.5 micron filter question

[SpiderDave]

I've been considering an air filter for my dust collector, instead of piping outside. Mainly just because of the winter months and wanting to keep the heat inside best I can. I keep reading that it's the stuff that's .5 microns or smaller that get you. I know an air filter can't filter 'everything' but I'm trying to understand how this would work? If the filter goes down to .3 microns etc, wouldn't I be breathing the smaller particles in concentration that cause the harm? Obviously it has great results or so many people wouldn't be using them. But I don't understand why it's okay to breath the super fine stuff? Or is it just a matter of having dust at such a low levels that your body can deal with it adequately? So how do you know if it's okay? If it's all bad for you, then at what point can you be satisfied with a filtration system on your dust collector? Can you see where I'm goin' with this? Maybe this has been specifically addressed already on the forum? If so, I must've missed it.

Mine has the 4 bags, two on top and bottom, 3 HP, 2800cfm Shop Fox W1687.  If went with the filter, where would be a good place to start? Any recommendations of a brand, model, how's and why's or experience to share there? 

Thanks in advance to all!

[jteneyck]

Do you have heat in your shop?  If the answer is yes, duct the exhaust outside.  I live near Niagara Falls; it gets cold here in the Winter and Winter is pretty long.  I've been ducting my DC exhaust outside for over 2 years now and my heated shop stays nice and warm.  A dehumidifier in the Summer, which I needed anyway, takes care of high RH in the warmer months.  
If you don't have heat adding it would be good not just so that you could run the DC exhaust outside but also so you could use WB finishes in the colder months.  

If you decide a filter system is best, go with the finest rated you can buy for your system.  If you want to see how well it works, buy a Dylos particle meter.  Fine particles are bad and I'm not aware of a lower threshold where they become OK again.  The engineering issue is how to build a filter system that captures those fine particles w/o restricting flow to the point where the DC can't do what it was designed for in the first place.  Manufacturers try to strike a balance of rated particle size, surface area, pressure drop, and cost.  You might be able to improve on a commercial system by adding more filters if space and cost aren't constraints.  

No DC system is perfect and PPE is still a near must in certain situations and for folks who are allergic to wood dust.  

John

[fredhargis]

Even a world class DC won't get it all, just think about the times you're doing stuff that doesn't use the DC (like routing). The particle counter is the only way to know if what you are doing is working...but there's no doubt that exhausting outside is by far the best way to do it. Despite John's testimony, I can't convince my self that pumping 1000 CFM+ out of my shop in the winter won't affect my heating bill. When I had a day job, we had to run big air capture machines around our filling machines to exhaust some bad stuff (these were 15 HP units with 36" fanwheels, 10 of them). The amount of make up air and the energy required to bring it up to temp was incredible....part of which leads me to believe I probably wn't do it; at least not all the time. Some guys build a diverter that allows them to exhaust out in warmer temps, and filter when it's cold. I may do something along those lines. Should you choose to replace the bags with filters, get ready for the sticker shock. But even so I would suggest looking at Wynn Envirionmental, they can really be helpful if you give them a call.

[Phil Thien]

Someone needs to make a heat exchanger for DC exhausts. The problem is the makeup air can’t come from the same area as exhaust.

[arnman]

I would like to know how many woodworking operations actually produce a particle smaller than 1 micron.  Or smaller than 0.5 microns.

[SpiderDave]

Yup, my shops heated. And with an electric furnace that only handles it just so. It had a lot to do with keeping the heat and money inside, but it doesn't sound like it's worth it. My hands also have good and bad days even with temps just below 60* sometimes. It's an extremely annoying circulatory condition that sends my hands into hypothermia mode, while everyone's standing around in t-shirts. I'm lucky in so many other ways, I don't dare complain.

I checked the filters,...sticker shock indeed! Luckily I have an enclosed work area from the rest of the shop. I'll keep caulking every single crack in the room and the DC system as recommended and make sure I have an adequate air return vent. I'll just suck it up. buy some expensive gloves and pipe it outside. I read an article that said it was 1 square foot of intake air vent per 500 cfm's exhaust,.. does that sound about right? Thanks everyone for all the input, puts my mind at ease that I'm doing the right thing here. It's been a much longer project than expected and it starts working on a guys mind, patience and second guessing etc.

Any suggestions for the exterior vent itself then? An 8 inch blast gate supplier to recommend? An in-line one way flap or anything to keep cold air form coming in? A thermal break for the pipe, etc? How did you do yours? Back when this came to mind, I did save the material to build a muffler. I wonder if that's even something I'll need? Does anyone with a 3HP unit think their's is loud from the motor or air rushing out? I gotta play nice with my neighbors, though they are further away than most. Perhaps that's best put in a separate thread? IDK

Thank you everyone!

[jteneyck]

Fred, I didn't say blowing the exhaust outside was free as far as make up heat goes, but it's not much.  There is so much mass in the concrete walls and floor of my basement that the temperature goes down less than 5 degrees even if I run the DC for an hour straight, and the boiler quickly brings it back to set point.  I think my gas bill to heat my shop is maybe $20/month more during the heating months, and nearly that much to run the dehumidifier in the peak Summer months whether or not I'm in the shop.  

OP, I duct my DC directly to a vent window that I fit a 1/2" mech screen over to keep critters out.   I toyed with the idea of blast shutters on the outlet and a barometric damper on the inlet side, but didn't do anything because I wanted maximum flow.  I leave the exhaust window open most of the time and just close all the blast gates when not in use.  I open the make up air window (also with 1/2" wire screening across it) manually when I'm going to use the DC system.  I have a larger shutter connected to a rope/pulley system over at the DC on/off button, and open/close that shutter each time I turn the DC on/off.  At the end of the day I close the make up air window itself.  All this does take some extra steps, but it's dirt simple and works well.  If I get motivated, I'll install some type of actuator to open the make up air window each time the DC is turned on.  

I vent about 1200 cfm with 1.5 ft^2 of make up air inlet.  I wasn't sure that would be enough area but my gas boiler still vents up the natural draft chimney OK, so it must be.    

John

[fredhargis]

It may be different for a basement shop, mine is a detached building so doesn't have all that much mass to hold heat . It's extremely well insulated, but even so I probably spend $300-400 year for LP (forced air). So there's a considerable difference in our situations. I knew you weren't implying it was free, but in my case I'm fairly certain it would be more than I wanted to pay.That said, I would still like to do it for one year (vent outside) just to see what the cost is.

[MichaelMouse]

I've been considering an air filter for my dust collector, instead of piping outside. Mainly just because of the winter months and wanting to keep the heat inside best I can. I keep reading that it's the stuff that's .5 microns or smaller that get you. I know an air filter can't filter 'everything' but I'm trying to understand how this would work? If the filter goes down to .3 microns etc, wouldn't I be breathing the smaller particles in concentration that cause the harm? Obviously it has great results or so many people wouldn't be using them. But I don't understand why it's okay to breath the super fine stuff? Or is it just a matter of having dust at such a low levels that your body can deal with it adequately? So how do you know if it's okay? If it's all bad for you, then at what point can you be satisfied with a filtration system on your dust collector? Can you see where I'm goin' with this? Maybe this has been specifically addressed already on the forum? If so, I must've missed it.

A filter for your DC is not a sieve, where the largest gap determines what will pass.  It is a maze, with all kinds of blind corridors where even the smallest particles can't find their way through, because the pressure is too low and the obstacles too many.
Get the largest filter area you can get, and you can even increase thickness as you increase area, resulting in more trapping, which is what you want. 
The OSHA exposure stuff you read is based on a hell of a large load and long exposures.  Not really applicable to a small shop.

If you're truly paranoid, get an electrostatic setup to grab and hold stuff that might eventually come through if you neglect unloading the filter.

[jteneyck]

It may be different for a basement shop, mine is a detached building so doesn't have all that much mass to hold heat . It's extremely well insulated, but even so I probably spend $300-400 year for LP (forced air). So there's a considerable difference in our situations. I knew you weren't implying it was free, but in my case I'm fairly certain it would be more than I wanted to pay.That said, I would still like to do it for one year (vent outside) just to see what the cost is.

Try it Fred; I think you will be pleasantly surprised.  When you exhaust the air out of your shop and replace it with cold, outside air, that's about all you have to reheat when you shut off your DC.  Unless you run your DC for hours on end, the temperature of the structure and contents of your shop won't change much.  Building materials, wood, and machines don't lose heat very quickly.  And a well insulated structure like yours should recover very quickly, too, if your heater is sized appropriately.  


You can easily measure how much more it will cost.  Put a minute meter on your heater.  Measure the on time to run your shop at steady state for a few hours, after you heat it up in the morning if you turn it down at night.  Reset the minute meter to zero, or write down the value if you can't, and then run your DC for an hour. Turn off the DC and wait until the heater turns off after getting back to set point, then read the minutes on the meter again.  The amount of extra gas required to exhaust your DC outside equals how many minutes the meter registers during the hour you ran the DC plus getting back up to setpoint minus how many minutes it runs at steady state over the same period of time multiplied by the cost to run your heater per minute.  

John