Phil Thien's Baffle and Bill Pentz

[Alan Schaffter]

I would need a consulting fee for that one! It would be nice if someone would figure it out, but provide and answer in $ for both cooling and heating. And of course that figure will vary widely depending on the location and temp spread- it will only affect some folks for a few months a year, others like our northern neighbors and those in the South more so.

If the large number of threads about remote controls for DCs I keep reading are any indication, I would bet few folks run their DC's that long, even over a 4+ hour shop session.

Anyway, the temp issue aside, you can't disagree that a DC with no filter is more efficient than one with a filter, all other factors being equal.

I know there are other issues- will the separator remove enough dust to avoid problems with the neighbors? Will it be no worse than a clothes dryer vent lint?

And you also have the issue with deadly Carbon Monoxide containing reverse flue gas if you have a gas or oil-fired furnace or hot water heater in your shop.

But for many this can be a less expensive and simple way to improve dust collection. I think too many folks get hung up on the idea of a filter. In the case of adding a cartridge filter to a single stage DC you are really handicapping your DC and it is a waste of money.

[Randy Klein]

Just to clarify: I wasn't trying to see how a Thien Baffle can be integrated into a cyclone (Bill's design or other).

I'm just doing my research on a DC and it seems like there is a few options:
1. Regular bag (or cartridge) DC
2. #1 modded with a pre-separator based on Phil's baffle
3. #1 with Phil's baffle internal to the DC
4. Stock cyclone
5. Clearvue cyclone

So has anyone combined #2 and #3. Any advantage or just redundant? Possibly with different radius for the 240 degree section - smaller radius on the pre-separator and a larger radius on the internal baffle. I'm thinking that the separator needs a larger one for the chips and the internal could benefit from a larger radius for the smaller dust.

[Alan Schaffter]

Phil...it's been a while since I used this part of my brain.

If your shop was fully warmed up to 70F and you turned on your dust collector which exhaused outside and had a window open to let the make-up air in...

BTUs/hr = Cp x Mass flow x delta Temp
BTUs/hr=1.08 x 800 x (70-(-5)) = 64,800 BTU/hr

Natural gas gives about 1000 BTUs/cubic foot...

64,800/1000 = ~65 cubic feet

Assuming your home heating system is 85% efficient...

65/0.85 = ~76 cubic feet of natural gas is actually used if you run your dust collector for 1 hour (continuous or in aggregate). Just multiply this number by the cuft rate on your gas bill to receive your heart attack.

-Jeff

This is actually a more complex problem- because you forgot to figure in the affect of thermal mass of the shop and how long it takes for the cold air and the shop mass to reach equilibrium temp after running the DC, what that temp is, and then how long and how many BTU's it will take to warm everything up.

[Jeffrey Makiel]

Alan...air conditioning is a little tougher because humidity reduction must also happen in addition to cooling the air. And, humidity reduction cost money. However, the pyschrometric chart comes to the rescue...

Outside 95F, 75%RH: Pysch chart says 52.6 BTU/Lb
Inside 75F, 55% RH: Pysch chart says 29.1 BTU/Lb

Also, the density of air is about 14.5 CuFt/lb at 95F

BTU/hr = (52.6-29.1)BTU/lb x 800cuft/min x60 min/hr / 14.5 cuft/lb
BTU/hr = 77,800 BTU/hr

Assuming your A/C is 80% efficient...

77,800/0.80 = 97,200 BTU/hr or about ~8 tons of cooling for every hour you run your dust collector. Understand that most homes units are 3 to 5 tons for the entire house.

Keep in mind, the figure above does not include normal heat gain from your shop walls.

-Jeff

[Jeffrey Makiel]

This is actually a more complex problem- because you forgot to figure in the affect of thermal mass of the shop and how long it takes for the cold air and the shop mass to reach equilibrium temp after running the DC, what that temp is, and then how long and how many BTU's it will take to warm everything up.

That's correct.

The example I used was steady state. If starting a shop from cold, it is an unsteady state problem and requires a lot of knowledge on how a person's shop is constructed in order to calculate this scenario, (e.g., wall construction, floor, etc.) as well as the amount of equipment/materials that are in it. It is well beyond a boiler plate formula or an accurate generic assumption.

The cooling calculation is also steady state. That is, the shop is already at its normal A/C temp and humidity.

-Jeff

[Mark Engel]

I think too many folks get hung up on the idea of a filter. In the case of adding a cartridge filter to a single stage DC you are really handicapping your DC and it is a waste of money.

Can you explain why you think a cartridge filter handicaps your DC and is a waste of money?

[Alan Schaffter]

I think if I left the refrigerator door opened for 60 minutes with an 800 cfm fan inside blowing out.... well, you get the picture.

Some analogies just don't hold up.

We are not talking about putting a 800 cfm fan in a fridge- we are talking about opening the door- in a few seconds the cold air tumbles out and is immediately replaced by air at room temp. In a typical small, closed, one-car-sized typical shop of 3000cu. ft. (12' x 25' x 10') it will take almost 4 minutes for the air to exchange 100% so the analogy holds, and in fact it is in favor of the shop, especially when you consider an 800 cu fan is probably only sucking 500 cfm or less. The location of the source of outside take-up air and the tool in use, might actually cause a lot less than 100% of the shop air to be replaced in that time. Some of the air will not be exchanged.

[Phil Thien]

This is actually a more complex problem- because you forgot to figure in the affect of thermal mass of the shop and how long it takes for the cold air and the shop mass to reach equilibrium temp after running the DC, what that temp is, and then how long and how many BTU's it will take to warm everything up.

Not to get too far OT, but...

If we're removing 70F air and replacing it with -5F air and enough energy to reheat it to 70F, why do we care about the thermal mass?

If some of the energy to reheat the -5F air to 70F comes from the thermal mass, then that energy will have to be replaced by burning the gas we didn't use to heat the air.

In any event, it looks like we'd have to spend $.88 to reheat the conditioned air for one hour of running an 800-CFM DC exhausted outside (assuming the national average of $13.68 per 1000 cubic feet of natural gas).

And yes, I agree that an hour is a long time. I figured it was at the very top end of what someone may do during a fairly busy weekend day in a shop.

Seems like a no-brainer, provided you take care of any CO issues.

[Alan Schaffter]

Can you explain why you think a cartridge filter handicaps your DC and is a waste of money?

That is for a single stage DC, with no pre-separator of any kind. The filter clogs very, very quickly since there is little to prevent dust from flowing up into the filter. CFM through the filter and at the source is reduced very quickly. That is why many of those systems have beater bars built into them. To work effectively the beater bar must be used regularly and often. The simple act of using a beater bar breaks down the filter media, so over time the filter passes more and more hazardous dust. At the prices for a cartridge filter it is a waste of money unless you add a cyclone or other efficient pre-separator. Or better yet get a pre-separator, discharge outside, and ditch the filter.

[Mark Engel]

That is for a single stage DC, with no pre-separator of any kind. The filter clogs very, very quickly since there is little to prevent dust from flowing up into the filter. CFM through the filter and at the source is reduced very quickly. That is why many of those systems have beater bars built into them. To work effectively the beater bar must be used regularly and often. The simple act of using a beater bar breaks down the filter media, so over time the filter passes more and more hazardous dust. At the prices for a cartridge filter it is a waste of money unless you add a cyclone or other efficient pre-separator. Or better yet get a pre-separator, discharge outside, and ditch the filter.

So leaving the 30 micron filter bags on the DC is a better option if outside exhaust cannot be used?

[Leigh Betsch]

I tried to figure out the heat lost once. I got a headache. I bought a Clear Vue and put it in a closet with .5 micron Wynn filters. I put another .3 micron heppa filter in the closet return just for good measure, and cause I already had it (free). Now I don't have a headache, just a lighter wallet.

[Alan Schaffter]

Not to get too far OT, but...

If we're removing 70F air and replacing it with -5F air and enough energy to reheat it to 70F, why do we care about the thermal mass?

If some of the energy to reheat the -5F air to 70F comes from the thermal mass, then that energy will have to be replaced by burning the gas we didn't use to heat the air.

In any event, it looks like we'd have to spend $.88 to reheat the conditioned air for one hour of running an 800-CFM DC exhausted outside (assuming the national average of $13.68 per 1000 cubic feet of natural gas).

And yes, I agree that an hour is a long time. I figured it was at the very top end of what someone may do during a fairly busy weekend day in a shop.

Seems like a no-brainer, provided you take care of any CO issues.

The main point was not that it wouldn't require more heat, but the affect on the shop temp wouldn't be as bad as many think. Wow, at only $.88 well worth it in my mind, and even more so for folks in temperate climates. -5 deg. F, yikes, we rarely get into the 20's here in NC.

Of course all this is academic for a roll-a-round DC unless you run some extra hose outside.

Have you done any tests with your baffle with and without the back-pressure of a filter? Do you see any change in pass-through?

[Jeffrey Makiel]

If we're removing 70F air and replacing it with -5F air and enough energy to reheat it to 70F, why do we care about the thermal mass?

If some of the energy to reheat the -5F air to 70F comes from the thermal mass, then that energy will have to be replaced by burning the gas we didn't use to heat the air.

Phil...that's correct. If we are only talking about the cost to heat up the make up, the calculation provides a pretty good idea of how much it will cost per hour.

In Alan's scenario, he's assuming that you just entered the shop after the heat was shut off for a very long time and everything is very cold. Now, your heating system must heat up the shop, warm its contents and also heat the make up air ejected by your dust collector as you work in the cold shop.

However, the cost to just heat up the make up air stays the same. What changes is the amount of time it takes to get your shop up to 70F when running your dust collector versus not running your dust collector. Alan's scenario addresses more of a comfort concern rather than a cost issue.

-Jeff

[David Hostetler]

if this link is right
http://wiki.answers.com/Q/How_many_b...f_air_1_degree

64,800 btus, assuming 100% efficiency.

Which just isn't going to happen... You are doing exceedingly well with anything to get 90% efficiency...

[David Hostetler]

So has anyone combined #2 and #3. Any advantage or just redundant? Possibly with different radius for the 240 degree section - smaller radius on the pre-separator and a larger radius on the internal baffle. I'm thinking that the separator needs a larger one for the chips and the internal could benefit from a larger radius for the smaller dust.

Funny you should ask. When I first set up my HF DC, I installed a Thien baffle in the inlet ring. I sucked up lord only knows what into the impeller when I took the hose off of the TS and dropped it on the floor, the bang sounded like a gun going off in my shop... I QUICKLY took the baffle out and built a pre separator based on a 55 gallon drum.

I have thought about reinstalling the baffle, but I get so little blowby into the bag, or filter on my HF DC (I have taken the bag off to look at the filter, no buildup yet to speak of). I have probably 2 cups or so of fine dust, a couple of packing peanuts which seem to completely bypass the baffle, and 1 Home Depot plastic shopping bag that somehow was in the belly pan of my table saw that spin around my lower bag... It is actually somewhat entertaining to watch the shopping bag swirl around...