Messages

Subject:
more discussion

Bill Tindall, E.Tn.
You are correct in your discussion. I failed to consider that this is how people were using the dehumidifier. (though I now see that this seems to be a reasonable way if one had never dried lumber before).

I presumed one would run a lumber dehumidifier in a home environment by pulling in room air, passing through the unit and exhausting dehumidified air out the back and into the lumber environment, like a commercial dehumidification kiln..........The commercial unit then heats this exhausted air, dropping its relative humidity to near zero and upping the diffusion rate of moisture out of the lumber. I think Keith runs his drying this way, and , it works as expected.

Mine works by pulling in room air, passing the air over a chilled coil to condense moisture and then exhaust freezing cold air to the room, or lumber pile.

This dehumidified exhaust is joined by warm air from the compressor when used to dehumidify a room. The net thermodynamics is to warm the total from work done by the compressor and fan. Indeed if the unit was sealed in the enclosure with the lumber, there would be a small net rise in temperature. But, this mode of operation will never get the net humidity low enough to dry the lumber to 7% MC and the rate will be glacial. I doubt the drying rate from this way of operation would be as great as just blowing ambient air through the pile with fans. Until the lumber gets to around 25% moisture content moving air through the pile at a good clip is the fastest way to dry.

Poplar dries readily. When we air dried poplar in the summer, if there was a breeze through the stacks the exiting air would be cold from evaporation.

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