solar or dehumidification kiln

Engineer · January 18, 2004, 08:49:54 AM

Do any of you guys have a small solar or dehumidification kiln and can share your experiences with it? I'd like to build one this summer to accompany my sawmill operations, and was looking for some input as to operating experiences, cost of materials, and ease of use.

Larry · January 18, 2004, 10:54:46 AM

Got both types. The solar kiln is very easy to operate, cheap to build, and slow. I dry 3 and if lucky 4 loads a year with it. In your location I would think 2 to maybe 3 loads a year would be max. Hardly any drying is done in the winter. When I first built it, I checked the lumber every day to see how it was drying. After 10 years I only check about 3 times during the cycle and adjust the vents about twice.

My Ebac DH also does a good job a lot faster. I check the water extraction daily along with my moisture samples during the critical period. Increase the compressor run time as the lumber dries. It's got a Freon leak right now but the unit was old when I bought it.

I would make my decision based on how much wood I wanted to dry in a year. You could also think about having somebody custom dry for you.

I would like to build a new solar kiln with three 1,000 BF compartments along with one of the Nyle small DH kilns but that is just a dream right now.

Norm · January 18, 2004, 11:08:58 AM

Larry since you've been running a solar kiln for some time what are some of the things you would do if you were to build a new one. Things like H x W x L. I would like to build one this summer.

We have the Nyle L200. I only use it to finish off what has air dried to around 20% moisture. It has been a good unit, wish I'd built the chamber different. Wider and longer.

shopteacher · January 18, 2004, 12:16:46 PM

I also would like to build a solar kiln this summer. What do you guys think of this idea. I read the solar panel should be directed somewhere between south and west. I'm thinking to build a kiln with either a triangular or semi-round collector so that once the sun is up some part of the collector will be in the direct rays of the sun. I was considering building one that would track the sun as it moved throughout the day, but think this might work almost as well with a lot less mechanics and electrical apparatus. What's your take on this idea?

UNCLEBUCK · January 18, 2004, 05:39:06 PM

I have seen alot of pictures of solar kilns and on some there is no insulation , why is that? I am guessing it must be that the solar kiln is in the southern states why some dont show insulation . I am not waiting another year for dry boards , no way ! sounds like Larry has it down to a science, I took the fan out of the grain dryer bin for airflow , plugged it in and the little thing DanG near knocked me over , suprised me ! hey I finally got to say DanG in a thread, I used it in a good way and always will :D

Carl_B · January 18, 2004, 06:37:37 PM

I have a solar kiln that i built last spring. I have to agree with Larry you will not dry much lumber in the winter I put a batch of lumber in november that was air dryed for four months before going in. It was down to 10 percent today. 60 degrees in the kiln today outside temp was 15 degrees. There has not been a lot of sunshine in the last 2 months and the fans are only on 5 hours a day. From may to november I ran 3 batches of lumber threw the kiln nice lumber with not much labor in watching the kiln. I am real happy with the way that it works. Carl B.

Dave_Fullmer · January 18, 2004, 07:55:10 PM

Jim Birkner at timbergreenforestry.com has some info on the solar kilns he uses. He has lots of good ideas on managing a woodlot also. It's worth checking out.

Dave

UNCLEBUCK · January 18, 2004, 08:49:06 PM

Carl_B , how thick is your walls and is your kiln insulated and if so what with and what kind of exterior sheeting did you use, I was thinking of 3/4 inch chipboard o.s.b. stuff .

mhasel · January 18, 2004, 09:27:04 PM

Dave,

Thanks for the link to Timbergreen, what a great site and a wealth of ideas and management practices. I too am looking for a good kiln design, after the sawmill shed this spring that is going to have to be my second project.

Mike

Norm · January 19, 2004, 04:23:12 AM

Hey Carl I would sure like to hear more about your kiln too. I suppose I could cross the fence and see the Dr's design but what I'd really like is to hear from you folks that have actually built and used one. Stuff like where you'd put the vents how much air speed you think is right and size and dimensions.

Larry · January 19, 2004, 05:31:49 AM

My solar kiln is based on Dr. Genes design. The height, width, and roof angle are all pretty much fixed at least for a 4' wide stack with 25 layers of 4/4 wood. The reason is the ratio of board footage to roof glazing needs to be about 10 to 1 to insure proper drying speed. You can increase the amount of glazing but run the risk of checking hard to dry species like oak with the increased heat. The length can be anything you desire.

I have helped four other people build solar kilns. Two are neighbors that I saw for a couple times a year. Each one is slightly different with improved ideas. Last one went up in October.

From what I have learned I offer the following suggestions in decreasing order of importance.

Easy to load with a machine. Either swinging or sliding doors on the back of the kiln full width with a good seal.

Corrugated translucent or clear fiberglass/vinyl glazing for the outside layer. For the inside glazing don't use plastic sheeting. It has to be replaced every year or two and seems like to me it's always in August when its 160 degrees inside there. Plexiglass would be good. Farm Tek has some attractive greenhouse glazing that might also work.
http://www.farmtek.com/ Can't find the glazing in their on line catalog but its in the printed catalog.

Closed foam insulation is the best as no need to worry about it getting wet from vapor leaks on the inside or leaks on the outside.

I think attic exhaust fans might be the way to go. There meant to operate in high heat. I used a squirrel cage fan out of an old furnace. It has worked well but uses more electricity than the attic fans do. Any other fan seems to quit after a year or two.

Don't build one too big for your needs. One guy I helped, built his to hold 16' long lumber. He is a part time sawyer like me. Never saws 16' long hardwood boards and told me it takes to long for him to fill it up completely.

I am going to build a new solar kiln. It's going to have 3 or 4 separate thousand board foot chambers under the same roof. That way I can dry different species at the same time. The solar kiln also is an excellent place to store lumber after it is dry. Turn off the fans and crack the vents a little and the lumber stays in the 6 to 8% mc range until you're ready to use it.

Unclebuck – Used 3/8" exterior plywood for my sheathing.

Frank_Pender · January 19, 2004, 07:36:59 AM

Engineer, I took a 24' semi refer trailer and reinsolated the walls, installed a hot water heat exchanger and added an Ebac 800 to remove the moisture, very slowly. I have had great success. For my heat source I have installed a Tayulor hotwater furnace. Now, I know I have more than enough heat source, but the idea was to determine if ht e kiln was a viable entinity to develop. I sure is. I have had great success with the unit for the last 5 years. I cvan get the temps in the trailer up to 165* for the last 4 days of the drying cycle to make sure there are no homesteders in the wood fiber being dried.

Norm · January 19, 2004, 08:17:17 AM

Thanks Larry that helps to hear what ideas you have. I sure appreciate it. The door on my kiln is the major design flaw. The way it's built keeps me from changing it. Rather invest the work in new chamber.

Frank how wide and tall is the reefer you converted? Where did you find one? How did you finish off the inside.

I know,.... curious little guy aren't I. :D

Percy · January 19, 2004, 09:00:13 AM

I been kickin the kiln idea around for a while and wonder if this is a dumb idea or not ;D. Up here a solar kiln by itself wouldnt be all that practical, sun angle, not so much sun as Id like, yaddayadda. The greenhouses here sure do get warm though so I was thinkin, if you have a solar kiln right next to your dehumidification/hotwater/whatever kiln and with the boards on carts, just roll them right thru,(The solar kiln pre dries the green stuff while waiting to get into the nasty unit ;D) Would this cut down on the time that youd need the lumber to stay in the non-solar kiln?? Would it be cost effective?? I hope Im makin sense here ;D ;D

Frank_Pender · January 19, 2004, 10:08:08 AM

Yes, Percy, you have a good idea on the pre heating of drying. You would have to watch it closely as not to push tooooo hard on the pre drying or heating, as you might cause more checking than desired. I let all of my hardwoods set at least 30 to 60 days stickered with one inch stickers prior to the kiln.

Norm, as to the trailer I purchased it from a neighbor who wanted to dispose of it for a good price to me. I borrowed a semi dolley from some farmer friends and towed the trailer home with my JD 5300, about a mile. It was fun for sure.
I am sure that you can find them at truckng firms. Some friends that operate a rather large Oak mill have purchased two sea going refer trailers that are all stainless steel inside and out for &3,000 each. They use a wood fired furnace for heating both 42' units with a dehumidification system in each. In my trailer in simple replaced the wall insolation and place paper covered chip board for the new wall covering. Before I did all of that, I wired one wall for several 110 plugs and the heat exchanger.

Carl_B · January 19, 2004, 10:37:23 AM

Check out this post for the info about my kiln. https://forestryforum.com/cgi-bin/board/YaBB.pl?board=sawmill;action=display;num=1057887972;start=0

Norm · January 19, 2004, 12:11:26 PM

Thank you Frank.

Carl I went back and re-read your posts, thanks for pointing it out. Now that you've had it for awhile would you do anything different if you were to build a new one?

karl · January 19, 2004, 04:11:21 PM

I have a Nyle 200 in a 18' reefer box. I am happy with the DH unit- would like to have a building that I could load directly with the fork lift rather than using a cart. I bring the thing to temp with a diesel fired job heater now but will be firing with a wood boiler as soon as I find an economical heat exchanger.
As far as a solar unit - I don't get a bunch of sun here- I'd probably be looking for a market for spalted and denim lumber!

Carl_B · January 19, 2004, 05:35:27 PM

Norm Yes if I were building another solar kiln I would build it bigger. The one that I have now will only hold 8 foot long boards holds around 500 board feet. This works real nice for my use . If you are thinking of selling lumber you want to go longer. When we built the kiln we were using a procut chainsaw mill now we have a LT 15 . In a bigger kiln may want to think about a way to load with a fork lit or loader. one other thing is to air dry for awhile before putting in the kiln will get more batches per year.