enhanced solar drying

[Acer Forestry]

I have been using a polytunnel to expediate drying for a few years. You would assume there could not be any argument that it works, but referring to the excellent book "The Wood fire handbook" by Vince Thurkettle (I'm pretty sure it was this title, I'll check) he mentions a professionally carried out test that supposedly proved that there was no further / faster drying benefit to timber in a polytunnel than normal air drying...as unlikely as that sounds. In the summer for example, how can say, a month of average 30 degrees daytime temp in a tunnel not be faster drying than 20 degrees, assuming there is plenty of wind flow?

[Woodworks]

1 minute ago, Acer Forestry said:

In the summer for example, how can say, a month of average 30 degrees daytime temp in a tunnel not be faster drying than 20 degrees, assuming there is plenty of wind flow?

That's the thing though a tunnel by nature inhibits air flow. If you add lots of ventilation you will lower the temperature through excessive air changes. My gut feeling is you are best off drying outside to start with and finish with a poly tunnel but be great to see some studies on it. Sure a tunnel must get you to a lower moisture content given enough time.

[openspaceman]

1 hour ago, Woodworks said:

That's the thing though a tunnel by nature inhibits air flow. If you add lots of ventilation you will lower the temperature through excessive air changes. My gut feeling is you are best off drying outside to start with and finish with a poly tunnel but be great to see some studies on it. Sure a tunnel must get you to a lower moisture content given enough time.

Yes managing the ventilation must be  a major point and my small experiments at home seem to show natural ventilation in an enclosed part of the stack isn't likely to be optimal which is why I mentioned fans and monitoring humidity.

 

Still I'm surprised that the book Acer mentions claims there is no benefit in the extra heat captured.

[Stere]

Found this paper explains pretty well the need for air flow in a solar kiln.

 

http://repositorio.lneg.pt/bitstream/10400.9/1585/1/Towards a competitive use of solar - paper.pdf

 

[sandspider]

Not scientific, but I season some wood outside and some in a (well ventilated - side vents open, one door fully open, one door open a bit) polytunnel. The wood in the polytunnel seems to dry much faster. Silver birch that I put in the polytunnel in October or November was around 14% by March - much dryer than the seasoned logs at 25% plus I was buying in.