Solar Lumber Drier - Part 4

[ianab]

The advantage of a solar kiln is that dries in "bursts" each day. Then at night the temp drops and the humidity in the kiln goes up to ~100% for a while. This reconditions the wood and helps remove drying stress etc. So the temp and humidity in the kiln at the hottest part of the day can be too extreme for a regular schedule. But your wood only sees those conditions for ~8 hours, then it gets to relax again. 

The solar kiln dries slower than you can run a conventional kiln, but is more forgiving about the amount of control you need. The temp and humidity will cycle up and down every day, losing a bit of moisture each cycle. 

Winter or cloudy days the drying is much less, but there is still some.

[jteneyck]

The advantage of a solar kiln is that dries in "bursts" each day. Then at night the temp drops and the humidity in the kiln goes up to ~100% for a while. This reconditions the wood and helps remove drying stress etc. So the temp and humidity in the kiln at the hottest part of the day can be too extreme for a regular schedule. But your wood only sees those conditions for ~8 hours, then it gets to relax again. 

The solar kiln dries slower than you can run a conventional kiln, but is more forgiving about the amount of control you need. The temp and humidity will cycle up and down every day, losing a bit of moisture each cycle. 

Winter or cloudy days the drying is much less, but there is still some.

Thanks Ian.  Your explanation is consistent with what I've read.  But does that mean any temp. is OK as long as you don't exceed the max. drying rate/day?  

John

[ajkoontz]

Not at all.  I think I'm around $1800 right now, including the solar panels and fans.  It won't take much more, maybe two gallons of paint.  That's consistent with estimates I read for a couple of designs with 8 x 12' footprints.  I can post a detailed list of costs if you are interested.  

John

Not necessary to itemize costs, I just wanted a ballpark estimate. I've looked at those plans a bit and I'm way early in the process. I'm wondering how this would work as a lumber storage area. It would be nice if it would perform double duty, but I don't think there is any way to 'turn it off'. Have you come across anything about using it to store lumber after it is essentially dry??

[jteneyck]

Not necessary to itemize costs, I just wanted a ballpark estimate. I've looked at those plans a bit and I'm way early in the process. I'm wondering how this would work as a lumber storage area. It would be nice if it would perform double duty, but I don't think there is any way to 'turn it off'. Have you come across anything about using it to store lumber after it is essentially dry??

All said and done I think it's going to cost about $2K.  You could take out $200 for the solar panels and fans if you have 120V power available.  

I'm sure you can use it store lumber in, too, but I haven't seen any protocol on how best to do that.  I would think you would turn off the fans and leave the doors and vents open, as a minimum.  You may need to cover a portion or all of the glazing, too, but I'm not sure.  I'm sure I'll need to store lumber in there at some point, but that's a long way off as I have several stacks of lumber to put in the kiln and more logs to mill.  

John

[ianab]

Thanks Ian.  Your explanation is consistent with what I've read.  But does that mean any temp. is OK as long as you don't exceed the max. drying rate/day?  

John

The kiln sorta self regulates. If the temperature goes up, some water evaporates from the wood, so the humidity in the chamber also goes up. Doesn't really matter how hot it gets, if the humidity gets close to 100%, the wood wont dry any more until you vent some of the moist air. So the control is the vents. Mostly closed they keep the humidity higher, and slow the drying. Open the air vents, fresh outside air comes in, gets warmed by the solar collector (which drops it's RH), blows through the wood and out the vents again. 

So for woods you want to dry fast (like pine) you leave the vents open. If you need to slow the drying (for white oak etc) then you mostly close the vents. Temperature goes up, but so does the humidity. 

At some times the conditions in the kiln might seem extreme compared to a conventional drying schedule, but it's only for a few hours each day. Then the chamber cools off, the humidity goes up to 100% over night, and the wood "relaxes", ready for another burst of drying the next day. 

Dr Gene that worked on the design has an actual Doctorate in wood processing, and he literally helped write the book on wood drying. He's done all the maths and practical experiments to get the VT design correct, and it's designed so you don't need a doctorate to make it work,