What about this technique for a DH kiln?

[kelLOGg]

I try not to get my kiln over ~100°F because I use a home DH which I don't want to fry at more effective higher temps. Suppose I turn off the DH unit, turn on the elec heaters to get the temp up to about 120°F, leave the circulator fans on and then vent. Any ideas for tweaking that schedule?

I currently have a friend's 1.5" RO in the kiln; I put in in at 16.5% MC 4 days ago and it is currently at 15.5%. The pins are inserted 3/4" deep.
Bob

[pineywoods]

We use the home DH units in solar kilns. They don't work very well at temps much over 100 deg, but the heat doesn't seem to bother them. Most of them will have a high temp shutoff that cuts off the compressor and leaves the fan running at much over 100. 150 degrees is fairly common in our kilns. I just leave the fans and DH running 24/7 for the first week or so. The only failure I have seen on the dh units is corroded aluminum coils from the acid in oak lumber...

[Cazzhrdwd]

You could put the unit on the outside and pull air out and return the drier air into the unit.

[woodman58]

I run the same home DH in my kiln. I use a ceramic heater to heat the kiln. Can I get some responces on what type of heater everyone uses with a home DH. Thanks

[GeneWengert-WoodDoc]

The pins should be driven 1/4 of the thickness to get the average MC, which is what we use for drying most of the time.

If you go over 100 F, the motor loses lubrication from the compressor gas and so will wear out.  That is why many have a high temp limit switch.

So, let's assume you have 30% RH in the kiln.  The surface MC will be 6.0% MC.  The core is 15.5%.  The moisture from the core is moving very slowly as you have only a 8.5% MC gradient.  We can speed it up by lowering the humidity in the kiln even more, but often the will only get the surface down to 4% MC, so the gradient from the core to surface is still fairly small.   A dense wood like oak just does not let the moisture flow very fast with such a small gradient.  The other alternative is to boost the heat...at 150 F the moisture will move much faster, but you will have to remove the DH unit.  To be energy efficient at 150 F we need a well insulated building.  With the moisture coming out of the wood, this will keep the humidity in the kiln from getting too low, unless you have a leaky kiln.

Make sense?

[kelLOGg]

Thanks, Gene.
So, the DH unit should be removed even if it is not running if I boost the heat ? After I reach the new high temp I suppose I immediately vent. OK?

Bob

[kelLOGg]

I run the same home DH in my kiln. I use a ceramic heater to heat the kiln. Can I get some responces on what type of heater everyone uses with a home DH. Thanks

I have 2 electric baseboard heaters but I have not used them ... yet, but that is about to change. I think they are 250 watts each. My kiln is about 6 x 6 x 16 with fiber glass insulation all around.

Bob

[GeneWengert-WoodDoc]

It is best, even if the DH is not running, to avoid 150 F.  The heat can damage the seals on many units.

[kelLOGg]

I removed the DH from the kiln and turned on the electric heaters and let the temp climb. It took most of the day to reach 120. Then I vented and put the DH back in. This must have been what was needed because the MC began to fall to ~10% over the next few days. That load being finished, I put the last load in a few weeks ago and now it is done. The 2nd load was around 19% MC when I put it in the kiln and it dried nicely to 9% with no electric heat boost.

[xlogger]

Bob, I order a new DH from amazon last week and it sure works good. It has a one year warranty, so if it last that long I'll be happy. At $200 a year if I had to get one every year and it does what I like that great. This time of year my kiln only gets to around 115°-120°  with low sunshine so I just leave it in. Did you have your kiln when I was down the other year? Ricky