Wind drying?

[Nate Surveyor]

I live on a VERY windy hill top. It seems that SYP (Southern Yellow Pine) that is stickered and set to dry here, is drying really fast. Has anyone any experience with heat (solar kilns etc) vs airflow?

I have never heard anybody discuss lots of wind, as a factor in drying. It does dry clothes on the line pretty fast too.

I am judging dryness by the weight of the wood. Sure gets light fast.

Thanks,

N

[Den Socling]

Air flow provides two things. It carries heat to the wood and it carries evaporated water from the wood. High speed air flow will carry vapor away quickly but the wood can become only as dry as the temperature has set moisture content. As MC decreases, it takes an increasing amount of energy to evaporate the remaining water. In other word, 100mph wind isn't going to achieve 8% unless it's hot. But it could quickly get SYP down into the 20's or even teens pretty fast.

[Nate Surveyor]

So, you are saying that the wind carries the water fast, but the temperature determines how much water that wind can carry? You are saying that I have part of the equasion, but that heat is necessary too. (Do I have it right?)



Well, if the temperature around here is 30°, we always have a windchill. That windchill will take ice to vapor, skipping the wet state!

Thanks,

N

[Den Socling]

Water in wood is not like ice on a sidewalk. As MC goes down, the remaining water is increasingly chemically bound inside the wood. It takes heat to break those bonds.

[Ga_Boy]

Nate.

There are two types (if you will) of water inside the cell structure of wood.

Type one is free water, which is not chemically bound.  Free water exist inside the wood cell and takes very little energy to remove it from the cell.

Type two is bound water, which is chemically bound to the wood cell structure.  Bound water being attached to the cell structure requries ever increasing energy to remove it from the cell structure.  Thus why as wood drys using conventional schedules you increase the temperture and decrease the relative humidity inside the kiln chamber.  Air speed is constant in the small scale chambers discussed on this board.  When you get in to the big commercial kilns; capacity of 30MBF and more; variable speed, reversable pitch fans are used.

There is a great deal more science to drying wood than I have eleuded to here.  I have grossly over simplified the drying process so if this seem elemintary to you I am not trying to insult you I am not aware of how much you know about the science of drying wood.





Mark

[Nate Surveyor]

I do not insult easily.

I am as dumb as a 3 cent brick.

And I appreciate your effort to steer me in the right direction.

I have heard that it is ok to build with 6-8 wk air dried  pine. Build to a dried in state, BUT leave the walls open for a year, before closing them.

Is that true?

Thank you sincerely,

Nate

[Tom]

It's done all of the time around here, Nate.  Usualy 6-8 weeks, while not producing dry pine, will bring it to a point of rigidity and it will support weight sufficiently enough to use for most building purposes.

'Course I live in a warm and breezy place and, except for the humidity in the summer, don't have much trouble drying wood.  A pole barn exposing the stack to good air movement is good too.  I'm not talking about the 'fast' air of the above conversation, I just mean that there is enough air flow to keep the wet air in the stack moved out.  Without a good breeze, the air in a stack of wood becomes stagnant and the wet surfaces are a good garden for fungus and algae.

[Riles]

Another thing to keep in mind is that SYP rarely spends more than a day in a commercial kiln. Granted they're only taking it down to around 19%, but this stuff isn't on a 2 week schedule. Pretty forgiving stuff.

Around here the 2x6 you buy on Saturday afternoon was probably a tree on Monday.  :D

[Ianab]

Your clothes line anology is probably a good one. Clothes will dry on a warm day, but it's slow unless there is a breeze. Likewise they will dry on a cold windy day, but much slower than if it was warm.

It requires energy (heat) to convert the water from a liquid to a vapour, the more heat thats around, the faster this can happen, then the wind can carry it away. Some drying will take place even in a very cold environment, but it will be SLOW compared to a warm place. Likewise if there is no wind, the humidity in the drying stack will go up to 100% and no more drying can occur. (good for growing mould and fungus though  ;) )

As for building, local regulations here say your wood has to be below 20% when it is used, and below 14% (?) before the walls are enclosed. This extra drying will usually occur naturally during the building process. By the time the builder has finished the roof and installed the joinery the wall framing is dry enough to put up the wall linings.

In a warm (and breezy) climate you could dry pine to under 20% in 2 months and build with it. Then another month or two drying in the partly completed structure and it should be ready to line. A moisture meter will tell you exactly.

Cheers

Ian

[Nate Surveyor]

OK, I'm relieved that I can really do this rumor. (build with air dried wood)

But, can you suggest me a moisture meter?

And tell me about them?

I have seen pics, and they look like they have 2 pins on them, and I guess you drive them into the wood...

Thanks Ian, that seems like thoughts that line up with my logic, which is good, because I don't have to tear down as much misconception that way!

N

N

[Ga_Boy]

Construciton material dried in a commercial kiln is dried at arond 250 degrees F, I have been told that the air speed is so great that when the wood first enters the chamber the free ware acctually pours out the end of the material.

Also the specs for construciton material is usually around 19 % MC.  As construction material is usually stored outside it does not make any sense to take it any lower.  As for air drying the absolute lowest you will ever reach in the contential US is 12%.  The rule of thumb is one year per inch to reach 12%.  This maily applies to The Oaks.  I let some Cherry sit stacked and stickered for about 10 weeks waiting for the kiln to open and it reached 20% MC when it entered the kiln.  Now this number is calculated using a lab oven to dry samples and scales to weigh the samples.  But, so far the calcualted MC is in line with the measured using my J-2000 Delmhorst.   





Mark

[footer]

  As for air drying the absolute lowest you will ever reach in the contential US is 12%.  The rule of thumb is one year per inch to reach 12%.    
Mark

Ga_Boy ,
Not that I am going to try it, but are you saying that if I put a stckered stack of lumber in the Arizona or Nevada deasert or Death valley, that it will never get down below 12%?

[Ga_Boy]

The 12% MC number is a national number.  As for what you can get in a arid environment such as a deasert I am not sure.  The national number of 12% is what I was taught in school and is in my kiln operators manuals.