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Author Topic: Sterilization Experiment in Solar Kiln  (Read 1217 times)

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Online btulloh

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Sterilization Experiment in Solar Kiln
« on: June 04, 2018, 08:42:27 PM »
There has been a lot of discussion here about using a solar kiln for sterilizing lumber and the generally the conclusion has been that it wasn't really possible or practical.  In spite of that, I thought I'd give it a try and see what could be accomplished.

I had some SYP odds and ends (literally) that I'm going to build a sticker house out that added up to about 200-250bf which I put in the kiln and sealed up the openings as best I could.  Today was the first time with any meaningful sun in quite a while, so I closed up the kiln to see how it would go.  We had full sun until around 2pm and then the rest of the afternoon was on and off with cumulus clouds passing.

Since I have the data logger in the kiln (which I have yet to use on a load of lumber), I collected the results until this evening and it looks pretty interesting to me.

Some notes:

- I made a sample from a piece of SYP that was 5/4 x 6 x 16 and drilled a 3" deep hole in one end and put in a thermocouple and wired this to the logger.  The hole was plugged with fiberglass insulation after the sensor was inserted. I put this in the middle of the stack.

- The lumber was mostly 1x6 SYP with an average MC around 18%

- I put in a separate stack of stickers (20 or so) that were rain-soaked from a couple days ago (to raise the humidity)

- The doors were closed about 11:00 am and the fans were turned on when the collector temp hit 110F.


The sample temperature at the core reached 140 and maintained that for about an hour.  


(The chart is not very useful at this reduced size but . . .)

Here's some of the data from the hot period:
TimeAmb TempFAmbient rHCllctrTempFStack Temp FClltr rHStack rHSmplTmp

(The far right column is the core temp or the sample.)

So  - - - even without a perfect day, and without all of the collector panels in place inside the kiln, the sample seemed to get the 140F mark and maintained that for an hour or so.  Comments?

Offline pineywoods

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Re: Sterilization Experiment in Solar Kiln
« Reply #1 on: June 04, 2018, 08:53:44 PM »
I have documented via a chart recorder, 180 + degrees in my solar kiln. I have no doubt it will go even hotter. How long it will hold those temps depends mostly on the amount of lumber inside. A large stack of lumber will store more heat than you would think...
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
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Offline YellowHammer

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Re: Sterilization Experiment in Solar Kiln
« Reply #2 on: June 04, 2018, 11:21:01 PM »
That's very intersting data.  When is your next oak load?  
It would be intersting to see the max temp and gradient slope on a capacity oak load, where the wood acts as a thermal ballast, slowing the thermal cycle time.

I know under certain circumstances my solar kiln won't seterilize, as in yesterday I pulled a load of walnut and there were ants in the wood and on the kiln floor, moving about.  
Please keep publishing your data.

Take steps to save steps.

If it wont roll, its not a log; its still a piece of tree.  Sawmills cut logs, not pieces of trees.

Kiln drying wood: When the cookies are burned, theyre burned, and you cant fix them.  Dont burn the cookies.

Online Southside

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Re: Sterilization Experiment in Solar Kiln
« Reply #3 on: June 04, 2018, 11:26:23 PM »
What are you using for a data logger?
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Online btulloh

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Re: Sterilization Experiment in Solar Kiln
« Reply #4 on: June 05, 2018, 07:14:31 AM »
I made a logging system back in January. It was covered here:

Kiln temp and humidity logger using the Raspberry Pi platform in Drying and Processing

YH:  I need to run some WO but it's not sawed yet.  I have not been able to get any sawing done due to schedule overload.  Every week, I plan to saw next week, but so far next week never pans out.

I want to try a load of WO right off the saw.  What's your though on that?  The main reason to do this is to retard the early drying issues.  I also want to try a load of SYP right off the saw, mainly to control mold.  I don't have a good place to run fans on a stack of lumber and I thought I'd try using the kiln to get around that.  ??

(Attaching a .ods file with the data and chart.)


Offline GeneWengert-WoodDoc

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Re: Sterilization Experiment in Solar Kiln
« Reply #5 on: June 05, 2018, 02:39:15 PM »
A solar kiln (VT plans with two layers of clear roof and insulated walls and floor) that is not doing any drying (drying uses energy) will get very enough to melt plastic fans.

The VT solar kiln was designed to dry 4/4 oak at a safe rate, starting with green lumber.  It may take 45 days.  For this reason, air drying, especially if under a roof with no walls, is suggested so that the solar kiln can dry more loads per year.

When syp is in the solar kiln, green, the rapid release of moisture means you need high venting, which means there is little benefit from solar.  You could run the kiln 1/3 full with green syp and do fairly well.  In fact, a fan shed is better for syp and similar fast drying species.  The solar kiln then can be used with a full load of lumber that has MCs under 20% MC to quickly achieve lower MCs...or to sterilize.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Online btulloh

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Re: Sterilization Experiment in Solar Kiln
« Reply #6 on: June 06, 2018, 04:33:55 PM »
Right you are Gene.

Some of us doing this for non-commercial purposes just need to make do with what we have.

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