Drying Rates and Settings in a Dehumidifier Kiln

How to understand your dehumidifier kiln's capacity and drying rate. December 6, 2012

Question
I am still new in drying lumber and I have a question about setting temperatures. I am drying 4/4 with mc of 25% +/- , and my settings are 125 and 104. The WB is staying at 106 with the compressor running nonstop, and it is losing 1.3% daily. If I raise the dry bulb, will it lose more mc? Or will it not make any difference once the compressor is running?

Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Basically, the DH unit will run and extract more moisture if it is a bit hotter, but I do not think it will change the drying rate that much if it is already running full time. When it begins to cycle, then go for it.



From the original questioner:
OK, so how can I change the drying rate to 1.6%?


From contributor J:
What brand of kiln do you have? I have a Nyle and I set temp at 100 degrees when mc over 25% but less than 35% - cubic air flow of 500--600 cfm. The compressor is set to 85% for white oak in this range of mc. Don't dry it too fast, it will get checks in it and cup.


From the original questioner:
Itís a Nyle, so is 1.3% daily is good enough?


From Gene Wengert, forum technical advisor:
With the compressor running all the time and your RH being still quite high, you are getting the maximum drying possible from your equipment. You need more HP to go faster.


From contributor W:
If the compressor timer is set at 85% then the compressor shuts off every hour for nine minutes. The water on the coil re-evaporates and when it starts again, it has to cool the coil down. All this reduces the effective drying capacity. Set it at 100% which is safe as long as you are sure everything in the kiln is below 20%. You didn't say how much lumber is in the kiln or how old the unit is, but if you check the manual, you can figure out if you are running right.