Sawing and Drying

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Message Thread:

Solar Kiln - Ash drying questions

2/24/18       
Carl

A couple of questions about drying ash in a
Virginia Tech design solar kiln

The VT publication mentions that the design
(1000 bd/ft) is based on the ratio of 1 sq/ft
of collector to 10 bd/ft of one inch oak lumber.
And, for slower drying material, a portion of
the collector can be covered, for faster drying,
the amount of lumber reduced.

The accompanying chart shows the max rate for
red oak at 3% MC loss per day, and lists ash
at 10.4% (one inch lumber).

Is it correct to assume that to dry ash at the
fastest recommended rate, the pile should contain
roughly 300 bd/ft?

Also - there is mention that a closed kiln
can reach temperatures near 200 degrees ...
what would be the best strategy to follow
when trying to reach insect killing
temperatures? Is there merit to choosing a
certain time in the drying cycle and leaving
the kiln closed (and closely monitored) so
desired temperatures are reached and held
for the time recommended to get the lumber
core up to insect killing temps (135 degrees
for a couple hours?)

Finally, if the kiln is built to the 1,000
bf/ft VT specs, it can hold 12 foot long material.
If the load were made up of 8 foot material
centered in the kiln, do the open areas of kiln
at the ends of the lumber pile "short circuit"
the air movement from the fans?. If so, and
temporary baffles are placed at the ends of the
pile, should they run all the way up to the
collector roof, or held short so air heated
in the unused portion can contribute to the
drying process?

All thoughts and comments appreciated

Carl

2/25/18       #2: Solar Kiln - Ash drying questions ...
Gene Wengert-WoodDoc

Indeed, 300 bf is best for ash to achieve the whitest color when starting with green lumber. If air dried first, the 1000bf is ok.

For shorter loads, baffle the holes so that all the air goes through the lumber pile.

A closed kiln without lumber can indeed reach 200at the peak of the roof. With lumber in it, you might reach 30 to 40 F above outside, but even if the air is this hot, the lumber internal temperature will not reach 133 F required for sterilization.

Ok?

2/25/18       #3: Solar Kiln - Ash drying questions ...
al

Gene,
How do you get it hot enough for sterilization? This part of solar kilns has always confused me. In NJ it rarely gets to 100 degrees and even at 100 if we add 30 we are only at 130.

2/25/18       #4: Solar Kiln - Ash drying questions ...
Gene Wengert-WoodDoc

A solar kiln does not get hot enough for sterilization.

Due to its poor energy efficiency- -the clear roof- -you would need to get a separate building with a separate heater. If you use a solar kiln, with auxiliary heat and the collector covered with insulation, the heat might affect the fans and building components.

 

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