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Thread: BTU's needed to heat air

  1. #31
    Join Date
    Feb 2007
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    Well after a day of Einganearing I have the makings of a system that should do what I need. I borrowed a air velocity meter and used it to evaluate various configurations of my dust collector system. And along with an Amp Probe to measure motor current I found a configuration that with a bit more tweaking should take care of most of my issues. I think I'll go with hooking my 1 1/2 hp DustKop and my 1 1/2 Delta in series, with 8" main trunk line and 6" drops to the machines. By doing this I can put 1100 cfm right at the machine hood, with 5700 ft/min air speed. Right now I am testing using the original Delta bag as the filter resistance, so when I build my filter unit I probably will reduce some of the cfm. I have tuned the prototype system to pull about 3.5 amps (220 volt) on the 3phase DustKop and 14.5 on the 110 Delta motor. I have a little upside capacity on the DuctKop (nameplate amperage is 4.2) but the Delta is pretty much maxed at 14.5. The Delta will pull 18 amps with out a load and the DustKop will pull about 6 amps. I'm trying to run the amperage right up on the high nameplate limit but not go over so I don't damage the motors.
    Like I said before the DustKop unit was made for metal grinding dust so I'm not sure how well the cyclone will work for wood dust. The fan is in front of the cyclone which presents problems with wood chunks going thru the fan before the cyclone. I put the delta fan after the cyclone. If I remember correctly with both units running I get about 4000 f/m and 1300 cm right at the unit. My numbers might be a little off, I don't remember the exact numbers right now. But the really good news is that I can see my way to a system with enough air flow and hp to overcome the resistance of a decent filter so I can vent into the shop, and I shouldn't need to exhaust outdoors. Thus ends the "BTU's needed to heat air" problem that I was trying to work out. So tomorrow I start to build the filter system. Since I'm not confident in the DustKop cyclone separating ability, I'm thinking of exhausting the air from the DC into a plenum, with a clean out on the bottom. This should slow the air speed down and let the left over chips/dust settle out before going into the filter. I have a bunch of 3M Filtre furnace filters, couple of 95% industrial air handler filters, and (best of all) two large 2' x 4' powered Heppa .3 micron filters out of a clean room. Each of these filters has a 650 cfm internal fan to move the air through. So tomorrow I'll calculate the plenum size needed so the air speed drops, figure out how to mount the furnace prefilters, then the 95% industrial filters, and then how to get the heppas mounted inside the shop.
    I'm also going to look into building a cyclone so I can put it in front of the DustKop fan and eliminate the wood chunks going thru the fan problem, that I see coming.
    Seems like a lot of work but I've got about $400 invested and a Oneida system is going to run me $1900 by the time I get it here. And this is a lot more fun that writing a $1900 check.

  2. #32
    Join Date
    Sep 2008
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    Raleigh, NC
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    I suspect you're going to find that your set-up doesn't have enough "oomph" to run HEPAs as dead-end filters. They take a lot of power to run, and again, unless you're doing a lot of ROS sanding, you just don't need it for bandsaw, tablesaw, jointer and planer dust and chips.

  3. #33
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    Feb 2007
    Location
    South Dakota
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    Actually, I hooked up one of the heppas to the system on Sunday afternoon. The input air velocity didn't change much, about 1500 cfm, right at the opening of the DustKop fan. The air speed going out the heppa was really to small to measure accurately. When I kicked on the heppa blower, along with the DustKop and Delta, I could measure about 2100 cfm on th filter output, but still the velocity was very low and I doubt I got an accurate measure. The Delta motor was pulling about 17 amps but before I could experiment with choking down the input air from the DustKop, my amprobe quit on me, so I couldn't continue to measure the amperage and see what the heppa output would have been with the delta running closer to 14 amps. Now I didn't have any input piping on the input side of the dust collector so it was just running free and I know I wont get that kind of cfm when I get everything connected. I don't really know what to expect when I get the piping all installed and the pressure losses start to add up. There isn't a fan curve for a system with two fans, (plus Two powered heppas) all in series so I'm on my own trying to guess what will happen when I get every thing hooked up.
    I built the discharge plenum tonight, installed two furnace filters, one on top of the other to act as pre-filters to the heppas, I've got room for a whole stack of furnace filters if that is looking like the way to go. Then I pulled out what I thought was going to be industrial air handler filters from the storage side of the shop and discovered that they are actually heppa filters also (.3 micron, 99.97% efficient, 1" wc at 1080 cfm). So I have the filter end covered, just gotta hope that I don't choke the unit on the input side.
    I'm thinking about building my own duck work out of mdf, try to save a few bucks. It would be rectangular duct. I found an on line calculator that calculated the equivalent rectangular and round duct sizes. With out a fan curve and being able to predict what the pressure drop will be through the duct work I'm a bit hesitant to just buy duct. I want to maximize duct size to minimize the pressure loss but don't want to get too large of duct and loose too much air velocity. So if I build my own rectangular duct I can always take it apart and make it smaller if I can't keep the air speed up.
    A lot of work but what else is there to do in SD in the winter?

  4. #34
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    Sep 2008
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    Leigh - I'm having a hard time believing that you can make MDF ductwork cheaper than 5" PVC pipe. MDF if relatively inexpensive, but that's really stretching it. Wouldn't it also be really heavy?

    I'll admit that I'm a bit surprised at cfm measurements when you have your HEPAs in-line. Generally, when I've measured it before in industrial applications, there's roughly triple the airflow with single-stage HEPA filters in/out of the process stream. I've tried pleated non-HEPAs in the same application, and that resulted in about a 1/3 reduction in airflow between the filters in/out of the airstream.

  5. #35
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    Feb 2007
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    South Dakota
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    You could be right about the air flow restriction with heppas. I may have been loosing more airflow out the bottom of my cyclone that I thought, I didn't measure the leakage. It was a jury rigged set up so I could be introducing more error than I thought. The heppa I was using is a MAC 10 FFU (Filter Fan Unit) by Envirco, rated at 650 cfm at 90 ft/m and .44 in w.g. 2 ft x 4 ft. with a 650 cfm airfoil fan.
    I'm going to try a CamFil Mirotain filter in the final construction, cause I have a couple and then I can save my powered units as room scrubbers, which is what I use them for now.
    MDF for ducts, well maybe it isn't a good idea but I'm thinking 1/4 mdf rectangular ducts could offer an advantage in being cheaper, and easier to attach down pipes to. Just bore a 6" hole and hook a flange any place you want a drop.

  6. Quote Originally Posted by Leigh Betsch View Post
    MDF for ducts, well maybe it isn't a good idea but I'm thinking 1/4 mdf rectangular ducts could offer an advantage in being cheaper, and easier to attach down pipes to. Just bore a 6" hole and hook a flange any place you want a drop.
    I have the same idea floating around in my head, using MDF or any other suitable material (hardboard, etc., perhaps with one plexiglass "wall" for visibility, etc.) You could make longer sweeps for ells and do some other "custom" things, but you also have to be able to take it apart to clear any obstructions, etc.

  7. #37
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    Feb 2007
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    South Dakota
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    I hadn't thought about taking it apart to clear jams. Maybe the bottom would have to be screwed on. I've been thinking that I could pull the air out the side rather than the bottom so I wouldn't get dust falling down into the drops, similar to Sonny's horizontal hook up only with fewer pipe fittings. I'm thinking the drops could either be standard HVAC 30ga Borg pipe or maybe custom bent PVC, heat and bend into sweeping arcs. This would eliminate the cost of hoses. I like the idea of a plexiglass window although I would go with Lexan, much, much tougher. It would get very expensive to make an entire side of Lexan.

  8. #38
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    Sep 2008
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    Raleigh, NC
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    Leigh - Your post cleared up a few questions - I was thinking in my head you actually talking about a true ductwork out of MDF, now I'm thinking you're talking about making a plenum out of it, and attaching drop hoses - that makes a lot more sense. I can imagine that cutting and fitting all the curves for ductwork out of MDF would be a major pain in the tail.

    But since you're thinking of this, I've another suggestion. While unconventional, if you've a friend or relative in the HVAC business, you might ask whether they use/make 6" plenums out of sheet metal, and whether they sometimes have misfits that they can't use (made a bit too short, or the wrong shape, etc...) and that just get thrown out.

    A plenum made from sheet metal would have a couple of advantages that I can think of - extremely lightweight, both compared to MDF and PVC, and generally spark-proof, so long as it's grounded.

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