I’m sort of a cross over from Knots, but I spend some time here as well. What I mean to say by that is that I’m a woodworker, not a house builder.
I’m planning to add a dust collection cyclone system to my basement shop this year. I REALLY want to vent the thing outside instead of using a filter. Since cyclone systems seperate most of the dust, only a little makes it to the filter, but the dust that does make it to the filter eventually decreases the airflow and makes the system less effective. Also, the filters ain’t cheap. Some dust where the system will vent is not a problem. So,,,, I want to vent it outside, but I also know the hazards of having the 1200+CFM collection system suck air back down chimneys and the like. Is there a generally accepted way of adding the make up air (and heat it some)?
Replies
QS:
You've created a very difficult problem to solve (I'm guessing the answers you were getting on Knots weren't very encouraging either)...
I've got a Woodsucker 2hp cyclone in my shop - noisy as hell... Stuck a kludgy 6' section of 8" insulated flex duct to the outlet which quieted it maybe a dB or two. You can DEFINITELY feel the breeze in the shop when it's running. Works extremely well, however - virtually no trace of dust at the cyclone exhaust outlet...
1200 cfm is a substantial air movement. Replenishing that isn't easy. Restaurants do it for their hood vents by locating make-up close to the evacuation source. Cold air through a constantly fired-up 300,000 btu range won't send the line cooks grabbing for their sweaters...
Problem with a shop (with more than 1 tool being serviced) is that the inlets are distributed. Those with inlets far away from the make-up air duct will likely result in the room cooling down some...
Heating the intake air would be quite difficult - heat "exchanger" techniques will negative affect airflow, and brute force warming that volume of air any appreciable amount would negatively affect your gas (or electric) bill!
You ought to re-evaluate why you really want an "outside" exhaust. Don't want residual dust? Get a finer filter. Don't have room for it? Consider a smaller system. Don't want the noise? Consider baffles, isolation, mufflers, and any number of other techniques.
You've got a basic goes-inta's versus goes-outta's problem. You need to balance airflows, and if your temperature differences are appreciable you're going to find it very expensive/difficult to achieve what you're seeking...
EDIT: Just noticed the "instead of a filter" remark. My experience is that the filter does not impede air flow anywhere near as much as your run length layouts, diameters, number of bends, etc... You can get some amount of decreased airflow "resistance" in the filter by simply using a larger (surface area) equivalent...
Edited 2/2/2007 2:46 pm ET by willflysatellitesforfood
Like Will said, it ain't easy to makeup that kind of air in any manner that is cost effective for a HO. To do it right and keep the space heated and conditioned you would need to install a forced air heat exchanger in-line with your exhaust otherwise you are sending a whole lot of energy in the form of heated or cooled air out your dust collector. Option B is to open a window and install a downdraft heater above the opening like you see in retailers front doors. With the upfront cost of equipment and the continuing cost of additional energy to condition the makeup air the filters might suddenly become more cost effective.
You really need to describe your situation better. What kind of furnace, how old and tightly-sealed is the structure, etc.
If you have any unsealed combustion appliances then it's probably a bad idea unless you can either seal off the shop or provide powered makeup air. You're looking at volumes that would likely overwhelm a simple 8" round passive makeup air duct.
But one idea might be to install some sort of forced air heater so that it draws from outside, then rig it up so that it's fan comes on when the dust collector does. It could probably be rigged with a weighted damper on the return flow (splitting return between inside and outside) so that it would maintain a slight positive pressure.
Within the past year, I created a thread (I believe) entitled, "900 CFM make up air."
I've spent the last hour going thru the searches and threads trying to find it, but unsuccessfully.
Somebody on better standing with Prospero that can help?
If so, I believe it addresses the issues...
http://forums.prospero.com/tp-breaktime/messages?msg=71249.1
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
My hero!
How'd you do that?
Well, the hard part was spelling your name correctly. Just used advanced search to look for all posts from you with "air" in them. (Tried "makeup", but apparently it was spelled "make up" there.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
You musta had to look thru a lot with the "hot 'air'" within!
When I use my 38" drum sander, quite a bit of fine dust collects in the filter pan of my cyclone. I would not want to expell that dust to the exterior.
So did those encouraging words help?