Dry-Bulb and Wet-Bulb Settings and Kiln Control
From contributor B:
Actually, if the wet bulb was set at 155 degrees, you can't vent until you actually achieve 155. (I am confused by the response above this.) More likely, you didn't have enough moisture in the kiln to reach 155, either because the wood was too dry and there was not enough water in the wood to raise the wb that high, or because you had the spray turned off. If you are trying to KD and HT the pallets, you might need to use the spray. If you're just trying to HT, you might not. Give us a call at SII and we can help, as needed.
From contributor R:
Didn't mean to cause confusion. Contributor B is right - the machine didn't vent, because the conditions in the kiln never reached your WB setpoint. By lowering the setpoint, the kiln would vent moisture. My overall point was that running a kiln schedule with 10 degrees depression for green hardwood, especially when drying defects are not a concern, is more than a little conservative.
From contributor B:
He confirmed for me he is not using the spray, so I don't think he can achieve the wet bulb setpoint that he wants. He's going to try with the spray on automatic to see how it works. The concern is not just drying the pallets out, but quality as well, so too large a depression may adversely affect the quality.
From Professor Gene Wengert, forum technical advisor:
The wet-bulb temperature cannot exceed the temperature of the coldest spot (wall, floor, roof) in the kiln. So, if the spray is adequate, then if there is a poorly insulated spot, that will limit the WB temperature. This cold spot will condense water and essentially act like a dehumidifier at higher WB temperatures. This limiting effect is common in older kilns.
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