BIG PROBLEM --- DH4000 Drying too fast.

[DR Buck]

The last two loads through my kiln caused me some concern with a fast drying rate.   One load was 8/4 white oak and the other was 5/4 walnut.  In both cases the wood was cut green just a few weeks before going in the kiln and the measured mc was above 35%.   I typically follow the schedule Nyle has in the owners manual, which is based on RH and not wet bulb.   In the last 6 or 7 years I've never had a problem like this before.

I normally start out with temp set to 90º and RH to 80-85%.  Neither load was I able to get RH over 40% and it kept going lower regardless of the temperature setting.   The white oak ended up checked and split and down to 8% mc  in 3 weeks without ever raising the set temperature above 90º.   Temperature readings were as set and remained constant unless I changed it.  There has not been any changes in the physical condition of the kiln box and I can't find any air leaks. 

What's going on?  Could the compressor be cycling on too often, or staying on all the time?   Could the moisture probe be faulty?  Could  I have a bad Partlow controller?  I guess I can measure current and watch to see when and how long the compressor cycles, but is there a way to test the probe or controller?

[Den Socling]

Partlows are pretty reliable. And, when they do fail, it's rarely "almost". It's apparent. Are you using a 7000 or 1160? RH sensors are not reliable. However, since your wood was destroyed, it wasn't done by an artificially low reading. Did the temperature stay down at 90'? Does your system vent when the temperature is too high?
Maybe the kiln was venting because the compressor was running too much. The only thing I can think of that could cause that is a sticking starter. I never saw one but that doesn't mean it's not possible. Sticking relays aren't that rare.

[DR Buck]

Den

The controllers are Partlow 1160 series and they both seem to be outwardly OK.  One is for temp and the other is for RH.   THe kiln maintains the set temperature OK, just the RH never seems to rise to where it should.  I have an over-temp vent fan that functions off it's own temp sensor and it indicates the same inside the kiln temperature as the Partlow.    I'm thinking the dehumidifier unit is not properly cycling.   I just need to figure out how to test it.

[Den Socling]

Control is pretty simple. There is a little relay in the 1160. When the controller calls for DH, the relay closes and sends power to the starter for the DH unit. There may be a switch and/or fuse in there but nothing more complicated. If you set the RH 1160 under the sensor reading, the DH should kick in and stay on. If the setpoint is above the reading, the unit should shut off and stay off. When we have built DH controllers, we had ON/OFF/AUTO switches. If I were you and you have such switches, I would turn the OVERTEMP to OFF. Also, if you have such a switch for RH, trouble shooting is a snap.

[DR Buck]

Control is pretty simple. There is a little relay in the 1160. When the controller calls for DH, the relay closes and sends power to the starter for the DH unit. There may be a switch and/or fuse in there but nothing more complicated. If you set the RH 1160 under the sensor reading, the DH should kick in and stay on. If the setpoint is above the reading, the unit should shut off and stay off. When we have built DH controllers, we had ON/OFF/AUTO switches. If I were you and you have such switches, I would turn the OVERTEMP to OFF. Also, if you have such a switch for RH, trouble shooting is a snap.

Thanks -  I'll have to check it out when I get some free time.  My day job is interfering again.   :D     The over temp is totally independent of the controllers.  It uses a Honeywell  controller that is triggered by the temp probe and turns the venting fan on or off.

[GeneWengert-WoodDoc]

If your 8/4 white was 35% MC after a couple of weeks, that is when it checked and that is when it dried too fast.  We would expect it to lose 1% MC a day in the best drying conditions.  Also, all checking begins above 45% MC for white oak.

So, if you did not run the compressor, what would happen to the RH?  And to the temperature.  If the RH would not go above 40% RH and the wood was drying, where was the moisture from the wood going?  Why didn't the moisture being evaporated raise the RH?  Either you have a big leak to the outside or the compressor was running.

[DR Buck]

If your 8/4 white was 35% MC after a couple of weeks, that is when it checked and that is when it dried too fast.  We would expect it to lose 1% MC a day in the best drying conditions.  Also, all checking begins above 45% MC for white oak.

So, if you did not run the compressor, what would happen to the RH?  And to the temperature.  If the RH would not go above 40% RH and the wood was drying, where was the moisture from the wood going?  Why didn't the moisture being evaporated raise the RH?  Either you have a big leak to the outside or the compressor was running.

If the compressor was running, the temperature of the kiln should also go up.  It did not.   It stayed at 90º.    This is beginning to hurt my head.     :

[OneWithWood]

Dave, take a close look at the kiln chamber.  I had a similar experience and found upon close inspection that one of the plywood sheets had popped out opening a seam.  Reset and recaulked it and all was good again.

[GeneWengert-WoodDoc]

If the compressor is running, the kiln temperature may not go up as the small amount of heat from the compressor could be lost through the walls.

White oak checks above 45% MC.  All honeycomb is a check first that got worse.  Once you are down to 35% MC, the risk of checking is zero; the risk of honeycomb without already having checks is zero at your conditions.