Thread: Workshop Air Ventillation and Filtration

Originally Posted by zelk

You suggested building a one foot square exhaust ducting from the enclosure to the window, I am wondering if a 6in flexible hose would be better as the higher exhaust air velocity would be better for waste air dispersal?

A 6" hose has a cross sectional area of ~9/16 of a sq ft.
A 1 sq ft duct has 1 sq ft but the square ducting shape will have a relatively poor transmission efficiency so while it will transmit more than the 6" hose it won't give you quite and extra 7/16.
I would use 3 x 6" diam lengths of flexy hose - thats 27/16 sq ft of exit - that will also look WAY cool

Next, for extra collection points, I would go super simple - just put a 3 way PVC connector in the entry port of the DC fan. Connect the Panel saw to one and put blast gates on the other tw.

To run the panel saw close the blast gates, to vent the room open the blast gates.

BONUS: If you need another DC collection point for another machine you are then already plumber for it!

As far as Tim's comment is concerned, I disagree, your DC may be slightly less efficient but at 1200 CFM or 600 L/s it will still outpump a 300 L/s fan set into a window. Plus the DC will partially filter what's in the room before it dumps the air outside - the fan will not do this.

To get fresh air into your shed I suggest just leaving the entry door and openings open and/or set a a secure weldmesh panel into them. That way you get a nice 2 way cross breeze cleaning up the shed. You should make the one on the door bigger than the other to make sure it draws more from the door because it is further away.

This is what you dead zones will look like.


If it is still not clean enough you can add the window fan but I don't reckon you will need it

You have to be a bit careful adding a window fan since it will compete for air with the DC but seeing as they are both on the same side of the room and the openings into the shed can be made quite large it should be OK.

Gday BobL

I think we can have a robust debate here.

My following coments are not ment as a personal attack, nor any disrespect to you personally.

I would like to know how you get the air movment to follow your red line in your drawing.

Bearing in mind the air movment is only infulenced by extraction. I would suggest the majority of movement is in a straight line between the inlet and the outlet. Sure you will get some extraction from the rest of the room but the majority of the airflow is in one direction only. I don't see how you get this airflow to go around corners, as suggested in you drawing.

My experience with my own setup, which is very simular to Zelk's with my main capture point in in the centre of the short wall, is that to make any changes to the above mainly straight line airflow you have to push the air in the direction required. This means using suplementry fans behind work stations or in corners pushing the air to the collection point.

My own workshop has 4 fans that I use as required and depending on the job in hand and which workstation I'm using. I often use contact adheasive so my system also doubles as fume extraction. The air movement requirement remains the same.

My dust extraction unit is an industrial 2HP Woodfast fitted with a high capacity bag system (9 small diameter bags).

Using this as an air filter is nowhere as effective as one 12" extractor fan.

I'll await your response with interest.

Best wishes

Cheers

Tim

Originally Posted by Tim the Timber Turner

Gday BobL
I think we can have a robust debate here.
My following coments are not ment as a personal attack, nor any disrespect to you personally.

No worries

I would like to know how you get the air movment to follow your red line in your drawing.

The area inside the red line represents a nominal area that is likely to reach a suitable low level of dust (habitable zone) after the DC has been run for some time. The area outside represents the most likely dead zones. The actual size of the habitable zone depends on the amount of continuous dust generation, the air volume removed and its velocity. It could well be that so much dust is made that there is NO continuous habitable zone eg ZELK accidently tips over a vacuum cleaner! or discharges the output of a belt sander into the air. The system is just not going to keep up. Or there is very little dust generation and the habitable zone creeps closer and closer to the walls. I am not one one these people that turns on a DC or fan for the x seconds while the dust is being made. I assume the air extraction system runs continuously and dust generation is intermittent and that dust collectors are left on for at least 15-20 minutes after dust is made.

Bearing in mind the air movment is only infulenced by extraction. I would suggest the majority of movement is in a straight line between the inlet and the outlet. Sure you will get some extraction from the rest of the room but the majority of the airflow is in one direction only. I don't see how you get this airflow to go around corners, as suggested in you drawing.

Well all I can say is that it does, and it does a lot more than one might think. I have mapped many rooms with similar setups and similar air flows using a hot wire anemometer and there is a measureable bernoulli effect that drags air in from the sides of the major air stream. The amount of air that is drawn in is related to the velocity of the major air stream and the distance it is away from a fixed barrier like a wall. This picture show what we are both talking about.

At work we model and measure these air flows and the theory and practice match well so that I can now basically look at a room and say what the dead zones are. I did perhaps over estimate the extent of ventilation in the bottom RH corner of Zelks setup and it wont quite penetrate that far into that corner.

My experience with my own setup, which is very simular to Zelk's with my main capture point in in the centre of the short wall, is that to make any changes to the above mainly straight line airflow you have to push the air in the direction required. This means using suplementry fans behind work stations or in corners pushing the air to the collection point..

I agree that fans will help stir the air and help reduce dust in dead zones but (leaving the contact adhesive issue aside for the moment) there is no need to push the air if you can create vent points behind the dead zones.

My own workshop has 4 fans that I use as required and depending on the job in hand and which workstation I'm using. I often use contact adheasive so my system also doubles as fume extraction. The air movement requirement remains the same. My dust extraction unit is an industrial 2HP Woodfast fitted with a high capacity bag system (9 small diameter bags).
Using this as an air filter is nowhere as effective as one 12" extractor fan.

Well I'm sorry but I wouldn't call your system a fume extraction system - all this is doing is diluting the concentrated fumes from the immediate vicinity of the work area into the rest of the shed where they will just be hanging around in dead zones at sub-nasal-detectable levels. Just because you nose is not detecting them does not mean they are not there so this does not pass any sort of reliability or OHS test - in fact we would be shut down if we were to do this. If I were working regularly with something like a contact adhesive I would construct a proper fume hood or semi enclosed cabinet and extract direct from that using a proper exhaust fan and chimney stack. I would not be spraying it around the room

At work we have a lab that is basically 400m^2 ultra clean room. In one section we purify (distill) our own acids, including hydrofuoric acid (one whiff and the inside of your nose starts to turn into jelly), so we have to know exactly where our air flow in all our labs is. We have to treat air flow very seriously so we study it and design special labs and air flow patterns to suit. We don't even trust specialist laboratory construction companies (who can pass all manner of OHS tests) to do this because we have been caught before with their incompetence. Here is a picture of one of our ultraclean labs.

These labs have less than 1 particle of dust per cubic metre of air of 0.3 microns or larger, until someone goes inside them. Even though the human body makes about 100,000 particles per minute, the particle count goes up to about 8 particles of dust per cubic metre of air of 0.3 microns or larger. The reason is, the person wears a sort of a bunny suit with only their face exposed, and the airflow inside the labs is ~ 5000 cfm and we use 99.997% efficiency HEPA filters. The toilet (and 3 showers) inside the lab use deionized water (because mains water has too much dust in it!).

BobL In response to some of the points you have raised and in no particular order.

I totally concede to your technical knowledge and expertise. You are obviously an expert in this area.

My knowledge is based on dust control in my own workshop. I have made my living from this workshop for the last 19 years. I realised right from the start that if I wanted to do this into my old age that dust control was vital to my health.

My workshop area is 5 x 5 x 3 meters high. The layout was designed around my ducted extraction system. It was modified many times and fine tuned as machinery was added or changed. This unit is fitted with thick, heavy duty needle felt bags and exhausts back into the work area where I can choose to evacuate the air with the exhaust fans, Exhaust fans 2 x 12” and 1 x 8’ were added and are used in times of high ambient airborne dust, such as power sanding or blowing down the machinery and benches ect.

Also added was an air filter, seldom used because the 3 fans are much more effective.

The air inlet to this 75 cubic meter space is through one or both of 2 standard access doors. The direction of the air movement can be controlled depending which door is open.

The exhaust fans also are used when using solvent base glues or finishes. I arrange my work station so I am working in a gentle cross breeze. This is not a dedicated hooded fume extraction setup as you discribed. However it is very effective and the best I can achieve in my present setup.

Your second version of the plan made a lot more sense to me and I would agree with your suggested air movement.

I am careful to keep my work space clean and tidy. Most people that visit accuse me of never doing any work. That said, I suspect that my workshop would not pass an OHS test. I don’t know if many other home based workshops that I have visited would pass.

I sorry, I can’t see the point of your reference to, and specification of, a dedicated clean room as you described. This bears little similarity to a home base workshop. Were you trying to blind us with science?

Remember the people that read this forum are mostly hobby woodworkers and are best served with practical information relating to steps they can take to control dust in their own workshop.

I’ll finish by repeating the 3 step KISS principle.

1: capture and control as much dust as possible at the source.
2: get as much clean air into the workshop ASAP.
3: consider personal breathing equipment.

How you achieve dust control will differ, this depending on many factors including physical limitations, budget and degree of exposure to mention three.

Cheers

Tim

Originally Posted by Tim the Timber Turner

I sorry, I can’t see the point of your reference to, and specification of, a dedicated clean room as you described. This bears little similarity to a home base workshop. Were you trying to blind us with science?

I'm sorry if it looked like that. Dust is dust, or maybe it isn't ? - I have done a lot of research on it for many years - I don't know how else to explain my involvement with dust. It's not even my main line of research but I have to do it to do what I want to research. My point is I'm fortunate (courtesy of you the tax payer ) to have access to a heap of expensive a testing gear and an amazing environment that allows us to see and understand what our eyes and nose cannot. This is how we know about dust particle size distributions, various filter types, room design, dead spaces and the extent to which they can be cleared. We have studied regular labs that can get very dirty (eg using powdered rock samples) and very complicated but studying simpler extreme situations provides us a handle about what is going on and then extend these to more complicated everyday dirty situations. We have studied a range of materials and activities their dust generation capability. For example, most people have no idea that wood by itself sits there decomposing and making very very fine dust and lots of it, the more shavings and exposed wood you have the more of it is decomposes making this dust. The first thing one should do entering a shed that has not been used for some time is vent the shed. I have done a brief investigation of my shed and found out it is very complicated (see below) and has too many variables to control. However, because I have done measurements in less complicated environments that do not have all these variables I feel confident about what I am saying. I know very few people in Australia who have this experience.

This unit is fitted with thick, heavy duty needle felt bags and exhausts back into the work area where I can choose to evacuate the air with the exhaust fans, Exhaust fans 2 x 12” and 1 x 8’ were added and are used in times of high ambient airborne dust, such as power sanding or blowing down the machinery and benches ect.

This is by far the weakest link in your system. Your DC is continually contaminating your shed air with the most dangerous finest dust there is in your shed. It would be like a hospital collecting all the bugs in a ward, then keeping a good swag of the worst ones and spraying them back around the ward and trying to collect them all back up again after that. Once collected it is far better to get rid of them. Adding extra exhaust fans will certainly help clear the air but you would need to run them all the time your DC is running and for 15-20 minutes thereafter and why continually recontaminate your air if you can easily direct the DC outlet outside? You might have been doing this for 19 years - but some smokers also live to be 90, which a few deluded smokers hang onto as a reason not to stop smoking.

Let me just improve on your three excellent KISS principles
1: capture and control as much dust as possible at the source and get it outside the shed ASAP.
2: get as much outside* air into the workshop ASAP.
3: consider personal breathing equipment.
4: design and use large area cross ventilation (a door at one end and an exhaust at the other) into your shed.
5: Reduce dead spaces by adding in extra inlet vents in those areas that help clear the air.
6: Keep a tidy shed (I wish )

* Fresh outdoor air is not clean, it is in fact filthy and has a heap of other (ie not much wood) dust in it, that is why it is really hard to do accurate dust measurements in a shed (as I said I have tried - it's very hard to do). Fresh outdoor urban air still has somewhere between 100,000 and 1,000,000 particles per cubic foot (P/cuft) with a size greater than 0.3 microns (please excuse the units but this is what I remember). Inside a shed you might perform some activity and get a reading that has 200,000 P/cuft but a particle counter cannot tell what these particles are. If the majority is regular dust that will be less of a worry than if it is dangerous dust - the only way that can be done is to sample the dust and then analyse with an electron microscope ie very expensive. One also cannot just take differences between external and internal air readings, and between internal air readings before and after a process, because the human body itself makes dust and the mere act of air moving from one space to another changes its dust content. My point here is this is much harder than it looks and the majority of woodworkers who have bought particle counters to try to come to grips with this problem simply do not know what they are doing.

There's quite a lot of valuable information floating around in this thread.

For a while I was happily working in my workshop with the doors closed to minimise noise to our living area and neighbours. In the workshop, my dust extractor pumped out air which I assumed was relatively clean, how stupid to think that. Finally I realise that the constant filtering of recycled air would inevitably increase the concentration of the minute and harmful dust particles that the dusty is incapable of filtering. To add to this, using particleboard and MDF, I believe there are waste gases that concentrate as a result of this recycling situation.

Although, installing an extractor fan is required, more importantly, the filtered air from the dusty needs to be dealt with first.

Bobl, in regards to venting the dusty to the outside, if the dusty intake opening is a 5 inch diameter, why should the exit be significantly more than this ( 3 six inch hoses, as you suggested)?

Originally Posted by zelk

Bobl, in regards to venting the dusty to the outside, if the dusty intake opening is a 5 inch diameter, why should the exit be significantly more than this ( 3 six inch hoses, as you suggested)?

Hopefully it will be quieter (you have after all go to a lot of trouble to make it quieter) than the intake. Start with one 6" and see what happens, Try adding another and see if it helps?

Back in Jan 29 2009, Bill pentz said

I spent a good part of late 2006 and 2007 traveling around and testing air quality in various woodworker shops. Except for a very few shops almost all tested with dangerously high residual dust amounts. The exceptions were those who had a big exhaust fan with good cross ventilation and the few who went to the trouble to upgrade their stationary tool hoods, put their dust collector outside or build a cyclone and use good fine filters, plus also use a good down draft table. So yes, a good exhaust fan like my 30" put in a side door blowing out with the garage door cracked does wonders on keeping down the residual dust problems. Sadly, the air cleaners only seem to be effective at addressing the larger particles which are not as big of a health risk.

The more of these you can enact the better.

Bobl,

Sorry to do this to you, but I have a few more questions.

My 2Hp Carbatec tradesman dust extractor is claimed to be 1700 CFM, should I go down the path of using the dusty for air ventilation purposes, would it be possible to keep the balast gates open and maintain efficient dust extraction at the saw, by varying the amount of gate opening? The cross section of the saws internal ducting is significantly less than the ducting ( 5 inch dia ) that connects to it.

For air extraction purposes, would it make sense to reach the dead zone areas using a duct from the dusty?

Should fresh air vents in doors be placed at any particular level?

Zelk

Originally Posted by zelk

My 2Hp Carbatec tradesman dust extractor is claimed to be 1700 CFM,

That figure will be for free flowing air - ie no bags or filters in the way. As you as you add filters etc they will drop 20 - 40%, as soon as the filters start to clog it will drop even more.

should I go down the path of using the dusty for air ventilation purposes, would it be possible to keep the balast gates open and maintain efficient dust extraction at the saw, by varying the amount of gate opening? The cross section of the saws internal ducting is significantly less than the ducting ( 5 inch dia ) that connects to it.

It is really difficult to say which is best without measuring . Ideally you want maximum grunt at the dust generation point. Ideally one would add an extra dust collection point at the saw eg one on the cabinet and one on the saw guard. Keep the other gates closed when sawing so the dust is not drawn away from the saw. Once finished sawing open up all gates and run DC for 15-20 min. Leave any other exhaust fans on for the same time as well.

For air extraction purposes, would it make sense to reach the dead zone areas using a duct from the dusty?

It's better to put vents rather than extraction into dead zones. You don't really want to get the extraction points too far apart and fighting each other for air. Same as if you put two fans at opposite walls - they will fight each other for air and won't be able to move as much air as if you were to have them both on one side of the shed and vents on the others - this gives you a cross flow ventilation which is most efficient..

Should fresh air vents in doors be placed at any particular level?

The location on the door should be as far away from the collection point as possible. If you are collecting at head height I would put the vent at floor level and VV.

From what I understand, usually 1200CFM is enough for a saw, especially in my case where there is only one short 5 inch duct and a 2.5 inch one that feeds off it to go to the saw guard. I thought I had more than enough CFM and the surplus could be used for air extraction purposes. As mentioned, the cross section of the saw's internal ducting is small in relation to the main duct, and I wonder if there is a point where extra CFM is not effective.

Would air vents in strategic positions that are adjustable for flow have some benefit for balancing the air flow?

One question that wasn't quite answered before, am I better off using two 300mm fans that have 300l/s in the same location or one 350mm that has 600l/s or there's no difference, as far as air extraction concerned?

Zelk

Finally, I finished the job of installing a louvered extraction fan and venting out the exhaust from the soundproof dusty enclosure. The whole assembly clamps over the existing window frame with no modifications to the frame. The structure can be removed at anytime and is easily modified.

I now, have more sound escaping to the outside, particularly through the extractor fan unit. You will note that internally, I have mounted a louvre covering over the fan, in the hope of minimise the escaping machinery noise.

The 300 l/s fan is more than enough to ventilate the 5 by 7 by 2.2 m workshop. The internal louvre covering slightly reduces the extraction air flow rate, which I don't mind. I can further reduce the flow rate by closing the door.

It certainly is colder now in the workshop but I don't mind as there is less suspended dust.

Not sure if the louvre covering is all that effective in cutting down escaping noise, I need to do some measurements, but I would not mind some other ideas.

Zelk

Nice job Zelk - very very tidy and should be very effective.

I can understand you concern but if it was me, rather than install a fan in the window, I would have preferred natural light from the window and just used the DC to vent the shed.

Originally Posted by BobL

Nice job Zelk - very very tidy and should be very effective.

I can understand you concern but if it was me, rather than install a fan in the window, I would have preferred natural light from the window and just used the DC to vent the shed.

Thanks Bobl.

The window is one of two on the westerly side of the house, you'll note, I left a bit of window at the bottom, for when I work at the metal vice. The fan assembly helps with afternoon glare.

I have excellent fluoro lighting which I find myself using through the day anyway. I can open the north facing garage door, but my little boys would inevitably wander in.

I don't mind leaving the extractor fan on all the time as it is certainly quieter than the dusty, but at the end of the day, I can use either or both.

Zelk

Originally Posted by zelk

Thanks Bobl.

The window is one of two on the westerly side of the house, you'll note, I left a bit of window at the bottom, for when I work at the metal vice. The fan assembly helps with afternoon glare.

I have excellent fluoro lighting which I find myself using through the day anyway. I can open the north facing garage door, but my little boys would inevitably wander in.

I don't mind leaving the extractor fan on all the time as it is certainly quieter than the dusty, but at the end of the day, I can use either or both.

Zelk

Good points!