Cherry Air Drying

[doc henderson]

here is a pic of my covered stack, passive ventilation (wind) black cover just storing.



 



 

shrinkage in maple, the band twanged a high C when first under there.



 

moisture of a 2" thick elm slab under the eves but left outside.  gave half to a friend and they thought they would come back for the other half and It would be hard to stack so got left out.



 

a maple 4 x 4 under the tarp



 

a 2" elm slab from the same tree, left under the tarp.

[YellowHammer]

A couple things to maybe help things make sense.  Each species of wood has a maximum acceptable drying rate, based on its thickness.  Cherry for example, has a max safe drying rate of about 5.8% for 4/4, and about half of that for 8/4 (some say more or less, but I round to half).  So if you dry more than about 2.9% per day, the wood will split and check.  In reality, I would go conservatively with cherry, as it like to split, so would keep it down to about 2% per day for 8/4.  This is one of the things about a kiln, in many cases it's important to slow down or regulate the rate of drying, not to accelerate it.  It's all about controlling the environment of the wood.

As has been mentioned, moisture is driven from wood with the help of heat.  So the more heat, the more moisture is evolved from the wood.  When the wood is very wet, and the moisture is close to the surface, it will come out easily.  When the wood gets dryer, it is more difficult for the moisture to travel from the core of the boards, and heat is required.
  
Air velocity also plays a very important factor in lumber drying, the same as you would think, wetter boards, more surface moisture, the more the effect the air movement in drying.  Dryer boards, less effect.
Temperature also greatly effects the strength of the boards.  Cooler wood is stronger and more able to withstand the stresses of drying, hotter wood is significantly weaker.

So when you put all this together, and I have just scratched the surface with this info, for thick, wet wood, it's best to try to get to just under the max allowable drying rate while keeping the wood as cool as possible.  As the moisture removal rate starts to drop for a set of conditions, the temperature is increased, or allowed to increase gradually.

The way to track things is by calculating the water removed from the wood using the oven dry method, or an accurate moisture meter, or by the amount of water in a bucket, or a combination of them.  It's important to know how much moisture is being removed when using a DH system, or its just guesswork. 
   
So typically, the best DH kiln schedule for thick or green wood that I'm just getting a feel for, starts at 90F and gradually increases through stages, until a max of 120F.  There should be no need to go higher than that unless the wood has stalled.
  
Using a DH unit is fine, but it must be able to keep up with the amount of moisture removed form the wood, to achieve low enough humidities to dry the wood at the lower temperatures.  Remember that a house will dry the wood at 70F, but it takes too long.  Also, most houses are at too low a humidity for green wood, and will immediately begin to crack it.  If the wood is further along, or basically air dried, the low humidities are required.

OR

The other solution is to air dry the wood from the start, or use other conservative methods.  Personally, I really like air drying as a first stage, and it will step right through many of the risks and issues.  A solar kiln is great, and some of these other techniques @doc henderson uses are also very effective.
To dry wood successfully, the maximum allowable moisture removal rate must not be exceeded.  
 

[CEaston]

@YellowHammer Wow, Thank you for the information. Here are the numbers I plugged and they seem to be in line with the numbers you are saying.

I have about 200 BF of Cherry right now. After I did the calculations of the "Calculations of Weight of Lumber" document posted early with my MC. It is saying I have roughly 961 lbs of wood/water weight.

If I were to dry the wood at the suggested 2%/day that would be about 19.2 lbs of water/day. 

After doing the water weight/ gallon ratio and the fact that my DH has a 2 gallon reservoir, I should only be filing that reservoir once a day.

These are not exactly 100% but are pretty close and error on the side of caution.

My setup is not exactly tight as well. I am working on bettering this, so I have a nice and controlled environment.

[CEaston]

So I moved into my current house about a month ago and just had to close down the pool. All of the pool supplies were kept in a 10' x 10' room, after going through them all were  most junk or not need and  the rest could be consolidated to a storage rack.  

Now I have this empty room that I though would be a decent idea to use as the wood drying room. It needs some help/ work to get there( insulation added, electrical gone through, sealing the room, ect.)   

I am a controls engineer by day, and this room got my head thinking about some things I could get out with the room. I currently have  a halogen light, box fan, and dehumidifier in the room for testing. I could use a micro PC/ industrial PLC to turn these peripheral equipment on and off depending on variable feedback from sensors.





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[CEaston]

Update.

I have sealed the door and made them function again, I still need to add a back stop to the doors and put a seal on it so when the doors are shut the gaps are sealed off.

 




ripped out the peg board and added insulation to all the walls.


 


Started to test out a heating method. It utilizes a PID controller, heater bands, gas pipe, and RTD feedback sensor. Essentially it works by the PID controller heating up the pipe via the heater bands, a fan blowing air around the pipe to heat the air up, and the RTD sensor providing feedback to the PID controller on the heat of the output air. My first test worked well, but I did take away some things that I am going to change for the next test. I am only testing in controlled environment with my full attention to it.


 

I have been able to get the room up to 84 degrees so far with just running the halogen lights. I plan on running a trial with the lights and heater bands once I get a better method for heat transfer to the air flowing around the pipe. My process right now is to have the box fan running both day and night, halogen lights during the day to increase temperature, and the dehumidifier at night.

[Al_Smith]

I've probably got 5-800 bd ft of cherry that has been stickered and stacked 8-10 years as well as oak, ash ,maple some hickory .Total of over 4000 BD ft .So far if I need  some aside from digging through the stacks to find what I want it's all been good and dry and stable .I have no idea what the moisture content is .
As far as cherry goes they say make certain your cutters, saw blades etc are good and sharp because it "burns " easily .Most of mine are carbide so it hasn't been a problem .
I have a few shorts but mostly 12-16 feet long .Try latching on to a 16' white oak 1" by 12" .Eat your Wheaties first, it  certainly isn't balsa :D

[rweiss1110]

I just put a load of Cherry 400 bd/ft in my DH box that I don't run in winter. Would having it under fan for the next 4 month help dry it out? mind you that I'm up here in the icebox of the nation with temps below 20 degrees.

 

[doc henderson]

if you could add a little heat, that would help.  lots of guys add halogen work lights.  I would monitor the humidity.  If it is running high with no way to get out, might get mold on your wood, and even damage your box.  we get some warm days occ. in the winter, you prob do not.  if you get it over 40° inside, could kick on the DH unit.  Or what ever the bottom temp is for your unit.  @GeneWengert-WoodDoc

[Jeff]

Please do not post duplicate posts. Once is plenty.