Solar kiln - with solar panel and revised for correct air circulation

First, kudos to Dr. Brian Bond, students, and staff at Virginia Tech (VT) Department of Wood Science and Forest Products for developing a solar kiln and providing the well-written plans at:

http://woodscience.vt.edu/about/extension/vtsolar_kiln/

I, of course, modified the VT plans. The solar kiln is basically a box with a greenhouse roof that generates hot air with a internal solar collector. The hot air is blown through the wood with two (2) fans. A load of wood should take approximately one (1) month to dry.

Revision for correct air circulation:  I had initially installed the fans on the outside of the kiln, blowing cool, outside air into the kiln.  After visiting the sawmill which had two (2) solar kilns and rereading the VT plans, I realized that the fans should be installed inside the kiln to recirculate the heated air within the kiln.  Blowing in cool air would lower the kiln temperature too much and reduce the drying effectiveness.  I constructed and installed an interior baffle with the fans mounted on the baffle and cut holes in the solar collector to allow for recirculation.  It would have been easier to construct the baffle prior to installing the greenhouse roof but live and learn. Refer to Step 9 for baffle installation.

The kiln is also made completely solar with the addition of a photovoltaic solar panel shown in Step 10.

The wood is being dried to build an 18 foot Grand Banks dory which will used to haul picnic supplies and picnic princesses to islands offf the coast of Maine. Google the Maine Island Trail Association to get a sense of the place. Building a kiln before building the boat in order to haul picnic supplies is my typical, over-zealous approach.

Thanks to all who voted for my Instructable in the Green Contest.

List of materials:
Enough wood to build structure - I used a combination of new and salvaged materials so don't have a list; the longer pieces and treated lumber were store bought
plywood - 3/4 inch thick, exterior grade, 2 sheets
Polygal and brackets - 10 ft x 6 ft piece; cut in half
flashing - aluminum
styrofoam insulation - 2 in thick, 2 sheets
Reflectix bubble wrap insulation
DC fans - 2, 16 inch with ring frame
GRK screws - exterior grade; various lengths
paint - green for solar collector
oven thermometer
photovoltaic solar panel - 65 watts

Step 1 Building the base or floor

The first question when building anything is where are you going to position it.  A solar structure needs as much direct sun as possible and your neighbor may not be so keen on you cutting down their trees, even for a "green" project.  I also positioned it uphill and adjacent to our workshop/garage to allow future duct work from the kiln to heat the workshop when not drying wood or other items.  The position is a compromise between these functions.  

The "foundation" is limestone blocks on the uphill side and a treated 4 inch by 6 inch posts on the downhill side.  I set the floor level so that future duct work would intersect the adjacent workshop without hitting any wall supports.

Also my relatives on Fogo Island off the north coast of Newfoundland, had a sport of moving houses.  Refer to the excellent book titled "Tilting - house launching, slide hauling, potato trenching, and other tales from a Newfoundland fishing village" by Robert Mellin for more information on this "sport. "  I constructed the kiln so that it could be moved, if needed.

The next question is size.  The VT plans use a base with dimensions of 160 inch by 78 inch but I reduced the dimensions to 144inches by 48 inches or 12 feet by 4 feet.  I choose these dimensions to reduce building costs and the roof panels have a combined width of 12 feet and a plywood sheet is 4 feet wide.

The base is constructed of 4 inch by 6 inch treated lumber cut to a length of 11 feet 9 inches.  All wood near the ground is treated lumber due to termite issues in our area.  I used 2 inch by 6 inch by 4 feet long treated boards and screwed them the ends of the 11 feet 9 inches timbers to create a 12 foot by 4 foot box.  Measure twice and cut once is the old carpentry policy.  

Within this box, I installed cross-members.  The 2 inch by 6 inch boards are connected with Simpson Strong-Tie connectors using Simpson nails (http://www.strongtie.com/).  It won't be to building code without the Simpson nails.  (A neighbor's contractor had to remove and replace all the wrong nails on a project of theirs; the weight of the structure is borne by these nails.)    I also used leftover 4 inch by 6 inch material and attached with galvanized lag screws.  I counter-sunk the lag screws so that siding could be placed over the screws. 

Comments

[Chocolate Moose]

Could you modify to dry/ fire clay?

[dorybob]

Hello - It may be possible but I think it would depend on the temperatures you need to achieve. 150-170 F are the warmest temperatures I have seen to date with this configuration. Another clay artist described a Japanese firing method where they built a fire at the base of a hill and the clay "oven?" extended up the hill. You may be able to use a solar collector in a similar configuration and use the naturally-rising warm air instead of fans. It would be an interesting experiment. You may also want to contact Dr. Brian Bond at Virginia Tech (VT) Department of Wood Science since they developed the wood kiln design and may know of other designs/examples that would suit your uses better. Good luck and send any info on your build.

[twighahn]

also one cud use solar powerd fans

[twighahn]

wud be good for drying food too

[paintphone]

Was thinking of making something like this for drying painted parts in the colder months
great job

[dorybob]

Good idea. I think the kiln could be used dry anything. PS. I have just ordered a solar panel to run the DC fans and make it completely solar. Good luck on your build.

[weldor]

As they say aboard ship, " belay my last." I found what I needed here at Instructables. Who'd a thunk it?

[dorybob]

Glad you found the information. And in answer to your question, yes, the kiln could be modified to heat other structures. I positioned a side door of the kiln to allow a duct to be constructed to blow heated air into the adjacent workshop, without interfering with any workshop posts or purlins. If I got really fancy, I might blow the air through some concrete blocks to create some thermal mass and direct the air flow at the concrete floor. Many possibilities.

[weldor]

What exactly is a pop can collector? I know I could look it up on line but I would rather hear it from other members of the Instructables family.

I am wondering if this unit could be modded to become part of a heating system for a small shop or maybe even a green house.

[RedneckEngineer]

Cool build! I've seen solar kilns in woodworking mags before but I like the looks of this one better. As I read this I had a thought. Have you ever thought about useing something like the popcan solar heater on this? Depending on the size you could generate more heat and use heat convection to move the air around and maybe not need the fans. Just a thought, but some reworking of the design may be needed for best results.

[dorybob]

You and Bob from Kansas Wind Power are thinking alike. A pop can (or soda can depending on where you live) collector would work well, especially if constructed below and in front of wood box. Refer to my reply to sam D.

I used the metal roofing because it is somewhat easy to remove panels, if needed, and I was able to salvage scrap roofing from a friend's metal roof project.

[sam D]

Gday - great instructbale. I want to build one to dry clothes!
Have you thought of placing a cheap / removable reflector in front of the unit to increase the light capture?
People are doing this for solar panels - a kiln would make sense too. I have put a picture of a concept on my blog - sorry for relinking! http://samdidgaf.blogspot.com/2011/08/solar-concentrator-linear-reflector.html

[dorybob]

Gday also. Interesting idea on the additional reflector. Only my guess but seems like a reflector would work better with photovoltaics than a solar collector. The best answer would be to test with and without.. In a similar vein, Bob at Kansas Wind Power made the suggestion of putting the collector below and in front of the wood container and allow the natural rising of warm air to dry wood and not even use fans.

[graaille]

(removed by author or community request)

[dorybob]

Thanks much for attempting to vote. I submitted late yesterday (8/24) and I guess it takes a day or two to be entered into contest. Vote early and often, as they say in Chicago, once it does get entered. The Instructable kids did put it on the home page which I take as high praise.

[dorybob]

Good question; I did not mention exhaust. Currently, moist air exhausts through one of the side doors. The VT plans call for vents on the lower side of the back doors. I may need to add vents there also.

[russeadie]

Thanks for posting I've been wanting/needing to build a kiln for some time. But I must have missed something, where does the moist air exhaust?

[dorybob]

Thanks for compliment; I put a lot of work into it.

[zazenergy]

That is such a great idea! Thanks for sharing how you built this kiln.