Thread: Air extractor question

Originally Posted by plantagenon

I've got a 4.5 (L) x 3m (W) x 2m (H) insulated and lined metal shed with the only opening being sliding doors at one end. ....

hi Plantagenon,

I think that the biggest problem would be the fact that it is only one opening. And being a sliding door I am guessing that it will only open to half the width of the shed if that. good ventilation requires a cross-flow.

The fan you are proposing would change over the air in your whole shed every 30 seconds, but I cant see how you are going to be able to do that very easily with only one opening for the air to get out of and come back in through.

Is it possible to make an opening in the back wall or one of the side walls near the back of the shed and mount some kind of exhaust fan in the back of the shed?

I also think that the capacity of that fan for your size of shed is overkill. My own shed has about three times the cubic capacity of yours. It has roller doors at the front, a regular door halfway down on one side with a window in the wall opposite the regular door. I have a piece of plywood cut to fit into the window with two bathroom-style exhaust fans set into it. By turning on the fans and leaving the door open I get cross-flow. the two fans expel the cubic capacity of the shed, from memory, every 3 minutes. They are very quiet to run and I can turn them on or off at will from anywhere in the shed as they are plugged into a remote control powerboard.

I really cant see how you will be able to set up the fan you mentioned to do what you want, without choking its capacity severely with ducting which would add to the clutter in the work area.

Mate I haven't seen your shed and I might be misunderstanding your setup but if nothing else it might be another solution to consider. Exhaust fans are cheap and economical to run. In my case I can choose to run either one, two or none, depending on the level of dust/fumes being generated. It also keeps the shed cooler on those hot days when the sun on the roof beats down and heats up the air inside.

If you decide to go this way, make sure the fans you buy have roller bearings, not nylon bushes and make sure they are rated to be used vertically, not just horizontally.

Hope this helps,

Doug

Hi Greg

I'm no expert and am certainly prepared to be corrected on this but I would have thought for the best turn over of air that the extractor should be on the opposite side of the shed to the door and the air from it dumped out as far from the opening as possible.

cheers
WH

Originally Posted by plantagenon

I can either place it near the open door and let it extract directly to the outside or I can put it further into the shed and put an extraction pipe on it which will then be fed out of the door. My question is where is the best place to set it up? Given that there is only one opening to the shed will there be a problem getting airflow back into the shed or will it just be sucked in through the same door at fairly high volume? Also,will noise be a problem as I have neighbours not too far away.

As doug has already said exhausting anything anywhere near a single opening shed is a sure way of recycling back into the shed. You need to do the same thing you are doing with the dust extractor ie locate the vent the fan/DC on the other side of the wall opposite the opening as shown in the upper part of this diagram (I assume that is what you are doing with the DC?). If you vent the fan or DC anywhere near the door the air path will be as shown in the lower part of the diagram and will immediately recycle it back into the shed.

If you want to vent the shed, why buy anther fan, just take the bag off the DC and vent the shed with the DC


BTW the top drawing is also not ideal as it uses a long length of ducting. You would be far better off cutting a hole in the shed and using the shortest possible length of ducting possible.

Thanks for your replies. If I had half a brain I would have included the photos originally to show you my set up.

The first photo is the interior of the shed showing the sliding doors in the foreground.

The second photo is the outside of the shed. Where the gate frame and see-saw are located is where I move the DE to when I am using it so it is away from the front doors.

The third photo shows the only spot in the shed that has bare metal walls (lower left) and this is where I was originally going to put an air-conditioner outlet. The mobile air-conditioner appears in the first photo in the middle at the front (white object).

It is only a light metal shed and fairly small as I described earlier. I did manage to insulate it with rock wool insulation and form ply to hold that in position.

Although I would love a much bigger shed, I don't have the space for one and this one gives me just enough room to do my wood working.

I checked out the bathroom air exhausts as suggested but they will not fit unless I cut through the form ply and insulation and as you will see there is not a lot of room to install them because of the shelving at the rear.

Giving it a bit more thought I could probably put a couple of air vents on the bare metal wall to allow air to be sucked in if it was extracted through the sliding doors. Although I am not sure if they would be large enough to do the job.

I know the H&F exhaust is very overpowered but it is the only thing I have found so far that might work. I was a bit concerned about the decibel level of the fan.

I would very much appreciate it if you would have a look at the photos and offer suggestions.

Thanks

Greg





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Originally Posted by plantagenon

. . . .
The second photo is the outside of the shed. Where the gate frame and see-saw are located is where I move the DE to when I am using it so it is away from the front doors.

I'd forgotten your shed was so small. Because of the small dimensions of the shed a standard DC will develop a lower pressure inside the shed than for a larger shed, and with the DC just around the corner, unless there is a decent breeze the fine dust is just going to be sucked right back through the door. If you cannot move the DC around the back of the shed opposite the door the next best thing would be to keep the door closed and put a vent in the wall opposite to where the DC is located.

Hi Greg,

The photos do put it all in a new light. However, for the most part I will stick to my original advice.

You could still mount exhaust fans in the back of the shed; you would just have to cut through the ply and insulation as well as the tin.

You do realize that even a small exhaust fan, when running will neutralize any benefit of the insulation anyway. When you are not in the shed and the exhaust fans are not running, the insulation will be having an affect, but as soon as you turn on the big hare and forbes fan, in 30 seconds the temperature of the air in the shed will be the same as it is outside, because that's where it all was 30 seconds ago (that's in theory, in practice give it 5 or 10 minutes). That may at times be a good thing and at times be a bad thing. Using a small exhaust fan will have the same affect, it will just take a few minutes longer.

I see little point in putting the h&f fan in the doorway blowing outwards as the size of the doorway will mean that most of the air would be just sucked back in again, even if you had some small vents in the back of the shed.

You could consider a couple of whirlybirds on the roof, but they would only work when the wind is blowing and would neutralise the benefits of the insulation a lot of the time.

Greg, I still think the exhaust fans is your best option. You would need to place some sort of awning over their outlet to protect them from the rain, unlike mine, where I just pull the board out of the window at the end of the day. I am actually looking at weatherproofing mine so that the board can stay in the window and I can put them on a timer to run for a couple of hours after I finish work to expel more of the invisible dust before it lands.

I also agree with BobL that your dusty may not be far enough from the shed door to stop re-entry of dust that escapes the filter. While you are busy cutting through the insulated walls to fit the exhaust fan/s, cut a hole to take your dusty pipe out through the back wall too. Then before starting work, take the dusty to the outside rear of the shed and plug it into the pipe coming out through the wall. You can get a cap for the pipe to provide protection from the weather for when the dusty is not in use and is inside the shed.

Doug

Originally Posted by plantagenon

Giving it a bit more thought I could probably put a couple of air vents on the bare metal wall to allow air to be sucked in if it was extracted through the sliding doors. Although I am not sure if they would be large enough to do the job.

Just re-reading your post, Greg. Another idea is to do what you are suggesting above, put some vents in the back of the shed. Then cut a sheet of plywood say 15 inches wide and high enough to fit in your sliding door (similar to the board I stick in the window of my shed). Mount as many exhaust fans as you like into it and also cut a hole for the dusty pipe to exit through the board too.

Then, when you want to work, go into the shed, take the dusty outside to its regular spot (on second thoughts DOnt put it in its usual spot - put it as far out the front of the shed as you can to get it as far away from the vents in the back of teh shed as you can, insert the board between the sliding doors and slide them up to the edges of it, connect the dusty pipe from both sides, shut the door, turn on the fans and away you go!

No cutting through insulation, far better protection against dust re-entering the shed, five minutes setup and able to be adapted and modified if required.

Doug

I would be tempted to look into vents or a cupola in the roof and close them off from the inside when you don't need them. You could also put filter cloth over them on the inside to keep dust from re-entering the shed.

Pete

All of this sounds like a lot of work, when yo can buy internal filters that are designed to remove the finest of dust.

If memory servs me correct steve (?) at micro clean is the the bloke to talk to his number is (02) 95848273

Mark

Originally Posted by salty72

All of this sounds like a lot of work, when yo can buy internal filters that are designed to remove the finest of dust.

This isn't going to help as he has doesn't appear to have the space to hang anything from the ceiling in his shed and more importantly he wants to vent the shed of "CA fumes and the like".

Greg I think its time for a bigger shed mate

If only I had the room for a bigger shed

I had another look at the shed this morning and forgot that behind it is a very small garden shed. It is big enough to store the DE if I run ducting to it through the wall of the shed. However, the ducting would need to be 7.5 metres in length and I am wondering if this will be too long for the DE. Its only a H&F DC25 which is fairly small.

If I can make that work then I could put in vents at the end of the shed and some sort of an extraction device near the door and if necessary with ducting off it to extract the air 5 metres from the shed door into the back of the yard. I just have to be careful about putting vents into the side walls of the shed as it will let noise escape towards the neighbours who will not be amused.

Originally Posted by plantagenon

If only I had the room for a bigger shed

I had another look at the shed this morning and forgot that behind it is a very small garden shed. It is big enough to store the DE if I run ducting to it through the wall of the shed. However, the ducting would need to be 7.5 metres in length and I am wondering if this will be too long for the DE. Its only a H&F DC25 which is fairly small.

Yep - 7.5 m of 4" ducting would hamper the performance of that DC. Using 6" ducting will drop the air speed too much so that dust may fall out of suspension.

Would the same apply to a collector in the shed by the lathe blowing the dust to the second shed where the filters are located? II was told once that by blowing the dust and air it can be move further than sucking it with the same power.

Pete