Wood dryer

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Grelinette
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Wood dryer




by Grelinette » 15/02/11, 23:12

Perhaps this subject has already been discussed ...

That's my question:

This winter I cut a lot of trees to clear the bush and in general I stack the logs at the feet of the trees and use them the following year.

Wood drying is very variable, depending on the climate, where the wood is stored, and when I take some logs to put them in my insert I realize that some do not burn well and make a lot of smoke. I think it was the drying which was not ideal.

So I thought I would make a small wood dryer that I could fill regularly and which would allow me to have dry wood at all times.

How to do ?...

I thought for example to recover a fairly large box, either a metal tank (fuel, we find bcp), a barrel, an old metal cabinet or an old hs freezer in which I can store a good amount of logs (1 to 2 m3 or more),

and then speed up the drying of the wood either by solar heating (paint in black), or by passing hot air coming for example from my chimney, or even when I burn large quantities of plants which gives off an enormous heat.

How do you see the thing?

For example, in the case of a cabin, a cupboard or a log tank in which I pass hot air from my chimney, or even very hot (burner tank against), in your opinion, in how much long will the freshly cut wood contained in the cabinet be dry enough to burn well?
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by dedeleco » 16/02/11, 00:36

Wood stacked outside dries poorly, especially in wet winter.
In fact if it dries a little during the day or in very dry cold it rewets in the rain and especially by condensation at night, even under tarpaulin !!
Obvious observation !!

So dry it in the summer and keep it under a covered shelter (rigid plate and no tarpaulin against the wood), to prevent condensation from falling on the wood canceling the daytime drying !!
The wood thus in a well ventilated covered shelter is then very dry.

See the hygrometry values ​​of wood as a function of T and hygrometry put on econology by Christophe.

Otherwise a solar drier (see for algae on econology) is ideal, comprising a simple thermal solar panel (glass greenhouse) heating the air with what is to be dried and a short chimney to ensure the draft of hot air to do circulate.
Your proposal fits that.
I had put in early 2010 on econology a very detailed pdf link for a static fruit dryer on this principle.
If you can't find it, I'll look for it.

The drying depends mainly on the humidity, even in cold and dry weather it is good.
Heating with the sun under glass and air circulation decreases the humidity and dries very well;
But we must avoid that at night cold air condenses its humidity on walls and wood, canceling drying.
It is therefore necessary at night to close the draft of the ventilation chimney of the day.

Finally if the wood is left warm for several days near the hot stove it will dry out without loss of energy, because the evaporated water is condensed in the cold spots of the house by restoring its lost energy to evaporate it !!

A lot of stoves have a box in the stove to finish drying the wood as well.

It is even a simple way to burn wet wood by drying it before automatically (40 ° C to 60 ° C is very effective) by the heat of combustion of the wood once dry and recondensing the vapor evaporated on a cold condenser, recovering all the heat of evaporation.
It is unfortunate that this efficient pre-drying is not often done automatically.

The drying time depends on the diameter, the temperature and the humidity.
But considering the slow diffusion in the wood, it is good to split it a lot and to put it very warm and dry, like 40 ° C, near stove or with solar heating under glass of greenhouse and air circulation by chimney effect.
A solar collector glass is better than a black sheet which is more cooled by the outside air.
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by dedeleco » 16/02/11, 01:06

I found the algae and fruit dryer:
https://www.econologie.com/forums/post164108.html#164108
and detailed study of a simple efficient solar chimney dryer :
http://hal.archives-ouvertes.fr/docs/00 ... _625_0.pdf

which avoids errors and delays.

Wood drying course
http://passion.bois.free.fr/le%20materi ... ois%20.htm

for furniture it is all difficult work, cracking. chapping,
drying one cm per year !!!!
Fortunately to burn the wood we do not care about the alterations which allows to dry quickly with dry and not humid air which avoids the cracks of the wood !!!

http://www.crea-menuiserie.com/cours/sechage.php

http://fr.ekopedia.org/Chauffage_au_bois

More info on drying mechanisms:
http://en.wikipedia.org/wiki/Wood_drying
http://gabierschimeriques.free.fr/modelisme/bois.htm
http://www.chauffages-bois.fr/faire-boi ... 2f9048fa82
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by bernardd » 16/02/11, 09:33

If you work directly on crushed or sawdust wood, drying becomes even faster since the water is no longer blocked by the thickness of the wood.

It seems that some people use controlled fermentation to heat a pile of crushed wood, which will dry them faster.

But for domestic consumption, I can clearly see the use of an antique "corn dryer": a mesh "cabinet" with a roof, placed at the end of a field. In my opinion, a very cold winter, and the wood is dry.
http://www.lejsl.com/fr/votre-region/lo ... ssane.html
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by Grelinette » 16/02/11, 11:18

Thank you for all these answers and advice.

I think a simple, inexpensive, practical and aesthetic solution can be this type of small metal garden sheds:
Image Image

It is not airtight enough to let the humid air escape while keeping the wood safe.

To heat the interior, I will start by placing it in a place where it will take the sun well and paint from above the roof in matt black to absorb the maximum solar heat on sunny days even in winter.

Later I will see how to make a simple system of solar panels placed on the roof with a large window covering black metal tubes to accelerate the rise in heat.
A small fan powered by a small photovoltaic panel should allow the hot air to circulate.

What do you think of this solution?

I just found this one at € 139 new at Rongeurama which would be ideal:
http://www.castorama.fr/store/Abri-en-m ... ction=jump
Last edited by Grelinette the 16 / 02 / 11, 11: 24, 1 edited once.
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by bernardd » 16/02/11, 11:24

The drying attics in the chalets are more open than that: you should be able to save on the walls :-)

Cold and frost are at least as important as heat for drying. The frost / heat contrasts being ideal as the material does not suffer from it.
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by Forhorse » 16/02/11, 12:08

By my place the wood is simply put to dry outside. You just have to respect the following 2 rules:
- The wood must not touch the ground, so we sacrifice some logs put in 2 rows perpendicular to the pile
- The wood must be covered while allowing free circulation of air, so exit the plastic sheets! A few steel tray-like sheets are sufficient on the top of the pile, making sure that water does not trickle onto the wood. The sides are left in the open air and can take on water without being annoying.

The wood cut in winter is stored with this method, and then cut into logs at the beginning of autumn and stored in a dry place: attic, shed, lean-to. The important thing is that the wood remains sheltered from water and condensation.
The drying ends in good condition and the wood can be used from the first cold.

The drying method only accounts for half of the drying and preservation of the wood.
The slaughter period is as important as the rest.
The wood must be cut between mid December and the end of January. Before or after the wood still contains sap (which ends up going down or starts going up) and that greatly compromises drying!
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by dedeleco » 16/02/11, 12:18

A metal shelter is misleading because it will heat less than a greenhouse where the sunlight is trapped to heat under a window or a transparent plastic (anti UV polyane) and especially at night the condensation on the cold metal rewets the wood !!
I have a metal tool shelter like this one at Castorama for 15 years, and the condensation at night, especially the wet winter is enormous and insufficient ventilation during the day to dry and excessive ventilation at night to condense the water vapor.
The ventilation must be adjustable depending on the temperature and humidity.
Otherwise the condensation at night causes all the drying of the day to be lost again. !! (except in extreme cold from the east with dry air)
Totally agree with forhorse, no tarpaulin, but shelter far above, well ventilated to the minimum.

It takes a solar collector which lets in warm sunlight like the pdf article indicated above or this link:
http://tilz.tearfund.org/Francais/Pas+% ... olaire.htm
http://hal.archives-ouvertes.fr/docs/00 ... _625_0.pdf

Therefore essential, solar collector with transparent glass or plastic facing the sun (at 60 ° vertical in winter) large area above the wood in one layer and air circulation by chimney, with sun and closed at night without sun.
In addition, put slopes inclined at 40 ° to allow condensation to flow !!
To dry at 40 ° C it takes 12 days indicated on a site.

Depending on the assembly, the drying speed is very different between 12 days at 40 ° C or 7 days at 50 ° C and good air circulation without condensation at night and 2 years without care, and again.
Read all the links I put.

Avoiding condensation as much as possible is crucial in wet weather after
In extreme cold and often dry air (east wind) drying is good, similar to freeze-drying, but often lost in the humid weather which follows full of condensation.
The temperature when heating is mainly used to decrease the relative humidity of the air for drying, but if you have this low humidity when cold without heating, drying will also be effective.
Carefully read this link and the curve above:
http://fr.wikipedia.org/wiki/Point_de_ros%C3%A9e
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by airsp » 18/10/11, 12:24

Hello everybody

I am committed to the realization of a solar firewood dryer.

I understood that a chimney was needed to circulate the air and therefore evacuate the humidity.

In your opinion, is it interesting to manufacture insulating sides to enclose the heat?
While the chimney will dissipate a large part of the heat.

These sides I envisioned on rock wool between wood panels or lime-straw mixture: less insulating but having more inertia.

At night, should you close the chimney to keep the humidity inside the box?

Thank you
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by dedeleco » 18/10/11, 13:43

Read thoroughly the links (especially the .pdf) of my answer on this forum :
https://www.econologie.com/forums/post194121.html#194121
because in summer we can dry wood much better at 40 ° C than usual and have a much better yield and much less pollution as well, if we keep it dry afterwards and at 20 ° C at least, because the wood reabsorbs moisture from the air, partly (especially at night outside, even in the shelter ).

At night, should you close the chimney to keep the humidity inside the box?

keep dry, not humid air and therefore stop the air circulation, as soon as it risks being wet and rewetting the wood by condensation of the humidity of the night !!
So the spontaneous air circulation by chimney must be controlled by sun, thermometers and humidity measurement, by automatically closed hatch if the incoming air (hot or not) is humid.

In your opinion, is it interesting to manufacture insulating sides to enclose the heat?

depends a lot if you dry in winter or summer, because the insulation required depends on the outdoor T and the heating power and therefore drying in winter requires more insulation and care.
A real T test with and without insulation.
See Apper and solar collectors.
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