Anyone got a kiln to dry timber?

[spuddog0507]

4 hours ago, Rough Hewn said:

Might have something in the pipeline.
I'll post it if it happens

You got a pipeline as well now ! is it oil or Gas ?

[Ratman]

You got a pipeline as well now ! is it oil or Gas ?

I’m feeling a dejavu moment!!!

[Forest2Furniture]

On 10/03/2020 at 22:20, wisewood said:

Are the solar kilns any good?
I don't have electricity at the yard.

Solar kilns are fine if time isn't an issue but you'll still need some form of electricity to run the fans to move the air around.

[trigger_andy]

2 hours ago, Forest2Furniture said:

Solar kilns are fine if time isn't an issue but you'll still need some form of electricity to run the fans to move the air around.

 

Add Solar Panels and a Deep Cycle battery? 

[openspaceman]

9 hours ago, Forest2Furniture said:

Solar kilns are fine if time isn't an issue but you'll still need some form of electricity to run the fans to move the air around.

I would expect control to be more of an issue for sawn wood, the hotter the kiln gets the more important the control of humidity becomes.

[Forest2Furniture]

3 hours ago, openspaceman said:

I would expect control to be more of an issue for sawn wood, the hotter the kiln gets the more important the control of humidity becomes.

With a solar kiln, the kiln itself doesn't get hot. 

The timber sits in a chamber below the collecter that warms the air that's what the fans are for to circulate thewarn air. 

Solar kilns a fairly straight forward, heat the air up, circulate the warm air, open the top vents to draw cool air in, open the bottom vents to let cold moisture laiden air out, turn fans off at night and close all vents. Repeat until wood is dry. 

[openspaceman]

16 minutes ago, Forest2Furniture said:

With a solar kiln, the kiln itself doesn't get hot. 

The timber sits in a chamber below the collecter that warms the air that's what the fans are for to circulate thewarn air. 

Solar kilns a fairly straight forward, heat the air up, circulate the warm air, open the top vents to draw cool air in, open the bottom vents to let cold moisture laiden air out, turn fans off at night and close all vents. Repeat until wood is dry. 

I am sure your experience is better than my knowledge of the process but let me explain a bit about the theory:

 

Wood starts off at ~40% moisture content, about half of the moisture is liquid and occupying spaces in the wood, this migrates to the surface fairly quickly where it can be carried away if the surrounding air is not saturated. The rest of the water is weakly bound to the wood structure and this doesn't start moving until the surrounding cell water has gone. It is the removal of this bound water that causes wood to shrink.

 

Before kilns everything was air dried and milling was often done in the winter when the air relative humidity was high, i.e. it has a low capacity for evaporating water from a surface, and the ambient temperature is low, so there is little heat available to supply the energy required to turn the liquid water at the surface to a vapour in the air. Also as it is cold water takes a long time to migrate from the middle to the surface. So everything starts slowly and water migrates evenly from  the interior. As summer progresses  the temperature goes up, RH goes down and water moves more freely in the wood, so everything speeds up a bit. On large sections it becomes necessary to control how quickly the wood evaporates off the surface because if the outer bits of the wood  dry down to their fibre saturation point (the point at which cell water is gone and only bonded water remains) and starts to shrink before the middle has lost its cell water then you start to develop surface cracks and other defects. This control can be done with stickers and shade and isn't largely a problem in our climate.

 

We mostly all know that things happen faster as the temperature goes up so kilning gives us the ability to speed up the process but the increase in temperature is mostly speeding up the way moisture moves from the wood to the surface. The problem is this heat also decreases the RH of the air at the surface and thus increases the rate at which it removes water from the surface.

 

Kilning schedules aim to ensure water removal from the surface never exceeds the rate of water moving out of the wood and this is done largely by increasing humidity in the kiln.

 

From my experiments with drying logs in a greenhouse structure, where one is not concerned about defects in the wood from drying,  I thought the solar kiln would get into the temperatures and low humidity  which would cause problems unless coupled with some way of controlling humidity.

[Richard Ayling]

Ive got an ebac dehumidifying kiln and built a OSB/timber framed box about 12'x6'x8' which is fibreglassed inside to make it water and air tight. The outside has jablite insulation. 2nd one of these Ive had over the years, works a treat but I never use it to go from green timber to dry. Based near Swansea if you ever want to see it if passing and COVID free times.

[Tom at Heartwood]

We have a small farm-based sawmill in Cumbria.  We made a kiln from a shipping container that is heated by our boiler.  We also have small dehumidifier kiln.  I'm happy to discuss further. Cheers. Tom.  07769676536. [email protected]