collector orientation 40° East

[BClean]

Hallo everybody,

I registered after long time reading only. I find this is a great forum which combines lots of sophisticated knowledge to a gentle, harmonious style, which encouraged me, despite my poor english, to register an try to get active. Please accept my apologies for my broken english, I hope we will understand eachother though.

I am 60 years old and living in Germany close to Ramstein Airbase, an area surrounded by forest. I have access to wonderfull oak trees and found it regrettable to cut them down for firewood. With my brother in law, who is a carpenter, I came up with the idea, to quartersaw the best trees using my Granberg Mark III and Husqi 3120 XP, dry them and build doors for old houses as well as furniture and floors for my own home.

Now here is my question. We need to have perfectly dimensioned, finally prozessed pieces 68 mm thick, 145 mm wide and 2150 mm long dried down to MC of 10 to 12 %. Regardless of many hours reading your forum and other sources, I was not able to find a formula by which I can calculate the dimension of the solar collector needed to safely dry green oak  of 3 3/8 ". I guess, the respective function is exponentiell, but I am not sure. So I need to know the formula by which I can scale down the 1 sqf collector needed for 10 bdf of timber, which is relevant for 1" thick boards of oak. Mine will be around 3 3/8" green in order to finally get dried and readily processed pieces of 68 mm thickness.

Next problem is the orientation of my place, which allows for a solar kiln with 40° east orientation at the best. This could be advantageous as the timber I want to dry is rather thick, so less solar radiation doesn´t mean poor performance in this case. But how do I get the two variables to fit together?  Will the - 40° orientation be sufficient or would it be wise to consider a smaller collector additionally? If so, how much do I need to reduce the solar collector?

We are located at 49° north, lots of wet conditions. Time is not an issue as it should remain a hobby. I only want to make sure, that I safely avoid the production of quartersawn firewood  8).

By the way, the VT design of a solar kiln and solar kilns in general are almost unknown here in Germany, which I find remarkable as well as regrettable in terms of protection of the environment. Wood drying equipment here is complicated and expensive and not accessible for the hobbyist and small business. This is why I am hoping to get good advice here and with a little bit of luck even from the pope of wood drying Gene Wengert  ;) as to how I can build my VT solar kiln best.

Regards Bernhard

[beenthere]

Bernhard
Welcome to the Forestry Forum.

Your command of english is great, no need to apologize.

Drying thick oak is a tough assignment but hope someone will offer a schedule and a plan that might work for you.  Often it is a 'trial and error' game to finally arrive at a schedule that works for your dry kiln conditions and equipment.

[BClean]

Thanks for the compliment and the welcome as well.

Reflecting experience made with photovotaik generators on roofs the orientation -40° could count for roughly -15 % in terms of performance...estimated. I assume this alone will be nowhere near the safe drying rate at least until the saturation MC of 30 % is reached. I would prefer not seeing 1000bdf of quartersawn oak going down the drain due to try and error procedures, which in my case are usually following Murphy´s law ;-).

I really wonder if there is an algorithm which takes into account the orientation in combination with the thickness of the timber and its MC over various phases of the drying process. If not, it must be trial and error, which leads to the idea of building a modular solar kiln which you can build small in little sections or bigger by linking other identical sections to them.

Regards Bernhard

[beenthere]

Commendable ideas and thoughts. Maybe the drying guru's will chime in and maybe there is such an algorithm..  I also think there are some scientists who get into the real basics of the physics in drying on a nano scale.  Converting to the thick oak is a giant leap for mankind, so to speak.

[Ianab]

I don't think the East orientation has any effect does it? You aim the collector to the South, and slope it depending on your North latitude. So base your roof slope on the 49° location.

The cloudy weather will slow drying of course, but that may be a good thing with thicker Oak?

[BClean]

I cannot aim the collector exactly to the south due to the given structural situation. The maximum of southern orientation will be -40°, which should indeed result in a minor performance as compare to an exact 180° orientation. I estimate this minus in terms of performance to be around 15 %. I am concerned these 15% will not be enough to meet the safe drying rate for 3 3/8 oak timber as the VT design meets the needs for 1" thick oak.

I have no idea as to the appropriate size of a collector with a 140° orientation for 3 3/8 oak. The cloudy conditions should support a slow drying process but I still fear that even under cloudy conditions the solar collector needs to be much smaller as the original VT design for 1000bdf.

Regards Bernhard

[GeneWengert-WoodDoc]

You will get the maximum amount fof solar energy if you orient the kiln to the due south (within 5 degrees).

To slow down the drying, you can cover the collector or even paint it black.  Maybe next year you will dry 1" material and so the south direction would be desired.  Compared to the 1:10 ratio (square feet to board footage) for 4/4, you will want to reduce the area by 4.4 for 12/4.  Further, 12/4 will take 4.4 times longer than 4/4.  Now 4/4 might take 6 weeks with good weather.  So, that means 12/4 would take 6 months of good weather, but you do not have warm weather for six months and the sun angles get quite low, so I suspect you might be looking at a drying time of close to a year for 12/4 oak.  As you likely appreciate, this long time is required to prevent checks and honeycomb...in any kiln, if we had more heat or drier air or more air flow, the 12/4 oak cannot handle this faster drying and maintain the quality we want.  A conventional hot air kiln could possible dry 12/4 in 5 months if the wood is really good quality.

For this reason, 12/4 oak would almost always be air dried slowly for 6 to 9 months or more, prior to entering the kiln...a shed (roof and open walls) would be best.  Even so, very few operations even try to dry 12/4 in the U.S., as quality losses are common and so it is hard to make a profit.  (In a kiln with 12/4 in it for 6 months, I could dry 15 to 18 loads of air dried 4/4, and make a lot more profit than with one load of 12/4.)

Questions?

[BClean]

Thank you Gene, this is exactly the kind of information I was hoping to receive here.

To summarize, I should find myself a place which allows for due south orientation. In the meantime I can cut my 12/4 and give it until next spring to slowly predry. Thereafter put it in the new hopefully exactly south oriented kiln and dry it to the desired MC.

As I mentioned, profit is not an issue. My main profession is lawyer. My grandfather was a carpenter, so I go back to the roots. We want to select premium wood, quartersaw it and use ist for private projects and maybe for some doors for historical houses.

Do you recommend to have the lumber rough sawn while air driying or should I better have an already processed (graded, sanded) surface in order to further prevent checking on the surface? Machinery and working time are no issue. Quality of the final product is what counts.

Regards Bernhard

[GeneWengert-WoodDoc]

Rough sawn is fine.

The thinner the lumber, the better.  Avoid drying it too fast, even in a shed.

Once in the kiln, cover part of the collector to avoid too much heat.

[BClean]

Many thanks for your advise, appreciate it a lot.

Regards Bernhard