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Solar kiln : Leave Circulation fans on after sunset

7/24/14       
Frans Member

Hi,

I build my solar kiln a few years ago and it's working very well.
I had to move it to an other place this winter and the shade of the trees kicks in earlier than before.

When the collector is shaded, the kiln is still very warm and stays warm a long time. There's an avarage of 3 tons of wood in the kiln and concrete slaps on top of the stack so i have indeed quite some inertia, and the kiln is very well insulated.

I'm wondering : should I use the stored solar energy and continue the air circulation a few hours, or should i stop it as soon as the sun does not add any energy anymore ?

I think i can continue the circulation until 10PM in the summer (8 PM solar time) without loosing a lot of head, wich is gone the next morning anyway. But will it be usefull (as there is not any head added ?)

Thanks for your thoughts.

Frans

7/24/14       #2: Solar kiln : Leave Circulation fans ...
Gene Wengert-Wood Doc

Continue until the kiln cools and the RH inside reaches over about 50% RH with dry lumber and over about 80% RH with wet lumber. This is usually going to mean that two or three hours after sunset is when they shut off. They turn back on two or three hours after sunrise on a sunny day.

7/25/14       #3: Solar kiln : Leave Circulation fans ...
Frans Member

Thanks for your response.

I'm a bit confused what to understand by "sunset". Does it mean sunset for the kiln (when there is no sun on the collector anymore (6PM) or effective sunset (8:30PM), far behind the kiln.

I'll run the kiln today at 45% RH and leave it on tonight untill i reach 50% RH and - or the temperature has dropped 10 °C, and see how long it takes.

As the venting of the kiln is done automatically by an electric extractor fan coupelled to a hygrostat, the RH should remain stable but the temperature will drop.

I'll post about what happens tomorrow,

Kind regards,
Frans

7/26/14       #5: Solar kiln : Leave Circulation fans ...
Gene Wengert-Wood Doc

We do want to achieve 100% RH with lumber so that we remove a small amount of drying stress (casehardening) every night. So, the fan you have needs to shut off. Sunset is when the kiln stops getting solar energy.

7/29/14       #6: Solar kiln : Leave Circulation fans ...
Frans Member

Thanks,

Infact, we have had cloudy and now even rainy wether since my first post.... so i couldn't do the tests.

But I have seen the kiln could continue for quite some time on a cloudy day.

Thanks for your confimation on the meaning of "sunset".

What I understand is that continuing the air circulation a few hours wile no solar energy is added, is usefull.

Thanks again,

Frans

2/22/22       #7: Solar kiln : Leave Circulation fans ...
William Murphy Member

This is usually going to mean that two or three hours after sunset is when they shut off.


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