Solar Kilns and Wood Sterilizing

Solar kilns don't get hot enough to sterilize wood (for that you should have an artificially heated supplemental chamber).July 7, 2011

Question
Anyone out there operating a WM kiln? I am trying to determine if temperature and MC will be sufficient for black locust sterilization. I believe my goal is 133 degrees F for 30 minutes measured at core of wood. Help! I have no supplementary heat, only solar gain. Kiln is located in Western NC.

This mill is not built yet, so I have no operating data. I am considering partnership with someone who needs to treat wood prior to shipping.

Forum Responses
(Sawing and Drying Forum)
From contributor D:
The WM kiln can sterilize. While that unit is designed to do the drying at around 120F (50C), the temperature can be increased at the end of the drying cycle to as high as 160F (72C). Find out what you need for records to prove that you achieved sterilization. Some will accept your word, but most need some sort of printed record of the cycle and some require third party certification. That affects what control system you need.


From Professor Gene Wengert, forum technical advisor:
I do not believe that a solar heated kiln can get hot enough to sterilize (133 F) wood. I believe that contributor D was referring to the DH kiln they [Nyle] sell, which does need outside power and will do the job.

As he mentioned, almost always you need records to prove that the load went to 133 F and also a certification stamp that is applied to each piece. You might check out the NHLA certification program before you go further.


From the original questioner:

Thanks for info. It brings to light further questions, such as NHLA requirements my potential partner may need. My learning curve for sterilization treatments is very steep at the moment.

I have access to a wood furnace with integrated blower. I intend to set it up to provide supplementary heat to the kiln for drying purposes and hopefully to meet sterilization standards. Some of the USFS pubs regarding sterilization have been very helpful.


From Professor Gene Wengert, forum technical advisor:
The heat losses from a solar kiln are so large that using extra heat is a poor decision. Either use solar or the wood furnace. In your case, an insulated building with the furnace sounds like your best option. In other words, forget solar (even though I do like solar a lot ordinarily).

From contributor D:
Sorry about missing the point about solar before. Using a furnace that has an integrated blower is okay, but you have to seal the furnace off from the chamber when the fire is out, otherwise the furnace becomes cool and the water in the air from the wood starts condensing on the surface and it rusts away really fast. It can get to be a dangerous situation if not done properly. A hot water system is much safer.

From the original questioner:
Thanks for all the input. We will be setting up the kiln for drying and I am optimistic that we can get the temperature and duration required. I guess in the end I have nothing to lose, as the main objective of drying lumber can only be enhanced with supplemental heat (even with heat loss). I have a kiln, stove, and slabs (fuel). Little financial risk at this point. I am going to give it a shot.

From Professor Gene Wengert, forum technical advisor:
Solar for drying is fine, but appreciate that drying time is variable. I strongly encourage you to build a small insulated chamber with the required controls to do sterilization. You will appreciate this approach indeed, and you may even take a few outside orders for sterilization. It will be much easier to get certification as well.
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