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Ideas for getting my solar kiln hot enought to sterilize wood

Started by Kit B, September 26, 2022, 08:07:59 AM

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Kit B

First let me say that I've been reading and learning from the forum for awhile and really appreciate everyone who shares their experience and knowledge.  I have a solar kiln built with the Virginia Tech plans.  It seems to dry wood just fine but I haven't able to get it hot enough, long enough, to be confident that the wood is sterilized.  On a hot day I usually max out in the low 130's.  So I bought a couple of small (10") electric heaters and got the temp up greater than 140 for about 3 hours.  I'm wondering if any of you fine folks have any helpful hints to get and hold the temp greater than 150, which it seems is the temp I need to get to, to assure the bugs and larvae are dead.

doc henderson

halogen work lights is a common answer.  a solar kiln like the VT has the glazing that is not well insulated, and is part of the reason you cannot get the temp up. the core needs to get to 133° and the consensus tends to be 160° over night is enough to get there.  you could put a insulating blanket lie moving blankets over the glazing (plastic) to hold in heat.  you can melt cheap box fan blades if you get too hot.  you could try to measure the core temp.  thicker slabs could take longer.  i placed a meator probe in a drilled hole once to see, and it seemed to work.   :)
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

Kit B


doc henderson

plan b is to make a dedicated "hot box"  just for that.  depends on your space and turnover time for the kiln.  you are welcome.  it has been discussed if you want to search for other threads.  you will get a broader bit of info.  
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

kelLOGg

I actually measure the core temperature by drilling a hole the diameter of my thermocouple probe into a sample the same species and thickness and turn resistance heaters on. As soon as it reads 133 F it is done. The hole is about 4" deep and the thickest I dry is 2.5 to 3".
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Sod saw

.


I have had some success in sterilizing wood in my solar kiln.  It's an effort.  

Without extra supplemental heat the sun can heat the kiln up to almost 160 degrees F. in the afternoon with full sun all day long.  With that extra supplemental heat, it will stay warm, in the kiln, overnight and the next day will be enough hours to finish the sterilization cycle

Kit B, I have some questions before I comment further.

Where are you located?  Don't be afraid to fill out your information on this forum so folks can better answer your questions.

What size is your kiln?  What is your clear glazing made of and how many layers?

How many hours of full sun per day? In other words do you have your kiln in part shade?

What month were you attempting to sterilize your wood?  How thick were the boards?

What insulation do you have in the walls?  Floor?  Doors?  Door gaskets?


KelLOGg - Sounds like you have a method figured out to keep track of the temperature.  How long does it normally take for the core temperature to reach your desired 133 degrees F ?   I am confused.  If the wood is 2.5 to 3 inched thick, how do you drill a 4 inch deep hole?

What brand is your thermocouple that you use for the temperature?  How many do you distribute throughout the loaded wood?


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LT 40 hyd.          Solar Kiln.          Misc necessary toys.
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It's extremely easy to make things complicated, but very difficult to keep things simple.
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doc henderson

hole likely in from the side.  like I did in my maple thread with the meator probe.  it is over half way in.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

Sod saw

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Thanks Doc.  That makes more sense now, considering the wood is stacked within the kiln.

Do you have a link to your Maple thread?


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LT 40 hyd.          Solar Kiln.          Misc necessary toys.
.
It's extremely easy to make things complicated, but very difficult to keep things simple.
.

Kit B

Sod saw,

My Kiln is built to Virginia techs specifications, roughly 6'x13'.  The solar collectors are 2 layers of tuftex panels. There are 4 solar powered fans.  I'm hoping to sterilize boards up to 8/4.  The walls and doors all have standard fiberglass bats with backing.  The floor is kinda skimpy with a single layer of some aluminum backed insulation I ran across.  Everything is caulked inside and out.  

I'm located in Northern FL and it's plenty hot most of the year and when it's not there's usually plenty of daytime sunshine.  Recently we've had a string of hot day's but the kiln never got over 130 degrees.  I have my sensor in the middle of the stack so it's possible it's hotter at the top of the stack.

If I can figure out how the create a gallery I'll up load some pic's

Kit B

Actually I mispoke, the kiln temps get into the mid-130's on hot day's.


doc henderson

yes sod, go back 6 comments (or post #3) the way my computer counts, but i am usually off by one because I choose to look/work in reverse.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson


some cottonwood in my "heat box" fluid and blanket warmer from an old hospital.



 


nice kiln by the way.  to heat treat you can cover the glaze with moving blankets, and put several halogen work lamps inside.  monitor the temps so you do not melt good stuff in the kiln.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

aigheadish

Moving blankets over the outside of the windows?

Also, I agree, that kiln looks nice, I'd like to do something similar with my shed one day...
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doc henderson

yes, I think if I were doing it, that would be the easiest temporary insulation I can think of.  I would hit the high temp of the day by solar, insulate the glaze and turn on the lights and fans.  then monitor the internal wood temp by what ever way I have.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

kelLOGg

Sod saw,
Doc is right /I drill into the end. I use just one thermocouple and it came with the protimeter moisture gauge I use. With fans in my kiln I assume the temperature is uniform throughout the kiln so I think I can get by with 1 thermocouple. 
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Sod saw

.


kelLOGg,  If I am reading this correctly, your thermocouple is a moisture gauge ?  That is drilled into the edge of the wood.  Does that thermocouple moisture gauge also measure temperature?  or only temperature?  How does a humidity gauge fit into this equation ?  I believe that I am confused again (still). Confusion is my middle name, sometimes.

Kit B,   Your kiln is the same length as one of my chambers. And about the same width.

Since we are so much further north than you all, I decided make the roof, here, at approximately a 45 degrees slope (roof pitch).  Our summer sun is warm enough; so to allow a little more efficiency in the fall and spring I kept is somewhat steeper than some folks suggest.  This probably makes my overall roof height higher than yours would need to be.

To help me understand your roof covering, did you use the tuftex that is manufactured with the tubes built in or the single layer sheet.  Yes I understand that you doubled up the layers, but did you double up the single layer sheets or did you double up the two layer kind with the square tubes built in?  Sorry to ask so many questions but it helps to understand some of the design details.

Are the two roof layers separated?  By how much (distance)?

It appears that your door hinges have thru bolts as does mine.  But I am unable to make out what kind of gasket to seal up the closed doors.

I like your solar panels up high away from grass shade and lawn clippings etc.

Does your indoor curtain extend to each end wall?  Does it block air movement around the ends of the wood pile?

Yes your assumption is probably correct about having only one thermometer in the middle of the pile.  I have found that my thermostat controller is at the bottom of the stack with thermometers above the doors and also near the bottom layer of boards gives an idea of heat spread and fan efficiency.  I have been known to move them around from load to load (just curious).

Everything inside and out, of mine, is flat black paint except the floor which is gloss white to help keep the enclosure cooler when empty.  Does the white help?  I don't know because I don't leave it empty for long.

OK. . . .  enough questions for now.


.
LT 40 hyd.          Solar Kiln.          Misc necessary toys.
.
It's extremely easy to make things complicated, but very difficult to keep things simple.
.

kelLOGg

A thermocouple measures only temperature. The MC is measured by a probe assembly that is driven into the wood to measure electrical conductivity due to the moisture content of the wood. 
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

Sod saw

.


kelLOGg   In post # 16 you stated that the thermocouple came with your protoimeter  moisture gauge.  Does that gauge come with both the thermocouple for temperature as well as pins for humidity?   I attempted to find one on line but was not able to locate one with both options, heat and humidity.


.
LT 40 hyd.          Solar Kiln.          Misc necessary toys.
.
It's extremely easy to make things complicated, but very difficult to keep things simple.
.

kelLOGg

My meter measures moisture content and temperature, not humidity. My meter was given to me by a neighbor forester and it is not a very common meter. No one on the FF talks about this meter which I think is a British one. 
Cook's MP-32, 20HP, 20' (modified w/ power feed, up/down, loader/turner)
DH kiln, CatClaw setter and sharpener, tandem trailer, log arch, tractor, thumb tacks

doc henderson

humidity is usually the gas form, in the air.  relative humidity is the amount of water the air is holding relative to the amount it could hold total (or 100%).  MC is the weight of the water in the wood relative to the weight of the dry wood.  so MC can be over 100%.  meters that can be corrected for species, use the known specific gravity.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

at 100% you get rain or condensation.  the relative humidity raises as the temp drops.  as it drops and gets to 100 RH, that is also known as "dew point".  you can look on a table and take the average relative humidity, and find the predicted or estimated moisture content.  EMC.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

Kit B

Just a little follow up.  I tried using 2 halogen lights, which got my temps into the 140's, still shy of where my goal of 150.  Then I went back and re-did all the weather stripping around the doors and added insulation to the floor.  The kiln had a 1.5" drop from the 2x4 that ran the length of the kiln at the front, so I added 3/4" rigid foil back insulation panels, covered them with 3/4" plywood, calked, sealed and repainted my new floor.  My next step might be trying to separate the 2 layers of tuftex to get a layer of air in between them, or replace them with panels that have 2 layers and sealed sides.

I'm also considering Doc's plan B, building a "kill box" for sterilization.  I have 2 old metal corn silo's. One I use to store dried wood, the other I use to air dry  large cookies and smaller slabs.  I'm thinking of sealing one up and adding a heat source.  Propane, woodburning?  Wondering if anyone has heard of converting old silo's for similar uses?

YellowHammer

If you are up to 140F with 2 x 500W lamps you are in good shape.  That's only 1,000 watts which is surprisingly good.  Throw in another lamp or two and you'll be there. Most of my kilns need 2,000 to 4,000 watts to get to 150.
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

rusticretreater

Do you mean using the silo as a kiln along with an external heat source?  That would be blazing a trail. 8)

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Kit B

Thanks for the reply Yellow hammer, I'll be getting a couple of more lights.  

A question, how long do you hold the temp at 150?  Do you take an internal temp of your wood?

YellowHammer

It normally takes me 24 hours for my two DH kilns to rise from operating temp of 120 to 150. 

Then I will hold for 24 hours at 150 and then let it slowly cool back down, to relax the wood.  

No I don't take internal temp, there are several publication that have the core rise time of 4/4 and 8/4 wood and it's generally under 6 hours.  So I hold for a day generally because it's way overkill and also most convenient for me, I check my kilns in the morning so a 24 hour cycle is easy.  I take a time stamped picture when I start the 24 cycle, and then another at the end, to give me the elapsed time.  I don't worry about it as long as it's 24 hours at least.  

The FDA only requires 133 core temp.

If you measure internal core temp you could drastically reduce the time, but I prefer just letting the wood cook.  Success is based in seeing lots of little dead bugs in the surface of the wood, looking like pepper, or even the larvae itself, fried to a crisp like this little bugger.  



 
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

samm

What about supplementing with electric or LP wall heaters? The kind of little ones that attach to the inside of a garage wall?  Do they allow you to keep them on, or do they have a safety shut off after 90F or so?

By the way, how concerned are we of getting the internals of the kilns to 140-160F or maybe even spiking higher, and the durability or safety of the stuff we have inside these hot kilns? For example the fans, or for example let's say the wall mounted heaters themselves -- since they will be subjected to drastically higher internal temps than a residential setting? What items are most sensitive to these higher temps?
Someone above said fan blades.. how about other important things like gas line teflon tape or pipe dope, etc, would these high temps be no-bueno for anything safety-wise?

I will be following this discussion thread, as I am interested in kiln sterilization as well. I haven't yet constructed my kiln, but I will soon!

Keep your stick on the Ice!

doc henderson

If you pick a max temp of 160° F, then choose your components accordingly.  Higher temp items will prob cost more with better insulation, and metal components over plastic.
I would avoid any gas open flame non vented type of heater.  fire risk, and it will add water as a product of combustion.  I have searched for clothed dryer heaters on amazon and am considering this for a hot box.  
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

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