Anyone build a solar firewood kiln?

[DHD]

A small solar firewood kiln is an interesting idea.
In building a solar kiln, is it more important to produce heat or to encourage air circulation ?

 

[dragoneggs]

A small solar firewood kiln is an interesting idea.
In building a solar kiln, is it more important to produce heat or to encourage air circulation ?

Air circulation I think is most important next to being dry and sheltered. Heat would be nice but in my book it would need to be passive. Some throw away windows or something that you could orient sunward (is that a word?) would add to the heat part of the equation.

 

[Garandman]

A small solar firewood kiln is an interesting idea.
In building a solar kiln, is it more important to produce heat or to encourage air circulation ?

Answer seems to be "both." The UVA design Pappy60 referenced has a lot of info.
https://pubs.ext.vt.edu/420/420-030/420-030_pdf.pdf. The basic idea is that by having a black painted insulted box with a collector to absorb heat, you can warm the air substantially. By warming the air you drop the relative humidity and that helps draw the moisture out of the wood. But the hottest (and most humid) air rises to the top of the chamber, so you need some means to circulate it, and remove the moist air.

My thinking right now is to build the sloped box per the UVA design, only smaller, and using whatever I can get my hands on for glazing (old double pane windows or sliding doors would seem to be ideal. If glass I'd leave it closed in front and have doors in the back for loading and unloading.

Instead of the multiple electric fans, I'm thinking of buying a relatively inexpensive solar powered vent fan. I can tap into the wires to the motor and add a thermostat so it doesn't start drawing air until it reaches the set point, or add a battery backup and timer. That way I won't be pulling in cold moist air if it rained, for example. Even more simply, I could just put it on the west-facing wall and partially shroud it so sunlight didn't get to it until the afternoon, when presumably the box would be warm.

 

[Sfrankland]

Answer seems to be "both." The UVA design Pappy60 referenced has a lot of info. https://pubs.ext.vt.edu/420/420-030/420-030_pdf.pdf. The basic idea is that by having a black painted insulted box with a collector to absorb heat, you can warm the air substantially. By warming the air you drop the relative humidity and that helps draw the moisture out of the wood. But the hottest (and most humid) air rises to the top of the chamber, so you need some means to circulate it, and remove the moist air. My thinking right now is to build the sloped box per the UVA design, only smaller, and using whatever I can get my hands on for glazing (old double pane windows or sliding doors would seem to be ideal. If glass I'd leave it closed in front and have doors in the back for loading and unloading. Instead of the multiple electric fans, I'm thinking of buying a relatively inexpensive solar powered vent fan. I can tap into the wires to the motor and add a thermostat so it doesn't start drawing air until it reaches the set point, or add a battery backup and timer. That way I won't be pulling in cold moist air if it rained, for example. Even more simply, I could just put it on the west-facing wall and partially shroud it so sunlight didn't get to it until the afternoon, when presumably the box would be warm.

I think this is an excellent idea. I have some hard to dry wood that would be perfect for a solar kiln. Thanks for the link Garandman.

 

[Garandman]

For such a small amount of wood, I would just stack and then make a leanto out of black plastic facing south to put over it. ught air movement. Might of worked better if he had of turned on the fan, but he didnt and so I dont know.

Here is the U Alaska case study. http://www.familyforests.org/research/documents/DryingFirewoodinKiln.pdf

The makeshift kiln was 4-10 degrees warmer than an open pile, but showed some evidence of growing mold. They suggested that all that was economically justified was a top cover.

I have a few other experiments going already: a "Holzmiete", a conventional stack with top covering, and a conventional stack with no cover.

 

[pappy60]

One point of importance... the Alaska study was using UNSPLIT wood... I have noticed there is a very LARGE difference between split and unsplit wood..
Apparently by splitting there is greater area for the moisture to leave, also it is from torn wood vs smooth wood..

In the winter (Dec,Jan,Feb) where I live (Shenandoah County, VA 22824) there is very little difference in drying between the kiln and a covered pile. Probably because the wood freezes.
There is a LOT of difference from Mar to Nov between the kiln and a covered pile..

The kiln in the photo is about 4' wide, 9' long, 4' high in front, 8' high in back... Used double insulated glass from standard doors (was free)..
Uses (2) 20" box fans from Walmart... Timers are used for fans when in use...
Set timers for fans to run from about 9 am to 8 pm..
Back wall has doors...

Would I build a kiln just for firewood ?? NO.. Cost and work (loading/unloading) not worth it.. but since it also is a convenient place to store firewood when not using for lumber, I use it.. Makes the wood super dry for starting a fire in stove...

 

[muddstopper]

I like this one, altho it looks more a shed than a kiln. Off on Adventure: Morgan Mountain & Cooper Kiln Pond - Taylor Pond Wild Forest - 12/25/13 have to scroll down a bit to see it

 

[Baby Grand]

I'd like to try this using 3 basic components:
1) A "knock-down" box, roughly 4'x4'x6' tall, painted a dark color, with a pitched roof.
2) A solar chimney - basically a tall section of vertical pipe; painted black.
3) A flex hose - something like dryer hose - 6" diameter?

The box would be pinned together (butt hinges?), so it's easy to remove from the pile and reassemble around the next pile to be dried.
The hose would be attached near the top of the box and to the bottom of the chimney.
As the chimney heats in the sun, it creates an updraft in the column of air inside.
This draw is used to pull the heated, humidified air out of the top of the box.
The wood pile would be stacked on top of a pallet, set on a bed of gravel, to allow air to flow in from the bottom.
Once the pile has dried, you disconnect the hose, remove the box, pick up the stack & pallet with your forks & move it to a storage area for later use.

 

[PSEbowhunter]

I'd like to try this using 3 basic components:
1) A "knock-down" box, roughly 4'x4'x6' tall, painted a dark color, with a pitched roof.
2) A solar chimney - basically a tall section of vertical pipe; painted black.
3) A flex hose - something like dryer hose - 6" diameter?

The box would be pinned together (butt hinges?), so it's easy to remove from the pile and reassemble around the next pile to be dried.
The hose would be attached near the top of the box and to the bottom of the chimney.
As the chimney heats in the sun, it creates an updraft in the column of air inside.
This draw is used to pull the heated, humidified air out of the top of the box.
The wood pile would be stacked on top of a pallet, set on a bed of gravel, to allow air to flow in from the bottom.
Once the pile has dried, you disconnect the hose, remove the box, pick up the stack & pallet with your forks & move it to a storage area for later use.

I would still recommend using a fan of some sort to move the air out. The solar chimney will help pull the warm air but you will still be creating moisture/humidity in the air from the wood that needs to be expelled from the box. That is what will create your mold when it cools at night and allows the air temp to meet the dew point in the box.

Also make sure to lay a moisture barrier between the ground and your stacking surface (even if it's under the gravel) otherwise you will be pulling the moisture out of the earth and up through the wood stack. The wood in the middle of the stack will be cooler than the air from the ground and draw the moisture to it. And you'll never draw all the moisture from the ground.

And for what it is worth, splits will expel more moisture faster than rounds so split it first.

Just my $.02

 

[PILOON]

A while ago I had some lumber I wished to dry.
I stacked it with sticks between the boards with 1st layer on concrete blocks at both ends and middle.
Had about 30 boards in the stack.
Next I folded old tin roofing in a U shape to make a kinda roof with old tins on both sides tucked under my 'roof'.
Couple of stones to weigh down the 'roof'.
After 6 months sitting under the hot sun that wood was 'kiln dried'.

I always dry my split fire wood the same way. Under old roofing tins.
Works great. Rounds do not dry as well and tend to grow fungi.

Old tin roofing material is sought after 'round here by any one that heats with wood.