How small can you go with solar?

[AnthonyW]

I had originally done a design in sketch-up or a VA tech solar kiln base on my latitude and limited to common lumber lengths. It came out to about 8'x15'x12'. I have been rethinking the plan. I don't cut that much lumber, I'm not sure how movable a kiln that size would be, and if the project was smaller it might actually get finished sometime this decade.

So I pose the question: how small can you make a VA Tech solar kiln and still have it work properly? I thinking a typical stack to dry a stickered stack 3 1/2' wide, 12' long, and 4 feet tall.

[Ianab]

I don't think there would be any specific size limits (big or small).

The thing will be to keep the solar collector in proportion to the volume of wood in the kiln.

So if it's the same length, but 1/2 the width and height, that's 1/4 the wood in there, and you would want 1/4 of the solar collector area. Otherwise you risk getting too much heat in there and damaging the wood. It would be easy enough to replace some of the clear collector panels with roofing iron to reduce the collector area, and it should then work the same.

[Ljohnsaw]

I don't think there would be any specific size limits (big or small).

The thing will be to keep the solar collector in proportion to the volume of wood in the kiln.

So if it's the same length, but 1/2 the width and height, that's 1/4 the wood in there, and you would want 1/4 of the solar collector area. Otherwise you risk getting too much heat in there and damaging the wood. It would be easy enough to replace some of the clear collector panels with roofing iron to reduce the collector area, and it should then work the same.

Interesting math problem.

Ian,
Funny, having NO experience or background in solar kilns, my initial thought was just the opposite.  I was thinking in terms of solar collection area and the area of the insulated walls.  The diminishing collection area would be shrinking faster than the reduction in wall area creating a greater loss of heat.  However, when you figure the volume is shrinking faster than the wall area, it probably balances out.  I think Dr. W. will have the answer! ;)

[GeneWengert-WoodDoc]

You need to maintain the 10 BF per 1 sq ft of solar collector.

In May, we will be building a 350 BF solar kiln as part of a class in Indiana.

The smaller kiln plans were also developed as a reduction in size and published at the univ of Wisconsin.

Basically, any size is fine.

[AnthonyW]

Does anything bad happen if the ratio of BF to sq ft starts to approach 10 bd ft to 1.5 or 2 sq ft of collector?

[cjhertz]

I made a small kiln to test it out.  I make it to fit one stack of 10, 14" by 8' boards.  I make it out of black plastic stapled to 2x4s with a piece of clear corrugated plastic roofing.  Would easily get up to over 130 degrees on an 80 degree day.  Dried the stack from 18% to around 6% in a few weeks.  I had vents and a fan to keep the hot air blowing through the pile.

[GeneWengert-WoodDoc]

the 10:1 ratio assures that green oak will not dry too fast.  With more collector area, you can get too much energy for some species.  however, pine, poplar, ash, soft maple, etc. will enjoy the extra energy, as fast drying is best for those and some others.

The kiln in my picture here is 1/2 scale model of a small kiln.

[AnthonyW]

Gene, Does your half-sized kiln still have all the features of the full sized kiln? I see the vents. I don't see any baffles or fans. Are they needed at that size?

[MattJ]

I made a kiln about the size you are talking and it works well.

https://forestryforum.com/board/index.php/topic,76042.msg1348693.html#msg1348693 

[MattJ]

Sorry, the only thing I would have done different is made the doors on the back to make loading easier.  I might still make that change someday.

Matt

[GeneWengert-WoodDoc]

My half scale model is only 4.5 feet long.  The 9 foot model holds 350 BF or a bit more.

[AnthonyW]

Sorry, the only thing I would have done different is made the doors on the back to make loading easier.  I might still make that change someday.

Matt

I looked through your post. I must agree, the door on the end like that doesn't look like it would work too great. I'm thinking slightly smaller. Two 8ft pieces of the corrugated would be 4ft x 9ft when overlapped and finished. I'm also thinking of a hinged collector (car trunk) and barndoor hinged knee wall.