Phil Thien's Baffle and Bill Pentz

[Harry Hagan]

Is there any reason why you couldn’t route the air from your DC system directly into an air filtration unit like the JDS to ensure maximum air filtration while your machinery is running? In other words, make it a two or three-stage system?

Cyclone > DC > JDS

That would certainly decrease the level of contaminated air in the shop.

Having a stationary DC might be necessary; but making the DC/JDS connection shouldn’t be a problem if space permits. You’d also have to include an input door for airflow into the JDS unit while running it to filter shop air in “normal mode”.

I’ll have to give JDS a call . . . see what they say.

[Alan Schaffter]

Is there any reason why you couldn’t route the air from your DC system directly into an air filtration unit like the JDS to ensure maximum air filtration while your machinery is running? In other words, make it a two or three-stage system?

Cyclone > DC > JDS

That would certainly decrease the level of contaminated air in the shop.

Having a stationary DC might be necessary; but making the DC/JDS connection shouldn’t be a problem if space permits. You’d also have to include an input door for airflow into the JDS unit while running it to filter shop air in “normal mode”.

I’ll have to give JDS a call . . . see what they say.

You are back to the issue we are trying to avoid- back pressure and reduced CFM caused by using a filter. First the JDS won't handle the DC's CFM, and second unless you have really good, multi-stage filters in the JDS it won't capture the fine dust.

[Nathan Callender]

Could an air-air heat exchanger be added to recover some of the heat (cooling) loss? I really have no idea if the pressure loss of one of those would make the idea pointless. I do recall (it's been a while since I looked at this) that they can deal with the humidity issue to some extent in the summer also.

Just a thought,

mark

Mark, that is definitely a really interesting idea. I'm thinking it would need to be physically rather large to exchange that amount of heat at 800cfm, but maybe someone could do that math (not me on a Saturday :-) ).

Generally, however, once the complexity of the system starts going up from 'simple', then implementation really becomes painful for most people and it doesn't get done. This is probably the biggest issue with Pentz' recommendations. No doubt a 220V, 5HP DC and good cyclone with several excellent 0.5 micron filters and 6-8" ducting to all machines with custom fabricated hoods is 'the way to go' but how do you convince a novice woodworker of that when he/she just bought their first table saw and wants to make a couple of end tables? That's where a broom and $50 face mask and working in a temp setup in the garage are the best choices.

FWIW, I'm still looking for that perfect DC solution, but I do know that it's never going to be a cyclone because 1) I don't have 220V and probably will never 2) I am realistically not going to install duct work 3) I don't have the space in the garage to put one - I'd just rather have another tool. So, that means I'm much more likely to wind up with something based on the thien baffle.

[Steven Green]

IMHO John hit it first shot. Go as far as you can, test if you can, and use a filter to snag suspended detrius. Then wear a mask. I exhaust outside in the winter when it's not around zero. In the summer I have a final filter that is in the vent that returns air from the Separator, and the collector. Then I run an air filter. I also avoid most wood the I'm sensitive to or know to be harmful. Add the mask when I need it and I'm as good as I'm gonna get and that's ok. Love Phil's separator by the way. I hate changing those bags under the collector.

[Jerome Hanby]

I have a somewhat related question. How does the exit run effect overall performance if you are venting outside? I know long runs between tools and the dust collector mount up, but could I have a long exit run without killing performance? Reason I ask, I've setup several smaller dust collectors instead of one huge system so that I have "islands" of tools with the dust collector only a few feet from each tool. If I can have fairly long exit runs, I could incorporate that into my new shop...

[Dan Hintz]

How does the exit run effect overall performance if you are venting outside?

From a practical perspective, it doesn't matter where the line length resides, entrance or exit... it's still a resistance that must be overcome by the blower. Whether or not it's pushing or pulling doesn't much matter from an efficiency standpoint.

[Jerome Stanek]

From a practical perspective, it doesn't matter where the line length resides, entrance or exit... it's still a resistance that must be overcome by the blower. Whether or not it's pushing or pulling doesn't much matter from an efficiency standpoint.

But if you are venting outside you are not forcing air through a filter

[Anthony Whitesell]

But if you are venting outside you are not forcing air through a filter

True, but you are still pushing air through a duct. If you were to use StaticCalc at Mr. Pentz's website, the length of the run would still exist, only the SP for filter loss would be 0.

[Dan Hintz]

But if you are venting outside you are not forcing air through a filter

The use of a filter wasn't specified in the question... he merely questioned about having numerous short entrance runs and a long exit run (as opposed to multiple long entrance runs and one short exit run). The difference between using a filter versus a length of tubing would have to be considered as a separate issue.

[Michael W. Clark]

The others are correct, losses are losses regardless of which side of the fan you are on.

However, if you are downsteam of your collector (clean side with particulate removed), you do not have to run the duct velocity at the higher speed to keep the dust entrained. You can put in larger duct running at a lower velocity and reduce the outlet losses tremendously.

[Mark Blatter]

I also avoid most wood the I'm sensitive to or know to be harmful.

Steven, which woods are you sensitive to?

Personally I am not aware of any species that bothers me, yet I do find that as I have gotten older dust bothers me a bit more. Being young and foolish years ago I was not as careful with things like hearing protection as I am today. I don't want to look back in 20 years and realize that I was still foolish, though perhaps not so young, with regards to dust control.

[Jim Neeley]

Scanning back I see several posts talking about the cost of natural gas to heat the make-up air for exhausting outside. I agree that for the hobbiest the cost is pretty small. The assessment I recommend for someone considering it is the capability of their heating system to generate heat fast enough to keep up, if you care about this. I have no preconceived recommendation for you; do the simple math below.

It takes a little over 1,000 BTU/hr to heat 1,000 CFM of air by 1 degree F.

Here in Alaska I have a 40,000 BTU heater in my garage. It is (I am assuming about 80% efficient), giving me 32,000 BTU/hour of shop heating.

From this I can roughly calculate that if my DC is exhausting 1,000 CFM outside and I've got a door, window or other vent open to allow make-up air to come in from outside, and I was to run my DC for a fair period of time, the heater could keep the average shop temperature about 32 degrees above the outside.

If it's in the 30's my shop would stabilize in the 60's (with the heater running full-bore, full-time). If it's 0F outside, my shop would stabilize around 30F. At -20F it'd be around 10F.

If instead of a gas heater I had a 5KW electric heater, it would generate about 17,000 BTU/hr, giving me a 17 degree temperature rise.

If I was using a 1,500 watt electric heater it's about 5,000 BTU/hr giving me about 5 degrees rise.

You should adjust your numbers if your CFM varies significantly from the 1,000CFM. If you had only 500 CFM you could expect twice the rise; if 2,000 CFM, half of the rise.

As a practical matter, check out the size of your shop heater and do the math.

Please note that I'm offering this for a guide line calculation and do not clame it to be precise, as there may well be folks piping in to point that out.

It will give sufficient accuracy for you to assess whether or not your heating system will be able to generally keep up during extended periods of DC usage if you plumb it to exhaust outside.

Jim in Alaska

[Ty Williams]

I would also suggest figuring out if your heater can even run a 100% duty cycle without hurting itself. Most residential ones probably can't/won't. So you need to factor in the max duty cycle. You also need to determine initial cost excess for buying a furnace large enough to keep up with the DC vs one "correctly" sized to the thermal efficiency of the structure. I'm sure there's probably increased maintenance costs on the bigger furnace as well. Then you get to do it all over again for the air conditioner, which is going to be much more critical in most places in the US due to the fact that the air conditioner is responsible for dehumidifying the air during the hotter, wetter summer. Having a shop where the humidity spikes to the point that the interior temp of the shop (and the stuff in it) is below the dew point in the shop every time the DC kicks on is NOT going to be good for the wood or the machines. You could try running an Enthalpy Recovery Ventilator (ERV) to regain control of the temp and humidity, but I have a feeling an ERV that'll keep up with 1000CFM over a ~20* temp change and ~40% humidity change would make your eyes water when you saw the price.

I would prefer to dump the waste air outside because it's easier to be safer that way, but the total system costs prevent me from doing it.

[Michael W. Clark]

I may be in the minority, but I do not see that air conditioning and dehumidification is a requirement for the process of woodworking and furniture building. I think it is more of a creature comfort.

Heating, yes. I could understand wood behaving much differently when its very cold (no personal experience, just theorizing), plus the safety issue of the bulky clothes required to tolerate the cold and getting near sharp, spinning objects.

I think Jim's quick calcs are very good. Anyone that goes through these and determines that it is not feasible for them, should probably stop right there. No need for additional analysis.

[Dan Hintz]

I may be in the minority, but I do not see that air conditioning and dehumidification is a requirement for the process of woodworking and furniture building. I think it is more of a creature comfort.

I never looked at it in any different way... if I'm not comfortable, the rest doesn't much matter. I don't like freezing or sweating in my shop. Never considered any short-term issues with the material itself.