Solar kiln build.

[Jimmy in NC]

So it looks like the site is stable again....any pictures or tips on building a solar kiln. I realize I'm going to have to do something with all of this wood I'm starting to mill and dried is much more marketable. All of the old threads are all messed up...

 

[GrantD]

These are the plans I'm using to build mine this spring...

http://forestandwildlifeecology.wisc.edu/sites/default/files/pdfs/publications/98.pdf

It seems simple enough, and I hope it can dry efficiently/effectively enough so I can use some wood by the end of summer.


Sent from my iPhone using Tapatalk

 

[jrhannum]

My designing mind...
has gotten this far; any negatives?

 

[VA-Sawyer]

It isn't about moving the air out of the kiln. It is about moving the air through the stack of wood. You want all the boards in the stack at the same point in the drying process at the same time. If the air passing through the stack is too dry, it will cause checking. You need baffles to direct the air through the stack and back to the solar collector for reheating. Only a small amount of air should be vented to the outside.
You can download some very good information on kilns from the Forest Products Laboratory website.

 

[VA-Sawyer]

I built and operated a 17' solar kiln in VA for 5 years. Had to leave it behind when I moved to NC. I learned a lot about drying wood from that experience. My next solar kiln will be a better design that deals with issues from my first kiln.

 

[kimosawboy]

Keep in mind the location...I dont mean just location for the best sun. You are probably going to want to sticker and air dry wood before it goes in the kiln, Is that close to where your kiln is or where you are milling?? After you have dry wood, where are you going to store it???
Just so you dont have to move your wood too many times over unnecessary distances, its something to keep in mind.
G Vavra

 

[VA-Sawyer]

http://www.treesearch.fs.fed.us/search.php?in_words_phrases=kiln drying&in_author=&in_title=&filterByDate=&in_pub_year_start=2004&in_pub_year_end=2014

Try this link. Lot of good information about kiln drying.

I don't suggest you air dry and then kiln dry a wood stack. You will have higher losses due to degrade. It is better if the wood can go straight from the mill to the kiln.

 

[Jimmy in NC]

Lots of good reading there.

 

[VA-Sawyer]

"Drying Hardwood Lumber" is excellent. I'm not a fan of Dr Wengert, but that book is well worth studying. Another good one is 'Kiln Operators Handbook'.

 

[rwthom279]

My next solar kiln will be a better design that deals with issues from my first kiln.

Would you mind sharing the issues from your first one??

Lots of good information to read about, but there seems to be little feedback on the long-term short coming's of the various designs. opcorn:

 

[Greenland South]

Here is some usefull info. http://www.solarkilninfo.com

 

[Dave Boyt]

Every time this subject comes up, there is more information, which is fantastic. My initial reaction is that with stickers and room for vents & baffles, you will get, at most, 100 board feet into the kiln. Even a kiln this small will need at least 1/2 h.p.-- or 500 Watts to circulate air through the stack. That's roughly 10 times the output of the photovoltaic system you propose-- and that's with it facing directly at the sun, about 3 hours at best. I've been trying to come up with a practical way of moving air through the stacks, but everything leads back to conventional electricity as the most cost effective. Heat, however is at least 80% of the energy requirement, so if you can just do that with solar, you've achieved a lot! Keep us posted on your progress.

 

[VA-Sawyer]

Would you mind sharing the issues from your first one?

Lots of good information to read about, but there seems to be little feedback on the long-term short coming's of the various designs. opcorn:

My first solar kiln was about 18'X 10' on the outside and designed to be loaded from the end. I could get about 2000 bd-ft in a full load. I had two attic vent fans mounted in the floor of the collector and blowing down into the rear plenum. I used clear corrugated roof panels ( lexan, IIRC) on the collector and front wall.
Framing was 2x3 SYP for the lower section, and 2x2 for the collector. The rear wall was 2X3 all the way up. The outside was covered in UV resistant black plastic, and the inside had a few metal diagonal braces with 1/2" foil covered insulation. I had two layers of insulation in the lower section. I used driveway paint to cover the inside of the collector and lower section.
The number one change I would make..... load it from the rear! Or set up tracks, so the whole stack can be rolled in. The Bobcat is useless on an end loading kiln.
The first kiln was a concept test, so was built light and cheap. Next kiln will have something more durable on the outside.
When the stack was in place, I had no access to the front inside of the kiln.
I could access the collector by climbing on top of the stack and going up through a trap door.
I had no panel to vent the collector. Any work done inside the collector had to be done on cold mornings or with the lower section open and fans running. Not good if half way through a load.
If you intend to dry Oak, use Stainless Steel nails, screws, hinges ....everything!
The air at the top of the collector would exceed 200 degrees F if the fans were off. I had concerns about some of the materials lighting off.

The biggest plus from the first kiln was the clear roof panels on the front wall. The warm wet air coming from the stack would condense on the inside of those panels. I just let the water drain to outside. By adjusting how much of the air flowed against the panels vs. up the false wall to the collector, I could control humidity without venting warm air.

 

[rwthom279]

I used driveway paint to cover the inside of the collector and lower section.

1) The number one change I would make..... load it from the rear!

2) ....use Stainless Steel nails, screws, hinges ....everything!

3) The air at the top of the collector would exceed 200 degrees F if the fans were off. I had concerns about some of the materials lighting off.

4) The biggest plus from the first kiln was the clear roof panels on the front wall. The warm wet air coming from the stack would condense on the inside of those panels. I just let the water drain to outside. By adjusting how much of the air flowed against the panels vs. up the false wall to the collector, I could control humidity without venting warm air.

1) I agree on loading from the rear. With or without support equipment. Gotta be easier on the back.

2) Stainless is great for anything involving moisture!!

3) That is impressive to reach those temps. I understand there are a lot of factors affecting this question, but: Do you recall what temps you averaged w/ the fans running??

4) That's an interesting development. I assume the panels were not sealed/weather-striped at the bottom of the corrugations?? No need for a de-humidifier then??

Thanks for the great information/feedback....

 

[VA-Sawyer]

1. The problem was having 16+ feet of unsupported span when the back was open.

2. Oak moisture is very acidic! I was aware of that, but didn't realize how bad it was. The fans had to be replaced every 18 to 24 months.

3. Early in the cycle the air is at close to 100% RH. Temps would run 90 to 100 degrees F during the day. At the end of the drying cycle, temps would run 115 to 120 degrees F. I would adjust the amount of reflector in the collector to keep the temps under control. Hot wood is weak wood, and checks or splits pretty easy. I could not get the temps high enough, long enough, at the end of the cycle to 'sterilize' the wood. If the customer wanted that, I had to add heat with a space heater.

4. I had the shaped foam seal installed when I built the kiln. Water would puddle on front floor, so I removed the seal. Modified the front false wall to control how much air flowed against the front panel. The kiln was ventless.

 

[VTWoodChucker]

Has anyone built a solar kiln for drying firewood? What are the issues with doing this?

 

[windthrown]

Has anyone built a solar kiln for drying firewood? What are the issues with doing this?

Yes, I built a cheap one on a 1/2 PVC frame with 4 mil plastic. It was based on this design by OSU:

http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/27963/EC1389.pdf?sequence=1

I designed it to cover my several wood stacks on pallets in rotation, meaning it was light enough to move from wood stack to wood stack. The snow loading destroyed it the first winter though, and I have not rebuilt it. UV is also hard on plastic, so it turns to corn flakes in sunlight. They also blow around in wind storms. You have to get the good nursery greenhouse UV resistant plastic, or re-cover it in plastic it every year. You can also use something like a plastic 'garage' that they sell online, or a hoop structure greenhouse. They all do a good job capturing heat and keeping the wood dry.

 

[groundup]

Yes, I built a cheap one on a 1/2 PVC frame with 4 mil plastic. It was based on this design by OSU:

http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/27963/EC1389.pdf?sequence=1

How effective was it at drying lumber?

 

[windthrown]

I did not dry lumber in it, just firewood. It actually did a good job. I think half of it was just keeping the rain off of it in this climate, as well as keeping condensation off on cold nights. The air in there was noticeably warmer than the outside air, even on overcast days. Having the wood up on pallets is key. The pallet space allows cooler air to flow up under the stacked wood by convection, causing a draft. The combination of solar heat and air convection helps drive out the moisture. You need well spaced planks on the pallets as well. I had one stack of wood on tightly planked pallets two years ago and the bottom wood was not nearly as dry as the other stacks. I also found that having a plastic ground cloth is critical to keep ground water from wicking up from the dirt.

 

[windthrown]

BTW, pretty much everything you want to know about drying hardwood lumber is in here from Cornell University:

http://usda.mannlib.cornell.edu/usda/nass/general/ah/ah528.pdf