Thread: Dust extraction in a cold climate

Insulation and structure can't be part of the circumstance. Make-up air has to come whistling in at 1,000 - 2,000 cfm to replace what the DC pulls out over what? 30 minutes of sanding?
That's approx 2% of any 24 hr period.
BobL: you missed an option = don't make dust until the summer and the shed doors are open.
Some summer days up here, it looks like wisps of smoke, drifting through the neighborhood.

Anyway, congrats on squandering 20k post time. I enjoy your contributions.

Originally Posted by Robson Valley

BobL: you missed an option = don't make dust until the summer and the shed doors are open.
Some summer days up here, it looks like wisps of smoke, drifting through the neighborhood.

Anyway, congrats on squandering 20k post time. I enjoy your contributions.

Thanks RV.

Winter is usually when I don't mind making dust and using the DC - it only gets to zero here in winter about half a dozen times a year and by mid-day it could even be as high as 20º.
Summer is the killer but insulation/lining and AC makes the shed OK - DC used in the cooler morning or in short bursts after that.

For the last few years we have stopped deliberately heating our house - this year it got down to 13ºC in the living room early in the morning. With appliances and lights on it got up to around 15ºC during the day but I didn't find that too bad.

In the bedroom SWMBO insists on sleeping with the windows open so it got down to about 8ºC on my side of the bed
We've learned to cope, wear a tee-shirt under a flannel shirt during the day and under PJs at night.
We do leave the AC on in summer to make up for it.

Originally Posted by BobL

Blimey, I just realised I reached 20,000 posts!
At 5 minutes per post that 100,000 minutes , 1667 hours, 69 days, 2% of my time during the 11 years of WWF membership, gone!
Not to mention posts in the MW and other forums.
And think of all that hot air that could have been used to heat sheds.

Not that I have read all 20 thousand posts, but I do thank you for all the info you have shared on such a variety of subjects and interests. Your vast knowledge on so many interesting items makes me wonder why you haven't used up all those memory neurons.
I often wonder if you type all of your replies, or use some sort of speech recognition program. If you type them, your typing speed would have to be streets ahead of my 'hunt and peck' method!

Anyway, thanks again, now you can get back to the workshop for some more play time.

Alan...

There has been a couple of mentions of "make up" air. I would be interested to know how much incoming air is required if a workshop is 7.5 x6.5 with a ceiling height of 2.4 metres and the dc is exhausted externally.
Can the dc be run for any length of time without a loss in performance before a door or window is opened or should there always be an adequate entry point for incoming air.
Thanks

Originally Posted by safari

There has been a couple of mentions of "make up" air. I would be interested to know how much incoming air is required if a workshop is 7.5 x6.5 with a ceiling height of 2.4 metres and the dc is exhausted externally.

When venting externally, whatever CFM you are exhausting externally, the same MUST come back into the shed, If not the shed would collapse under vacuum.

Can the dc be run for any length of time without a loss in performance before a door or window is opened or should there always be an adequate entry point for incoming air.

It depends how air tight your shed is. If it's completely airtight it's impact will be like completely blocking off your ducting.

In terms of how long it would take, . . . .
Well a 7.5 x 6.5 x 2.4 m shed has ~4000 cubic ft of air.
In theory a decent DC should be able to drop the pressure inside a sealed shed by 2500 Pa which is 2.5% of atmospheric pressure.
2.5% of 4000 cubic ft = 100 Cubic ft so if the DC is doing 1000 CFM it theoretically takes about 6 seconds to remove that much air.
In practice, for a sealed shed, it takes longer than this because the first few CFM are removed quickly but as the vacuum generated by the DC approaches the pressure differential between the inside of the shed and atmosphere, the amount of air removed slows down and the last few CF will take much longer - whatever it takes it will only takes seconds to impact on flow.
Fortunately in practice, all sheds leak and if they don't they soon will.
2500 pa = 250 kg/m^2 so you can work out how many tons of pressure this would generate on the walls and roof of your shed.
If the shed was truly sealed this would buckle the walls and roof enough to cause leaks - or collapse the shed.

Originally Posted by Uncle Al

Not that I have read all 20 thousand posts, but I do thank you for all the info you have shared on such a variety of subjects and interests. Your vast knowledge on so many interesting items makes me wonder why you haven't used up all those memory neurons.

I often wonder if you type all of your replies, or use some sort of speech recognition program. If you type them, your typing speed would have to be streets ahead of my 'hunt and peck' method!

Yes I type most of them but I am reasonably quick - ~4 fingers on each hand.
Most of my Small Timber Milling posts are Aussified versions of my posts on the Arboristsite. As I have over 7000 posts there I'd estimate ~ 5000 of these are copies across to WWF and if needed edited to suit Aussie measurements etc.

Anyway, thanks again, now you can get back to the workshop for some more play time.

Cheers

Originally Posted by Chris Parks

The size of this problem depends on a couple of things, how long the extractor stays on and how warm the building is. OS it is common for the building to be heated 24/7 and if you could do that to a large extent the problem can be minimised if the extractor is used sporadically as needed the amount of air removed has little long term (relatively) effect. The building mass is what is costly to heat and the temperature of the building takes a long time to change when compared to air. if the building is up to temperature and the air temp drops because the extractor is turned on the air will very quickly be raised back to the same temp as the building because it is heated by the building.

BobL covers this somewhat in post #21, but to give you some "real" numbers.
The house I rent (I use part of the attached garage as a "shed") has a floor area of about 4000 sq.ft. The house's enclosed volume is about 40000 cubic feet. At 1000 cfm, it would take about 40 minutes to totally exhaust all the air inside the house. In winter, even 10 minutes of DC use would bring in a significant volume of super cold air (-30°C). I'm not sure the house's heating system is up to that sort of load.

Originally Posted by Chris Parks

in Oz we generally do not have anything like adequate insulation, in fact far from it.

This is an interesting observation.

In Oz there is a degree of conflict over insulation and breathability of housing. On the one hand a sealed house is easier to heart and cool, on the other hand, planners and architects encourage "cross flow" ventilation and breathability to avoid having to run an air conditioner -- the mantra is "energy saving". I've seen concept designs for high rise apartments that rely on cross-flow ventilation. All well and good if your Sydney apartment is located somewhere east of Balmain.

Originally Posted by BobL

This problem is far more common than not with most woodworkers in North America and Europe in this position.
There are DC filters that can filter down to a low enough level to be quite safe.
The problem with conventional DCs where the collection bags are under pressure is they leak - a dust detector can help pick up leaks would useful.

Cyclonic systems are better because their collection chambers are under vacuum but the impeller and motor need to be a decent size to overcome the back pressure that cyclones generate.
The cyclones also need to be efficient at removing chips and fine dust otherwise the filters will be rapidly overloaded and clog.
Clearvue cyclones are specifically designed be efficient and the filters they recommend are very effective but they can't easily be transferred to other DCs.

+1 on Bob's analysis.

I live in the Adelaide Hills and this is an issue for me during the long winters up here.

I went with the most efficient cyclone and internally vented filter + high efficiency hood mask + HEPA air filter I could get at the time.

My next cyclone will be a Clearview with a setup so I can switch between internal and external venting, depending on the season. I'm yet to work out the switching design for that. I will probably vent externally via an exhaust hood on the ridge of my workshop roof.





Sent from my ZTE T84 using Tapatalk

Originally Posted by ian

BobL covers this somewhat in post #21, but to give you some "real" numbers.
The house I rent (I use part of the attached garage as a "shed") has a floor area of about 4000 sq.ft. The house's enclosed volume is about 40000 cubic feet. At 1000 cfm, it would take about 40 minutes to totally exhaust all the air inside the house. In winter, even 10 minutes of DC use would bring in a significant volume of super cold air (-30°C). I'm not sure the house's heating system is up to that sort of load.

Presumably the room you do your WW in can be isolated from and prevent dust migration into the rest of the house?
However, leaving the door open between the workshop and the house, and the bigger and more solid/massive the house, the more Chris Parks concept of inertial thermal mass works.
When I say short burst use of a DC, its not 10 but rather 2 minutes. In that case, at 1000 CFM you'd lose 2000 Cub Ft or 5% of the house air, but you would lose considerably less than 5% of the total house warmth.

It also depends how the venting is done. The 5% warm air loss assumes ONLY warm air is vented, whereas what happens in practice, especially if the air inlet vent into the workshop is close to dust pick up point, is that a fair proportion of the cold air coming in is immediately exhausted - the air acts like a fluid broom. In the tests I have done where are door way or window is close to the dust pick up point and a preferential air stream is set up about half of the fresh air coming into a shed is immediately vented along with some existing room air. This halves the amount of cold/hot removed per unit time. It also makes it more difficult fully extract air from a shed air that is all contaminated with dust.

An interesting dust extraction proposition for a system that is able to collect dust from sources would be to have 2 sets of ducting, one that extracts the dust and another that delivers fresh replacement air direct to the source. This would leave even more of the warm/cool shed air in situ and reduce AC use.

In Oz there is a degree of conflict over insulation and breathability of housing. On the one hand a sealed house is easier to heart and cool, on the other hand, planners and architects encourage "cross flow" ventilation and breathability to avoid having to run an air conditioner -- the mantra is "energy saving". I've seen concept designs for high rise apartments that rely on cross-flow ventilation. All well and good if your Sydney apartment is located somewhere east of Balmain.

I think you are confusing "sealed", as in no cracks and gaps, especially around doors and windows, with "cross flow ventilation" which is meant to be vents, doors and windows set up in an way to promote efficient removal of air.

A sealed house can have good ventilation - it means that it vents efficiently when the doors and windows are open, but is sealed once they are closed.

Cross flow ventilation and Air conditioning are not meant be used at the same time. Good cross Cross flow ventilation is used to remove stale hot air before an AC is used, and if the air is relatively dry continue to cool occupants by evaporation without using AC. Once there is no breeze or it gets too humid the doors and windows are sealed allowing an AC to operates more efficiently.

I've generally found that layers of thermals work pretty well and by the time I start moving around in the shed i feel pretty toasty in no time, but thats with WA climate which doesn't normally stay cold for that long.

Instead of warming the entire shed could you consider looking at getting a heated vest pretty sure they make heated thermals also. This way you don't end up wasting heaps of electricity heating air that just gets pumped out of the shed.

the problem in my winter environment is getting the shed warm enough that glue will cure.
Typically that requires a temperature above about 10 degrees C.

Also minus 5 is pretty unpleasant on the fingers, not to mention -20 or colder.

to put "cold" into some perspective. this is the temperature chart for the first 3 weeks of December last year.

Originally Posted by tonzeyd

I've generally found that layers of thermals work pretty well and by the time I start moving around in the shed i feel pretty toasty in no time ...

I have cold fingers, which don't respond to a warm body very well. It used to plague me writing Uni exams mid winter in Toowoomba many moons ago. I find that some times in the shed I just need to stop because of it. My body is toasty, but my fingers ache, leading to a lack of dexterity. Unfortunately other than cleaning up, there's little productive work that can be undertaken successfully with unresponsive, stiff fingers.

To put it all in perspective however, if the sun is/was shining, the shed is generally toasty, and holds its warmth well. A double gray colourbond roller door with a northerly aspect, is a beautiful thing when it's soaking up the sun and radiating it inside.

Originally Posted by BobL

Cross flow ventilation and Air conditioning are not meant be used at the same time. Good cross Cross flow ventilation is used to remove stale hot air before an AC is used, and if the air is relatively dry continue to cool occupants by evaporation without using AC. Once there is no breeze or it gets too humid the doors and windows are sealed allowing an AC to operates more efficiently.

the concept designs I've seen pedaled were intended to REPLACE air con with cross flow ventilation. Not substitute cross flow for air con on mild days.

Originally Posted by ian

the concept designs I've seen pedaled were intended to REPLACE air con with cross flow ventilation. Not substitute cross flow for air con on mild days.

Maybe they were from Hobart?