Temperature maximums for dehumidification units

      and that's plenty. 1998.

by Professor Gene Wengert

Q.
Who might I contact to get advice on the construction of a dehumidification unit capable of processing 5-20k bf? I am not clear on the differences between a conventional dehumidification unit and one that is operated in an up to 180F environment.

A.
Because of the gases used in the original DH units (freon 20), the units were restricted to 115 F maximum, which meant that they could not sterilize the lumber and could not set the pitch. Plus drying was perhaps 3x longer than conventional.

When freon 12 was introduced to this industry, then the peak temperatures were about 150 F, which provided for sterilization and some degree of setting the pitch, but not total setting. Drying times were very close to steam kilns. I do not know of any that can go to 180 F and stay on DH operation.

Naturally, you can remove the DH unit and use steam to get from 150 to 180. But why? Nothing wrong with 160 F; in fact the wood is often better--it machines and glues better--if the maximum is 160 F.

I have seen plans and advice that NYLE Corp provides--they are in Bangor, ME.

Keep in mind that the difference between DH and steam is merely the energy source; the wood doesn't know how the heat got to 140 or 150 F or how the RH got to 45%. Therefore, either kiln, if properly operated, will produce the highest quality. (Don't fall into the trap of blaming GM for getting speeding tickets in your new Corvette--the operator determines the quality if you have a good system.)

Have you read "Opportunities for DH Drying" from the Virginia Forest Products Assn (804)737-5625?

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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