Fan settings for forced-air shed drying -- Eastern cottonwood
Right now, I'm running constantly and have seen no ring collapse, so I don't see where lower relative humidities (RH) are a real issue. Would I need to establish a maximum RH cut-off point to avoid regaining moisture content (MC) at sunrise, or during rainy weather?
Current airflow is in the 200 foot-per-minute (FPM) range. Location is southern U.S.
The lumber we're putting through these things is mostly 4/4 no. 1 clear and better. (Isn't the lower-grade lumber, cut closer to the heart, more prone to collapse?)
Suggested fan settings would be "off" at RH under 50 percent and at over 92 percent when the wood is wet. As the wood gets drier, set hydrostats to turn the fans off when the RH is over 88 percent. Though there's no bottom RH limit, having the fans shut off under 50 degrees F is smart, since little drying occurs with them running at this temperature and lower, yet you'd continue to incur a substantial electric expense.
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