Dust Collection questions

[Chilihead]

Well I can't add too much to the technical discussion, but I will add one point. Let's not lose sight of the fact that ANY dust collection is better than none, and ANY upgrade on your system you can make, now or later, is also better than none.
A shop vac collecting at the tool is a great start.
Add a cyclone collector to that shop vac and you've made a huge improvement.
Get a cheap HF dust collector, and you'll realize what a step up that is over a shop vac.
Put a Thien baffle or separator and/or upgrade the filter and again you've made a huge leap.
Getting a larger collector with more CFM....ditto
Getting more efficient ducting....ditto
Upgrading to a true cyclone machine....ditto

You can always make your system better and more effective, just remember to start doing something about it now....even it's a small step that you improve over time. That's far better than waiting until you can do the perfect (ie pricey) system and then realizing that you're waiting has already caused you health concerns.....too late then.

 

[Jeremy Scuteri]

Dust collection is one of my pet peeves since there is so much speculation and misinformation out there.
I have been in the HVAC business for 40 years I ran 80 pharmaceutical clean rooms so I think I might have a little insight.

One area that just wrong is the subject of air cleaners why are they mounted high?
Dust settles if you want to clean the air set it on the floor and collect all the dust that settles.
Having it high does almost nothing........

I thought that was a good point about where to hang the air cleaners (floor vs. ceiling). After all, I never generate any dust 8' up in the air. I already owned a Jet unit that was hung off the ceiling (in the center of the room) in the last shop (2 car garage). I figured I would try something new this time, so I took your advice.

I had some dead space behind the jointer because of the long bar that holds the fence. This seemed like it would just be wasted or get filled with clutter. This fit in there perfectly, and was a much easier install than hanging off the ceiling. That alone is a huge bonus.
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[KenOfCary]

I still haven't removed my air cleaner from the shop in Cary, but will need to do that soon. I hadn't considered putting it on the floor rather than hanging it overhead and restricting some overhead space. This has made me think twice about where to place the unit.

The new shop will be L-Shaped and putting it on the floor near the L should work well. I'll have to consider this solution well. I always learn new stuff here and that it what I like about this website. I definitely don't know everything I need to know about woodworking and shop setup, but I learn a lot here.

 

[Alan in Little Washington]

I'm guessing along the scale:

1. Woodworkers
2. Woodworkers who prefer broom clean
3. Woodworkers who prefer visually clean
4. Woodworkers with respiratory concerns

I didn't start doing calculations and reading more about the topic until trying it myself.

There are a lot of variables. A "very large thermal mass of the shop" implies insulated space and large cooling/heating equipment 24/7. That's a big cost, easily offset by a cyclone, filtration, and decent ductwork. For a weekend warrior, the mass won't get to working temperature. Or if the exhaust is only 250 CFM and is turned on and off frequently only for a minute at a time, it won't pull in much outside air. But I burned a DC motor trying that one!

What do you consider the thermal mass of the shop? I did the calculations (and post the results here) many years ago, so I may be wrong, but the thermal mass of a shop which includes, the wood, masonry, concrete, etc. structure and its wood, steel, and cast iron contents may be as much as 1000 times the thermal of the air it contains. The thermal mass will quickly reheat the new air once the DC is turned off with little loss to the thermal mass. Sure, if the DC runs continuously for a few hours, the temp will decrease. But, think about what happens in a refrigerator- every time you open the door, all the heavier, chilled air immediately dumps out on the floor. Once you close the door, the infill air is rapidly cooled, most of the time without the compressor running and that has more to due with the contents of the fridge than the plastic walls and insulation.

 

[SteveHall]

A "very large thermal mass of the shop" implies insulated space and large cooling/heating equipment 24/7....For a weekend warrior, the mass won't get to working temperature.

The thermal mass will quickly reheat the new air once the DC is turned off with little loss to the thermal mass.

The hobbiest doesn't have a conditioned shop, so this x1000x times thermal mass is the problem. If you spend an hour heating your shop air with a tiny 1500W electric on a cold 35°F Saturday morning, a big vented dust collector will empty that in eight minutes and you have to start all over again.

 

[Alan in Little Washington]

The hobbiest doesn't have a conditioned shop, so this x1000x times thermal mass is the problem. If you spend an hour heating your shop air with a tiny 1500W electric on a cold 35°F Saturday morning, a big vented dust collector will empty that in eight minutes and you have to start all over again.

Totally misses the point. If the shop is unheated and has been at the same temp as outside for some time the thermal mass of the shop structure and contents will be at equilibrium with the outside air. When you try to heat the air, the thermal mass of the shop structure and contents initially works against warming the air. If the shop air and structure start out at 32° F, the thermal mass will slow the heating process. However, once the air has been heated to some temperature comfortable temperature over some period of time- 1 hour, 2 hours, etc., the thermal mass of the shop structure and contents will also have been heated. Depending on the amount of time that has elapsed, it may not be to the full temp of the warmed air. If you stop running the DC after only 8 minutes or whatever time it takes to replace the warmed air with cold, make-up air, the cold shop air will be quickly warmed by the thermal mass of the shop's structure and contents. It is commonly called the thermal flywheel effect. Again, the thermal mass of the shop structure and contents is many times that of the shop's air.

Thermal mass is the ability of a material to absorb and store heat energy. A lot of heat energy is required to change the temperature of high density materials like concrete, bricks and tiles. They are therefore said to have high thermal mass. Lightweight materials have low thermal mass. It is distinct from a material's insulative value, which reduces a building's thermal conductivity.

 

[SteveHall]

If the shop air and structure start out at 32° F, the thermal mass will slow the heating process.

Agreed.

However, once the air has been heated to some temperature comfortable temperature over some period of time- 1 hour, 2 hours, etc., the thermal mass of the shop structure and contents will also have been heated.

I calculate more than 18 hours just for the slab...

450 SF shop, 4" thick concrete floor = 150 CF of concrete x 144 lbs/CF = 21,600 lbs of concrete

The specific heat of concrete is 0.156.

Assume concrete is 40°F and comfort is 68°F = delta 28°F

So...

21,600 lbs. * 0.156 * 28°F = 94,348.8 BTUs

My heater is 1500W hours (about maximum for a 15A circuit) x 3.413 = 5,120 BTU

94,348.8 total BTUs needed / 5,120 BTU heater = 18.4 hours
​

This does not include losses, the mass of drywall and steel tools, and a lower actual starting temperature.

Interestingly, here's my shop's air:

436 lbs. * 0.24 * 28°F = 2,930 BTUs / 5,120 BTU heater = 34 minutes
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Leakage and losses are high given the shop tightness and thermal mass, so I find it takes about 1-2 hours to actually warm the air. Someone else with better math skills could correlate these. Advanced material science/physics would bend these calculations into a curve, too.

....the cold shop air will be quickly warmed by the thermal mass of the shop's structure and contents.

I'm just not seeing that in the math or experience. My part-time shop never has the mass at comfort temperature in the middle of winter. That's why I value the air I heat so much--it's all the heat I have until mid-day sunshine through the windows. The one time I tried exhausting dust outside, it got cold in about eight minutes, almost exactly what I later calculated as make-up air.

 

[Alan in Little Washington]

I'm just not seeing that in the math or experience. My part-time shop never has the mass at comfort temperature in the middle of winter. That's why I value the air I heat so much--it's all the heat I have until mid-day sunshine through the windows. The one time I tried exhausting dust outside, it got cold in about eight minutes, almost exactly what I later calculated as make-up air.

Get a saw dust burning heater.

There is just no way around the fact that you will need to add BTUs in the winter to warm up a previously unheated shop and will continue to need to add if there is a lot of infiltration or the insulation is inadequate or non-existent. But getting back to the original discussion. If the entire shop (not just the air) has been warmed up, running a DC by discharging outside for short periods*, just doesn't have the effect on shop temperature, except briefly, that many think. *My shop is insulated and heated but I still don't run my DC continuously. I rely on auto gates and auto start. The rare exception is when planing a pile of stock for a major project.

You pays the price and takes a the chance- either recycle the air with good cyclone and filters which comes with its own set of consequences (reduced CFM and SP, possibly inadequate filtering, filters to clean, cost, etc.), or you discharge outside (if you can) and deal with heating (comfort and cost) or be able select either. If you have a commercial shop where it is necessary to run the DC for long periods then it is time to invest in good insulation and heating (I would never build a serious shop on a slab without considering hydronic in-slab heating), etc. and be prepared to pay for gas or electricity. Unless you live in the western mountains, shop heating is not a big deal here in NC, at least not like it is for the guy I talked to from Canada. There is always longjohns Like Star Wars, "Do, or Do Not, there is no try"

 

[Dee2]

Next shop, passive radiant floor heating and passive geothermal cooling. Maybe.

 

[sawman101]

Being more of a redneck backwoods hillbilly, I approached the dust collection problem with little idea of what I needed, rather I did it with what I had in my pocket and what was easy to obtain. Bought a used HARBOR FREIGHT 2 hp dust collector that came with a big Brute trash can, trash can/vortex type lid, a bunch of plastic blast gates, used 4" drainage pipe, many 4" clamps, and a bunch of dryer hose. Threw out the dryer hose first, then purchased additional 4" PVC drain pipe and fittings, and perforated metal strapping. Built a 6x8" room adjacent to the exterior wall of the shop and went to work. Use a remote DC switch with the little button unit clipped to my shop apron. I have more in PVC pipe, flexible hose, and fittings than the DC unit and remote switch. Cheap and works very well for me. I heat with wood and have no problem with heat loss due to air exchange, and I don't need a filter. Simple, cheap, and effective for my 24 x 32' x 8' shop. And yes, I do have fire insurance and contents on the shop, which is unconnected to the house.

 

[VTHokie]

Thank you for the terrific information and all of the considerations for installing an efficient DC system! Just thinking about the physics, it would seem that fine dust particles would easily become airborne and remain aloft for quite some time, even without much air circulation in the room. As such I would expect the concentration of those fine particles to diffuse and become evenly distributed throughout the room. For this reason, wouldn't a ceiling mounted filter be nearly as efficient as one that sits on the floor? Would a unit positioned on the floor be more limited by other physical barriers on the floor to efficiently filtering the air? I'm very curious about DC and want to make sure I get it right as Im setting up in an attached 2 car garage and want to make sure that Im not only protecting myself but my wife and daughters as well. Thanks for any insight!

 

[KenOfCary]

Filtering airborne dust is a secondary operation. It is always best if you can collect the dust at the source before it even gets into the air. Having said that I know most people also have an airborne filter unit of some sort. Whether in the air or on the ground is more efficient remains to be seen in my case. I think the most important thing will be that there is a clear path of some sort to actually circulate the air in the room when it is on.

I try my best to get dust collected at the source, but some always gets away from things like miter saws and such. I use a dedicated dust collector at the lathe to try and get as much as I can - especially the fine stuff when sanding for instance.

 

[Alan in Little Washington]

Three things to consider with an air cleaner- it is really only any good if it removes fine dust in the .5 - 10 micron (dangerous) range, the turnover is sufficient, and it doesn't just keep re-filtering the air in the immediate area. Many have called air cleaners dust circulators, that's kinda harsh but it may be true in some cases.

 

[Jeremy Scuteri]

....I'm very curious about DC and want to make sure I get it right as Im setting up in an attached 2 car garage and want to make sure that Im not only protecting myself but my wife and daughters as well. Thanks for any insight!

Good luck with your endeavor. With so much contradictory and incomplete information out there, "getting it right" is nearly impossible, but a good thing to strive for.

The following site is a good place for information if you feel inclined to look into this yourself. It tends to be a little bit on the "alarmist" side as far as the dangers of dust are concerned (IMHO), but the information seems objective and good. http://billpentz.com/woodworking/cyclone/


Just take everything with a grain of salt, use your own judgement and remember that risk never goes to zero.

 

[luckyGoose]

Concur with Jeremy, Bill Pentz' site does have an alarming tone to it, but it also does provide good information. I set up an air cleaner the way he's described: http://billpentz.com/woodworking/cyclone/air_cleaner.cfm. It's placed on the floor, but I've found it to be quite effective. Of course, as Ken said, it's important to capture dust at the source. Cleaning the air after the fact is secondary.

I wouldn't go to the extent of using a particle meter, I'm sure the particle count is high outside as well, so it might not be a fair assessment of how dusty the shop is. More info at https://woodgears.ca/dust/dylos.html.

 

[VTHokie]

The following site is a good place for information if you feel inclined to look into this yourself. It tends to be a little bit on the "alarmist" side as far as the dangers of dust are concerned (IMHO), but the information seems objective and good. http://billpentz.com/woodworking/cyclone/

Thanks Jeremy - Ive visited the Bill Pentz website on multiple occasions (and have it bookmarked) but I think you really hit the nail on the head when you said what you said about contradictory and incomplete information. After awhile, it becomes difficult to sort the useful information from that which is not. No doubt that capturing the dust at its source is the primary objective. I'm more concerned about capturing the fine dust particles that may escape and become airborne. I'll set up as best as I can (going to try the air cleaner on the floor) and adjust accordingly. Thanks for the great responses!

 

[Rwe2156]

WADR, Pentz is geared toward total lung protection, ie. OSHA compliant systems. As such, it is beyond reach for most hobbyist ww'ers unless you have the financial means.

IMO it is far more practical use personal dust collection (face mask or respirator) for lung protection, and design a DC system for the purpose of reducing broom time and keeping the air cleaner. For the average garage shop, a 2HP blower w/cyclone and 6" ducting will work very well. In combination with an air filtration unit I think you will have a very clean shop.

Keeping dust out of the house is a whole 'nother topic. The first step is ensuring the air handler cabinet is air tight.

 

[gmakra]

"Pentz is geared toward total lung protectionen"
Nope and I say BS first off someone please show me the OSHA guidelines instead of internet BS.
I think you will find that OSHA covers its self quite thoroughly on safety standards along with ASHRE, ARI and a host of other associations with various shades of grey.
And Pentz is geared to Pentz's wallet and that my friends is my story and I am sticking to it.
When I see some data that includes particle count meters meters and data based on industry standard NEBB air balance procedures then I will listen.
In the meantime this discussion is opinons by people not trained in the subject matter.

 

[Jeremy Scuteri]

I have zero training in the subject matter. Just someone struggling to understand it for the most part. You have made it clear that you don't like Pentz as a source of information. Can you point us to a better source for accurate information on woodworking dust collection?

 

[Rwe2156]

"The Department of Labor, Occupational Safety and Health Administration (OSHA) recommendation is no more than 5 milligrams per cubic meter (mg/m3) average over a full work day with no more than a 15 mg/m3 exposure during any fifteen minute period." Source:

Jeremy, its difficult to find practical advice on this subject. I think if you follow some basic concepts you'll be ok.

The system I have isn't even supposed to work according to the "experts" but, in fact it works quite well!

1 1/2HP blower, Super Dust Deputy cyclone, vented outside, 6" ducts, 4" flex to machines. I am collecting a 20" planer, 8" jointer, 19" bandsaw, 16" drum sander. These machines are all withing 12' of the unit. The cabinet saw is 20' away the floor sweep is 25' away.