Thread: Workshop Air Ventillation and Filtration

Get the bigger one, in fact get two. The faster you move air the less the dust drops out of suspension and keeps moving. I would try without the air filters unless you are right on top of your neighbour as I doubt you will see much residue once it exits the building.

Exhaust fans in the wall are the go.

If the neighbours don't mind.

One bit of advice, don't exhaust your shed over the washing line. This can result in you going hungry or having to sleep in the shed or both.

Exhaust fans will give you more suck for your dollar.

Cheers

Tim

Originally Posted by zelk

I am also considering making a box around the back of the fan which can hold commercially available filters, to minimise what is expelled to the outside.

Zelk, before you do your dough let me tell you this will not work (I have worked with air filtration for over 30 years). Those propellor style fans are designed to operate at their state flow rates with ZERO restriction. If you stick any sort of filter in the way (even a couple of layers of fly wire) they will start to cavitate and air flow will drop significantly. To drive air through half decent filters you need a squirrel or barrel cage fan or centrifugal impeller such as is used in a DC.

Squirrel cage fans look like this.



Expect to pay around $300 for this type of fan. One of the reasons they cost so much is they are designed to run for a very long time (20 years+ under continuous use!). A basic 300 W version of these fans provides around 640 cfm/300 L/s but can handle some pressure restriction. of

There is no cheap substitute to these fans except for that much you can buy a cheap DC and placing it outside your shed so that it vents outside. See my sig for external dust enclosure.

Thanks for that guys,
I was afraid that putting a filter would cause problems. I like the idea of using a filter, just in case the wind blows the expelled air back into our house, but I am not concerned that it does not filter anything less than 5 micron particles.

Placing the main dust extractor outside is not an option, as it would be in the driveway.

Bobl, I was hoping to use something compact and weatherproof, I gather using the fans that you suggested, would I require a box construction for the fan, similar to that of air filtration unit?

From my calculations using a fans that extracts air at 300l/s and 630l/s would change the air 14 and 30 times respectively, in a hour. would you notice a draft with the larger fans?

Zelk

Originally Posted by zelk

From my calculations using a fans that extracts air at 300l/s and 630l/s would change the air 14 and 30 times respectively, in a hour. would you notice a draft with the larger fans?

Zelk

IMO you need to notice a draught, if you don't the air is not moving fast enough.

What he said

Originally Posted by Mini

IMO you need to notice a draught, if you don't the air is not moving fast enough.

Fair enough, which fan would suffice, the larger or the smaller? The larger and smaller fans produces 65dB and 58dB, respectively.

The following photo shows the main dust extractor enclosed in a box, the window for the proposed fan and the panel saw.

Zelk

Originally Posted by Mini

IMO you need to notice a draught, if you don't the air is not moving fast enough.

If you attached the fan to an air exit box big enough you will not notice a draft and it does not matter if it is not moving fast.

A squirrel cage fan has a typical opening about 3" x 8" = 24 sq in or 1/6 sq ft.

At 600 cfm coming out of a 1/6 sq ft opening = 3600 ft/min = 60 ft/s= 66 km/h which is pretty darned breezy.

600 cfm is bout 300 L/s so 600 L/s will be twice as fast! However, it would be more efficient to use two fans so the speed would be the same as that also means a double opening.

If you feed the fan outlet into a shallow box say 2.5 ft x 2 ft x 4" deep and place a diffuser (deflection plate) in front of the opening and pack the box loosely with dacron fibre and hold it in with some light weldmesh, the air flow rate out of the box will be still 600 cfm but will now be 2 ft/s (2.2 km/hr) , make it bigger still and you can get it down to almost nothing !

If you are clever, you can build the air exit box into the wall of your shed.

BTW those squirrel cage fans are also a lot quieter than the prop type fans.

Originally Posted by BobL

If you attached the fan to an air exit box big enough you will not notice a draft and it does not matter if it is not moving fast.

A squirrel cage fan has a typical opening about 3" x 8" = 24 sq in or 1/6 sq ft.

At 600 cfm coming out of a 1/6 sq ft opening = 3600 ft/min = 60 ft/s= 66 km/h which is pretty darned breezy.

600 cfm is bout 300 L/s so 600 L/s will be twice as fast! However, it would be more efficient to use two fans so the speed would be the same as that also means a double opening.

If you feed the fan outlet into a shallow box say 2.5 ft x 2 ft x 4" deep and place a diffuser (deflection plate) in front of the opening and pack the box loosely with dacron fibre and hold it in with some light weldmesh, the air flow rate out of the box will be still 600 cfm but will now be 2 ft/s (2.2 km/hr) , make it bigger still and you can get it down to almost nothing !

If you are clever, you can build the air exit box into the wall of your shed.

BTW those squirrel cage fans are also a lot quieter than the prop type fans.

Well, if the squirrel cage fans are the go and they cost about $300, it may not be that much more expensive if I buy an air filtration unit and vent it through the window.?????
I believe they use similar fans, not sure about the quality. BTW who sells squirrel cage fans?
Zelk

Originally Posted by zelk

Well, if the squirrel cage fans are the go and they cost about $300, it may not be that much more expensive if I buy an air filtration unit and vent it through the window.?????
I believe they use similar fans, not sure about the quality. BTW who sells squirrel cage fans?
Zelk

yep that is one solution. But if you are going to do that why not just get a 1HP DC ($230 at carbatech), put it inside a cupboard inside your shed and vent the cupboard through to the outside. That way you have something useful inside the shed to pick up wood chips with from time to time. Side by side the DC is noisier but not if it is inside a cupboard.


If you just buy a DC with the 30 micron bags, most of the rest of the visibles will remain inside the cupboard and only the invisibles will escape. You will have to sweep/vacuum out the cupboard about once every 6 months or year - that's it.

Squirrel cage or barrel cage motors - try FASCO http://extranet.fasco.com.au/web/ and their agents.
315 W (0.4 HP) motor and fan is typically $275 (Carbatec is only 1/6 HP for base model and 1/3 HP for expensive model $900)

I guess it depends if you want a quick no-mucking-about solution or you have time and energy to make stuff.

It's starting to get complicated. I may be better off having the window fan (630l/s) without incorporating a filter. It will be minimal work, no bulkiness, can control the speed, not that noisy at 65dB, and should clear some of the dust that doesn't get sucked up by the main dusty.

Zelk

Way to go Zelk, but only if exhausting the dust is not a problem.

I did it this way and later doubled up with a second fan.

If you have an air compressor and a power respirator,the quickest way to clean the workshop is switch on the fans and blow down everthing with an air gun. I do this when the better half is not home.

The only time I use the air filter is when cleaning up on a cold day.

Good luck.

Let's know how it all works out.

Cheers

Tim

Originally Posted by BobL

If you attached the fan to an air exit box big enough you will not notice a draft and it does not matter if it is not moving fast.

I must respectfully disagree with that. If the air is moving fast enough to hold the dust in suspension you will notice a draught, coal mines are a prime example, the air speed in the drift of a mine is quite fast and it is that way to hold the dust in suspension, after all that is the aim isn't it? I read somewhere a post by an engineer who showed that the cubic volume of air in a room is not changed in direct realtionship to to the fan's expelled volume. I must try and find it.

Originally Posted by Mini

.... I read somewhere a post by an engineer who showed that the cubic volume of air in a room is not changed in direct realtionship to to the fan's expelled volume. I must try and find it.

Don't quite understand this.

Zelk