Operating Solar Kilns on a Rainy Day

On rainy days, close the vents and switch off the fans. March 16, 2015

I have a small solar kiln built along the lines of the Virginia Tech plan. I've achieved very good results, and tracking daily data has been very informative. I'm down to low teens now in terms of MC, so I've been leaving the out-vents closed. Yesterday I left the fans off due to rain. Understandably (I guess), the MC inched up a tad, about 0.3%. My question is: What to do on a rainy day? Should I close the in-vents and run the fans?

Forum Responses
(Sawing and Drying Forum)
From Contributor B:
Hope you don't mind a response over an answer, because I really don't have a scientific one. I considered a solar kiln, but due to my environmental conditions (I live in NW Oregon) it seemed like a bad idea; in those thoughts I had considered using a home type dehumidifier to finish the charge off on cool or wet times, but decided to go with a Nyle instead because cool and wet is the typical here. So does that make sense in your (or anyone else’s) situation?

From the original questioner:
I'm in the Piedmont section of N. Carolina, so normally I would have good days for a solar kiln even in the winter. The past two days though have been very overcast (and rain yesterday). I'm inexperienced with evaporators, although I understand the principle behind them. However, I do this to produce lumber for personal use only. I do have to limit my excursions into other options in order to have time to use the lumber. The solar kiln that I built is a good overall choice for me, though I can see that others might want to explore more options.

From contributor M:
Vents closed fans off. If your fans are on timers, the VA Tech site suggests using a humidistat to override the fan control on rainy days.

From Contributor H:
Taking it to the extreme you could measure RH% inside the kiln and outside and calculate absolute humidity for both inside and outside. Don't ever vent if absolute humidity outside is higher than inside.