Solar kiln build (help me)

[doc henderson]

can put a dehumidifier in there as well.

[Sod saw]

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scsmith is not wrong in that diagonal bracing is a good idea in many cases.

In the case of burdman and Dad not feeling that diagonal bracing is necessary:  If you use two thin layers of "plywood" glued together with the joints staggered you will end up with a very stiff wall section.

I used luan flooring type of plywood above my kiln doors.  The doors are just under 18 feet wide and the header above the door is about 2 feet high.  Using normal vertical studs sheathed (glued) inside and outside with thin luan (light weight) the snow here does not bother the door openings.

We also use that plywood truss idea for real buildings. Sometimes with a few thousand pounds of snow load over garage door openings.

But, if no stiff sheets are available, then diagonal bracing is very important.

have fun with your kiln


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[burdman_22]

 

 

[doc henderson]

moving right long.  did you put in a small door?  are you using osb inside as well?  how do you plan to seal.  vapor barrier?  coating?  how did you seal the edges of the glazing?  I see some foam or wood at the bottoms I think.

[burdman_22]

We've got the foam stuff around the edges, will probably use spray foam to seal the sides of the glazing (maybe the ends too), but not sure, that will be my dads department.

We'll be putting two coats of black concrete sealer on the inside of the kiln. I think that's all we had planned, no plastic or anything.

Mentioned this in another thread, but I've been looking at an electric bed bug heater as an idea for sanitizing. They heat to 140-150 by default, have a built in thermostat, and would be basically plug and forget....no engineering to figure out how to do anything...anyone used one before?

[Sod saw]

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What is the voltage that you plug into?

How many watts it the heater?  

Is there any sort of fan built into your proposed bed bug heater?  Is that heater designed for a whole house or just one room?  I wish I know about them when we had apartments.

Do you know the manufacture(s) who make these bed bug heaters?


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[burdman_22]

https://thermalflowtech.com/product/single-room-bed-bug-heater/

Hopefully we're allowed to post links.

They are designed for a single room, up to around 180 sq ft.

[Sod saw]

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Thanks for the link.  I did study their site and various heater products.  There are many sizes made for different size rooms as well as whole house bed bug treatments.

Let's start by noting that bed bugs need a temperature of slightly higher than 120 degrees (F) to be killed.  Their eggs will also be killed but it takes a few more hours than live bugs.  And you must leave the heat "on" for a few hours to be sure that inside walls will become warm enough.

If you wish to sterilize wood, the generally accepted temperature inside the core of a piece of wood is 133 degrees (F) to kill what ever is in the wood.   Larger pieces of wood will take longer for the core to reach that required temperature.  You also need to keep the core warm enough for long enough time.  Ask Yellowhammer  how long he keeps his kiln hot.

Before you can decide on a heat source to purchase, you need to know how many BTU's your heat loss is.

I trust that your stated location is correct in a warmer part of the USA south.  Your cooler season will be shorter that mine and your cool nights will not be as cool as mine.  But you still will be money ahead if you know heat loss.

Look up how many BTU's your roof will lose per square foot, then add all those square feet.

Look up how many BTU's your walls will lose,  then floor, then doors, then add a fudge factor amount in for leaky gaskets and vents.  

My gut tells me that it will be thousands of BTU's.  But I could be wrong and you should know for sure because those bug heaters are rated in BTU's.

Those heaters will require many 120 volt circuits for each heater and many good heavy cords to connect to those circuits on their own separate circuit breaker.  

You still need your normal kiln fans to properly circulate heat thru the layers of wood and prevent the upper ;layer from heating and the lower layers from cooling,  even though the included fan is powerful.

Those heaters are designed for max temperature to be 140 degrees (F) which is about 10 degrees lower than might be hoped for sterilizing wood due to the time it takes for the heat to penetrate into larger (thicker) pieces.  If you have a max of 140 degrees (F) you will need to leave it on for longer hours.  No, I don't mean to imply that your hours should be more than 60 minuets.

Your proposed 180 square foot heater would not work here for me on a cool summer night, so study your heat loss and do the math.  Perhaps doubling up your roof glass or adding more wall/floor insulation might help with heat loss.

Thanks again for the link. I am considering one for each of my chambers to supplement my current heaters.  I have all winter to consider.


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[burdman_22]

All good points to think over. One of the other thoughts I'd had was building a small shed beside my kiln, with a wood burning stove inside, and a short duct between the two. Then a fan in front of the duct to pump hot air into the kiln, with a thermostat controlled outlet on the fan, so the fan would only kick on to blow heat when the temp dropped below 150 or so in the kiln.

I'm sure something similar has been tried by someone in the forum before, and I know insulation and air leaks and all of that come into play again, it's just a thought. Obviously it's hard to sanitize in a solar kiln, period. Optimally in the future i will have a dedicated hot box for sanitizing...but that will require more time than I currently have

[burdman_22]

Long time no update, can someone help me out with some pics or threads with pics of how the fans are mounted in the VT solar kiln? 

I was thinking that they were mounted I'm sort of a wall that hung down from the top...so that all air was forced forward and down to the front of the stack, but I want to make sure before I have my dad do more work than what's needed

[burdman_22]

Oh, and anyone have advice on what do use for the baffle or whatever hangs below the fans?

[caveman]

We use spring clamps to hold soccer mom tents and tarps in place for our baffles.  There are several good threads on solar kilns here.

Solar dry kiln construction - Page 11 (forestryforum.com)  If you go back to the first page and read through to the end, you will have a lot to consider.

[burdman_22]

Kiln is pretty much done and ready to be loaded now, as far as I know....Quick question on sanitizing. I'm going to be building a hotbox and using a bed bug heater...the one I'm looking had has a thermostat that goes up to 140 degrees, and will kick on everything the kiln temp drops below 135.

I know this isnt optimal, and will look for one with a higher setting on the thermostat, but if I can't, can someone give me a rough idea how long it will take to get a 1x6s internal temperature to 133 degrees if the average temperature in my hot box is 137 degrees??

[burdman_22]

Alright, ill update with some pictures soon, but kiln is loaded with about 1100 bd feet of 1 inch red oak and sycamore that's been air drying for a few years. Red oak was at 16% and sycamore at 19%. Red oak was at about 12% when I checked it a year or so ago, so I guess it's just reabsorption some moisture (it was dead stacked)?

I am getting almost 40 degrees of temperature difference between the outside and inside of my kiln (temperature sensor in the kiln is above the stack, and should be sensing the lower temperatures in the kiln, after passing through the stack already).

What do I need to be looking for in terms of numbers to ensure my kiln is being productive? Temperature gradient between inside and out? Humidity difference between inside and out? A little of both? 

Currently the outside temp is 65.8 and the humidity is 38.2%. Inside the kiln is 101.6 degrees and humidity is 21.2%

We've got a few spots left to fix as far as sealing goes, but are these values decent? Will my wood dry like this?

[teakwood]

those values are awesome. when i built my solar kiln somebody told me that you only need a few degrees more inside than out to dry lumber and that is correct. and airflow of course 

[doc henderson]

great temp differential resulting in a significant drop in RH.  Maybe too much for oak, although air dried you should be good.  You can have a chunk to weigh and see the drop % daily or use a meter.  the result you want is to follow and try not to exceed too much on the dry rate.  You can calculate the end resulting MC from that RH, the EMC.  Prob would be lower than you want.  I assume the results are the peak temp and subsequent RH so it all balances out over 24 hours.  the beauty of a solar kiln.

[caveman]

I've noticed when the humidity is dropping inside the kiln, our wood is getting dry.  We live in a very humid climate though.  I try to open the doors for a few seconds during the hottest part of the day to dump a lot of moisture.  Now that our panels have aged, the kiln does not get as hot, and the differential is usually40 degrees.  It used to be more, but I think it dries better lumber now.  It just may take an extra day or so.

Most of the time we air dry our lumber to close to 20% mc before we put it in the kiln.  A week or so in the kiln, depending on species, thickness and weather is usually enough.  

[burdman_22]

Looks like it is drying. My dad and brother sampled some boards today. The sycamore appears to be at 9% and the red oak at 8%.

Is the wood done now? Or should I get both down to 8%? Or does it need to be lower?

And is there anything wrong with keeping the wood in the kiln AFTER it is finished drying? Just so we don't have to move it immediately? Or do I need to remove it pretty quick once it's dry?

[teakwood]

The difference between 8 and 9% is nothing, i bet you that if you take 20 different measures they all read different. a kiln never dries all board exactly the same. i just go under our EMC and then take the lumber out and within a day they all suck up moister again and have the same moister reading.

I often let lumber sit inside the kiln after drying because i don't have the immediate space in the storage. important is to open the doors of the kiln and shut the kiln off.  

[doc henderson]

I agree.  put the kiln in park and either leave a door open a bit and or cover the glaze some % with a tarp.  What is you MC in the environment the wood will be installed at?  If 7% then sterilizing will drop it all another % or so.  i.e. 8% is fine.  I think oak is denser that sycamore so if measured using the same setting on the meter, the reading of sycamore should be falsely lower given the same MC.  specific gravity (density relative to water) of sycamore is 0.49 and oak ranges from 0.59 to0.68 depending on species.  so at the same species setting on a meter and same MC the oak will read wetter than the sycamore.  SG of water is 1, so solids with a SG higher than 1 sink, and less than 1 floats in water.

[burdman_22]

Not sure what the MC of the environment is exactly, but it's going to be used as flooring in my cabin, so I assume around 8%.

I changed the settings when measuring the moisture content. I took the readings for the red oak with the red oak setting and the sycamore using the white oak setting. The red oak had been cut for several years and the sycamore a year or so less, so the red oak had a little bit of a head start.

My dad is going to try to start a sanitizing cycle in the next day or two, we'll see if we can keep the kiln hot enough. He is building a frame above the stack, and then laying foam insulation on top, two layers thick, with the seams staggered to hopefully prevent most of the leakage. We're using 6 500 watt halogen work lights....we'll see how warm we can get it. Hopefully we won't have to build a dedicated hot box

(Adding on to this....I used the White Oak setting for Sycamore because the jx-30 doesn't have a setting for Sycamore, and when I call Delmhorst about this, they said to use the White Oak setting)

[doc henderson]

should be in the ballpark.  white oak is closer to 0.65 so the sycamore may be wetter than the reading.  On my wagoner pin-less I actually put in 55 for  0.55.  I do not change it and just account in my head the difference.  it is good for many oaks, mulberry, elm ect.  i would change it for species that are way off for that reading.  cottonwood or hedge.

[burdman_22]

Figured I would add some pictures of my sanitizing setup. We've ran about 10 sanitizing cycles through the kiln, and can get to about 165 degrees before we shut it down. Just with the 6 work lights it takes about 6-8 hours to get to 145 degrees, which is when I start the 24 clock.

We've got supports built into the kiln, so that the insulation frame can be removed for drying. When it is time to sanitize we install the 2x6 frame, and lay two layers of foam insulation on top, staggering the seams. Heat is supplied by 6 halogen work lights. temp is monitored inside and outside the stack with two bluetooth/wifi enabled temp sensors. Takes about 30 minutes to change the kiln over from drying mode to sanitizing mode.

There is also an insulated chimney installed on the side...stuffed with fiberglass insulation most of the time, but we use it to jumpstart the sanitizing temps sometimes when it is super cold (otherwise it would take a full day to get up to 145).

The two maple chunks in front of my planer are going to be flattened and planed soon, they're 2 ft wide, so will JUST fit through the planer. The live edge slab is about 3 feet wide, we flattened one side so we could see how it was going to clean up.