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Author Topic: Building a solar kiln in FL  (Read 367 times)

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Offline relicshunter

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Building a solar kiln in FL
« on: September 03, 2019, 01:12:29 PM »
Hi all I am happy to find this forum and I am trying to search before posting questions. I have not seen enough on this so here goes my first question. I am building a 4x10' kiln in Florida, and it seems like I may have to be more concerned with too much heat then not enough. Maybe not but I want to be sure. I've scrounged a lot of the building materials, so my outer walls are hardy board/concrete board so they seem to be building up and holding heat more then wood would. Was this a bad idea?
 I have 2"foam insulation in the walls and floor with an inner wall of counter top formica ( strange but free and water proof)
I was planning on clear polycarbonite panels for the roof. 
I searched for if should use clear or opaque for the roof and got answers all over the place. I will go with clear unless someone jumps in and says opaque.
Should I double pane the roof? 
It is small I know but it is mainly to finish the drying of air dried wood that I can get from many small mills in the area. I want to be sure that the wood is totally dry and ready for indoor furniture making and to kill all bugs that may be in the wood. Florida is so humid but most people air condition the heck out of their homes. Don't want wood movement to kill my reputation when I am just getting started. I will be running green wood through it at time since I have to jump on choice wood at times and buy a clump of fresh cut. 
Any do's and don't for Florida heat please pass along.

Offline mredden

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Re: Building a solar kiln in FL
« Reply #1 on: September 04, 2019, 10:43:12 AM »


Noob here who has yet to start solar drying. :embarassed:

Interesting question that I will follow closely since I live in hot/humid South Georgia. Hopefully Gene will provide the real answers, but my initial thoughts are that it will not get "too hot". I have quite a bit of milled hardwood that is now down below 20% mc. I treated it with borax soon after milling, but want to be doubly sure by heat sterilizing it because powder post beetles are a problem in the area and like pecan wood that is the largest percentage of my lumber/slabs.

My thoughts (which may be quite wrong):
(1) the temp has to be quite hot to sterilize the wood as you intend to do - say 135+ maintained until the core reaches that point. Probably, most people apparently try to maintain 150. I don't think the average passive solar kiln reaches that temp except maybe at "straight up noon. However, your Florida attic under black shingles runs about 140-150 degrees. So, I think you can get to the sterilization point.

(2) what is "too hot?" Some kiln operators go up to 190 for hardwoods and are capable of going higher. From what I gather, most try to run about 175 during the sterilization process. This is hearsay for which I have no actual knowledge. However, I doubt your solar kiln will reach 175 - even in Florida and I don't think it will maintain that temp 24 hours a day. Possibly very wrong here.

(3) I assume you will be using mainly hardwoods so that does make me worry a bit about movement if too hot - too fast. However, you are starting with air dried lumber. If it is air dried to roughly emc, I don't think you can dry it too fast using passive solar. Proper stickering and top weight would seem to be the key.

My plan is to air dry hardwoods (pecan and oak) down to about 20 percent (when I think pp beetles become attracted to the wood), then solar dry (slowly) down to around 7 percent.   Once I reach the desired 7 percent, I think I can get to the sterilization point but may need to add a heat source for about 36 hours to reach and maintain the sterilization point.  This will require constant monitoring. My (only-occasionally-heated-in-Winter) Shop storage after that will probably raise it back up because the EMC around here runs around 13-14 percent.  I will store smaller pieces in the attic after sterilization. Hopefully I can keep it below ten percent while storing.

Now, Gene has a lot of my stupid ideas to snuff. stupid_smiley

Offline btulloh

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Re: Building a solar kiln in FL
« Reply #2 on: September 04, 2019, 10:48:13 AM »
I don't think too hot will be a problem.  You can over-dry a load of lumber if you let it stay in too long.  Just don't do that.  ;D
HM126

Offline relicshunter

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Re: Building a solar kiln in FL
« Reply #3 on: September 05, 2019, 07:35:41 AM »
So it sounds like the general conciseness is that it will not be too hot. The main use will be to finish air dried lumber that I can get locally, kill the bugs and get the woods to the proper % for quality furniture building that will last. It will be all hardwoods.
Any thoughts on single or double pane for the roof? I figure it will lose less heat during the night with double. I'll be working on that this weekend hopefully. 

Offline btulloh

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Re: Building a solar kiln in FL
« Reply #4 on: September 05, 2019, 08:42:25 AM »
Double for sure.
HM126

Offline relicshunter

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Re: Building a solar kiln in FL
« Reply #5 on: September 06, 2019, 09:58:01 AM »
Thanks all for the input. I hope I can get it done this weekend since it looks like a dry one.


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