Experience based solar kiln operation.

[Poindexter]

I built some passive solar wood kilns, build thread here:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/

My state of the art design, mark 4, is here in that thread:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2060948

with a pic of modules 6, 7 and 8 further down same page form there, and dimensions somewhere inthe last tow pages.

Once I had those built, I had an operation thread running for a little bit, here:
https://www.hearth.com/talk/threads/solar-cord-wood-kiln-operation.152699/

Thanks to all who have contributed along the way. Now that I have been running these a couple seasons I figure I can share what I have figured out the hard way and make it easier for the next guy/gal.

When I designed these, I knew they would work. Now I can write, or start writing the manual. I have seen a couple uninformed folks opine that running kilns "must" be a pain in the neck, but really it is just another opportunity to consume large quantities of liquor while the wife thinks a fella is doing hard labor out in the yard. I can assure you I am going to kill a lot more limes for gin and tonics in blistering summer heat than I am going to get bruises out of this.

Let us begin, on 3-2-18, with # 7 and #8 empty. I am currently burning out of # 6.

Here is 6-7-8 ribbed as built empty and with no membrane...https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2064332

It's one convective unit, one kiln, holds, ohh, 2.75 cords or so green.

Today, with me pulling out of #6 for active burning it looked like this, right after I had two cords dropped in the driveway out front, roof shed snow shoveled out and the side curtain in #8 opened. Todays pic is me standing on the stoop just outside the garage. Top left is second floor deck, tool shed back behind the raised bed hoop house, that SOB #5 to the right.



My biggest 'problem' with Mk4 framing is melted snow tends to collect between the three horizontal 2x4s at the top. I could get out there with a broom and knock most of that off the tops, but I have had a melt recently. I 'know' there is a bunch of ice up in there, if I get too aggressive with a broom I might tear the plastic, so better to just leave it for now.

I have a 'white' carpet in the stove room, so I try to handle as much cord wood as possible while I have good snow pack, less mud on the carpet that way. The carpet might be ecru or eggshell or light beige or whatever, I only have a few crayons in my toolbox, white is the closest. Happy wife, happy life.

Sled is a good tool, though it is well above the floor level of the kiln today.



I did add some diagonal bracing to #8 and #7 and a few others already. When six gets emptied I need to add some diagonals to that one. Note the top edge of the outer horizontal 2x4s - the headache bars - is even with, same height as the lower edge of the 2x4s that make the floor of the upper level. This will be important later, hopefully while the weather is still cool enough to get away with mere Corona before we get into serious GT and ice summer.



Current chore is to fill #8 to the absolute gills, then finish cleaning up the splits in the driveway, likely enough to fill #7 to the gills as well.

And empty #6. Turn that knob on the side of the stove baby, you are wearing too many clothes to suit me.

 

[Poindexter]

In a typical summer I will have light sprinkly rain in early May, hard hot sun in late May and through June, with serious rain starting in mid July, and continuing serious rain into Sept when the rain turns to snow. I am not looking for a typical summer. My plan is to get the wood in 6-7-8 dry (12-16%MC) muy pronto, and then keep it in the 12-16% sweet spot until temps drop to and stay below freezing.

The wood I am loading is really heavy for spruce, probably close to 50% MC, well over the 35% max my reader will read. The two hardest chores are going to be loading the fool things, and second dealing with summer's heat. Pulling the snow back to keep water out of the kilns during the melt is on the easy-peasy list.

 

[livetosail]

I have seen a couple uninformed folks opine that running kilns "must" be a pain in the neck, but really it is just another opportunity to consume large quantities of liquor while the wife thinks a fella is doing hard labor out in the yard. I can assure you I am going to kill a lot more limes for gin and tonics in blistering summer heat than I am going to get bruises out of this.

You, my friend, are a kindred spirit.

Kilns look good. Show us more pictures! (I’m too lazy to look through the original threads)

So you are planning a step-by-step guide to show us how to make these? I stand by in anticipation!

Ps, where are you located?


Sent from my iPhone using Tapatalk

 

[Woodsplitter67]

Always a good read. Thanks for posting this. We can all benefit from this and the pictures look great

 

[Easy Livin’ 3000]

I built some passive solar wood kilns, build thread here:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/

My state of the art design, mark 4, is here in that thread:
https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2060948

with a pic of modules 6, 7 and 8 further down same page form there, and dimensions somewhere inthe last tow pages.

Once I had those built, I had an operation thread running for a little bit, here:
https://www.hearth.com/talk/threads/solar-cord-wood-kiln-operation.152699/

Thanks to all who have contributed along the way. Now that I have been running these a couple seasons I figure I can share what I have figured out the hard way and make it easier for the next guy/gal.

When I designed these, I knew they would work. Now I can write, or start writing the manual. I have seen a couple uninformed folks opine that running kilns "must" be a pain in the neck, but really it is just another opportunity to consume large quantities of liquor while the wife thinks a fella is doing hard labor out in the yard. I can assure you I am going to kill a lot more limes for gin and tonics in blistering summer heat than I am going to get bruises out of this.

Let us begin, on 3-2-18, with # 7 and #8 empty. I am currently burning out of # 6.

Here is 6-7-8 ribbed as built empty and with no membrane...https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2064332

It's one convective unit, one kiln, holds, ohh, 2.75 cords or so green.

Today, with me pulling out of #6 for active burning it looked like this, right after I had two cords dropped in the driveway out front, roof shed snow shoveled out and the side curtain in #8 opened. Todays pic is me standing on the stoop just outside the garage. Top left is second floor deck, tool shed back behind the raised bed hoop house, that SOB #5 to the right.

View attachment 223738

My biggest 'problem' with Mk4 framing is melted snow tends to collect between the three horizontal 2x4s at the top. I could get out there with a broom and knock most of that off the tops, but I have had a melt recently. I 'know' there is a bunch of ice up in there, if I get too aggressive with a broom I might tear the plastic, so better to just leave it for now.

I have a 'white' carpet in the stove room, so I try to handle as much cord wood as possible while I have good snow pack, less mud on the carpet that way. The carpet might be ecru or eggshell or light beige or whatever, I only have a few crayons in my toolbox, white is the closest. Happy wife, happy life.

Sled is a good tool, though it is well above the floor level of the kiln today.

View attachment 223739




I did add some diagonal bracing to #8 and #7 and a few others already. When six gets emptied I need to add some diagonals to that one. Note the top edge of the outer horizontal 2x4s - the headache bars - is even with, same height as the lower edge of the 2x4s that make the floor of the upper level. This will be important later, hopefully while the weather is still cool enough to get away with mere Corona before we get into serious GT and ice summer.

View attachment 223740

Current chore is to fill #8 to the absolute gills, then finish cleaning up the splits in the driveway, likely enough to fill #7 to the gills as well.

And empty #6. Turn that knob on the side of the stove baby, you are wearing too many clothes to suit me.

Love your pioneering spirit PD.

http://www.shelterlogic.com/shop/firewood-seasoning-shed-10-x-20-x-8-ft

 

[Poindexter]

What I do with these things, the Mk4 design, is fill the offside to close to the top, then step in there standing on the nearside floor, and fill the upper deck, top bunk, honey moon suite, whatever you wanna call it, fill that without having to bend over much at all. , then refill the off side fromn the ground.

Looks like this with the top and offside full, ready to sweep the nearside and start filling that.



Then with the near side full to the gills, I get some crosswise pieces up in there on top. Looks like this.



Now why the heck would I do that? @ED 3000 is already at the head of the class, and can't be promoted further. Would anyone else care to guess why i am taking this step?

It ain't because i can fit more wood in this way. I have green wood in there, > 40%MC. Looking at end grain, from the lawn, all the way up to and behind the headache bar horizontal 2x4. Why would I put some splits on there turned 90 degrees with the bark facing out like that?

I will post the answer in probably late May.

In the meantime the only thing left to do with #8 for now is to shovel out the snow from the floor framing..



Get the plastic membrane clamped as low as possible as above, then shovel the excess snow off from in front of #7 to in front of #8 - so the bottom edge of the membrane over #8 can't be hurt by the wind.



#8 is good for 6 weeks, maybe 8 weeks. Go have a Guinness, its a lovely day for a Guinness. I'll be busy filling some other racks, but for now my work here is done.

 

[Poindexter]

Small problem, the melt is starting a few weeks early. I was looking for +20dF in early to mid April. +26dF today + solar gain = frost on the inside walls of the units with the green wood inside.



I have a small snow bank on the one side of the kilns as pictured in the previous post. Shoveling that out to let air in at the bottom edge of each kiln is going to be easy-peasy.

On the opposite side, its on like donkey kong.



Gonna take up a chunk of my weekend digging that out. What I want to do is open the bottom edge of the kilns all the way around where the plastic membrane meets the floor. That's going to let more air flow through, hopefully carrying out some water as vapor even with ambients below freezing - woot!!

I think the chain link on my back property line is 40". It is more than 36, less than 48. 26 above and a shovel, Guiness weather.

 

[Poindexter]

I got the south facing side shoveled out, at least far enough that melting snow won't be getting inside the kiln as liquid water.



I anticipate having all three cords loaded up mui pronto, I am getting into that part of spring time where the daily freeze/thaw thing is a PITA because there is so much moisture locked up in the snow. Gotta get the last of the splits out of the driveway so i can fire up the weedburner to melt a channel down the driveway for melt water to flow in.

 

[Poindexter]

I finally got the last one filled tonight. Racks, unit, module, whatever, #s 6-7-8 are full. I try to have all my wood for next season stacked on or before 03-17 every year.

My #3 (nickname dam) is still empty, it is two spaces over from (that SOB) #5. That is a different problem. If you decide to build some of these, jump straight forward to my framing plan mark4 and skip all the preliminary steps that hold less wood and are a PITA (#4) to operate.

Daytime high today was +33dF. I have 6-7-8 buttoned up for maximum temperature gain and minimum air turnover. They are filled with all green spruce that was winter felled in the last 45 days or so, real heavy splits for their size.

I will try to not refer to the dam PITA SOB other builds from here on in.

6-7-8 are full of green spruce way over 35% MC. My first step is to get them down to FSP (fiber saturation point) (~30% MC) without letting the temp inside the kilns exceed ~+95dF.

Tomorrow I will dig out the hard pack from the north side of 6-7-8. Southern face (qv) is already shoveled out. When my local daytime highs hit about +50dF I can look for about +70dF inside a buttoned up kiln.

For now i need to go deal with the snow pack on my driveway before I have a puddle of really cold water under the laundry machines for the wife to complain about.

I'll post again here when I get to FSP or the kiln temps exceed +80dF. For now the wood is up before spring melt really got rolling.

 

[Poindexter]

I am right at +32dF ambient this afternoon. I dont have a good way to get a thermometer into any of the kiln units, the snow is soft enough to be too treachorous for a ladder.

But i got ballooning. It's warm enough inside there to raise the plastic membrane off thr pvc rafters, and i got copious water dripping down the inside...

 

[Poindexter]

On the right is that SOB #5, chock full of splits i seasoned summer 2017. On the left, separated by vertical plastic, is #6, just filled with green spruce felled March 2018.



Clearly the ice collecting on the inside of the left membrane is from water coming out of the green wood. If accumulating frost was from melting snow it would be appearing inside both units, yes?

So far i have dried maybe 1 quart of water per stacked cord, 1600 pounds of water per green cord, stopping at 14 %MC, i got 687 quarts per cord to go... but my wood is already 0.15% done seasoning.

After that math problem, it's Miller time.

 

[Poindexter]

Weatherman says it's +22dF today, feels about right. This pic is from the other side, green splits right, seasoned left.

 

[Poindexter]

I have 2 out of 28 possible of these already.

 

[Poindexter]

I am thinking I could maybe open the vents a little more so I would have more water vapor pumped out and less ice on the inside of the membrane.

Snow is too treachorous to climb a ladder out there just now, and opening the vents would lower the temperature inside the kiln, so I have to let it ride for now.

 

[Poindexter]

FWIW end top vents at both ends are this big for three cords.



There is a bottle of tasty red waiting if you are with me so far.

 

[Poindexter]

Summer 2018 I never did change a thing. I spent most of June in the crawlspace under the house doing homeowner stuff. Come August the clips were all in the same spots, didn't change the air outlets, nothing, just let it go.



With the lowest clips up waist high, chest high off the ground like that the wood up at the top is dryer than the wood at the bottom. But as pictured mine will tolerate wind gusts of 35-40 mph without damage to the plastic membrane. Lets a little water in if it is blowing and raining at the same time, but I am coming up with 10.5 to 11% from the stuff off the top of the stack and 15% MC from the stuff at the bottom.

I am calling it eight cords at 13% MC. The only real work I did was stacking and shoveling the snow out from around the edges as the spring melt was starting. Otherwise I have just been walking by watching nature take its course. And running the string trimmer around the perimeter every second or third time I mow the grass.

Low impact, good results for 2018. FWIW most of this was felled in Feb/Mar 2018, stacked by St Patricks Day 2018, I lit the stove August 26th 2018 with all 8 cords at 13% MC. 6 Months, standing spruce to excellent dry fuel.

This year I am going to reload the kilns as I burn and not stack everything in the last three weeks of winter.

 

[kennyp2339]

Thank you for doing this and documenting the whole process, this thread should go into the hearth catacombs

 

[Woodsplitter67]

How are you stacking the wood inside the kiln. I have had problems with my stacks wanting to fall over. I stacked straight but after some time it wants to start to fall over

 

[Poindexter]

How are you stacking the wood inside the kiln. I have had problems with my stacks wanting to fall over. I stacked straight but after some time it wants to start to fall over

As pictured in #6, #11 and #16 above, it all just lays in there with end grain showing. The one exception is the lower two stacks are capped with perpendicular pieces to serve as shrinkage indicators. When I can see the bark on the shrinkage indicators below the headache bar, I know my wood has shrunk, so I know the average moisture content is less than 30%, so I also know I can heat the kiln up as high as it will go without trapping water inside the splits.

My maximum horizontal run between verticals is 7' 5", an 8' long floor pad with upright 2x4 framing at each end. What I have found is the longer the horizontal run of my stacks is, the more they sag as the wood dries. The more they sag, the more likely to fall. I don't know that I have ever been able to season wood in 12 foot long stacks at this location without having to restack at least once over the summer. Six foot stacks at my location with local forest products rarely need to be restacked.

I am not claiming to be an expert stacker. It is what it is. By having uprights every 6-8 feet, I haven't had to restack at all since building this system.

 

[Ashful]

Boy, your neighbors must talk...

“You seen what that Poindexter guy is doing this week?”

 

[twd000]

if you're able to get firewood down closer to 10% MC, rather than 20% MC as recommended, could you operate a catalytic woodstove with a lower exhaust temperature (higher overall efficiency) since you're not as concerned about creosote formation?

 

[Poindexter]

if you're able to get firewood down closer to 10% MC, rather than 20% MC as recommended, could you operate a catalytic woodstove with a lower exhaust temperature (higher overall efficiency) since you're not as concerned about creosote formation?

My stove runs best with fuel at 12-16% MC.

At 11% and under the (spruce) fuel off gasses really fast (burns hot) and doesn't have much left gravitas left for a long burn.

It might be possible to design a wood stove to run on fuel at say 8-12% MC and burn clean and have low emissions and low creosote formation and etc, etc. That stove would probably not sell very well as few stove buyers have got cords and cords of the stuff.

6-10% is another possibility, then the contractors building houses during construction booms could collect all the dimensional off cuts from building sites....

I suspect most of the cord wood stoves currently on the market are designed to run best at 16-22% MC because that is a pretty good national average for how dry wood can be gotten in a reasonable amount of time, and it is mandated for the EPA certification test cycle.

 

[chemie]

My stove runs best with fuel at 12-16% MC.

At 11% and under the (spruce) fuel off gasses really fast (burns hot) and doesn't have much left gravitas left for a long burn.

It might be possible to design a wood stove to run on fuel at say 8-12% MC and burn clean and have low emissions and low creosote formation and etc, etc. That stove would probably not sell very well as few stove buyers have got cords and cords of the stuff.

6-10% is another possibility, then the contractors building houses during construction booms could collect all the dimensional off cuts from building sites....

I suspect most of the cord wood stoves currently on the market are designed to run best at 16-22% MC because that is a pretty good national average for how dry wood can be gotten in a reasonable amount of time, and it is mandated for the EPA certification test cycle.

I looked at your pics and skimmed through the thread! I don’t know what you are doing for a living but you are a very handy and smart person! I wish I could be that handy!
I don’t think I’d have time, skills, or space to implement your design. I have a nearby forest filled with storm fallen dead oaks. I cut 8 large logs last week. After the split, I got MC of 22-28 %. I placed them on a rack and cover them when it is rainy, otherwise I let them fully open. I am hoping they would go down below %20 before March so that I can use them in Spring shoulder season. Do you think it is reasonable for an Oak to lose about 7-8 % during fall/winter in NYC weather?
About the solar kiln drying, for the coming Spring or Summer, do you think it would work if I cover 4X8 Landmand rack with a plastic cover like yours and adding some poles to the end to raise the top and opening some holes on the top to let oak obtained from fallen dead trees to be seasoned from %28 to below % 20? It is humid during summer months though.

 

[Poindexter]

@chemie, the main thing about solar kilns is getting the solar gain to raise the temperature inside the kiln. That lowers the relative humidity of the air in the kiln, increasing the diffusion gradient between the damp wood and the drier surrounding air, so the wood dries faster. It's all abotu EMC, equilibrium moisture content.


I have been PM-ing user @Woodsplitter67 diligently for him to start his own solar kiln thread. He is back east, deals with hardwoods, and bang for buck he kicked my butt with his simple and inexpensive but effective build.

 

[showrguy]

@chemie, the main thing about solar kilns is getting the solar gain to raise the temperature inside the kiln. That lowers the relative humidity of the air in the kiln, increasing the diffusion gradient between the damp wood and the drier surrounding air, so the wood dries faster. It's all abotu EMC, equilibrium moisture content.


I have been PM-ing user @Woodsplitter67 diligently for him to start his own solar kiln thread. He is back east, deals with hardwoods, and bang for buck he kicked my butt with his simple and inexpensive but effective build.

I'd like to see that too Poindexter..
I've been through all your solar kiln thread stuff, pretty impressive ..
I'm in hardwood country as well, so hopefully @Woodsplitter67 will enlighten us with his setup ??