Solar wood drying...

[Adios Pantalones]

I have read many times where people recommend covering piles with plastic with an opening at the top and bottom to create a solar heating effect. The only controled study that I've read for this showed no effect- probably because there was less area for moisture to escape. The increased heat was offset by reduced overall air movement, trapping moisture in the pile.

I have a strong interest in novel burner technology (like coffee-can gasifiers, etc that cost nothing and stretch fuel amazingly in impoverished places). Simple fact is that hot air rises (derrrr). What if a simple "plastic solar wood kiln" were amplified by the addition of a black sheet metal preheat box? This would be connected to the bottom tarp opening and act to more efficiently collect solar heat, and to increase convective flow through the "chamber".

How the wood is stacked to provide airflow across all portions would need to be thought out, as would wood access for reloading. I anticipate that small loads could be dried fairly quickly, and then just reload the suckah. This idea sort of springs from another idea that I had for a guy living in high desert to dry wood chips that he was going to use for fuel by putting them between 2 pieces of corrugated metal at an angle, and painting the top one black- the whole apparatus would heat up, and natural convection would pull air through. We also had an idea on reloading, and semi-automation.

Has anyone had any experience with trying to boost heat or natural convection in makeshift solar wood kilns?

Thanks

 

[Adios Pantalones]

See if this works

Probably rotate the wood so that one end of each stick is facing the sheeting- easier to brace as well

 

[Adios Pantalones]

LOL- I'll get out my digital chopper...

I think it will be somewhat self-limiting on moisture drawing: cooler and moister days, less solar gain, except an hour in the morning.

It would stink to have to cover the intake every morning, unless it was only a few days total to dry say- a face cord load at a time.

 

[billb3]

In terms of effort : result, I don't think you can beat the ages old long stack of splits.

 

[Adios Pantalones]

Well, that's not nearly "Rube Goldberg" enough.

http://www.fpl.fs.fed.us/documnts/fplrn/fplrn254.pdf

 

[begreen]

Here's another link for solar wood kilns:
http://www.builditsolar.com/Projects/WoodDrying/wood_kiln.htm

 

[Adios Pantalones]

I've seen all those big ones- generally used for lumber. My problem with them has always been that solar energy strikes one side, and the draft is normally driven by a fan. With a preheat-box, you may be able to do away with the fan, and with this energy necessarily being brought in with the air, it could more efficiently interact with all of the wood.

I also am looking for soemthing that couls be adapted to an existing stack- preheat box, wood stack on a pallet, plastic tarp- away you go

 

[fossil]

Well, gee whiz, Adios, just build the damn thing, instrument it, take a season's worth of data (days of sun, insolation, temperatures throughout the stack, wood moisture over time, etc.), write it up and submit it to "The Journal of Trends in Wood Seasoning Today", and see what the public reaction is. Rick

 

[savageactor7]

Well truthfully...I don't know what to think. This is way above my level of understanding...I just pile my wood up and let our friend mother nature weather it.

Here in CNY there isn't much sun but I suppose by using black or clear tarps with the correct scientific plan you could cure wood in 6 months or less and that would be a good thing....and I think that's what AP is leading up to. as long as it's not labor intensive I'm pretty much down with new ways of doing things.

 

[sapratt]

Seems like you'd moving wood alot or having a few of those kilns in your yard. Specialy if you go through more than 2 cords of wood in a season. Cause it doesn't look like it holds alot of wood.

 

[FatttFire]

Just tell me if I am wrong, but isn't a Holz house basically the same concept your trying to reach?

 

[btuser]

After a year of fiddling with the blue tarp under a mountain of snow, I knew a wood shed was in my future. I wanted to do a solar thing, because I'm so overgrown with tall trees (not for long) I don't get the sun/wind I desire. I also didn't want to make something taxable, so I was limited to 144 sqft.

I built a roof on stilts, open on all 4 sides. 16x8 with a 16x10 roof. The roof slope matches that of the ground. My goal was to make the shed disappear as much as possible, so all there was to see was a glorious pile of drying wood. My original goal was going to be rough sawn lumber, but cost was my major concern so I ended up with pressure-treated (very cheap last Summer) lumber. For the roof I used clear polycarbonate roofing panels. They weren't cheap, but the whole show ended up costing just under $300 (about the cost of a single cord of seasoned hardwood in November). Eventually I may side it with some of the 30" pines I'm taking down, but I've got to wait to make a friend with a sawmill.

 

[weatherguy]

After a year of fiddling with the blue tarp under a mountain of snow, I knew a wood shed was in my future. I wanted to do a solar thing, because I’m so overgrown with tall trees (not for long) I don’t get the sun/wind I desire. I also didn’t want to make something taxable, so I was limited to 144 sqft.

I built a roof on stilts, open on all 4 sides. 16x8 with a 16x10 roof. The roof slope matches that of the ground. My goal was to make the shed disappear as much as possible, so all there was to see was a glorious pile of drying wood. My original goal was going to be rough sawn lumber, but cost was my major concern so I ended up with pressure-treated (very cheap last Summer) lumber. For the roof I used clear polycarbonate roofing panels. They weren’t cheap, but the whole show ended up costing just under $300 (about the cost of a single cord of seasoned hardwood in November). Eventually I may side it with some of the 30” pines I’m taking down, but I’ve got to wait to make a friend with a sawmill.

Sounds interesting, do you have a pic?

Im bouncing ideas around and yours sounds like something I could do easily.

 

[heatwise]

I'm noticing that some places are better to dry wood than others, for example on the side of the house single stacked above a concrete path just off a brick wall just the top covered is my best spot. it gets afternoon sun and a breezeway between the houses. 2nd best is stacked under the back deck. not much sun but defiantly no rain gets to it, these 2 spots are reserved for the all night logs. all the rest are stacked in rows slightly spaced and covered on top. i have read about speed drying wood. i would think that laying some splits on some asphalt or concrete or other material and let the sun beat on it could dry it fast. lots of heat on a black driveway. i try to plan ahead but I'm sure if you need the stuff to dry faster it cant hurt to experiment. Pete

 

[woodgeek]

While I've been a skeptic of solar dryers before, I like the gen'l approach here. You should estimated how much air needs to pass through the system--how much moisture does the charge lose, over how many sunny days? At that water per hour, how much air cfm is required for the relative humidity to increase say 20% at your operating temp. I would then (as a first pass) just run a small forced air blower at that cfm rating. With a hygrometer/thermometer on the in and out, you can estimate the rate of water removal. If everything works as you like, you can then go passive with a stack to drive the airflow. Some folks report a lot of condensation/mold when the system shuts down--you could also run the blower in the dark to prevent that and get extra air drying.

The same unit could be useful for pastuerizing compost--I always get a ton of weed seeds surviving in my (or the town's) compost.

 

[Dune]

Let's simplify this a little. All theory derived from Mother Earth News, back in the day. There is no need for top ventilation. Having a vent at the top releases heat. Nor is forced air circulation needed. The working theory is that the bottom of the enclosure must be open. Water, as it is forced from the wood by heat, condenses on the glass or plastic and drips onto the ground. Every time I post this info, someone slams it down, and I really don't care. I will not get into a debate about this. MEN proved this out over thirty years ago. In their initial test kiln, drying time was reduced by over 60%. I am a member of the editorial advisory commitee of MEN, but I am not an employee, shareholder or even a subscriber.

 

[JotulOwner]

I just pile my wood up and let our friend mother nature weather it.

That's the way I do it now that I have tried my version of the solar kiln thing. I suppose a professional kiln setup (but maybe not solar) is very efficient and, for commercial purposes, allows for faster drying and longer distance transportation of firewood (legally), but for the average burner, I believe that the method that has worked for ages is worth sticking with.

A little planning and some patience goes a long way.