Control Issues in a Dehumidifier Kiln

      If you run the kiln too hot, a safety cutoff may shut down your compressor, interfering with the drying process. April 27, 2007

I have a Nyle 200 and am drying 5/4 cherry for a customer. I'm having problems getting the lumber down to around 6%. The wood is at 9 to 10 percent and that is as low as it will go. No more water is coming out of the compressor. My dry bulb temp is around 135. I'm afraid to go higher, causing damage to the compressor. If I can go higher, how high? Also, can I get the wood down to around 6% by increasing temp and shutting off the compressor?

Forum Responses
(Sawing and Drying Forum)
From contributor M:
The Nyle 200 is made to operate at 80-120 degrees. When you have the temperature set above 130 (or below 75), the system has pressure safety switches which protect the compressor from damage (see your manual). The compressor will not remove water from the wood under these conditions. If you have a wet/dry bulb thermometer, you want to target a dry bulb temperature of 120 and a wet bulb temp of 85, which will give a equilibrium moisture content of 3.7, which is the correct drying rate for cherry wood which is at 15% moisture content or less. The compressor run time determines the dry bulb/wet bulb differential. (More compressor time = greater differential). Be aware that pin type moisture meters must be corrected for temperature. Shutting the compressor off and elevating the temperature is essentially what you are currently doing.

From contributor B:
A good way to check your drying conditions, once you take the above advice and lower the temp below 120, is the small $19.95 rh meter at Radio Shack. It will tell you the rh and temp in the kiln, with which you can then find the EMC in the Nyle manual. The "Drying Hardwood Lumber" manual is a good resource also, but the published temps are mostly for conventional kilns and must be adapted to the dh kiln using the rh meter.

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