Solar Kiln Firewood Drying

I debated about trying this with the 1/2 cord of pine I put up today but it is already pretty dry mostly rain moisture and termite body content moisture
Though I contemplated it would kill all the termites (thousands of them) and apparently above 130F for 6mins they're toast - this wood is just not in the condition to be tested with this method

Found a couple other beetle killed pines that still have bark they should be suitable candidates

 

I have been drying wood like this for 2 seasons already. No testing needed, haha. In addition pine seasons in one season regardless so doing this is unnecessary

 

I have a Full Cord Tented and sealed off. Instead of stapling the plastic like usual I have used twine to secure it so I can pull out splits periodically and test them for those from Missouri.

 

What if you could shorten pine to six months? Or even have the kiln properties to kill insects

 

I didn't think a whole lot of this thread at first look, until I started reading. The core temperature of your stack, more than peaked my interest. I have two 5000' rolls of plastic wrap coming in a week (ordered it for a bargain through one of my customers), and will be wrapping couple stacks to see how it works out. I know it wont hurt anything. Heck, I have some year old un split oak down the road, that I am getting ready to split (and will also wrap), and will try to take some moisture readings, before and after (after being when I decide to use it, maybe this upcoming winter/spring).

Thanks for the read, I think you are really onto something and I plan on doing the same. Next spring I will wrap my piles as I get them split, and should still have plenty of wrap left.

 

Why not bugs get cooked in your car, pine may be done in a couple of months

 

I decided what the heck, this pine is ravaged with termites.
Didn't have any poly tarps but remembered the pallet shrink wrap I had laying around - brought me back to my days of building pallets in Hanaford's warehouse.
Tried using the chimney brush sticks to pull a piece of it underneath(didn't work out so well).

My neighbor(shares the driveway) always comments on my neat stacks....Pretty sure he is going to think I'm insane when he sees this

 

Nah, he'll probably think it's a good idea that you're keeping the wood from getting dirty.

 

With the stacks so close to the ground, I wonder if you even need to cover the bottom. Shouldn't wrapping the sides and top tight be enough to drive moisture out?

 

From some of the university studies I've read on solar kilns: Ground moisture is a concern, it evaporates and is trapped under the tarp.
Those timbers are up on bricks - termites around here will eat the cheaper landscape timbers

 

That makes sense. I guess the solution would be to lay a plastic sheet down before stacking, then you could wrap the stack with pallet wrap then staple the bottom sheet up after the stack is wrapped.

Darn it @Uncle Augie , I had no intention of doing this this year, but now I pretty much have to!

 

Curious where you got this? A 100 degree F shift from 50 degrees to 150 degrees causes water to expand less than 2%. Say hypothetically the dew point was 50 degrees. That 100 degree shift would drop the relative humidity from 100% to 4%. If the relative humidity was 100% in the kiln, by definition, the air would not be able to hold any more water, so as the kiln cooled the wood would absorb the excess moisture. Kilns work by either evacuating the high humidity air (while trying to maintain most of the heat inside) or by condensing the water on the relatively cool walls (as with clear plastic) and allowing it to run off and out of the kiln. I submit that between the freezing point and boiling point of water, relative humidity has everything to do with the rate at which moisture is evacuated from the wood since it is the vapor pressure that determines whether moisture is flowing into or out of the wood.. Now if we're talking above the boiling point of water, the issue completely changes as water expands exponentially when converted to steam. Interesting discussion.

Here's a little primer on fuel moisture that the pro's use.

http://ocw.usu.edu/Forest__Range__a...ent_and_Planning/Unit_5__Fuel_Moisture_3.html

 

I just took some readings - sun just dropping behind treetops. It was in full sun from 11am -430pm.
Probe type thermocouple
Ambient temp: 86
Top of stack: 106
middle: 96
Bottom: 92

Moisture droplets on the top of the stack and some areas in front of a few splits. Psychrometric chart caps out 104F(41C) at 70%RH.

I have a portable psychrometer at work could stick that in the top and test wetbulb vs drybulb to see how much depression actually exists

 

You are going to struggle with the process as your wood appears to be shaded much of the day.

I am going to point out again that I am not doing the basic work to prove that this concept works, it is well proven in wood working circles that by wrapping 1000 board ft of lumber in a sunny location you can take green wood to under 10% in about a month or two. We are not going that low, so it follows that you would be able to "season wood in a sunny location in a short period of time.

I will try to explain what I mean my "pushing the water out"

If you consider a green log as a bunch of water filled tubes the explanation will make more sense.

At 70 degrees the vapor pressure of water is 0.3631 Lb/Sq In. so at 70 degrees we have a force of 0.3631 lbs being exerted over every inch to push the water out of the wood. This is normal seasoning temp

At 160 degrees the vapor pressure of water is 4.736 Lb/Sq In. so at 160 degrees we have a force of 4.736 lbs being exerted over every inch to push the water out of the wood. This is Normal Kiln Temps during a sunny day.

This difference 0.3631 to 4.736 is an increase of 13 times. I know the kiln actually gets hotter than 10 as well.

Did that make more sense to you?

 

What I don't understand is what the actual conditions are to which you are referring... Got the 70 degrees vs 160 degrees. I'm assuming that you're talking about sea level pressure and any elevation higher than sea level, the wood would presumably give up water faster. So are you talking about the vapor pressure of gaseous water at 70 degrees when 70 degrees is the dew point and 160 degrees in the same conditions? According to this chart, air at freezing holds under 4 grams of water per kilogram of air while air at 104 degrees F holds nearly 50 grams per kilogram. As the temperature goes up, the capability to hold gaseous water goes up exponentially. Or are you saying that the water in the wood is in a gaseous state and thus at a higher pressure pushing the liquid water out of the wood? Just trying to understand the reasoning for saying that relative humidity has nothing to do with the drying...

I don't doubt at all that a kiln works, solar or otherwise. I believe in the concept and advocate people doing it for more efficient use of their firewood.. I did an experiment this past winter in which I brought wood from over 30% to under 15% in 3 weeks.. Here's the thread.. http://www.firewoodhoardersclub.com/forums/index.php?threads/what-is-it-20-questions.2393/

I'm assuming that you read the page that I linked that discusses how forestry professionals determine wildland fuel moistures using a variety of factors including temperature, humidity, wind and precipitation among other things..

 

This. Wood is a matrix of cells and tubes with both air pockets and water pockets. A live tree needs Sunlight, CO2, and Water for photosynthesis to occur. SO a dead tree has water, and air pockets within its matrix. In the Solar Kiln We have the gas pockets warming up pushing the water out and as the temp goes up the air pockets hold more water vapor from the water pockets pushing the water out from the inside. This is happening on a miniature scale millions of times in a small split.

 

Okay. Now we're getting somewhere. So the roots absorb the water and CO2 and transport it in liquid and gaseous form through these "tubes" to the leaves (and green twigs) where the photosynthesis occurs in the presence of chloroform and sunlight.. So for the gaseous CO2 to push the water out, it would seem that the H2O and CO2 share the same tube on the way from the root to the leaf.. Cut the tree, split the round, stack it under plastic and let the CO2 go to expanding under heat to push the water out. Now it makes sense..

 

Sorry I really thought you were connecting the dots with me.

Glad it is making more sense now.

Sunlight is the key

 

My head hurts.

I will probably try wrapping a stack next year that will be in full sun the majority of the day. It will also have a lot of air flow which isn't relevant if it is wrapped.