# Solar cord wood kiln operation



## Poindexter (Jan 29, 2016)

Distinct from design/ build.  I already have a design/ build thread here for the solar cord wood kilns I am running: https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/

What I would like to do in this thread is figure out how to run the fool things with out dragging all the build data back and forth off the hard drive in the hearth.com server.

Here is my passive solar "load one".  It is 1.8 cords of dead standing fire killed spruce that meters 22-28%MC per handheld gizmo.





The kiln is my module one and module two end to end, each 42x96", total foot print 42x192".  Long axis is almost perfect N-S.  I overlapped the plastic sheeting in the middle to create what I hope is one convective unit.




The unit is open at the north end for now (qv) and closed at the south end thus:




Realistically I can expect (without benefit of passive solar) to have this "load one" down to 12-16%MC around June first.   I would like to sell it ASAP when it is down under 16%MC, refill with green wood and see how fast I can get that dry with part of the summer already gone.  It will be what it will be.


----------



## Poindexter (Jan 29, 2016)

I have been reading up quite a little bit.  The US Forest Service (USFS) Dry Kiln Operator's Guide is free online as 9 .pdf's, one chapter each.  I find chapters 1, 2 and 9 to be especially relevant.  I anticipate reproducing here the appendix to chapter one that gives Equilibrium Moisture Content (EMC) as a function of dry bulb temp and wet bulb depression.

I don't own a wet bulb thermometer yet, though I have several in my shopping cart on Amazon.  I am a little concerned that I am not going to have good wet bulb reading because I won't have enough airflow to get a good wet bulb temp.  No room to really run a psychrometer in there either.

For now it doesn't matter, I have about 1 hour of direct sunlight daily on load one, outdoor ambients haven't been above +20dF in over a month. 

Also, incorporated herein by reference, Haque, N and Langrish TAG (2004) OPTIMISING DRYING SCHEDULES FOR HARDWOOD TIMBER IN SOLAR KILNS, New Zealand Journal of Forestry Science 34(3): 354–369 (2004). 

Entire article here: http://www.scionresearch.com/__data/assets/pdf_file/0004/5377/09_Haque.pdf

Relevant quotations:



			
				Haque and Langrish said:
			
		

> The diffusion model used in this study assumes moisture content gradient as a driving force and was applied successfully by Wu (1989), Doe et al. (1994), and Langrish et al. (1997)...The drying run was terminated when the desired final moisture content was reached, which was specified to be 12% (average)...At the start of the experiment maintaining very low wet-bulb depressions proved to be difficult...The long “tail” in the moisture content curve (Fig. 4) arose because of internal resistance to moisture movement, not internal resistance to heat transfer...The simulation program was formulated so that, once the strain reached its maximum, the difference between the dry- and wet-bulb temperatures (the wet-bulb depression) was adjusted to keep the strain within this limit, and so the maximum strain was considered as a constraint...[later when the wood was drier]...The slightly harsher conditions (higher wet-bulb depressions) made little difference to the strain because large moisture content gradients are not possible in timber at these low average moisture contents...For the drying process, it is evident from this analysis that strain is a constraint in the early and middle stages of drying due to moisture content gradients, whereas dry-bulb temperature is a constraint in the final stages of drying, because the moisture content gradient is then very low...[and finally]...A step-wise drying schedule is convenient to apply for kiln operators with simple kiln control systems. Once the actual average moisture contents fall below 35%, then the dry-bulb temperature can be increased to 35°C, with a 5° or 6°C wet-bulb depression (Table 2). The dry-bulb temperature may be increased to 53°C, with a wet-bulb depression of 16°C, for drying below moisture content 22%. A dry-bulb temperature of 60°C may be applied with a 30°C depression for drying below a moisture content of 18%. This may be a sudden change of drying conditions compared with the original schedule but, by this stage, the timber may be able to tolerate such harsh conditions. For this final stage of drying, from moisture content 25% to 12%, the new schedule predicts that in solar kilns 16 days may be necessary for drying if a constraint is put on the dry-bulb temperature (i.e., a maximum of 60°C for a solar kiln).



When I read this article I picture a rimmed cookie sheet on the kitchen counter next to the sink, brimming with water.  I mean over the top, relying on the surface tension of water for it not to spill, put one more drop of water in there and you get a tablespoon of water on the counter.

As a masters thesis in forestry, they figured out how fast they could tip the cookie sheet without spilling a drop.  They started slow, and then went faster and faster.  It makes perfectly good intuitive sense to me. 

It seems to me what they did was create and maintain a smooth diffusion gradient between the surface and center of each board.  If they ran their dry bulb temp up too high too fast the surface of the board would dry out faster than the middle, creating a step or notch in the diffusion gradient that is only going to be overcome by applying more heat than was absolutely needed.  Waste not want not and so on.

So I am going to start here and see how it works.  From green wood down to fiber saturation point (FSP) I am going to try to keep the dry bulb (regular) temperature under +95dF with really really good airflow to keep the wet bulb depression to a minimum.  Once I get to FSP, I'll let the dry bulb stick near and slightly exceed +95dF and let the wet bulb depression reach 25-30 degrees F.  Once the stack is under 22% MC I can really put the screws to it, let the dry bulb reach +140dF if I can get there, with a wet bulb depression around 55dF (so +95dF indicated wet bulb temp).. and expect to be at 12%MC in a matter of a few days.  If I get good weather.

Clear as mud?


----------



## Poindexter (Jan 29, 2016)

reserved also, running out of steam tonight.


----------



## KBCraig (Jan 29, 2016)

Why LANS, instead of E/W? 

I would think that one long side getting full sun the entire day would provide more solar gain than the glancing blows in morning/evening, and very small frontal area noon-ish, in an E/W layout.


----------



## Poindexter (Jan 29, 2016)

KBCraig said:


> Why LANS, instead of E/W?



That's a fair question I feel up for.  I am building 8 modules total, I anticipate dividing those into three separate loads.  Schematic:




Modules 1,2,4 and 5 are built.  1 and 2 are loaded and rolling as load one.  3 & 4 are going to hold my left over wood that I had going into winter of 2015/2016.  4 is already loaded, 3 is not built.  5 is built but empty, 6,7 and 8 are not built.

I anticipate filling 5-8 with less expensive green healthy standing timber, compared to the more expensive dead standing I used to fill modules 1 and 2.

I am on a tiny suburban lot at 64 degrees north latitude.  On summer solstice the sun will rise 10 degrees east of north, and set 20 hours later about 15 degrees west of north.  Notice "north" is upside down to standard lower 48 perspective, everything is south from here.

At this juncture I should tag @solarguy2003 .  He is one of several people I was planning to tag in post three, but not tonight.  solarguy2003 is running a solar firewood kiln I think in Indiana.  Besides firewood he is also keeping fruit trees, I wanna say fig trees, in his green house.  He is operating a legit solar firewood kiln and I hope he is willing to share his observations about his unit on his property here too.  When google users get to here I hope they are rewarded with observations from multiple people at multiple latitudes.


----------



## Poindexter (Feb 9, 2016)

Load two is up.  It is modules 3 &4 as platted above.

Filled with wood already seasoned one year in the open and likely to be left over at the end of this season.  Mix of birch and spruce at 18-20% MC, but with a bunch of mold and mildew and fungus growing on it.  My top covered wood pile got hammered on the sides with summer rain, I have the micro-organism ranch to prove it.

I also loaded, near the bottom, all the 16" splits I could find that have done duty holding down the plastic top covering on stacks in previous years.  Those have a bunch of crusty snow on them. MC unknown.

Short term I am going to keep the sides rolled up on this one.  The load is getting about an hour of direct sunlight daily, forecast highs are in the +20s dF.  I don't want the crusty snow turning into water vapor and condensing on the dry wood above it; hopefully with the sides open I can minimize greenhouse effect and give any liberated vapor a chance to blow away on the wind.

Long axis of load two is E-W.






55 gallon Ugly drum Smoker for scale, module 5 (part of future load three) is left edge of photo.  Proceeding left to right are modules 4 and 3 (load two) and then a 90 degree bend to modules 2 and 1 that make up load one as detailed above.

The east (left) end of module 4 is covered just like the south end of module 2 as picd in post one this thread to keep mold and mildew spores out of module 5/ load three.

At the west end of #3 I put another vertical sheet of membrane, but left an air gap at the top.




At the end of the burn season all my remaining moldy wood, even the chunks and uglies on the pallet are going into load two and i am going to cook it as hard as I can.  Might even seal up the air vent, dunno.  By the end of summer I want dry cord wood with non-viable organic debris smeared on it.


----------



## Poindexter (Feb 20, 2016)

So riddle me this.

A the north end of load one, total shade, ambient temps only, I have a growing layer of kosher salt grain sized ice crystals.  I am not super worried about them, but I see the accumulation get thicker on a week to week basis.  The black grains are charcoal off the fire killed spruce stacked in this module.


Ambient temps have been pretty much -10dF to +10df for about a month, relative humidity is running 70-95%, but at temps this low we are talking about precious little water vapor in the air.

North end looks  like this, no accumulation on the vertical surfaces, just a slowly growing pile on the floor.




But on the east end of module #5 I am getting about 1-2 hours of direct sunlight daily and I can't explain this.

Top of ice accumulation on vertical 2x4, 3-4 feet above the "grade" level of hard packed snow:




Same 2x4 lower down, say 6-24" above "grade" level of nearby hard packed snow:




Why is that?  Clearly the available sunlight on the east end is doing some "work" that isn't happen on the fully shaded north end...

I got my infrared tire pyrometer out, I'll see what I can find for temperature differentials tomorrow.


----------



## paul bunion (Feb 20, 2016)

On the north side there was no sunlight, so no energy, which means very little help with evaporation/sublimation.  With little evaporation/sublimation on that side there is little condensation/deposition so you all you have is a small pile of ice crystals.

On the sunny side your stack caught some sun giving it more energy on that side to make more water vapor out of the frozen water.  Then it hit the cold plastic, sublimated and you see the ice crystals forming.  

Yes, 10 degree air has a low absolute moisture content but RH is what really counts.  It hit 100% on the inner surface of your tent at your 2x4s.


----------



## Longstreet (Feb 21, 2016)

Sounds like you are having what I've heard as "accidental dehumidification" in building science.  Warm air with high relative humidity hits a cold surface and makes dew.  Just happens that it's so cold in AK that the dew freezes.


----------



## Poindexter (Feb 21, 2016)

"Riddle me this", well crud.  I came up with 8 data points, been wandering around the lawn every four hours with my IR thermometer for the last 24 hours to try to learn something about water vapor moving around in below freezing temperatures.

Well and truly above freezing today.  I got this (woo hoo!)




I did find a physicist at CalTech with "*The Physics of Crystal Growth and Pattern Formation in Ice. " *as his second research interest.  Primary is gravity waves, I am guessing he isn't answering a lot of snowflake emails right now anyway.  I didn't write him since I understand pretty good how water vapor moves around in above freezing temperatures.

Dr. Libbrecht does have an illustrated page of frost types here: http://www.its.caltech.edu/~atomic/snowcrystals/frost/frost.htm .   I suspect the ice crystals forming on my 2x4 and cord wood splits above are simple hoarfrost, though the mechanism of vapor transport is still mysterious to me.

The battle du jour at my house was the 'window frost' on the inside of all my plastic membrane was melting and dripping onto my cordwood.

From reading several of Dr. Libbrecht's pages I think what has been happening is when it cools off at night, the water vapor inside each kiln module freezes to the inside of the plastic membrane, plain old regular window frost.  The next day, as the air inside the kiln warms up it convects out, fresh water vapor laden air comes in behind, it freezes again and my window frost layer gets thicker.

I got most of the window frost off today, but it will be something to avoid this fall and next spring and next fall and next next spring.  Besides getting water out of the cord wood in hot weather I am going to have to minimize water getting into each unit during shoulder weather when outdoor temps are below freezing but temps inside the kilns are above freezing.


----------



## English BoB (Feb 22, 2016)

Poindexter said:


> Distinct from design/ build.  I already have a design/ build thread here for the solar cord wood kilns I am running: https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/
> 
> What I would like to do in this thread is figure out how to run the fool things with out dragging all the build data back and forth off the hard drive in the hearth.com server.
> 
> ...


Great job man, hope this works for you. Keep us updated.

bob


----------



## Firefighter938 (Feb 22, 2016)

Looks like they are working so far. I wouldn't be too concerned with the ice forming. As long as it has a way to get out when temps are warmer.


----------



## St. Coemgen (Feb 26, 2016)

Interesting. But complicated.

After drying wood for more than 30 years, and building all sorts of drying systems, I finally found the KISS principle works well for me (keep it simple stupid, or simply applying Occam's razor). And that is, and again this is my experience, this has converged on the "Holzmiete" method (requires nearly zero extra construction, maintenance or post stacking effort):

http://www.holzmiete.de/instruction.php

Yes, that is the method being used in my avatar image.

For cooler climates where wood dries slower, just buy and stack three years in advance.


----------



## Poindexter (Feb 28, 2016)

Hey @solarguy2003 , you remember when you first built that thing and put some wood in it and waited like a month, and then stuck a meter in some fresh splits "just to see"?

Were you speechless?  Like no way can this be right?  And you went had a beer and came back an hour later and split some more open and finally just had to sit down and cogitate a little while?

My load one from post one above is metering 18-20%, and burning in my stove right now like the moisture meter is working just fine.  I went from cold stove to engaged combustor in 19 minutes.  My IR thermometer is telling me I got dry wood in there.  My stack plume is clean.

I was not looking for this wood to be dry until June 1.

I'll wait and dig through the ash bed in the morning looking for tell tale chunks before I get to ululating.


----------



## kennyp2339 (Feb 28, 2016)

St. Coemgen said:


> "Holzmiete" method


I done did gots one of them in my yard.


----------



## Poindexter (Feb 28, 2016)

No tell-tale clumps in the ash bed this AM.  I am switching to burning out of load one full time.

I'll give it a week or two before I really really believe it, but "working awesome" does seem to be a fine description of a woodpile with a vapor impermeable layer under it to keep groundwater out. 

Gobsmacked I am.


----------



## Poindexter (Mar 27, 2016)

Too late for me to edit post #6 above.  "Load Two" was sold in early March at 19% average MC.  I put an ad up on CL 'just to see' at a bit below market rate because of the mold on it.  It sold in two hours, the buyer came and picked it up same day, brought cash, and paid the going rate for delivered dry wood with no mold on it.  

On the one hand I was kinda interested to know if I could achieve dry bulb temps high enough to kill micro-organisms.  I can still look for peak dry bulb temp values, but without 'needing' to achieve them.


----------



## Poindexter (Apr 9, 2016)

Load three (winter cut live spruce, probably felled around valentine's day 2016) was up on March 17.  The north side is pretty open, with the membrane rolled all the way down on the south side:





Most of the bottom clips on the South side are 36-40" off the ground.  I get enough breeze in the twilights to pull the clips off if I locate them lower for now. 

Around 4 or 5 oclock in the PM, before the breeze starts blowing I am seeing ambients round +50dF, and +50 to +52dF at the bottom of the load on the shady side.  At the top of the load on the shady side I am seeing +65dF on sunny days and +60ish dF on cloudy days.

Pragmatically it is early April outside the kilns and "early May" inside the kilns. 

Once load three is visibly shifting and settling, clearly having reached and dropping below FSP (Fiber Saturation Point, ~30% here); then I will roll down the membrane on the north side to trap some more heat in there.

I am feeling somewhat optimistic that green wood up on March 17 can be ready to go into a storage shed at 12-16% measured around June 1.  That _ought_ to give me enough time to season a second load of green wood each season, but there are many variables.


----------



## Poindexter (Apr 26, 2016)

Everything is down under 30%MC, I can tell because the stacks are shifting and visibly shrinking.  Even the spruce winter cut in early March that I got stacked in mid March has already shrunk visibly and *unequivocally**.  *The stacks are moving and shrinking.

At +50dF ambient I am seeing +15dF solar gain on sunny days and +10dF solar gain on cloudy days, and this with the plastic rolled up on the north side.

I rolled all the plastic down today so it looks like posts one and six above, not like post 16 above, only with the snow all melted. 

Some of my grass is starting to green up, my delphiniums are sprouting back, and the birches are leafing out all over town.  The Arctic geese got here about ten days ago and left last Friday, five days ago.  They stop in Fairbanks to rest on their way to the north slope.

I feel pretty good that I should be able to pull dry spruce out of all these units around June first ( from March 17 start) and maybe maybe not get a second crop of cord wood dried to 16%MC before freeze up.

For the next few days I'll keep a careful eye on the temps.  Per Haque and Langrish (above in post 2) I am planning to keep wet bulb depression to a minimum and hold dry bulb temps to about +95dF max until I am down to 20% average MC.  Once I have a good feeling for how much solar gain I am getting with the plastic rolled down I can hopefully kinda keep an eye on the weather forecast to know when I might hit +95dF dry bulb with the plastic rolled down all the way around.

No pics.  We have our big suburban house listed, an offer in on a small cabin on acres and my camera is in a box "open after showing" with some other stuff I don't want laying around the house with strangers coming through.

EDIT: Now that the plastic is rolled down all the way round I have the bottom clips about 12" above the floors.  I was catching a LOT of wind with the plastic up on the north side and down on the south side, hopefully there is less for the wind to get hold of with the plastic down on both sides.


----------



## paul bunion (Apr 26, 2016)

Why are you so keen on trying to us a drying schedule that is designed to minimize defects in lumber?  I don't think that warping and checking are concerns with firewood.   Go to their last step.  You should be trying to get it as warm as possible.  The heat results in a depressed RH level,  remember every 20 degrees F rise in temp cuts the RH in half.  Then figure out how much or little ventilation is needed to maintain your heat while allowing the water vapor to get out.  Condensation and direct draining of moisture also plays in.


----------



## Poindexter (Apr 28, 2016)

paul bunion said:


> Why are you so keen on trying to us a drying schedule that is designed to minimize defects in lumber?  I don't think that warping and checking are concerns with firewood.



I agree that warping and checking are not concerns in cord wood.  What I want to avoid is a dry shell surrounding wet wood in the middle of each split. 

There was a fair amount of discussion about this in the design/build thread I was running over the winter.  The outcome is admittedly buried in a six page thread, if I may kindly direct attention to posts 109 and 110 in that thread:

https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/page-5#post-2037109

The A#1 finding is get the water out of the tubules via capillary action so the remainder is down to FSP before heating it up.




paul bunion said:


> Go to their last step.  You should be trying to get it as warm as possible.



This is exactly what I don't want to do, for a couple reasons. 

One, I don't want a "burrito" made of a dry wood tortilla with a wet wood filling.

Two, while I am very familiar with local weather patterns, I don't "know" how many days of how bright of sunshine with how much wind I need to pull a completed dry load out of a module so I can reload the module with fresh green wet wood.  I need all of the wood in there now for this coming winter, I don't have anything left over from last winter.  Once I have this coming winter's wood in the bag, yes I will be willing to experiment with accelerating the drying process some more.

Three, I am trying to do this as cheaply as possible.  For 8 empty modules I am currently in for about $2400, never mind assembly time and the cords of splits in there drying.  I do have an Arduino system (still in the box from Amazon) that I hope to install in the kilns 'someday'.  I got the deluxe starter kit and a 5 pack of water proof temperature sensors  and a PCB, a shield I think is the correct term, so the Arduino unit in the back yard can connect to my PC via my wireless router and send me five data points of temperatures at whatever sampling interval I program.  Once I get to there Is should be able to push the data to my smartphone using the SMS text message format without too much trouble.

While I do want to know what is going on in there, I am specifically trying to not spend a bunch more money on controlling what does happen in there.  I could spend thousands of dollars on a live steam system, install a bunch of insulation and pull beautiful splits, cord after cord of them every couple weeks or so, but the break even point will be decades even if oil prices head back up tomorrow.



paul bunion said:


> The heat results in a depressed RH level,  remember every 20 degrees F rise in temp cuts the RH in half.  Then figure out how much or little ventilation is needed to maintain your heat while allowing the water vapor to get out.  Condensation and direct draining of moisture also plays in.



All true.  Alternatively, if my inlet air is at +50dF and 100%RH at one axe handle of water per bushel of air, I could heat the one bushel of air to +70dF, find the RH is now 50% with the one axe handle of water in it, pull another axe handle of water out of the drying cord wood to take the RH up to 100%, and then pump it out.

I am trying to not buy fans, and power to run the fans.  Just letting nature take its course if you will.

Having said all that, I too will be out of town at the first of the month, my youngest is graduating college.  I pulled some splits and measured some MCs today.  In the winter cut spruce (cut about 02-14-2016, split, and then stacked on 03-17-2016, I find today 27%MC inside the split and 25%MC outside the split.  I am maintaining a gentle diffusion gradient from the center to surface of each split - so I will not later in the drying cycle have to expend extra energy pulling water from the inside of each split over a notch in the diffusion gradient to the surfaces. 

So far Haque and Langrish are working for me.  I am seeing about +15dF solar gain on sunny day with ambients in the +50 to +60dF range.  At +80dF ambient (ish) I will expect to see about +95dF dry bulb inside the kilns.  I don't have a LOT of data to predict on, it could be I will see +95dF dry bulb inside the kilns at +75dF or so.  I expect and hope this happy circumstance will occur after the centers of all my splits are down to +/- 20%MC.  We are having odd weather patterns this spring,  but it should be weeks before I regularly see temps over +75dF. 

I am still on track to have all of this winter's wood ready on June first.  If I am wrong, it will likely be ready earlier.  When I get to working on green wood for Sep 2017 in June 2016 I'll see about speeding up the process.

Great questions, and timely too.  Thanks for contributing.


----------



## Poindexter (May 8, 2016)

In the last couple days I have found load one (post one) to be down to 13-18%MC per handheld meter.  Load three (post 18) is still in the mid 20s.

I sealed up the north end of load one this afternoon:




Leaving a tiny window at the top to let hot wet air dribble out and a temp probe from one of my BBQ thermometers in:




With out door ambients in the mid +50s dF I am seeing +93dF at the top of the kiln.  I went ahead and started pinging my local network, at 13-18% this wood is already very desirable for many local burners, I am looking to trade stick for stick, you bring me green spruce, I give you solar seasoned spruce.  The entire 1.8 cords is going on Craigslist Monday night if I don't get any takers.

EDIT: 5-8-2016, with ambients at +69dF I found +104dF at the top of load number one.  A small thing, but I don't know that ambients of +104dF have ever been recorded here.  This stuff is drying out, in mid-May faster than it ever will just top covered and open on the sides.


----------



## maple1 (May 9, 2016)

You want to trade 'even up', kiln dried wood for green wood? After going through all this? What did I miss?


----------



## kennyp2339 (May 9, 2016)

maple1 said:


> After going through all this? What did I miss?


I was thinking the same exact thing


----------



## Poindexter (May 9, 2016)

kennyp2339 said:


> I was thinking the same exact thing




Right now I just want data.  I want data real bad.  Giving away 2 cords seasoned in trade for 2 cords green and data (how fast can I dry wood starting with green on say May 15th?) seems like a good deal to me.


----------



## maple1 (May 9, 2016)

2 cords dry for 3 cords green sounds better.


----------



## Poindexter (May 12, 2016)

Today the max temp I read inside load one was *128dF*, with outdoor ambients in the shade around +75dF.  It is unseasonably hot here, I shouldn't be seeing mid 70s until early June.

Load three is still hanging in the low to mid 90s dF measured, but it is still open at the ends and not under 20% yet.

I think @paul bunion might be on to something since I am not worried about checking and warping.  Once I get load four in here and loaded up I am going to air dry it down to FSP with the side curtains rolled up and then just put the screws to it to see what happens.

It is freaking humid inside those units.  I pulled clips in a few places so I could slip behind the plastic like a shower curtain and stand "inside" the units with my feet on the lawn, wow, like a jungle in there.

Looking into how I can quantify sunlight exposure.  Anemometer to measure wind speed is easy.  My best idea for light is three small solar panels, one each facing E-S and W with an ammeter or voltmeter on them to see how much light is hitting the panels.  I would like to be able to say, eventually, a load of green freshly felled wood takes X amount of wind and Y amount of sunlight with average temperature of Z to hit 16% MC.

128 degrees in there in May 11th.  I am ecstatic.


----------



## Babaganoosh (May 12, 2016)

With a simple shrink wrap kiln I saw temperatures at 168 last summer. Not too shabby.


----------



## Poindexter (Sep 29, 2016)

I ended up doing other things this summer. All the wood, in every module, even the live felled in Feb 2016 is down below 7%MC in late Sept 2016.  Seven.  I can go from cold stove to engaged cat and clean plume in 10 minutes day after day.

I _think_ I can season two loads per year in each module, but I would need to build a wood shed to move the seasoned wood into.  I was down under 20 % everywhere I looked around solstice, June 22.  If I get rid of half the modules, I have plenty of room for a wood shed.  Waiting to hear from the wife on that one, but the solar kilns are "working awesome" to borrow a phrase.


----------



## Poindexter (Oct 15, 2016)

So I am interested in hearing about your experience with EMC (Equillibrium Moisture Content).

I lifted a lovely elegantly formatted table from these guys: http://www.volko.com/crawlspacevent.htm

The data sure looks like it came from the (public domain) US Forest Service, I don't see anything that raises an eyebrow here.





So if you got your wood up in say April and you have sustained temps in the +90s dF for August, with relative humidity around 90% for all of August, your stack probably reached EMC in late June or early July and then will tend towards 19.8% MC during August.

With me so far? 

So how fast will cordwood splits in a big pile reach a new different EMC when the weather changes?  A couple hours, a week, a month?  Two months?


----------



## Poindexter (Oct 15, 2016)

Here is everything I observered between May 11th and Sept 25 in my kilns:

Max temp I ever measured was +142dF.  I had about a week in early July when I was seeing 140-141-142 dF right when I got home from work in the late afternoons.  How high did they go during the day before I got home, I don't know.

I never yet have had a humidity sensor inside one of these modules; it would be real helpful data right now.

There were a couple nights in late July when we started having some darkness when the plastic over the PVC was ballooned out, as if the wood stacks were emitting enough heat (compared to the cooler evening air) to blow up the kilns like a hot air balloon.  A couple is two that I noticed.

That's really all the attention I was able to pay all summer while life had other plans.

The plastic seems to be holding up fine, I think they are still weather tight, except for the gable vents that I haven't moved since installation, and they are still open around the floor perimeter.


----------



## Poindexter (Oct 15, 2016)

in early September I pulled a huge sample, six splits from every cord.  Three from the south facing side of each cord, three from the north facing side of each cord.  One from the top on each side, one from the middle, one from within 18" of grade level, 48 splits in the garage for 48 hours.

Three data points each split on a fresh face, what is that 144 data points?  I could hardly get my MM to flicker.  7% MC faintly indicated here and there.  That's been an adventure worthy of it's own thread, but it seemed like my stove was either getting acclimated to drier wood, or my stacks are picking up moisture...

So I pulled another good sized sample Thursday afternoon and stuck them in the garage until Sat mid-day.




Just four splits from each cord this time, one from the top, one within 18" of grade.  The east end of the east facing splits selected were labeled with an 'E" and so on.

Here is the raw data from my appendiceal module that runs N-S and therefore has an East face and a West face:

FWIW a star (*) entry means less than 7%MC, I don't know how dry...

E ***   *** W
E 14-15-14  11-13-15 W

So only one cord left in that module, pretty sure the ones from on top are still too dry to measure, it is the ones closer to grade level that are a leetle bit heavier.


----------



## Poindexter (Oct 15, 2016)

The data from the longer set that runs east west and has a north and south face sorted itself in a similar manner:

S***  ***N
S***  ***N
S***  ***N
S***  ***N
S***  ***N
S***
S *-14-11  *-10-12 N
S *-13-15  *-14-11 N
S *-14-15  *-12-13 N
S *-14-15  *-15-14 N
S 11-15-11 
S 15-15-15  15-15-14 N

I did ignore two splits that were labeled inconsistently.  I can see now they were both off the north facing side...


----------



## Poindexter (Oct 15, 2016)

So looking at the EMC table in post #30 above (@BKVP ):

with current ambient conditions at +27dF and RH at 44-65% depending on who I believe, cord wood top covered outdoors should tend towards about 9.5% MC

wood inside the kilns based on previous observations in similar weather in April and May should be experiencing about +50dF and 25% RH, tending towards 5 or 5.5% MC.

I opened up the side curtains as soon as reached this conclusion.


----------



## Poindexter (Oct 15, 2016)

Hoping sustained subfreezing temps hold off long enough to get up to 12%...


----------



## Babaganoosh (Oct 16, 2016)

At this point I'd build a woodshed and get that wood moved so you can pack the modules back up.


----------



## Poindexter (Dec 7, 2016)

@bodhran , in nearby portland, or the temp is +35dF, with 51% rh.

with clear skies i would be looking for at least +60fF and rh around 25%, suggesting an emc of about 5% moisture content would be achieved in mid to late feb.

with cloudy skies i would be looking for perhaps +50dF inside kilns with the ends sealed up, rh maybe 35%ish, about 7% emc in mid to late feb

see post #30 above for emc table..


----------



## 2fireplacesinSC (Dec 8, 2016)

So the gist of this method is:

Elevate stack
Vapor Impermeable bottom 
Variable height side/top vapor barrier 
Persistent venting of some amount

Do I have that correct?

Interesting hobby.


----------



## Poindexter (Dec 8, 2016)

2fireplacesinSC said:


> So the gist of this method is:
> 
> Elevate stack
> Vapor Impermeable bottom
> ...



I think the impermeable floor layer is key.

Covered in top, open sides down to fiber saturation point.

From fsp down to finished dryness close the sides, just small vents top and bottom.


----------



## bodhran (Dec 8, 2016)

Poindexter said:


> @bodhran , in nearby portland, or the temp is +35dF, with 51% rh.
> 
> with clear skies i would be looking for at least +60fF and rh around 25%, suggesting an emc of about 5% moisture content would be achieved in mid to late feb.
> 
> ...


It's currently 25F here with 77% rh.


----------



## Poindexter (Dec 8, 2016)

bodhran said:


> It's currently 25F here with 77% rh.


Sub freezing temps are a monkey wrench, because of the latent heat of crystalization.

Are you seeing daytime highs above freezing?  that will help a lot.

Short version is it will take longer.  i spent i think winter of 01/02 in eugene or without a single hard frost.


----------



## 2fireplacesinSC (Dec 8, 2016)

Can you give a brief explanation of fiber satura as point?  Thanks


----------



## bodhran (Dec 8, 2016)

Poindexter said:


> Sub freezing temps are a monkey wrench, because of the latent heat of crystalization.
> 
> Are you seeing daytime highs above freezing?  that will help a lot.
> 
> Short version is it will take longer.  i spent i think winter of 01/02 in eugene or without a single hard frost.



No, the daytime is mostly below freezing as well. The usual weather pattern here is. Snow, changing to rain, changing to strong cold northwesterly winds. Tomorrow is 37F daytime with .80" of rain, changing to 27F nighttime with flurries and wind. I don't live here for the weather lol.


----------



## bodhran (Dec 8, 2016)

bodhran said:


> No, the daytime is mostly below freezing as well. The usual weather pattern here is. Snow, changing to rain, changing to strong cold northwesterly winds. Tomorrow is 37F daytime with .80" of rain, changing to 27F nighttime with flurries and wind. I don't live here for the weather lol.



Also, it's not unusual to have frost warnings into July month.


----------



## Poindexter (Dec 8, 2016)

2fireplacesinSC said:


> Can you give a brief explanation of fiber satura as point?  Thanks



In a living tree the cellulose inside each live cell is saturated with water, some if it bound to the celluose chemically (bound water) and some of it just in there.

The live tree also has sap (mostly water) inside all those vertical tubules.

When freshly split and stacked a top covered piece of cordwood will lose the water in the sap tubules in 2 weeks or so.

Once that water is gone, all the remaining water to come out is the free and bound water saturating the cellulose fibers, thus the fiber saturation point.

As the wood continues to dry below the fsp it will begin to change size and shape.  Above fsp the size and shape of the split does not change with varying moisture content.

Fsp is generally at or near about 30% for a lot of species.


----------



## 2fireplacesinSC (Dec 8, 2016)

Autocorrect has struck again!


----------



## 2fireplacesinSC (Dec 8, 2016)

Thanks poindexter for the info. Neat what one can learn on a wood burning forum.


----------



## English BoB (Dec 8, 2016)

Thanks for keeping us posted.

bob


----------



## Poindexter (Dec 31, 2016)

So wind, once again is my downfall.  In the last 72 hours, give or take, I have gotten 17" of snow on my lot, and then 24 hours of wind, 15mph sustained and gusts to 45mph.  I don't have an anemometer on my lot, going by the local weather station for the latter.

Binder clips from OfficeMax and plastic sheeting from Home Depot do OK up to 25-30mph gusts with 5-10mph sustained.  I knew I was going to have a mess on my hands.

This morning at sunrise I had this to deal with.

modules 1-4 on the west end...




and modules 5-8 on the east end.




I am going to have to get a big magnet on a stick to find the binder clips currently missing in the snow.

My plan was to consolidate my remaining wood on the east end, recover to keep snow out of it, and use every possible binder clip on the smallest possible sail area.

The half cord on the west end is already bought and paid for as primo grade spruce, FOB module 3.  I had to bang every two splits together to get the snow off them and recover so they are still primo grade when the buyer shows up to pick up the rest of the cord he already bought.


----------



## Poindexter (Dec 31, 2016)

Got 'er done.  I really need some outdoor storage cabinet of some kind to hold my BBQ stuff.  The cooking racks for pork ribs stuck in a cordwood kiln is bad enough, my charcoal chimney is full of snow and who knows what I will find when the snow melts.

After:





Looking for a little wind tonight.  i guess I'll know in the morning how I did.

What I would "like" to do is build a vapor tight woodshed under my existing second floor deck and ditch three of the modules for $$.  I am pretty sure I can harvest two 'crops' of dry cordwood out of these kilns every year.  Already have a buyer lined up for numbers 3,4 and 5, don't have permission from SWMBO to build a shed under the deck.

If I dry five, shed those, dry five more and then be donating, burning and selling out of the five still in the kilns I should get to this point in the year with a full shed of dry wood and nearly empty kilns ready to loaded.

Life expectancy of H-D clear plastic sheeting at my house is 10-11 months.


----------



## kennyp2339 (Jan 1, 2017)

I love the operation you got there! enjoy your in-depth explanations to


----------



## 2fireplacesinSC (Jan 2, 2017)

Yes. Very interesting, helpful, and informative. Thanks Poindexter!


----------



## Akon (Mar 13, 2017)

Babaganoosh said:


> With a simple shrink wrap kiln I saw temperatures at 168 last summer. Not too shabby.


I am behind on my wood for next year and am going to do some sort of plastic solar kiln. Price is right with shrink wrap. Was yours wrapped tight to the wood? Was thinking of using some Pvc to create some space and leave maybe leave the bottom third of the ends open.


----------



## WoodyIsGoody (Mar 13, 2017)

Poindexter said:


> In a living tree the cellulose inside each live cell is saturated with water, some if it bound to the celluose chemically (bound water) and some of it just in there.
> 
> The live tree also has sap (mostly water) inside all those vertical tubules.
> 
> ...



Interesting stuff. Since most of the moisture exits via the end grain, I wonder if the speed of drying could vary depending upon the sharpness of the chain on your chainsaw? In other words, does it make a difference if the microscopic tube ends are cleanly sliced or mashed?


----------



## Easy Livin’ 3000 (Mar 17, 2017)

Poindexter said:


> Distinct from design/ build.  I already have a design/ build thread here for the solar cord wood kilns I am running: https://www.hearth.com/talk/threads/experimental-passive-solar-wood-kilns.149388/
> 
> What I would like to do in this thread is figure out how to run the fool things with out dragging all the build data back and forth off the hard drive in the hearth.com server.
> 
> ...


It's this kind of passion that leads to real breakthroughs and innovation in our world. I nominate PD for the first Ph.D in cordwood drying from Hearth.com University.


----------



## SeanBB (Mar 20, 2017)

WoodyIsGoody said:


> Interesting stuff. Since most of the moisture exits via the end grain, I wonder if the speed of drying could vary depending upon the sharpness of the chain on your chainsaw? In other words, does it make a difference if the microscopic tube ends are cleanly sliced or mashed?




I think it does make a difference. I read somewhere that a firewood processing machine that used a shear rather than a saw meant that the logs seasoned quicker.


----------



## Poindexter (Jun 13, 2017)

The good news is live spruce felled split and stacked in March 2017 was already dry on June 11, 2017.

The bad news is I know this because the wife was cold on June 11 2017 and I am already in to my 17/18 stash.

I am counting it a win.  There is a very high probablility that spruce felled on June 10, split on the 11th and stacked on the 12th would be dry before freeze up.


----------



## 2fireplacesinSC (Jun 13, 2017)

So, burning in June?  When does freeze up happen?  No wonder you're such a wood burning expert!


----------



## WoodyIsGoody (Jun 20, 2017)

Poindexter said:


> The good news is live spruce felled split and stacked in March 2017 was already dry on June 11, 2017.
> 
> The bad news is I know this because the wife was cold on June 11 2017 and I am already in to my 17/18 stash.
> 
> I am counting it a win.  There is a very high probablility that spruce felled on June 10, split on the 11th and stacked on the 12th would be dry before freeze up.



Excellent! I would build a solar drying shed except my wood is all at my cabin where the only spot that gets better than tree filtered sunlight is my back deck which gets an average of 2 hours direct sunlight/day. Since my wood has to dry mostly in the shade, it takes 2-3 years! When I split a piece open that is about half-way done, it will read 18-20% moisture near the ends of the split but the middle is still around 30% moisture! This is how most locals burn it but it's far from ideal.

I'm still in burning season at my cabin. I have a cell phone app that let's me check the indoor/outdoor temperatures remotely. Right now it's 59 degrees outside and 60 degrees inside. By the time I arrive in a couple of days it will likely be about 59 inside. I could remotely turn on my mini-split heat pump so it's up to temperature when I arrive but I like building a nice hot but quick clean burning fire when I arrive. That's all it will take (a 2-hour burn) to bring the structure up to comfort this time of year. Then burning season will be over until September. Probably. You never know around here. I've burned in July before.


----------



## Poindexter (Jun 21, 2017)

2fireplacesinSC said:


> So, burning in June?  When does freeze up happen?  No wonder you're such a wood burning expert!



Freeze up, when the temp drops below freezing and stays there until spring usually happens in early October and runs until late March.

I am hardly a wood burning expert, but i do feel pretty good about operating the one stove i own .

21:49 of sunlight for solstice day this year, not a cloud in the sky, and my wood is already dry.


----------



## Hasufel (Jun 25, 2017)

Poindexter said:


> 21:49 of sunlight for solstice day this year, not a cloud in the sky, and my wood is already dry.


Wow! I'm light sensitive and have a hard time getting a full night's sleep this time of year, but I'm also much farther south. How do you manage with barely over two hours of darkness?


----------



## johneh (Jun 25, 2017)

Better question whats it like with 22 hrs of darkness


----------



## Poindexter (Jul 8, 2017)

So some observations.  I am still learning to operate this thing I have wrought.  Tagging @Woodsplitter67 .

1. The life expectancy of the cheap stuff clear plastic from Lowes-Depot in my application is around 12 months.  

What I have done this year is cut off the complete scraps that were (probably) on the shady north side of my stacks last summer and using those as top cover this year.  We are coming up on rainy season here, I am about to go buy a bunch of plastic sheet to keep my dry wood dry - and keep blowing snow out of it over the course if the winter.

2. After last years debacle (my wood was too dry) I am keeping the airflow through the kilns pretty high.  My stash should be local EMC, about 11%, here in the next month or so.  What I am running this year, really, is a super expensive way to keep my wood covered on top while drying, but really easy to cover the sides and keep the rain off here in the next 3-4 weeks when autumn starts.

I only operate the one wood stove, BK Ashford 30.0, and it ran pretty OK last year on wood at 7-8-9%.  Put out real good heat, but my burn times were shorter than ideal and my stack plume wasn't as clean as I am accustomed too.  At my house on 15' 6" of stack, 12-16% MC fuel is ideal, I have run the stove for extended periods both above and below that sweet spot.

So I am shooting for 12-16% MC again this year.

3. I do have one module running with mixed sized pieces in it, by accident.  It is about 2/3s full with my regular sized splits, the last one I was filling.  I had some enormous chunks left, big knots in them blah blah.  Some of those I noodled down to just epic size with my chainsaw.  I won't really know how well it worked until I burn them.  I couldn't split them open before, I don't see splitting them open to measure MC before burning later.  I'll see how they do; my hunch is accelerated kiln drying works best when all the pieces are about the same size.  It took quite a while for the bigger pieces to start visibly shrinking, and my spruce is easier to dry than a lot of the woods common here.

Were I running a bigger operation on more acreage I might just elevate and top cover all my regular sized splits and then build a single kiln (or two) for the oversize chunks and uglies.  I can't imagine two years in a passive kiln wouldn't be enough to dry them all the way through.

4. Having been able to operate the stove pretty normally on June 11, I have a pretty good shot at running these kilns to season two crops or harvests or rotations each summer.  To do that, I need a holding shed large enough to hold at least four seasoned cords, and a teenager to come over in early June to move 4 cords from kilns to shed..  Then I can ditch 4 of my 8 modules to get some yard space back.  To put the holding shed under my deck I first need to move the fire exit window in a downstairs bedroom around the corner of the house onto the adjacent wall... after the wife and I get home from the Paris trip she wants and I get a new boat.  But it should work, at least with soft woods.  

FWIW on June 11th 2017 the sun rose @ 0306 (am) 17 degrees east of north, set at 0034 (am) on the 12th 18 degrees west of north; 21:29 of daylight, and we had some civil twilight in there before the sun came up again.  YMMV with shorter days.


----------



## Woodsplitter67 (Jul 8, 2017)

So i decided to put one together real quick. So with in the first hour the inside was 110 inside and the outside temp was 85. Later in the day it was 86 outside and 124 on the inside. I would say that this would spead up the process of drying. I have some thick uglies and odd pieces with some large oak and cherry
I did a mid season check last week on the MC so i will see how this works on the hard woods.


----------



## Poindexter (Jul 8, 2017)

It doesnt take long running one of these to see why "they" say to never leave dogs and babies in the car with the windows cracked, eh?


----------



## WoodyIsGoody (Jul 8, 2017)

Woodsplitter67 said:


> So i decided to put one together real quick. So with in the first hour the inside was 110 inside and the outside temp was 85. Later in the day it was 86 outside and 124 on the inside. I would say that this would spead up the process of drying. I have some thick uglies and odd pieces with some large oak and cherry
> I did a mid season check last week on the MC so i will see how this works on the hard woods.
> 
> 
> ...



Is there any air movement in that thing? If the water can't get out, the humidity in the tent will be 100%.


----------



## Woodsplitter67 (Jul 8, 2017)

WoodyIsGoody said:


> Is there any air movement in that thing? If the water can't get out, the humidity in the tent will be 100%.



Its vented at the top with 2 vents. The vents are small to keep the warmth up, but large enough to alow fresh air in. I can feel the warm air coming out the vents. Definitely fresh air is going in.


----------



## WoodyIsGoody (Jul 9, 2017)

Woodsplitter67 said:


> Its vented at the top with 2 vents. The vents are small to keep the warmth up, but large enough to alow fresh air in. I can feel the warm air coming out the vents. Definitely fresh air is going in.



That's good. Although I would recommend a small slit along the entire length to insure all parts of the pile are getting even air movement. Faster airflow will pull more moisture off the surface of the wood than higher temperatures and slower flow.

Also, you want the pile to cool off fully each night. The day/night temperature differential is what will cause the wood to "breath" more which will result in faster drying.


----------



## Poindexter (Jul 9, 2017)

Though relatively tightly wrapped, i suspect splitter has good enough intake air at base around the entire perimeter.

Three things to track.

1.  Capillary action.
2. RH calc
3. EMC

Ill come back to this after church...


----------



## Ashful (Jul 9, 2017)

Poindexter, although it might not give you the same level of control as shifting cords from kilns to shed, when ideal MC% is achieved, have you considered just putting a transparent roof on your shed?  You could kiln in-place, then, and not need that teenager to move wood around for you.


----------



## Poindexter (Jul 9, 2017)

*The Hypotheses that work just fine for me so far.
*
I am going for gracious here.  I recognize this thread is text dense.  If you disagree with my methods I invite you to build your own kilns, run them your way and let us know how it works out for you.

1. *Capillary action* In a live tree there is sap in the tubules.  In above freezing temps with thoroughly thawed wood that isn't frozen on the inside capillary action and good air flow (with dry bulb temps less than +95dF which I'll get to shortly) takes about two weeks.

Two weeks, all the water in the sap is out of the tubules, the splits are at FSP or fiber saturation point and the stacks start to move as the individual pieces change size.  It's very simple.  If the stacks are moving you are below FSP.  If the stacks haven't started moving yet there is still wet sap in the tubules.  NO discussion, it's a definition.

If you run the temperature inside the kiln up above ~+95dF while the splits are above FSP you run the risk of shrinking the ends of the tubules shut and trapping wet sap inside the split.  Every year, without fail, we get a couple or three new threads in the wood stove section "I bought kiln dried wood, it lights good but doesn't burn all the way through.  I finally split one open and it meters 35% MC on the inside.  Did i get ripped off?  What's wrong?"  And within a day or two someone with similar experience will say they 'kiln drying' that happened to the wood was just to kill parasites so the wood could cross jurisdictional lines for retail sale, esp common in the NE US.

If you want to make little burritos out of all your splits, a wet wood filling with a dry wrapped wooden tortilla, you go right ahead.  I ain't got no time for that mess.

You may look up the FSP of whatever species you are wondering about here: https://www.google.com/search?q=fib...0j69i57j0l4.4036j0j7&sourceid=chrome&ie=UTF-8 

2. *Relative Humidity Calculation*  To figure out how dry the wood in the kiln is, or is going to be, the operator needs to know both the temperature inside the kiln, and the relative humidity inside the kiln.  Having BOTH pieces of data will allow anyone to look up the Equilibrium Moisture Content the splits are tending towards, EMC is point three.

One way to accurately measure RH is with a wet bulb thermometer.  I don't have room inside mine to do that.  Plus it is hot and humid in there and spinning the thermometer in there for minutes at a time every day is not going to be fun.

Another option is to buy a hygrometer.  The cheap ones are calibrated for typical household ranges.  They don't work well, and don't work very long in rain forest like environs.

The third option, and one that works "good enough" on my lot is to recognize, with a broad brush, the vapor carrying capacity of air doubles with each 20 dF rise in air temperature.  Thus a volume of air at say +50dF and 100%RH, inside a tank, or a baloon or what have you, will, when heated to +70dF and no vapor exchange with the rest of the atmosphere will have an RH of 50%.  Same volume heated to +90dF will now have a RH of 25%.  

It is the same effect as letting cold "dry" winter air into your heated home.  Say your house is +70dF and you are maintaining maybe 30% RH with a humidifier on your forced air furnace system.  Outside is +10dF and the RH of the outside air is 70%.  Your kid opens the door to watch the mail man work the door on the mail box.  You get a big slug of 10/70 air in, and the open door lets a big slug of 70/30 out.

When that cold air gets heated from +10 dF to +70dF it's vapor carrying capacity doubles on the +10 to +30 jump, and on the +30 to +50 jump, and doubles _again_ on the +50 to +70 jump.  Doubles three times.  it was 70% RH when it rolled in cold, gets cut in half to 35%, gets cut in half again to 17.5% and gets cut in half a third time to 9.25% RH when it finishes warming up. So it feels pretty dry.

Same thing in the kiln, except we are starting with "cold dry" air in the back yard at maybe +80dF and 80% humidity, but using the kiln to jack up the temperature and drop the RH.

https://en.wikipedia.org/wiki/Relative_humidity 
https://en.wikipedia.org/wiki/Psychrometrics 

*Equilibrium Moisture Content*  Once we know the temperature and RH of the air inside the kiln we can easily look up the EMC all the splits in the kiln are tending towards via diffusion.  The bigger the gap between EMC and actual MC, the faster the wood dries.  As it gets closer and closer to EMC the drying goes more and more slowly.

I posted a lovely table less than a year ago, it is on page two in this thread, post #30.  

https://www.hearth.com/talk/threads/solar-cord-wood-kiln-operation.152699/page-2#post-2105773 

I f we knew the temperature and RH in splitter's backyard we could easily calculate the RH inside his kiln, knowing the temperature inside the kiln is +110dF.  Today in Woolwich, NJ it is +82dF and 38%RH.  So looking at the table that you just opened in a new tab you can see that if it was just top covered the wood in his stacks is tending towards 7.6% MC, because that is the EMC of wood for +80dF and 40%RH.  

But with solar gain the inside of his kiln is +110dF.  And he isn't pumping water vapor in, other than what is coming out of the wood, so if we look at the EMC for 110dF at 20%RH were going to get a high number.  If we look at the EMC for 110dF at 10% RH we're going to get a low number, but the range is 2.2 to 3% MC for the wood to be at equilibrium with the air in the kiln.

That wider diffusion gradient he has created by lowering the RH and raising the temperature around his stack is going to make the stack dry faster than it would if it was just covered on top.

This seat of the pants rule of thumb SWAG is good enough.  Does the kiln need "some" air turnover, yes.  Does it need a lot of air turnover?  No.  A cord and a half, two cords like he has pictured above are going to do just fine with a couple holes at the roof peak, one at each end, each about big enough for a cantaloupe to pass, maybe 6-10" diameter.


----------



## Poindexter (Jul 9, 2017)

One other thing I guess I might oughta explicate.  Visible light passes through clear membranes like kiln covers, bounces off the cord wood inside, passes back through the kiln cover again unchanged and you can see the wood in there.

UV light passes through a clear membrane unchanged, then hits the cordwood inside and becomes heat, infra red radiation.  What you don't want to do is pay $$ for clear corrugated panels with UV blockers added in the mfr process.

UV blockers are a good thing if you are trying to grow orchids, not so good if you are trying to heat the place up.


----------



## Poindexter (Jul 9, 2017)

Ashful said:


> Poindexter, although it might not give you the same level of control as shifting cords from kilns to shed, when ideal MC% is achieved, have you considered just putting a transparent roof on your shed?  You could kiln in-place, then, and not need that teenager to move wood around for you.



Kinda sorta.  If I had more space I could see building basically a greenhouse with no UV blockers in the glass, and then rigging up some kind of opaque curtains inside to keep the sunlight off the wood after it was dry enough.

The shed I am planning on is gonna be shaded by the deck, opaque walls, as vapor impermeable as I can build it, expensive door with a good weather seal system, and one little tiny vent, probably 4" stove pipe ducting from inside the vapor barrier to the driest air I can get to under the deck.  

Couple screens in the stove pipe to keep squirrels out.

I though about collecting old freezers and refrigerators from the dump, but I would need a pretty big pile of them to hermetically seal four cords of wood for long term storage through the rainy season.


----------



## kennyp2339 (Jul 10, 2017)

Great read


----------



## Woodsplitter67 (Jul 10, 2017)

Poindexter
Thanks for the good reads and the time and effort you have put into your explanations. The hard woods that i have will be a good test to this experiment.  I will post back my findings if you dont mind.  Thanks for posting. I think its a great idea.


----------



## ElmBurner (Jul 12, 2017)

Poindexter said:


> UV light passes through a clear membrane unchanged, then hits the cordwood inside and becomes heat, infra red radiation.  What you don't want to do is pay $$ for clear corrugated panels with UV blockers added in the mfr process.


There's very little heat in UV, compared to infrared.

I wouldn't pay extra for something with UV blockers, but I wouldn't go out of my way to avoid them either.


----------



## Turd Ferguson (Jan 26, 2018)

You've been running this for a couple years now- is there anything you've learned since this thread went dormant that you'd be willing to pass along? I am in a situation that presents the need for a solar kiln, and I'm trying to minimize my mistakes and get the best bang-for-the-buck given the circumstances. Any design/operational changes? Advice?

Thanks!


----------



## Woodsplitter67 (Jan 26, 2018)

Turd Ferguson said:


> You've been running this for a couple years now- is there anything you've learned since this thread went dormant that you'd be willing to pass along? I am in a situation that presents the need for a solar kiln, and I'm trying to minimize my mistakes and get the best bang-for-the-buck given the circumstances. Any design/operational changes? Advice?
> 
> Thanks!



It would be super helpful if you could tell me about the area your going to be set up in as well as how much wood you plan to try to dry as well as your timeframe of when your splitting


----------



## Turd Ferguson (Jan 29, 2018)

Woodsplitter67 said:


> It would be super helpful if you could tell me about the area your going to be set up in as well as how much wood you plan to try to dry as well as your timeframe of when your splitting



Considering the expense involved, I'd like to try by designing this system for 1 cord of wood. Based on an 18" log length and stacking two rows (1 on each side of a 4x8' sheet of PT plywood), I get a height of roughly 64" tall.

My wood is currently in the 25-30% MC range. I'm finding it very difficult to burn in my Fire Chief FC1000 and I believe that the MC is having the largest effect on its ability to run unattended.

My long-term goal is, if this should prove effective, to build another, identical unit to be able to season a couple of cords every few months.


----------



## Woodsplitter67 (Jan 30, 2018)

Turd Ferguson said:


> Considering the expense involved, I'd like to try by designing this system for 1 cord of wood. Based on an 18" log length and stacking two rows (1 on each side of a 4x8' sheet of PT plywood), I get a height of roughly 64" tall.
> 
> My wood is currently in the 25-30% MC range. I'm finding it very difficult to burn in my Fire Chief FC1000 and I believe that the MC is having the largest effect on its ability to run unattended.
> 
> My long-term goal is, if this should prove effective, to build another, identical unit to be able to season a couple of cords every few months.



The expence is minimal. You could set up a cheep one like i did to start with for like 75 bucks or less depending on what you already have on hand. You could easly do 1 or 2 cords this summer and have it plenty dry by the fall of 18. Also well below the 20%  MC , not split smaller neather. You can get the larger splits down that far.
You can do 2 rows. I would start with 1 cord at a time, start at mid may and go to mid July put in a fresh cord and do mid july to October and your off and burning
I did my first kiln with 2 home depot wood racks and 6mil plastic. Took me and my son a couple of hours to put it together..


----------



## Turd Ferguson (Jan 30, 2018)

Woodsplitter67 said:


> The expence is minimal. You could set up a cheep one like i did to start with for like 75 bucks or less depending on what you already have on hand. You could easly do 1 or 2 cords this summer and have it plenty dry by the fall of 18. Also well below the 20%  MC , not split smaller neather. You can get the larger splits down that far.
> You can do 2 rows. I would start with 1 cord at a time, start at mid may and go to mid July put in a fresh cord and do mid july to October and your off and burning
> I did my first kiln with 2 home depot wood racks and 6mil plastic. Took me and my son a couple of hours to put it together..


I have a more immediate issue in the sense that I have wood right now that's 25-35% MC and need to get it down to 20% ASAP so my furnace will burn it. I was hoping this may be an interim solution with the wood I have on hand seasoning as fast as possible. Thoughts?


----------



## Woodsplitter67 (Jan 30, 2018)

Turd Ferguson said:


> I have a more immediate issue in the sense that I have wood right now that's 25-35% MC and need to get it down to 20% ASAP so my furnace will burn it. I was hoping this may be an interim solution with the wood I have on hand seasoning as fast as possible. Thoughts?



Looks like you in mass.. thats north of me. I dont think that your really going to dry anything in the dead of winter with the current sun angel and the temps were having right now.  A solar kiln is exactly that. A kiln that is run by the sun. Sun angle as well as duration is what drives the kiln.the kiln needs to heat.. ther needs to be enough time to get the temp up in the kiln to dry the wood.


----------



## Poindexter (Feb 5, 2018)

Just noticed, sorry.  When i build more i will probably duplicate my module number 6, i used the same plan for #7 and #8.  

Its the last one i took an end shot of and posted dimensions.

I think in the future ill maybe make the last little stubs the ridge pole sits on a tiny bit longer and flip the ridge pole over so the pvc elbows are under the ridge pole rather than above.

I am thinking about replacing the plastic sheeting with corrugated clear, at least on the sunny side.

Future builds ill likely use 2x6 for the floor framing.  2x4 is barely adequate, but it is adequate.


----------



## Poindexter (Feb 5, 2018)

I do agree with @Woodsplitter67 , getting enough solar gain to measurably dry out damp wood in the winter months is asking a lot.


----------



## Turd Ferguson (Feb 5, 2018)

Thank you for your replies. I'm noticing that once I have my wood indoors it is drying out a little better. I am much closer to 20% now than I was several weeks ago.

What is your opinion of using the PVC stake poles versus wrapping the stack with sheeting and shrink wrap? Is it worth it? I'm sure if condensation accumulates on the sheeting and can't be vented, it'll make its way onto the wood without the poles providing a barrier. However, in either of yours' experiences, have you had this issue before?


----------



## Poindexter (Feb 5, 2018)

Woodsplitter spent a lot less money than me for his setup, got results just as good, so bang for buck advantage @Woodsplitter67 .

I very very rarely have liquid condensate running down the inside surface of my kilns. I have seen it exactly one time. With that one exception, the water comes out of my wood as a vapor and gets pumped out without condensing -though I did design and build for  condensate on the inside of the sheeting to drip off the edge of the plastic sheet out on the lawn.

There is a user who just used shrink wrap on palletted stacks of splits with good results. Forgot user ID sorry, I think he has posted in this thread.


----------



## Turd Ferguson (Feb 6, 2018)

Poindexter said:


> Woodsplitter spent a lot less money than me for his setup, got results just as good, so bang for buck advantage @Woodsplitter67 .
> 
> I very very rarely have liquid condensate running down the inside surface of my kilns. I have seen it exactly one time. With that one exception, the water comes out of my wood as a vapor and gets pumped out without condensing -though I did design and build for  condensate on the inside of the sheeting to drip off the edge of the plastic sheet out on the lawn.
> 
> There is a user who just used shrink wrap on palletted stacks of splits with good results. Forgot user ID sorry, I think he has posted in this thread.



It wasn't my suspicion that the poles helped a great deal, maybe except for very high humidity days. But we don't get those very often here and the additional savings on this proof of concept would be a great help.

@Woodsplitter67 What does/did the top of your kiln look like? Just a 2x4 running the length of the pile to keep the sheeting raised? I think that's the only photo you didn't post that would be super helpful. Also, were you using some sort of vapor barrier on the bottom of your piles to prevent ground moisture from coming up?


I may split some rounds I've had for a few months now and stack them into a prototype kiln to see what happens. Worst case it's c/s/s for next year. A cord will fit nicely onto two pallets at a reasonable height.


----------



## Poindexter (Feb 6, 2018)

Iirc woodsplitters kiln had open slats at the floor.  I am on an ancient flood plain about 20 vertical feet above the current river surface, lots of groundwater at my address.


----------



## Turd Ferguson (Feb 6, 2018)

Poindexter said:


> Iirc woodsplitters kiln had open slats at the floor.  I am on an ancient flood plain about 20 vertical feet above the current river surface, lots of groundwater at my address.



Maybe I'll do a little experiment. Do one with, one without, and see what happens. I think the first priority is getting the temperature up in the kiln, then controlling ventilation. Without temperature elevation, there's no point to ventilation because the air won't be drawing any water out of the wood.


----------



## Poindexter (Feb 6, 2018)

I experimented when i was using pallets and tarps before the kilns.  I put a layer of plastic on some of the pallets before the green splits went on, then tarped above like the rest.

It made a difference at my house, but if you are on a thick gravel deposit it might not make any difference.


----------



## Woodsplitter67 (Feb 7, 2018)

I used some 1x3 for the roof. I had 1 2x4 on each end horizontal and attached the 1x3 to make the top portion of the roof.. draped the pladtic over it and wraped the bottom with contractors stretch wrap to hold the plastic in place. The wood was put in regular wood racks stacked Kris Kross and the wood racks were elevated up off the ground with pavers. The 2 sides had 5 inch round holes cut in for vents and 1 small vent in the middle of the roof


----------



## Chas0218 (Sep 10, 2018)

Why clear plastic instead of black wouldn't the black get it hotter for longer? If you are just taking measurements anyway I don't see how the clear would benefit? I understand the effects of the sunlight on the wood but I would think that the heat is more desirable than direct sunlight when kiln drying wood. I think you would see your temps level throughout the entire shelter and have less hot spots at one end than another.

I plan on building a wood shed with bays holding a around 1.75 cord using all black tin for the roof and sides I think it should heat the wood in the summer nicely with a clear sheet of plastic across the front and open top.


----------



## Ashful (Sep 10, 2018)

Woodsplitter67 said:


> The wood was put in regular wood racks stacked Kris Kross...



“Kris Kross”?


----------



## Poindexter (Sep 10, 2018)

Chas0218 said:


> Why clear plastic instead of black wouldn't the black get it hotter for longer?



I think the best answer is "it depends."  Mostly on where you are and what your local conditions are like.

When I was seasoning on Pallets with just sheet over the top, open sides, it seemed like maybe advantage black plastic.  It wasn't much different, but if there was a difference the black was a little quicker, at my place.

At my address, 64 degrees north latitude, I have 18+ hours of direct sunlight on my stacks for a couple months, very few addresses in the lower 48 have that.  

If someone wants to dry black plastic on kiln, I say go for it.    Who knows?

I also suggest trying both and dialing your system in for your conditions.  There might be another guy a mile down the road from you get different results because of a different tree line or different subsoil.

I got to here by starting with pallets on the ground, then pallets on cinderblocks, then some pallets with a floor layer of scrap plastic, I spent a lot of time figuring out what works on my land with my conditions.


----------



## Chas0218 (Sep 10, 2018)

Poindexter said:


> I think the best answer is "it depends."  Mostly on where you are and what your local conditions are like.
> 
> When I was seasoning on Pallets with just sheet over the top, open sides, it seemed like maybe advantage black plastic.  It wasn't much different, but if there was a difference the black was a little quicker, at my place.
> 
> ...


I understand was just curious, as of right now I don't have a lot of time to season my green wood before I have to burn it. I would like to get a few years ahead but that would mean cutting 18 cord worth of wood this year splitting and stacking then another 6 cord next year and so on. I managed to get around 9 cord CSS this year so hoping to get another 9 CSS this winter/following season.


----------



## Woodsplitter67 (Sep 10, 2018)

Ashful said:


> “Kris Kross”?




Yes.. i did not stack all in one direction.. aka all end grain out..


----------



## Ashful (Sep 10, 2018)

Poindexter said:


> I think the best answer is "it depends."  Mostly on where you are and what your local conditions are like.


He ain’t far from me, and this is my local forecast (and summary of this entire summer):


----------



## Easy Livin’ 3000 (Sep 10, 2018)

Ashful said:


> He ain’t far from me, and this is my local forecast (and summary of this entire summer):
> 
> View attachment 229474


Well, except for the handful of days that were oppressively humid and hot. My least favorite spring and summer in my recollection.  If winter is cold with this kind of precipitation, we are in for a workout.


----------



## Poindexter (Sep 10, 2018)

Alright now, look here.  On my lot I can, and have, run a line of pallets 64 feet long, stacked 8 cords on there in two parallel stacks, top covered with plastic and gotten to 16% in one season (softwood).

There are some disadvantages to that.

1. dealing with snow on top of the tarps when going outdoors for wood.
2. getting my boot stuck in a pallet space when getting wood from the stack on the far side of the pallet
3. Blown snow getting all up in my splits that aren't side covered
4. Having to go out there every time it rains to get the rain out of the center gutter created in the plastic by the weight of the rainfall on the stacks.
5. It looks kinda of trailerpark / ghetto
6. I had to restack at least part of the pile every year.  One year three times, that year I watched four cords fall in about 15 seconds, I was out there looking when it let go.  Sounded like an enormous bowling alley.

I did try a few top covering strategies.  I used some plywood scraps to bridge the two stacks under the plastic, worked good but was a Pain in the place the sun doesn't shine once it had snow cover on it.  I tried covering the two parallel stacks individually, but the ends to the inside that got plenty of rain and minimal sun, I bought a lot of bio-logs that year because the inside ends were pretty wet.

So with this system, I laugh at rain, it falls off.  For blowing snow, I laugh, I am side covered.  No stuck boots, plywood floors.   Looks kinda NASA, still not suburban, but not ghetto.  No restacking yet, my longest horizontal run is 7 feet 5 inches.  I laugh at snow accumulation, falls off.

The unproven thing still, how many crops or seatings or loads per year.  I feel pretty good that I could season 8 cords of spruce in one summer, four cords at a time.  I don't have a woodshed that will hold four seasoned cords, and I don't have a good place to put one.  I was hoping to see how fast I could get the spring load dry this summer, but life got in the way.

When I load these things, I just drop the splits in .  I am at too high a volume to spend time "stacking".


----------



## Chas0218 (Sep 11, 2018)

I agree, my stacks look trailer park esk. They have a pallet on the bottom one on top attached using 2x4's on corners and middles. The tops get plastic pallet sheet covers until I throw some junk tin or the like over top. I scavenged some fiberglass panels someone threw away at the dump to cover the stacks next. On average I get about .50 cords per each "house" my plan is to use the same concept but be able to move a "house" to and from my deck using the tractor and forks and being able to rotate stacks within the wood shed for better drying. Not sure if you can visualize what I talking about but basically small 4'x4'x'4 cubes of firewood that I can move around on pallets.


----------

