Replies

1. 
   HowardAcheson | Feb 25, 2004 04:24am | #1

   See if this helps.

   The two most important criteria for an air cleaner are the CFM and the filters. You want a CFM factor that will clean the size of your shop and a filter that removes the particle size that you are concerned about.

   To determine the size or required air flow, use this formula: Volume of your shop (Length x width x Height) times Number of air changes per hour (typically 6 - 8) divided by 60. This will give you an answer in Cubic Feet per Minute which is how air cleaners are measured. MOST AIR CLEANER MANUFACTURERS RATE THE CFM OF THE FAN ONLY, but there are losses due to the filters. If you are building your own or if the air cleaner you are purchasing rates only the fan, figure you will lose about 25 - 40% for filtering losses.

   As important as the air cleaner size is how and where you mount it. Try to mount at about 8-10 feet above the floor (no lower than 6'or 2/3 of the floor to ceiling distance if less than 8' ceiling). Mount along the longest wall so the intake is approximately 1/3 the distance from the shorter wall. Mount no further than 4-6 inches from the wall.

   The exhaust is the largest determiner of the circulation pattern. You are trying to encourage circulation parallel to the floor/ceiling so ceiling mounting is not recommended. Use a smoke stick (or a cigar) to observe and maximize circulation. Use a secondary fan to direct air to the intake if necessary. Also, consider that a standard 24" floor fan moves a lot of air and, in some shops, just positioning it in a doorway with a window or other door open can accomplish as much or more than an air cleaner. It's all in the circulation patterns.

   The exhaust is the clean air so that is where you want to position yourself. Do not place the air cleaner over the a dust producer. That will guarantee that the operator will be in direct line between the dust producer and the air cleaner. The operator wants to be in the clean air stream. If the dust has to pass your nose to get to the air cleaner, you get no benefits. If you have an odd shaped shop, two smaller units may be better than one large one.

   DO NOT RELY ON A AIR CLEANER TO ACT AS A DUST COLLECTOR. The purpose of and air cleaner is to keep airborne dust in suspension and reduce airborne dust as quickly as possible AFTER THE DUST PRODUCER HAS BEEN TURNED OFF.

1. 
   forestgirl | Feb 25, 2004 07:58pm | #4

   Hi Howie.  Given the excellent post you made above, I'd love to have your take on the following post in another dust-protection thread:http://forums.taunton.com/tp-knots/messages?msg=16481.22

   I read the quote through a couple times last night, found it a mixed bag.  See my response.  Thanks!forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)Another proud member of the  "I Rocked With ToolDoc Club" .... :>) 

1. 
   HowardAcheson | Feb 26, 2004 05:59pm | #7

   Hi Jamie,

   We are somewhat crossing posts in the two threads. I did read the article and responded to your thoughts there. You made a reasoned analyse of the article but I basicly agree with Witter's comments. A point not made about the AW tests and conclusions was that only two air cleaners performed in a satisfactory manner. All the others, failed. Yet, I still see reccomendations being made for the "failed" units.

   I have been against the notion of air cleaners being "health" devices for about ten years. I ran a company that had a large metalworking machine shop. We had individual station dust collection that was quite old. As part of the upgrade, it was suggested we look into air cleaner/scrubbers mounted strategically in the shop. We contracted with a workplace environmental consulting firm and they had tests that indicated that air cleaners do not do a very good job. At the same time, we consulted with OSHA and they told us that they had never tested a site where air cleaners removed enough particulates to make unsafe air safe to breathe. Our conclusion was to upgrade the workstation dust collection and to use individual respirators where dust collection was not effective.

   As far as I know, no manufacturer makes any health claims regarding the use of their air cleaners. The percieved health benefits are from the users who have no way of knowing whether their air is safer or not.

   The primary use of my air cleaner is to clear the air before I get to finishing. After I finish surface preparation, I get out my finishing materials, vacuum the project, turn on my air cleaner and get out. After two hours and changing my clothes, I go back, wipe down the project with mineral spirits and start finishing.

   Personally, I would recommend building a good sized downdraft sanding table before I would acquire an air cleaner. The largest producer of dangerous dust is the sanding operation. My downdraft table measures 24" x 44". It's large enough that I can get almost any item on top and it catches virtually all the dust. It's on wheels so I can move it anywhere. If I put it in the door and open a window on the other side of the shop, it rapidly clears the air.

1. 
   Mackwood | Feb 26, 2004 07:34pm | #9

   You do have both, an air cleaner and the big downdraft table?  Does your downdraft table draw it's suction from your DC system or elsewhere?  I've seen lots of plans/diagrams for downdraft tables; looks like a simple enough unit to design and build.  Any recommendations?  Do you know how many CFM you have at you 24" X 44" unit?

   Your comments about the OSHA experience convince me that a respirator is far and away the best solution albeit somewhat of a PITA.  The downdraft table makes a lot of sense from several angles.  I think I'll invest my energy there first and add the air cleaner later on.  Thanks for sharing!

   Regards,

   Mack  

   "WISH IN ONE HAND, S--T IN THE OTHER AND SEE WHICH FILLS UP FIRST"

   Edited 2/26/2004 11:43:24 AM ET by Mack

1. 
   mitch | Feb 26, 2004 07:51pm | #10

   i'd have to ask him, but P-2 sounds kinda familiar- did that plane have a 'name'?  maybe i would recognize that more.  he was a crew member (3 man crews?), not a pilot.  apparently they were some sort of submarine hunters?  he doesn't talk about it much- nothing traumatic, just another thing he did as a kid, i guess.  i suppose iceland sure beat hell out of korea at the time...

   m

2. 
   Mackwood | Feb 26, 2004 08:28pm | #11

   I think they may have been called "Neptune" but I'm not sure.  I only have vague recollections of the last few of them at Whidbey Island Naval Station.  I was a "puppy" in the Navy when they went away.  Replaced by the P-3 "Orion" which are still around today (China fiasco a few years back).

   I would say Iceland was a whole bunch better than Korea.  Iceland now is considered pretty choice duty especially for a family. Had a friend of mine did a tour as Command Master Chief there a few years back.  He and his wife loved it!!  But then if it's not haze grey and doesn't get underway; what's not to love!  LOL

   Us aircraft carrier sailors always referred to the VP guys as "perdiem, rent-a-car navy". 

   Regards to you and your dad!

   Mack"WISH IN ONE HAND, S--T IN THE OTHER AND SEE WHICH FILLS UP FIRST"

3. 
   HowardAcheson | Feb 27, 2004 02:09am | #13

   Yes, I have the Delta air cleaner. It was given to me and I installed it just to try it out. Works real well cleaning up the air before finishing.

   My downdraft sanding table is powered by a reclaimed furnace squirrel cage fan. The fan unit is probably 2000 plus CFM and driven by a 1/2 horsepower motor. It is enclosed in the box of the downdraft table. The basic plans came from an issue of Woodsmith magazine of 5 or more years ago.

   It's pretty simple. Build a plywood box with internal dimensions of 20x40 to fit two 20x20 high efficiency bag filters. Attach a continuous 1"x1" strip around the inside about 6 inches down. The filters rest on this strip. Put two 20x20 furnace filters on top of the bag filters to act as pre-filters and catch the big stuff.

   Mount the fan unit and the motor in the bottom with the outflow of the fan going through another filter. The top is 1/4" masonite pegboard with the 1/4" diameter holes bored out to 3/8" and chamford. It's mounted onto a sort of torsion box support that's in a frame that is hinged so I can get to the filters.

   Personally, I don't think a dust collector would have the CFM's to work well on a large downdraft table unless it was a big dust collector.

4. 
   WayneL5 | Feb 27, 2004 05:51am | #14

   I'm an engineer, and though industrial ventilation is not my specialty, I have some experience in designing and troubleshooting simple systems.  It's always better to collect contaminants at their source rather than try to remove them from a large volume of air.  So, I would recommend dust collection at your tools first.  And I'd recommend a collector with good filtration of the smaller particles, like the Oneida units and some others have.  It's the small particles that are the most damaging because they get down deep into the lungs.  Things like planer chips are hardly harmful at all.  Sanding is probably the worst thing for your lungs, but at the same time, one of the more difficult operations to contain dust from.

2. 
   jackiechan | Feb 25, 2004 04:33am | #2

   Mack,

   Placing an air scrubber in the rafters (or ceiling) is a way of removing the dust kicked up into the air - and as a means of freeing up floor space.  When a unit is placed on the ceiling, it should be located right above where the dust is being created (for maximum effect).  In my shop, I have multiple units with the larger ones on the floor rolling around on casters.  By utilizing both a ceiling mounted unit and a floor unit, the maximum amount of dust can be siphoned from the air (also using a dust collector for your power tools).

   This is a link to a previous post of mine that gives detailed instructions on how to build a shop-built air scrubber.

   http://forums.taunton.com/n/mb/message.asp?webtag=tp-knots&msg=16077.1&search=y#a3

   http://forums.taunton.com/n/mb/message.asp?webtag=tp-knots&msg=11626.1&search=y#a1

   If you have any questions, please feel free to ask!

   Dan Kornfeld, Owner/President - Odyssey Wood Design, Inc.

   
   

   ---

   Edited 2/24/2004 8:37:15 PM ET by Jackie Chan

   
   

   ---

   Edited 2/24/2004 8:39:11 PM ET by Jackie Chan

1. 
   Mackwood | Feb 25, 2004 05:42am | #3

   Dan,

   I have a print of your air scrubber in my briefcase.  How long it takes me to get at building it remains to be seen.  I think your statement about the large units you have rolling around on casters and Howie's comment about placement convinces me that "overhead" mounting is not mandatory but careful consideration is.

   Thanks for your response and thanks for putting your efforts out there for everyone to benefit from (and free!!).  Most folks would have put those plans on the E-bay or something for a fee.  You're a gentleman and a scholar!

   Regards,

   Mack"WISH IN ONE HAND, S--T IN THE OTHER AND SEE WHICH FILLS UP FIRST"

3. 
   stancalow | Feb 26, 2004 04:46am | #5

   Mack

   Your original question was about placement of the A-C.  I am just a hobbyist with a small shop, and mine hangs form the ceiling too.  However, I do recall reading an article in a book which said that it is best  placed at the level at which you are breathing - that is at head level.  The author was pretty convincing, based on the logic that at ceiling level, the dust particles have already passed through your breathing zone.  I can't recall the book or the author, but it seemed to me that it was one of the well-published writers on the subject.   I plan to lower mine someday, when I have time. 

   Stan

1. 
   mitch | Feb 26, 2004 04:24pm | #6

   i actually was reading this thread because i'm mulling over the eventual placement of the air filter units in my shop-in-progress, but your tagline really caught my eye.  my dad was a navy man in the early 1950's (north atlantic patrol bomber squadron) and if my siblings and i heard that expression once growing up, we heard it a thousand times!

   m

1. 
   Mackwood | Feb 26, 2004 06:56pm | #8

   Was your dad working on/flying P-2's?  They were still around but being phased out when I went in the Navy in 1969.  Hope my use of this time worn phrase brought a smile! Enjoy!

   Mack"WISH IN ONE HAND, S--T IN THE OTHER AND SEE WHICH FILLS UP FIRST"

4. 
   kensshop | Feb 26, 2004 11:15pm | #12

   Before spending any money on an air scrubber, read this:

   http://www.oneida-air.com/airfilterspop.htm