Kiln drying schedules

[Woodslabs]

This maybe a stupid question but why do kiln schedules provide the dry/wet bulb and temps?  Don't you only need dry bulb temp and RH?

[Den Socling]

You can use DB and RH to run a kiln but RH transmitters are more finicky than WB.

[Woodslabs]

is there a simple way to convert dry/wet bulb into RH? I looked at the formula and i havent a clue ;\

[Den Socling]

Yes there are charts available that show DB, WB, RH and EMC. Just about any book on drying has one. Jim Fuller's book has a nice one.

[Woodslabs]

thanks i found a conversion tool.

I came across another question:

When conditioning the wood how do you raise the RH inside the kiln?  I assume you would close all the vents.  Would adding a bucket of water suffice or would you need to add a humidifier? 

[Den Socling]

You can spray steam or use atomizers to spray water. I would use steam if I ran conventional kilns. Atomizers can drop the DB because of evaporation.

[Denny]

"When conditioning the wood how do you raise the RH inside the kiln?"

I have dedicated steam pipe with holes drilled in it that spray steam into the kilns.  I believe they're 3\8 holes and there's about a dozen of em drilled into the pipe. I have a knob on my control panels to turn the steam on or off.  I equalize and condition all my charges with this steam pipe setup.

Iv'e heard that atomizers can be a pain in the butt sometimes. Too large of droplets, condensation on the lumber, clogging, stuff like that.

[Woodslabs]

where does the steam come from?  How to you vaporize the water?

[Den Socling]

With most conventional kilns, you use a steam boiler as the source of heat. There's your steam. "Evaporated" water is "vaporized" water. Same thing.

[Woodslabs]

My kiln will be a solar kiln where every night the wood is conditioned as i understand it.  Do i still have to condition the wood with a high RH before the wood comes out of the kiln?

[Den Socling]

You shouldn't have to. Conventional kilns cause case-hardening. It's pretty much part of the process. At the end, you steam some moisture back into the over-dried shell. Solar kilns are suppose to allow the wood to relax at night with time for moisture to migrate to the dryer shell.

[GeneWengert-WoodDoc]

Den is correct about nighttime stress relief, but this happens only when the RH reaches about 100%.  Solar kilns with DH will not have this treatment.  The stress occurs early in drying, so solar drying or air dried wood does not add stress or Casehardening.  Also, the high RH when air drying also relieves most casehardening stress.  Remember than cutting prongs to check for stress requires NO MOISTURE GRADIENT.  With a gradient, you will indicate stress even if there is none.