DC, indoor air quality and climate control

[Scott Winners]

How low is the threshold for power on time relative to indoor DC exhaust? It seems pretty low thresh hold.

I reviewed 10 pages of threads here eariler today. I get indoor air quality. I live in an area where we have really bad outdoor air quality, one of the two chronically worst places in the USA. I know more about PM2.5 than any human ought to have to learn. I get that lung exposure to fine particles is lifetime cumulative and irreversible.

It looks to me like before retirement I need to upgrade my DC to 220/240vac so I can get enough air flow to pick up my dust and get it filtered for indoor exhaust. I don't run any AC in the summer, but my heating bills, blazing blue barnacles. Heating is my second biggest reccuring expense, second only to the mortgage, even spread out over 12 months.

On the one hand, for six months of the year, I can roll my jointer or planer, and roll my DC (cloth bag exhaust filter) out onto the driveway for chip collection and let the dust blow away outdoors. If I exhaust the DC outdoors ( I can do that, though few of us can) I am going to need a big whopping wallop of BTUs to keep all my edged tools from rusting at the worst places in the cold months.

So fundamentally my question is can anybody exhaust their DC outdoors without getting rust on their plane irons or chisel edges? Or planer knives? Where, roughly, do you live and how often are you running your DC? How robust is your HVAC? I am thinking if I want the option of running my planer or jointer pretty much every day I am going to have to keep the DC exhaust indoors and filter agressively.

Thanks. I wonder if we should have a sub-sub forum, workshop threads not DC related.

[Jim Becker]

I've (fortunately) never had a rust issue with my tools in all the years I've been woodworking, despite living in what is generally a humid area. (SE PA) (91ºF today with a "real feel" of as much as 95ºF expected) Until the last couple of years (prior to moving here a few months ago) I did not have AC during the warm/hot months, either. My DC has always exhausted inside.

So where I'm having trouble following things around your question is why the concern with DC exhausting inside relative to humidity? It's the same air that went in the duct from the tool along with the chips and dust. And in your case, exhausting outside would be a bad idea for thermal reasons when you are heating.

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As an aside, the Workshops forum includes DC specifically because it's more and more often a "built in" system, much like electrical and air. More and more subforums isn't something likely to happen because they take resource to manage.

[Scott Winners]

So where I'm having trouble following things around your question is why the concern with DC exhausting inside relative to humidity?

All the absolute humidity calcs I can find are in metric, so please bear with me. There are 35.3 cubic feet in one cubic meter.

At 77 degrees F and 100% relative humidity outdoors, each cubic meter of air has 22 grams of water vapor in it.

Imagine I keep my shop at 68dF and 50% relative humidity. I run my DC, exhausted outdoors, 1000cfm actual, for one minute. I have pumped 28.3 cubic meters of conditioned air outdoors, and brought in 28.3 cubic meters of hot humid air.

When the HVAC system catches up, and the shop is back at 68dF and 50% RH, I have 367.9 grams of condensed water somewhere in the shop. A little more than 12 ounces, 12 oz beverage cans are typially labeled 355mL in my experience, and that just from running the DC for one minute.

In my shop I would look for that water to make slippery spots in dark places on the floor, and the honed edges of all my tools. I might collect some of it with a dehumidifier slaying electrons.

I have been looking at this because I am not constrained from venting a DC outdoors, though many users here are because of zoning/ neighborhood tranquility issues. Even though I am not constrained by zoning or neighbors, it doesn't look like venting a DC outdoors is a good idea for even a casual user in a mild climate.

[Jim Becker]

In your OP you asked about venting indoors which would be recirculating the same air. That's why I was confused. If you were exhausting outside (which I wouldn't do in your situation), I'd worry more about the humidity problem for sure. I don't vent outside here...well, that's not true if the door is open. But with my previous shop and the planned shop having HVAC via mini splits, I'm going to stick with venting inside. I put DC (and compressor) in a separate closet with the filter in that space and then have a non-linear return air path. That cuts noise because there's no direct path for it and I suspect it helps with air quality as there is more initial containment of anything that escapes the filters. (that latter part is speculation) When the new shop goes up, there may be some additional filtration on the return path to kick that up a little, too.

[Ron Selzer]

keep your DC exhaust inside and stop worrying about filtering every last bit of dust out, use a good cyclone, this will collect the bigger particles
Use a Air Filter Device, either bought or made, running it when in shop up to 24 hrs a day depending on how much fine dust you generate.
My air filter device is home made. I have a furnace blower mounted under workbench, have half the bench enclosed around the blower.
there are two intakes to the enclosed area, each one has a 24x24x18(? don't remember exact) bag filter with a 24x24x4 prefilter(sometimes 2-24x24x2)
prefilter gets changed when it looks dirty every month to 4 months depending on how much sanding gets done on bench
added a shop vacuum pulling thru a cyclone on 5 gallon bucket and now connect to sanders and routers, this has really helped with dust control
there was a really good discussion about how to filter indoor air and how to measure indoor air quality not long ago on here
don't have to spend a lot of money to make a big difference
good luck
Ron

this is the post I was referring to
Which Air Filtration is Better?? (sawmillcreek.org)

[Frank Pratt]

keep your DC exhaust inside and stop worrying about filtering every last bit of dust out, use a good cyclone, this will collect the bigger particles
Use a Air Filter Device, either bought or made, running it when in shop up to 24 hrs a day depending on how much fine dust you generate.

There are 2 paths to choose for air quality:

1. Use HEPA filtering right off the cyclone and possible a separate HEPA air cleaner. By going this way, you can avoid the use of a respirator most of the time. But it's important to have an air quality meter to tell you when particle counts get high.

2. Use less than HEPA air filtering and wear a respirator whenever generating dust and for a good while after, maybe hours, until all the dust settles out.

It's important to know that you cannot tell by site or smell whether or not the air is full of the most dangerous (and hardest to see) submicron particles. Decent air quality meters are available for less than $50, so there's no reason to not have one.

Of course, one is free to choose what one inhales.

[Alan Lightstone]

There are 2 paths to choose for air quality:

1. Use HEPA filtering right off the cyclone and possible a separate HEPA air cleaner. By going this way, you can avoid the use of a respirator most of the time. But it's important to have an air quality meter to tell you when particle counts get high.

In my experience this is absolutely not true. Particle counts, even with a HEPA filter on a 5HP cyclone get significantly higher than you should breathe. This measured with a Dylos meter in my workshop. The wide belt sander is the biggest culprit, but many other machines qualify. My running rule of thumb is that I wear a respirator whenever the woodworking I am doing raises particle counts above ambient. It takes an air filter (actually, I have 3 now) with MERV13 filters on them to achieve that quickly. And until they do, the air is bad to breathe. Lesser quality filters also accomplish this, just more slowly.

It's your lungs, and as Frank says "One is free to choose what one inhales", but I choose far more safety.

[William Hodge]

I vent outdoors in North Dana, Massachusetts. The only time I have a moisture problem is in the summer, if I leave the entry and exit blast gates open. Warm humid air has come in through the duct work and condensed on the cold machines. I have blast gates on the exhaust to keep air from seeping in when the blowers are off.

When it's really cold, like 20 below zero, it can be cold in the shop if I run the big blower for long. It will go down to 55. Radiant heat helps keep the steel and cast iron warm, adding temperature stability. Having the right size dust collector for the job at hand cuts down on exhaust air. I have several dust collectors. One has an 11" inlet, one has a 6" inlet, and then there's a central vac.

In a one person shop, the dust collector doesn't need to run that much.

[Scott Winners]

Appreciate the data point William, it is too late for me to edit the first post, I was looking at exhausting outdoors the whole time and inadvertently threw Jim Becker a curve ball.

[Jim Becker]

Appreciate the data point William, it is too late for me to edit the first post, I was looking at exhausting outdoors the whole time and inadvertently threw Jim Becker a curve ball.

Which I swung at and missed... LOL I haven't played baseball since I was a pre-teen I think...and it shows...

[Frank Pratt]

In my experience this is absolutely not true. Particle counts, even with a HEPA filter on a 5HP cyclone get significantly higher than you should breathe. This measured with a Dylos meter in my workshop. The wide belt sander is the biggest culprit, but many other machines qualify. My running rule of thumb is that I wear a respirator whenever the woodworking I am doing raises particle counts above ambient. It takes an air filter (actually, I have 3 now) with MERV13 filters on them to achieve that quickly. And until they do, the air is bad to breathe. Lesser quality filters also accomplish this, just more slowly.

It's your lungs, and as Frank says "One is free to choose what one inhales", but I choose far more safety.

Notice that I qualified that with "it's important to have an air quality meter to tell you when particle counts get high." But I should have said "I can avoid the use of a respirator most of the time" With most sanding operations, I still need the respirator. I have HEPA filtration on the DC and the shop furnace. The furnace fan is switched to run continuously when I'm working in the shop. With both the DC & furnace fan running, the counts go down quite quickly, maybe 10 - 15 minutes.

[Alan Lightstone]

Just trying to promote safety. I've seen way too many bad lungs in my career.

[Frank Pratt]

I understand, I was just wanting to correct my over generalized earlier statement