 x 3) thats 2000 m^3/hour or ~1200 CFM (i.e. a 3HP DC with 6" ducting and with all ports open)
This may be more difficult especially for a larger shed.

BUT if you had a a 3HP DC with 6" ducting and used it while turning you'd collect much more dust at source so the levels will be much less and 2 - 3 room air changes may be enough.

That's why I advocate running a DC for 10-15 minutes after wards

Being the ever vigilant scrounger I found a couple of "Swamp Boxes". One I set up on the verandah of the house and ducted cool air through a hole in a piece of Masonite into the lounge room. Another, as you can see in the picture, I fitted high in the roof part of the shed. Mainly to shift hot air in summer but also any air born dust. I used some siding off an old caravan as ducting/exhausting to the outside. It does work but high summer is still not very nice in the shed around midday.
Its abit hard to get the proportion but its a house hole Evap Cooler minus the pads. (About 800 X 800 X 800mm cube) I had to replace the bearings in the motor as well as the fan. The switch was surplus. I have the motor running at its slower speed

Originally Posted by chambezio

Being the ever vigilant scrounger I found a couple of "Swamp Boxes". One I set up on the verandah of the house and ducted cool air through a hole in a piece of Masonite into the lounge room. Another, as you can see in the picture, I fitted high in the roof part of the shed. Mainly to shift hot air in summer but also any air born dust. I used some siding off an old caravan as ducting/exhausting to the outside. It does work but high summer is still not very nice in the shed around midday.

Yeah that corro is going to re-radiate pretty strongly into the shed from underneath and probably heats the air as fast as you ventilator will remove it. A bit of insulation on the underside would make a big difference to that.

Originally Posted by BobL

It depends on the efficiency of your dust extraction at source, the ventilator arrangement, the size of the shed and length and nature of the activity.

For example turning in a small shed with a mediocre dust extractor for a few hours might send the dust levels up to over 100 ppm i.e. 100 times above OHS
say 10 room air changes in about 30 minutes or 20 room changes per hour.

BUT if you had a a 3HP DC with 6" ducting and used it while turning you'd collect much more dust at source so the levels will be much less and 2 - 3 room air changes may be enough.

Thanks for a great explanation BobL. Your numbers are spot on as far as my research into recommendations are concerned. Notwithstanding the dustie turned on as you recommend (which is effectively providing additional ventilation), 15-20 changes per hour seem to be industry consensus for many dust laden occupations. Everything is a compromise of course, and while I'm super concerned about my lungs and sinuses, I also have the added challenge of keeping dust (and fumes) out of the house.

Therefore I expect my solution will be to have a base level of ventilation in the order of 15 changes per hour, with an additional fan which can be brought into play to almost double that. Note that the standards for spray booths recommend 100 changes per hour! I will be able to achieve that by limiting the area of the enclosure using one of the above fans.

Roll on November!

Cheers,

P

As critical as the number of room changes is the placement of ventilation.
If the exhaust fan is not on the wall opposite the major air inlet and not ventilating across the longest dimension of the shed then even 10-20 room changes may not adequately ventilate the whole shed.

Originally Posted by bitingmidge

Note that the standards for spray booths recommend 100 changes per hour! I will be able to achieve that by limiting the area of the enclosure using one of the above fans.

Yep the effect of limiting the volume is very significant.
For example, my small welding bay is 1 x 1 x 1.5 = 1.5 m3
The flow is ~30 m^3 per minute = 1800 m^3/hr so there are 1800/1.5 = ~1200 changes evert hour.
I can do things like weld zinc coated steel, and do all manner of dirty work in there in comparative safety.

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