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Author Topic: Using Fans for the initial Air Drying  (Read 6680 times)

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Offline Den Socling

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Re: Using Fans for the initial Air Drying
« Reply #20 on: November 10, 2014, 09:53:07 AM »
You ought to try 12/4!

Offline OneWithWood

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Re: Using Fans for the initial Air Drying
« Reply #21 on: November 10, 2014, 01:45:50 PM »
I have more trouble with the red oaks, especially black oak, than I do with white oak.  One thing I have learned is you cannot rush the oaks.  4/4 is going to take 28-30 days and 8/4 will take 56-60 days.  I go from mill to kiln with very little air drying so your times will vary.
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Offline Denny

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Re: Using Fans for the initial Air Drying
« Reply #22 on: November 10, 2014, 03:24:30 PM »
Danny, will you flood your kiln or somehow add moisture during the last few days?

Yeah I've been wondering if you guys condition/de-stress your lumber and how you go about conditioning in a solar or dehum kiln.

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Re: Using Fans for the initial Air Drying
« Reply #23 on: November 10, 2014, 08:13:06 PM »
OWW,

No, I don't add moisture for conditioning. 

Den,

12/4  ???.  Now I will have nightmares  :)
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Re: Using Fans for the initial Air Drying
« Reply #24 on: November 10, 2014, 09:06:42 PM »
Danny, will you flood your kiln or somehow add moisture during the last few days?

Yeah I've been wondering if you guys condition/de-stress your lumber and how you go about conditioning in a solar or dehum kiln.
I tried dumping water into the kiln and other such techniques at the end of a drying cycle because I used to have a lot of stress in my kiln dried lumber, and fought it for a while.  Somewhere along the line I heard about "making the boards sweat" at the end of a drying cycle, which involves increasingly heating the boards to a point where the remaining core moisture is driven out through the case and eventually to the outside of the board without the kiln dehumidifier running so as not to remove the moisture from the atmosphere.  Since the dehumidifier is not operating, the moisture driven out of the boards just stays in the kiln chamber and is recirculated, significantly raising the RH, pretty much the same as if moisture was introduced into the kiln externally for equalization. Coincidentally, this happens naturally in a DH kiln during the sterilization cycle when the temps are driven up significantly over the normal drying schedule maximum allowable temperature and the dehumidifier is turned off to protect the compressor against overheating (at least in my kiln model).   There may be some other factors at work here, but it is very rare for me to have lumber come out of the kiln with any appreciable case to core differential moisture content and very rarely will I have any stress in the boards anymore, and I try to dry them on the fast side of the drying schedules, which normally induces drying stress.  So for me, the high temperature dehumidifier off sterilization cycle serves multiple purposes, and is a step I never skip.  I hadn't thought about it before, but happy, relaxed boards coming out of a sauna is a pretty good description. ;D

As far as a solar kiln, it gets equalized every night.
YH 
     
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Re: Using Fans for the initial Air Drying
« Reply #25 on: November 11, 2014, 07:27:34 AM »
I do the same thing as Robert.  I run the kiln at 150 degrees for 24 hours, and usually let the load sit for a while with all the vents closed and all the fans running.  I have let the load sit for 24 hours after sterilization, and the temp in the kiln will still be above 130 - 135 degrees with every thing including the fans shut down and the vents closed. 
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Offline OneWithWood

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Re: Using Fans for the initial Air Drying
« Reply #26 on: November 11, 2014, 02:05:53 PM »
I do the sweat-em-in-the-sauna thing for most of the hardwoods, but I still flood the floor with about 20 gallons of water before running the temp up for oak.  My kiln chamber is 21'x10', the DH unit is a Nyle 200 and controller is a Honeywell (Woodmizer sold this setup as a DH4000 back in 2002).  I have had good results with the oak doing this, especially the 8/4. 
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Offline Glenn1

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Re: Using Fans for the initial Air Drying
« Reply #27 on: November 11, 2014, 02:28:35 PM »
I do the sweat-em-in-the-sauna thing for most of the hardwoods, but I still flood the floor with about 20 gallons of water before running the temp up for oak.  My kiln chamber is 21'x10', the DH unit is a Nyle 200 and controller is a Honeywell (Woodmizer sold this setup as a DH4000 back in 2002).  I have had good results with the oak doing this, especially the 8/4.

How are you containing the water on the floor?  Are you keeping it away from the walls or not worrying about it?
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Offline GeneWengert-WoodDoc

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Re: Using Fans for the initial Air Drying
« Reply #28 on: November 11, 2014, 06:25:08 PM »
Air dried lumber has very little, if any, stress.  However, when running the stress test with prongs, if there is a moisture gradient, the prongs will show stress.  The prong test must be made with no gradient.  So, keeping the vents closed with heat may actually be eliminating the gradient, which would have shown stress.

A commercial kiln will use 180 F and very high humidity for 18 - 24 hours.  It is hard to understand how a very mild condition (heat and vents closed) would be just as effective.  For this reason, I suspect that the amount of stress in many instances is very low.  Adding a great deal of humidity will cause the surface to gain moisture and swell (or try to swell) so that even a piece with stress will show no stress, until the moisture on the surface (moisture gradient) is dispersed.

To get a good reading with the prong tests when there is a gradient, put an individual prong in a microwave on high power for 15 seconds.  Then take it out and wait a couple of minutes before reading the results.
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Re: Using Fans for the initial Air Drying
« Reply #29 on: November 11, 2014, 08:31:27 PM »
A commercial kiln will use 180 F and very high humidity for 18 - 24 hours.  It is hard to understand how a very mild condition (heat and vents closed) would be just as effective. 

Is 150 degrees for 24 hours considered a 'mild condition"?

Another question.  If the wood going into the kiln is already air dried to 15%, will much additional stress develop between drying from 15% to 8%?
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Offline GeneWengert-WoodDoc

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Re: Using Fans for the initial Air Drying
« Reply #30 on: November 11, 2014, 08:45:39 PM »
Yes, 150 is mild.  We know that stresses are not removed well at 150 compared to 180.

Virtually all stress develops during the loss of the first 1/3 of the moisture, from green.  So, no stress develops at low MCs.  Short answer...need more?
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Re: Using Fans for the initial Air Drying
« Reply #31 on: November 11, 2014, 08:49:17 PM »
No.  Mostly what I am drying in the DH kiln has pre-air dried.  I am not getting much stress at all, therefore the question about the "mild" 150 degree sterilization. 

I still hate white oak.  All thicknesses  :).
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Offline Peter Drouin

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Re: Using Fans for the initial Air Drying
« Reply #32 on: November 11, 2014, 09:16:30 PM »
Thanks for the info guys. It will help in the spring when I can get my kiln together. :D
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Offline OneWithWood

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Re: Using Fans for the initial Air Drying
« Reply #33 on: November 12, 2014, 05:57:13 AM »
I do the sweat-em-in-the-sauna thing for most of the hardwoods, but I still flood the floor with about 20 gallons of water before running the temp up for oak.  My kiln chamber is 21'x10', the DH unit is a Nyle 200 and controller is a Honeywell (Woodmizer sold this setup as a DH4000 back in 2002).  I have had good results with the oak doing this, especially the 8/4.

How are you containing the water on the floor?  Are you keeping it away from the walls or not worrying about it?

The kiln is very well sealed along the floor wall boundary and the walls are coated.  With a 3000bf charge of 6-7% wood the water does not stay on the floor long enough for me to worry about it. 
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Offline OneWithWood

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Re: Using Fans for the initial Air Drying
« Reply #34 on: November 12, 2014, 05:58:36 AM »
I am quite fond of white oak, all thicknesses.  It brings out my more caring patient side  :D :D :D ;D
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Re: Using Fans for the initial Air Drying
« Reply #35 on: November 12, 2014, 07:46:34 AM »
 :D :D :D

Actually, I love everything about white oak except for drying it. 
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Re: Using Fans for the initial Air Drying
« Reply #36 on: June 06, 2021, 10:10:01 AM »
I have two stacks of 2x6x10&14' of (mostly SYP) pine on sticks under the open roof on the front of my shop. Each stack is a bit over 1,000BF stacked 3.5' wide.

 I have one 20" box fan on the end of each stack blowing 24/7 into the end.

 In my area, about how many days will these fans serve an effective purpose toward drying this lumber? 
Thanks!
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Offline customsawyer

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Re: Using Fans for the initial Air Drying
« Reply #37 on: June 06, 2021, 11:12:17 AM »
I have two stacks of 2x6x10&14' of (mostly SYP) pine on sticks under the open roof on the front of my shop. Each stack is a bit over 1,000BF stacked 3.5' wide.

 I have one 20" box fan on the end of each stack blowing 24/7 into the end.

 In my area, about how many days will these fans serve an effective purpose toward drying this lumber?
Thanks!



If I am reading it right your fans are blowing against your stickers instead of through your lumber. I don't think your fans are going to help much. Look back at the pictures of YH fans and lumber. Bigger fans will help more and have them moving the air parallel to the stickers. 
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Re: Using Fans for the initial Air Drying
« Reply #38 on: June 06, 2021, 01:10:38 PM »
I see what your say & it's true and I considered that when I placed them but not smart enough huh? ;D I'm gonna move the fans to the open walkway between the stacks and opposite ends from each other, then move them along the stack a bit as they'll be pretty close to the wood-maybe 24" from the stacks. I have these box fans sitting on milk crates to position them above the base. 

Now, back to my question? 
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Re: Using Fans for the initial Air Drying
« Reply #39 on: June 06, 2021, 01:51:16 PM »
If it's framing lumber you are after I bet they would be under 20% MC in a couple weeks. 
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