Night-time Reconditioning in Solar Kiln Operation

      The nightly humidity increase in a solar kiln is not harmful to the drying lumber, but helps to relieve stress. December 31, 2013

Question
WOODWEB Member:
According to all I've read about the VT designed solar kiln, when it cools down at night and the RH rises, it effectively conditions the lumber and relieves stress introduced during the day.

I read recently from a supposedly knowledgeable source (formerly with the Forest Products Lab) that the RH humidity increase at night was not only an unintended consequence of the design, but was in fact detrimental to the lumber, since re-wetting the boards would lead to surface checks and worse.

My response was that "re-wetting" was not the correct terminology for the absorption of water vapor, but I'd like some additional information on the subject. Dr. Wengert, if you read this, please respond with clarification on the nighttime conditioning issue with a solar kiln. Does it degrade the lumber or not?

Forum Responses
From Professor Gene Wengert, forum technical advisor:
The high RH is indeed a good thing. The info from the other source is incorrect regarding rewetting and damage in a solar kiln. The slow increase is safe.



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