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.

[WDH]

Nope, no slab or other weight.  I have had minimal problems so far.  I don't think that weight relieves tension in the wood. 

[YellowHammer]

I don't use additional weights, either.  About the only thing I do, and is one of the advantageous of the pallet method, is to reverse the order that I stack the pallets in the kiln opposite of when I'm air drying them and use their weight to my advantage.  In other words, the top pallets of lumber in the air drying area go on the bottom of the stack in the kiln. If there is any cup, that helps flattens them.  I think the best way to keep lumber flat is lots of stickers, drying and sawing technique.

YH

[thecfarm]

hackberry jake,going to cut the boat dock styrofoam blocks on the sawmill?? Seem like they are about a feet thick??

[hackberry jake]

hackberry jake,going to cut the boat dock styrofoam blocks on the sawmill?? Seem like they are about a feet thick??

it sure is cheap insulation. Im kind of worried about the mess though.

[OneWithWood]

Thanks for all the information.  You all have giving me some things to ponder. 

[pineywoods]

hackberry jake,going to cut the boat dock styrofoam blocks on the sawmill?? Seem like they are about a feet thick??

it sure is cheap insulation. Im kind of worried about the mess though.

Jake, the way to cut that foam is with a hot wire. Piece of nichrome wire (heat element out of a defunct clothes drier). Stretch the wire taunt and hook a battery charger to the ends. The wire needs to be just barely red hot. I like to use a flexible piece of wood with the wire strung like the string on an archery bow. Leaves a nice smooth finish on the cut. Yer right, cutting foam blocks on the sawmill gonna be messy..

[kelLOGg]

I found box fan bearings did not hold up to the heat so I use attic fans in a frame

As for weight on top, I use ratchet straps.
Bob

[GeneWengert-WoodDoc]

For fairly wet lumber (above 40% MC roughly), if the fans are providing 500 fpm velocity (about 10 mph), the wood will dry twice as fast as if the velocity is 300 fpm...at the same RH and temperature.  However, this higher air flow at 500 fpm will require more than 4 times more electricity than at 200 fpm.  On the other hand, faster air flow is also going to mean more uniform air flow, which can be helpful.

At around 30% MC and lower, air flow rates have no appreciable affect on the drying rate...what is taking time is the rate at which the water molecule can move from the within the piece to the surface...this rate is controlled by RH and temperature.  So, small fans will be adequate and will save money if the lumber is air dried before going into he kiln.

Here is a formula that can be helpful:

cfm = (air velocity in feet per minute) x (sticker thickness in inches /12) x (length of lumber in feet) x number of sticker openings (or number of layers of lumber + 1)

For good drying of wetter wood, a target velocity of 250 fpm is good, although for white woods like maple, 500 fpm will mean whiter in color.

Rearranging the formula

velocity through the load in fpm = (cfm from the fan) / [(sticker thickness / 12) x (length) x (number of sticker openings)]

For example, assume two fans at 850 fpm, 3/4" sticker openings, 20 layers, and one 12' lumber bundle.  Then, if there are no leaks of air, these fans will provide about
1700/[(.75/12)*12*21] = 108 fpm velocity air flow

--------------

Fan efficiency is an interesting topic.  With the same motor, you can get various amount of cdm from a fan.  Certainly, tight bearings can reduce air flow, but the clearance between the tip of the blade and the housing or shroud is critical...the bigger the gap, the more inefficient the fan (fewer cfm for the same hp).  Also, if the shroud itself is curved gently (so it looks like the throat of a carburetor if you are old enough to remember them), you can get perhaps 20% more air cfm.  Without the curve, the air generates eddies that result in wasted fan power.

Does blade diameter matter?  Once you are over about 20", diameter, there is no benefit in going large from an efficiency standpoint--that is, the relationship between motor hp and cfm is a constant.  However, large means you can add more power (large motor) and get more cfm, as the tips are moving so much faster.  With larger fans, the higher power means heftier frame and shafts.  Large fans also mean fewer motors, switches, wiring, etc.

Fan bearings are expensive.  That is why some fans cost more than the $20 box fans.  Box fans do not have bearings, but have bushings that tend to wear faster, as well as a weaker frame.  The motors also have less ability to withstand high RH conditions.

The most expensive fans will have blades that have adjustable pitch (using a wrench, etc.).  So, one adjusts the pitch prior to starting a kiln, to give the desired velocity without over-taxing the motor.  A large kiln should have an ammeter on each motor so that current draw can be measured and compared to the rating of the motor.  Note:  When starting a kiln with cold air, the current draw will be higher because the air is more dense.  On the other hand, velocity will be higher too.

Bottom line is that you basically get what you pay for, so all you need to do is decide what fpm or cfm you need and how big is your pocket book.

[Larry]

I used a old belt driven furnace squirrel cage fan.  No idea of the cfm or fpm other than a lot.  When I first built the kiln I experimented a bit with air flow using smoke and tissue paper to see what was happening.  I also varied the speed by changing out pulleys.  Had plenty of power with a ¾ hp motor.  Used an ammeter to see the effects of different size pulleys.  A motor with a light load doesn't use near as much juice as one loaded to its full load current rating.

The results of testing found if air flow was too low my bottom layers were drying at a slower rate than the top layers.  Tweaked the fan until drying was nearly even from top to bottom.

It's interesting that these solar kilns will dry wood to without any fans at all...just takes forever.  One fall I put a fresh load of lumber in the kiln but didn't turn on the fan because winter drying is slow.  Few months later I checked the load and was surpised to find it was actually drying.

[Escavader]

Our kilns have 4 giant 48 to 54 inch fans ,it's hard to keep  your hat on  :Dgood air flow in drying pine is important to avoid coffee stain

[GeneWengert-WoodDoc]

One way to make a solar kiln work without fans is to bring in the outside air at a low point in the rear and have the bottom baffled so that the incoming air must go through the load.  Then, when the air in the front is heated, it will rise, so put a vent neat the top at the rear.  This hot air will rise and top out the vent and pull fresh outside air into the load.  It will be similar to air drying, but perhaps faster as there will be added velocity in some cases..  Plus, not all the air will exit the kiln, but some will recirculate a few times.  Overall, the air speed is slow, meaning slow drying, but it will dry the lumber.  Eventually, when the lumber is getting quite dry, the vents can be nearly closed which will build up heat in the dryer and thereby lower the RH and create lower final MCs, but again, it will take a while for this to happen without fans.

[hackberry jake]

I originally planned on using two layers of 2x4 stud walls for the chamber construction (along with 1" blue or pink 4x8 wrap). I was goint to stagger the two bys so they didnt line up and fill inbetween with the boat dock foam. I am pondering using the 1x8s instead though. It would save money because I wouldnt have to buy 2x4s and it would give me about an inch more depth (full 8"). It would also be less cutting of foam and less assembly time. Any reason I cant use 1x8s as studs? Other than it will be a little harder to hit with a screw when im putting my plywood on...

[WDH]

Should be fine with a good R-value.  A well insulated kiln is a more efficient kiln. 

[caveman]

https://www.sullivansupply.com/cart/ia/p-502-sullivans-24-turbo-fan.aspx
I have located a couple of fans similar to the one listed on the link above and I am curious if one of these would be enough to adequately move air through the kiln we are building if we construct the plenum and ducts to distribute the air.  The inside of the kiln chamber is about 20' long x 6' wide and 5' high on the short side and about 9' on the high side.  I do not mind using two but these things really push some air and I do not want to over do it.  I would appreciate suggestions from those who have already built solar heated kilns.  The search for the proper fans has stalled this project for several weeks.
Thanks,
Caveman

[WDH]

You can buy 3 of the mechatronics fans that come in the Nyle L53 for the price of that one fan.  The mechatronic fans produce 850 CFM each. 

[caveman]

Thanks, WDH, for the lead on the fans.  I have located some of the fans like the ones on the link that I can get for free from a barn that I helped to tear down.  I do not mind buying new equipment but we try to spend sawmill money on the mill and kiln project and we are running low on sawmill dollars.  There are four of them available.  Two need blades but two are in good working order now.  I just did not know if they are compatible with our kiln or if they would be overkill.   These draw 4 amps and have 1/2 hp motors.
Caveman

[LorenB]

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.

My kiln is still under construction (has been for a few years now) but I'm slowly making progress.  A while back someone (may have been Don Lewis) told me about the possibility of using a waterbed mattress as weight.  You don't fill it until it's on the lumber and drain it before you tear the load apart. 

Sounds like a good idea to me, but I don't know how much a waterbed mattress will cost.  Probably cheaper than concrete though. 

-- Loren

[PC-Urban-Sawyer]

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.

My kiln is still under construction (has been for a few years now) but I'm slowly making progress.  A while back someone (may have been Don Lewis) told me about the possibility of using a waterbed mattress as weight.  You don't fill it until it's on the lumber and drain it before you tear the load apart. 

Sounds like a good idea to me, but I don't know how much a waterbed mattress will cost.  Probably cheaper than concrete though. 

-- Loren

Here's one (http://www.amazon.com/InnoMax-Sanctuary-Free-Waterbed-Mattress/dp/B00ARV4MZG/ref=sr_1_1?ie=UTF8&qid=1404826532&sr=8-1&keywords=waterbed+mattress for $50...

[jueston]

caveman, when i read your post, this is what i thought you meant....  :D

We are running low on sawmill dollars, There are four of them available. 

[LorenB]

Here's one (http://www.amazon.com/InnoMax-Sanctuary-Free-Waterbed-Mattress/dp/B00ARV4MZG/ref=sr_1_1?ie=UTF8&qid=1404826532&sr=8-1&keywords=waterbed+mattress for $50...

PC-Urban,

Thanks.  It's even cheaper than I expected. 

– Loren

[bedway]

I have my kiln in the build stage and am thinking ahead as to temperature and humidity sensors. Ill have the kiln located just outside the shop and want to be able to view readings inside my shop. I don't want to mortgage my house to get these units but neither do I want el cheapo. Input please?

[Larry]

I have a Radio Shack indoor/outdoor weather station.  It has a wireless sensor.  The problem with any of these units is they won't read much if any over 120 degrees.  My unit has been working perfect for a couple of years and is fairly accurate.  I compared humidity/temperature readings to both the local National Weather Service and TV station.  I'm using my unit as a weather station and the outdoor sensor is on a covered porch so I don't know how it would stand up to humidity in a kiln.  I also don't know if the wireless unit will go through both a kiln wall and a shop wall. 

My unit is discontinued but I think virtually the same as this one.

http://www.radioshack.com/product/index.jsp?productId=23147756

I have a much older RS unit with a wired sensor that I did use in my kiln for over 10 years with no problems.  Its an antique as these things go, so no links to it.