Solar Kiln ?

SPD748 · August 01, 2013, 05:40:05 PM

Hello all,

My Dad and I are in the planning stage of a 'Piney/Planman' solar kiln. I think we have most of the basic design stuff ironed out. I do have one question. The polycarbonate panels used for the roof appear to mostly be the very thin stuff sourced from one of the box stores. At $32 ea (24" x 12'), going this route would cost ~$250. A quick online search yielded a greenhouse poly panel which is 8mm thick and double walled. At $124 ea (6' x 10'), going this route would cost ~$372. These prices are for the panels only, no hardware or shipping. My question is; would the double wall 8mm panel perform better than the standard corrugated single wall panel?

-lee

pineywoods · August 01, 2013, 07:29:51 PM

IT depends. You are right about the glazing we used. Thin polycarbonate from the box stores. whether the thicker greenhouse glazing would make any difference depends on whether or not you put a de-humidifier inside. The thicker stuff is designed to hold in heat at night, a desireable feature for greenhouses. Our experience shows that with the dehumidifier it is desireable to have the interior cool down at night, for 2 reasons. The wood seems to stabilize with less checking. Dehumidifiers remove water from the air by cooling it to a temperature below the dew point. When the air is already cool, the efficiency goes up considerably..Heat loss will be offset when the sun comes up by the larger amount of heat generated by the black sheet metal on the bottom of the rafters..in short, the green house glazing may actually degrade performance if used in conjunction with a de-humidifier...

SPD748 · August 01, 2013, 09:15:06 PM

Piney,

We will be running a dehumidifier per your design. In fact, my Dad has already found three working units at various flea markets and such. Given your post here, it looks like we'll be installing the thin, single wall panels. When we get started, I'll post a 'journey' thread!

-lee

Planman1954 · August 01, 2013, 09:34:31 PM

Take lots of progress photos. It will be fun to watch your progress....it makes the effort of documenting my own progress fulfilling! (Oh, and I told ya'll that you could find those dehumidifiers at flea markets for next to nothing!

)

SPD748 · August 03, 2013, 12:10:42 PM

Plan,

I'll definitely take oodles of pictures! Your thread has been the driving force for the next step in my mill project.

I hope this hasn't been answered before somewhere and I just missed it; regarding the fans and dehumidifier, do I leave one or both running 24/7 or does one or both require cycling?

-lee

Planman1954 · August 03, 2013, 06:55:23 PM

When I begin drying a stack, I turn on everything (fans and dehumidifier) and leave it on 24/7 for about 4-5 days, and then check the moisture content. My kiln gets pine to about 12-14% in that time. If I'm using the boards outside, I go ahead and use them and turn everything in the kiln off. If I'm using the stack of lumber inside a building, I'll keep it in and monitor it until it gets down to around 6%. This takes another 4-5 days. Then I'll turn everything off and let it stay in the kiln to stabilize until I use it.

WDH · August 04, 2013, 09:59:01 PM

Have you dried oak?

Planman1954 · August 04, 2013, 10:14:20 PM

No, I have not. I probably will do it in a few years when I can FINALLY get back to furniture making. Right now in my life, I'm continuing to finish all of my personal home/rec room building projects. I use SYP pretty much for everything...framing, lap siding, and soon....interior walls and ceilings. I hope one of these years to document the entire process of my barn build, which turned into a rec. room, music room, apartment conversion! I've taken a lot of photos. But, bottom line, the kiln does a great job.

AnthonyW · December 06, 2013, 02:38:22 PM

In regards to those of you that used the corrugated panels from the box stores for your solar kiln. Did you or how did you seal the wavy panels to the frame of the kiln?

I was looking at all of the pineywoods and planman pictures I could find as well as any others but I am not seeing how the collector panels or clear panels are sealed to the frame. Looking at the planman photos it appears there are huge air leaks around those panels. I know there can't be, but I can't figure where the airflow is directed or how the panel edges are sealed.

Planman1954 · December 06, 2013, 02:57:40 PM

I did not caulk between the top clear panels and the rafters. I could have...I just didn't. The kiln still achieves temps over 180 d. farenheit. I have other rough areas around the doors, etc., where air leaks occur. The floors/walls are sealed well though, and the interior heats well. I went out (into the cold and rain since I'm a dedicated foretryforummmmeerr) and took a closeup photo for you. Remember, you could simply run a bead of silicon caulk at the intersection and get a great seal:

AnthonyW · December 06, 2013, 03:39:28 PM

Thank you PlanMan. That wasn't really necessary.

Since it is not sealed, some hot air may escape at the top of the glazing sheet. My concern about the sealing is two fold. First, I'm in the northeast as compared to Louisiana, so I don't think I can withstand as much heat loss as you. I don't think I will have the solar oomph to recover as quickly or efficiently as you do in the lower lattitude. Secondly, spiders and mice seem to breed like a California wildfire on my property. The kiln might make a tidy home for them. The more I read, the more concerned I am about getting bugs in my lumber while air drying or waiting for use. I'm thinking a small kiln would do the trick, made from lumber from my own mill of course. I have the time to wait. I don't consume lumber quickly nor do I produce it quickly. I am planning to size it based on the output of 4-6 average logs. I would also like to be able to move it around, so I'm thinking a sled shaped base. So the kiln would be on the smaller side.

From the photos on this page https://forestryforum.com/board/index.php/topic,50281.60.html It appears there is a gap between the collector and the walls at the top and bottom. Is that true? Why did you leave the gap?

The fans look to be pointing downward. So the airflow would be down, through the stack from back to front, up across the collector (top and bottom sides of the collector), to the top of the kiln and the top side of the fans and then back down. Does that about sum it up?

MattJ · December 06, 2013, 04:42:23 PM

I saw at home depot they now have a "great stuff" foam rated to keep mice etc from chewing through it. Wonder if that spray if foam in a can would be an option. Didn't read the can but found a link here http://www.homedepot.com/p/GREAT-STUFF-16-oz-Pestblock-Insulating-Foam-Sealant-11034540/203282346#.UqJEjNJDvkU

AnthonyW · December 06, 2013, 05:11:40 PM

Quote from: MattJ on December 06, 2013, 04:42:23 PM
I saw at home depot they now have a "great stuff" foam rated to keep mice etc from chewing through it. Wonder if that spray if foam in a can would be an option. Didn't read the can but found a link here http://www.homedepot.com/p/GREAT-STUFF-16-oz-Pestblock-Insulating-Foam-Sealant-11034540/203282346#.UqJEjNJDvkU

Yes...If you can keep it dry. It is the open cell foam so it will collect water if it gets wet.

pineywoods · December 06, 2013, 05:30:49 PM

Anthony, there is a sort of seal between the wavy panels and the top and bottom walls. The box store had 8 ft pieces of 1x2 sawn out to match the panels. A strip of thin weatherstriping on that seems to seal off ok. If you decide to try sealing as much as possible, be aware that some types of acrylic sealant will attack lexan. Silicone should be ok. Yes, the fans blow downward. This will require a baffle (mine's an old canvas tarp) from the top of the lumber stack up to the fans to force the air through the stack. The gap at the top and bottom of the collector metal allows an entry and exit point for airflow between the collector and glazing. there is a significant amount of airflow up that convective chimney, even without the fans running. I have wondered if that would be enough to dry lumber effectively, never tried it without the fans. Would be an interesting experiment.

AnthonyW · December 06, 2013, 05:39:24 PM

I was aware of those wooden pieces, but was curious as to if they were used or not. From Planman's recent photo, it does not appear they were used in the lower section of his build. Planman?

Thank you for confirming all the information about your designs. It is very appreciated.

Planman1954 · December 06, 2013, 06:37:18 PM

No. I didn't use a seal between the two. That's what the photo indicates above. You can see the 1x4 under the plastic top panels nailed to the rafters into which the panels are screwed into. I believe that you can buy a foam premade strip which matches the contour of the panels as a trim (in lieu of the wood strips.) Anyway, the main thing is to BUILD YOU ONE! 8)

GeneWengert-WoodDoc · December 06, 2013, 06:41:22 PM

Home Depot sells corrugated strips of wood, corrugated on one side and flat on the other, for this purpose at thirty cents a foot...if you do not want to make your own. They are cedar. A little silicon caulk on the wood strip is good for a perfect seal. An overhang for the ends of about 6" is also a good idea. Also, use screws with a rubber washer. Predrill holes in fiberglass to avoid cracking.

scsmith42 · December 06, 2013, 08:44:02 PM

There are also foam strips available that match the corrugations. My solar kiln utilizes them.

thecfarm · December 06, 2013, 09:59:59 PM

I have them foam things on my steel roofing. But with a solar kiln I wonder about the heat over a few years eating that foam up. If I was using caulking up by the roof to seal it,I would almost think high temp would be the way to go or something that was a very high grade of clauking. My wife had greenhouse panels put onto some 2x4's for a small greenhouse. Where the corragated roof touched the 2x4 was all black,like burnt.