kiln fans

[hackberry jake]

I sent pineywoods and Larry a PM that asked about which fans would be better for a dry kiln and then I realized that the rest of you guys will probably have some good advice too. I figured up that I need about 3,000 cfm of airflow for a 900 bf load. I came up with a couple different ways to go about it. One is to use three of these fans
http://www.surpluscenter.com/Electrical/Blowers-Fans/AC-Centrifugal-Blowers/1000-CFM-FH280-115-VAC-REVERSE-CURVE-IMPELLOR-16-1461.axd
and the other is to use twenty of these fans
http://www.surpluscenter.com/Electrical/Blowers-Fans/DC-Fans/150-CFM-48-VDC-NIDEC-FAN-16-1371.axd
along with a $45 power supply.
The twenty smaller fans would cost more to buy but they would only use 268 watts of power. The three larger fans would use 1,068 watts.
The larger fans are also all metal construction so they should hold up to the heat, but a maintenance guy at work said small cabinet fans are rated for pretty high temps as well. I also think a piece of plywood with 20 fans would create more even airflow. oppinions?

[WDH]

Jake,

Here is a link to the extra fans that I put in my Nyle kiln.  The dehumidificatrion unit came with two, but based on Yellowhammer's experimentation and advice, I added two more.  They are 850 CFM each giving a total CFM of 3400.  They are small but powerful. 

https://www.carltonbates.com/Fans/MECHATRONICS/AC-Tubeaxial-Fan-125W-Metal/UF25HC12-BTHR/p/40026698893-1

Looking at the fan on your first link, I suspect that it would be difficult to direct the air flow like you need to. 

[jim blodgett]

I'm wondering what type air movement you're looking for, Jake.  Are you trying to get a consistant wash of air across the stack in the kiln?  Or simply evacuate as many CFM as you can?

[hackberry jake]

Jim they are mainly for recirculating the same air through the kiln. And wdh, I was kind of on the same assumption about the first fan. I dont know how one would utilize all the cfms and get them going in the same direction. They are also power hogs.

[Bill Gaiche]

Jake, I have two of these if your interested. I used them for a while and then went to Solar powered fans. bg
http://www.bvc.com/gmventilators.html

[pineywoods]

Which fans ??  I think you will find it's not at all critical. Of the 3 solar dh kilns locally, mine uses a single 24 inch walmart box fan, LeroyC uses 3 small box store fans and Planmann has 2 all metal box store fans. Air flow distribution is   not much of a concern. The fans don't blow directly through the stack, they pressurize a plenum formed by the floor, roof, back wall, and one side of the lumber stack, ensuring fairly even distribution. I have a new, larger kiln in the works. Planning on using 2 or 3 small residential ceiling fans, 3 speed reversible. Air flow calculations assume constant conditions, which a solar kiln is anything but. Everything varies all over the place. Another confusion factor if you use the black metal under the rafters. That metal and the clear glazing form a convective tunnel. there is a considerable amount of air flow up that tunnel, even without the fans. (hot air rises, physics 101) If you haven't found them, look at the threads by Andy White and Planman1954. Build it and experiment. A fellow as resourceful as Hackberry Jake will likely come up with some improvements..

[WDH]

Jake,

You are a hardwood guy, right?  With all the heat capable in the Pineywoods kiln, that is great for fast drying woods like pine and yellow poplar, but for some of your hardwoods, like the oaks, too much heat and too little air flow/venting might be an issue. 

Pineywoods, what has been your experience on drying the harder-to-dry hardwoods in your kiln design?

[hackberry jake]

While I have had my mill most of what I have cut has been hardwood. Really it is whatever logs I can get for free/cheap. I came across a good amount of pine last year and hopefully I will finish cutting it this weekend. I just had a thought. I have been looking for fans with low wattage and high cfm to cut down on the electric bill since the fans will likely run most of the year. Efficient fans cost more than inefficient fans. Then I realized that inefficient fans waste most of their energy as.... Heat! Which is kinda needed in a kiln anyways so, cheap fans it is!

[YellowHammer]

I have both a solar kiln and a dehumidification kiln and each have very different behaviors related to fan and drying characteristics.  For example on my solar kiln I run two $20 Wal Mart box fans and have been doing it for many years.  I never bothered to calculate air velocity because the nature of the kiln is that it is very forgiving within its limitations. The best I can characterize the air flow is a "gentle breeze."  However, I have had drying issues directly related to air velocity causing defects in certain species and solve that by simply not using it to dry those species.
My DH kiln on the other hand is very critical of fan characteristics and other parameters because of the high rate I push wood out with it.  I  have talked with Nyle several times on the subject and there are lots of very good papers on the web concerning airflow but here are some of the highlights I stick with:
Above 40% MC wood will dry faster as the air velocity increases.  Below 20% MC wood will not dry appreciably faster as air velocity increases.  Between 40% and 20% MC the effects of air velocity diminishes.  At higher air velocities drying is more uniform.

Wet hardwoods will not tolerate high air velocities without creating significant defects. I like to use 200 to 250 fpm on wet oak.  Wet softwoods will tolerate and actually need much higher airflows, up to 600 fpm to force rapid drying and reduce sticker stain.

Using auxiliary fans to increase drying rate in a DH kiln saves money because it reduces the time the compressor has to operate.  Using auxiliary fans to increase airflow in a solar kiln costs money because the sun is free and natural convection and other methods can sometimes be used to move the air and remove moisture instead.

Too low an airflow velocity and uniformity in a DH kiln will result in mold formation on the walls and subsequent contamination of the wood.  I have never had mold form in my solar kiln because, I believe, the higher daytime temps kill it.
Although my cheap solar kiln fans are from a box store my DH fans are more expensive commercial units designed for this application.  I never mess with my solar kiln fans but switch my 6 DH fans on and off based on wood species and their optimum airflow and drying rate characteristics.
My goal on the solar kiln is to dry wood defect free and not be in a hurry but my goal on the DH kiln is to dry wood defect free as fast and economically as possible

Anyway my 2 cents on the subject
YH

[OneWithWood]

YH,
Which Nyle are you using?  How are your six fans spaced?  Do you turn them on/off individually or in groups?
I currently have the two fans in my Nyle 200 that came with the unit but have often contemplated adding one or two more.  The current fans are spaced evenly across the kiln.  If I add more I was thinking about rebuilding the entire mounting system so the fans would be evenly spaced.  Does the spacing matter that much or is it more a function of capacity?

[Den Socling]

This has nothing to do with fans in a DH kiln but it was kind of humorous. I used to do technical work for conventional kiln operators. One was having trouble with uneven MC's. I was in the kiln checking air flow through the stack and came to a dead spot. All the fans were running so it had me stumped for a couple minutes. It turned out that one fan was running backwards.  :D

[pineywoods]

Jake,

You are a hardwood guy, right?  With all the heat capable in the Pineywoods kiln, that is great for fast drying woods like pine and yellow poplar, but for some of your hardwoods, like the oaks, too much heat and too little air flow/venting might be an issue. 

Pineywoods, what has been your experience on drying the harder-to-dry hardwoods in your kiln design?

I am probably lucky, but I have yet to really mess up any lumber in my kiln.  BUT, I generally air dry outdoors under old roofing tin before it goes in the kiln. Either that, or load the kiln with lumber sawn from logs that are already somewhat dry. There's a load of 1X12 red oak in mine right now. Going for kitchen cabinets. Plannman recently ran a stack of beech through his, worked fine. Mold has never been a problem, even when LeroyC loaded 900 bf of freshly sawn  cypress in his.

[hackberry jake]

I was pondering a kiln cart type set up but it makes the whole build more complicated. It would be nice to be able to stack the lumber out in the open then just wheel it into the kiln.

[WDH]

A pallet system using purpose made pallets to sticker the wood on with the same # of layers on each pallet makes loading and unloading the kiln pretty easy with a tractor with FEL forks. 

[hackberry jake]

You got any pics of these pallets?

[WDH]

Jake,

There is a pic on my website that shows the kiln with a load of three pallets.  I can't seem to find the original pic.

http://hamsleyhardwood.com/lumber-drying.php

[hackberry jake]

Sweet website!

[hackberry jake]

I was looking into insulation and found a Boat-load (pun intended) of boat dock styrofoam blocks. I wonder if I could cut these into insulation blocks to fit between the studs with the mill.

[WDH]

I am sure that would work, and it will save a boatload of money as insulation is very expensive.

[YellowHammer]

YH,
Which Nyle are you using?  How are your six fans spaced?  Do you turn them on/off individually or in groups?
I currently have the two fans in my Nyle 200 that came with the unit but have often contemplated adding one or two more.  The current fans are spaced evenly across the kiln.  If I add more I was thinking about rebuilding the entire mounting system so the fans would be evenly spaced.  Does the spacing matter that much or is it more a function of capacity?

I'm using a Nyle L53, one of the first ones made.  I really like the horizontal, fixed fan baffle and mount as opposed to a vertical baffle.  The fans are spaced symmetrically on the horizontal baffle, relatively evenly spaced, with one pretty close to the wall of the kiln so that it blows out any stagnant areas in the kiln corners, which is where mold will begin to form.  The next one is about midway across he baffle and the final one is pretty close to the center third of the baffle.  They are spaced the same on the other side of the kiln baffle.  I switch them on and off in pairs depending on the load size, species and moisture content.
The fan spacing is very important so as not to have any dead spots in the kiln, and to insure even drying.  I've had much more problems with even drying from top to bottom of the stack instead of horizontally, but that can be fixed by adjusting the plenum width, or the spacing between the front and back of the kiln and the faces and sides of the stack.  I just sample the moisture content of the lumber when it is drying at many places on the plenum face of the stack to detect any wetter regions.
Besides sticker stain, the biggest problem I have with uneven drying is that it requires the wood stack to stay longer in the kiln, sometimes for several days, for everything to reach the same moisture content.  So it costs time and money, and really slows the throughput of the kiln down.
I do my absolute best to get a fully sterilized, defect free load out of the DH kiln every weekend, and have been able to do that for some time once I started fiddling with the airflow as well as everything else in the kiln, including pre drying.  This species I can kiln dry and sterilize in a week are cherry, hickory, walnut, sassafras, cedar, pine, red elm, poplar, beech, basswood and maple. Red oak I have to slow down to get a load out about every 9 days, and white oak I just dry in the solar kiln because it likes to go slower.  Here a few pictures of a few stacks of wood on pallets (as WDH mentioned) ready to go into the kiln.  You can see a couple big barrel fans blowing and sucking on 3 pallets of maple prior to going into the kiln. 


Here's the kiln loaded with three pallets full of wood with baffling to control airflow.  The lumber comes off the mill directly onto the pallets, gets staged in various areas for pre drying and air drying, then goes in the kiln, and finally to post processing and planing without double handling, all on the same pallet.

YH

[beenthere]

I was pondering a kiln cart type set up but it makes the whole build more complicated.

Saw a kiln once that was on tracks, and the next kiln charge sticker'd while the kiln was "down the track" finish drying a load,
then when ready for drying, the kiln was rolled over the wet charge, while the dry lumber was removed from the stickers.

Just kept moving the kiln back and forth.

[WmFritz]

Well now, that's thinking outside the box! smiley_sidelightbulb

[WDH]

I am still handling the lumber too much, but I am slowing working my way to a more efficient process like Yellowhammer described.  You need a whack of pallets  .

In my Nyle L53, I have not had any mold, mildew, staining, etc. primarily because I learned from Yellowhammers experience and took his advice when designing and building my chamber and also with the addition of the extra two 850 CFM fans.  I added more space in the front of the stack (front plenum) and in the back of the stack (back plenum between the lumber and the dehumidification unit), and that has seemed to work very well.  I also benefited from his experience in learning how to size the load going into the kiln based on the species and the capability of the compressor to condense the water vapor from the drying wood, keeping things in balance.  However, I have yet to dry a load of green oak because so far, I have been able to pre-air-dry most of my lumber to below 30% before going into the kiln, so I am a bit past the danger zone for the worst drying defects.  I will probably royally screw up my first load of green oak  .

The extra air flow has resulted in very even drying in my kiln, or at least that is what I believe to be the reason.  I have not found any dead or wet spots so far.

This kiln has really opened doors for me by giving me the capability to do things right.  I will have to say that Yellowhammer's finished product is about as well prepared as any lumber that you could buy.  That is another goal that I have, but the difficulty for me is that my woodworking shop and equipment for breaking down boards like the jointer, chopsaw, and tablesaw are 3/4 of a mile from the kiln and my new planer room.  So, I have some logistical issues to overcome. 

[YellowHammer]

I will have to say that Yellowhammer's finished product is about as well prepared as any lumber that you could buy.   

Aw shucks,    That makes my day
YH

[hackberry jake]

No weight on the top of the stack in the kiln? I read someones post (dont remember who) where they poured a reinforced concrete slab that they pick up with the tractor and set it on the top of the load. I liked that idea.