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Solar Kiln Project:  

Three weeks of drying in the solar kiln

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Last updated on 11/05/2016
Image full image full kiln and stack

The indifferent weather of the past seven days slowed down the rate of wood drying inside and outside the solar kiln.

In the kiln the blocks lost on average 5.6% of their weight during the third week of the drying process while those on the stack shrank by 3.6%. 

Those that had been in the kiln for just a week reduced by 6.6% during the second week while those outside on the stack gave up 4.5%.

It’s clear the kiln continues to outperform the wood stack with the cumulative effect growing over time.

Putting some of the numbers together from this week and last week and we generate some interesting findings about the solar kiln.

Since I didn’t weigh the first set of blocks when they were first deposited in the kiln, I have to estimate how much water they lost. Using the second set as a proxy, I estimate over the first two weeks the blocks decreased in weight by 25%. That implies that over the entire three week period they have been drying in kiln, the wood has lost almost 30% of its weight.

What that in turn means depends on just how much moisture was in in the blocks when the test began. They came from a beech log which had been cut down but was left lying at the bottom of a bank in undergrowth. In other words it had not really been seasoning. Tests with two different  meters indicated moisture levels of over 35%. Probably closer to or over 40%. 

Assuming it was either 40% or 45% and we have two different results. The first would mean the wood right now has a moisture level of 15%. If the second, the wood has a moisture level of 22%. I suspect the true figure is in between.

If you’re wondering why I just don’t split the wood and check with the meters, the answer is that I want to continue the experiment with the blocks in the same shape as they went in and secondly the meters are indicating different results with the same pieces of wood. The two moisture meters by the way are produced by Danish stove maker Morsø and by German electronics company Brennenstuhl.

I haven’t frankly worked out how to resolve this yet. The moisture levels can be gauged by placing the wood in an oven for a protracted period but that seems a bit excessive.


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