The science behind forced log drying

[Woodwanter]

I am considering trying this for my own consumption and want to learn more. Looking to dry about 300t per annum

 

i am assuming the 3 main ingredients are heat, dry air and surface area? I can do two out of three but can't easily get the air temp above 35/40

 

Guessing most on here have containers converted with fans in front of heat exchangers? How long does a batch take to get down to 25/30% and how many kWh would you need? What air temp / RH are you producing?

 

all advice / tips very welcome!

 

[SbTVF]

Rough figures. Kiln is timber framed in a building with 100mm of kingspan on all sides.

We have 90kw of heat exchangers with 3 fans pushing 9200m3 per hour through 16m3 of logs in cages.
Air is cycled under a sub floor 10” deep and the full width of the kiln (2.5m)
Takes roughly 7-9 days depending on outside temperature and how dry logs are on start up, to get them to sub 15% moisture.

Gets up to roughly 65degrees within the first 8 hours but gets up to 75 in the latter stages.

[richardwale]

Hi, got any pictures of your kiln? Would be very interested to see your setup. Thanks

[SbTVF]

Subfloor prior to lifting into place.

[Woodwanter]

That's impressive, thanks.

 

as none of mine is caged up I will struggle to move it in. I do have drying floors but I cant get the temperatures you can, I could spread approx 160m3 1 meter deep on the floor though? 

 

Air temp would be 30 degrees tops but air RH about 30-40. I would not get the air flow you have but it would be 'a strong breeze'! Could you see this working? I only need it down to 25-30% though

[SbTVF]

That's impressive, thanks.
 
as none of mine is caged up I will struggle to move it in. I do have drying floors but I cant get the temperatures you can, I could spread approx 160m3 1 meter deep on the floor though? 
 
Air temp would be 30 degrees tops but air RH about 30-40. I would not get the air flow you have but it would be 'a strong breeze'! Could you see this working? I only need it down to 25-30% though

My knowledge of the science is limited, but as I understand it the Lower the temperature a) reduces the moisture carrying capacity of the air b) slows the speed at which the water can escape the logs (can’t think of the fancy word for that)
I would think it’ll still do a good job. I’ve heard of quite a few people using drying floors for logs. How quick their cycles are or how good their final product is I can’t comment.

Why are you only aiming for 25-30%?

[Woodwanter]

Yeah I agree with you ref the science! I know for grain drying, dry air helps, I think it helps 'suck' moisture out.

 

my biggest issue will be breaking down what I have, trying a cone splitter but it's on a 3.5 t machine so concerned it won't be fast enough for my liking. I imagine your stuff is split for a domestic stove I am burning in a commercial boiler that can take wetter logs all though there will be a (yet to be found) sweet spot between cost of drying vs extra heat output? I have done all my calcs on 2500kwh @ the meter which I hope is going to be much lower than reality.

 

trying to keep cost down by only moving it around by walking floor which will take some logistics!

[SbTVF]

Would it not be much simpler to leave it stacked up for 9-12 months? Most species wouldn’t be far off your target by then. Or don’t you have the time to wait?

[Woodwanter]

I could but it's not very stackable, mix of rings trunks and cordwood, doubt much air would pass, going to try piling in a windy shed and review but like to plan ahead!

[SbTVF]

A windy shed will be as good as anything. Especially during the summer!
Split it down to your final needed size as soon as you can and it’ll dry out pretty soon.