Sorta solar kiln

[OlJarhead]

This is the stack before moving it into the 'kiln'


No heat source other than sun and what little the dehumidifier puts out.  One week in and some lowering of the MC.
Once uncovered I saw and was disappointed by a LOT of movement in the wood.  I can only assume it was part stress (there was a lot) and part how rapidly the wood started to dry in the dry desert climate here.

The 'kiln' is just 6mil plastic laid on the ground, two box frames on the end and some 1x6ish stringers to hold it together -- all plastic wrapped and sealed with a fan and Dehumidifier inside.


After one week some of the wood showed higher readings and I assume that's due to water movement.  it was all right around 12.5% at the start.


Some showed promise though!

The weather has not cooperated at all though as our usual sunny and hot late summer/early fall weather has not materialized and so far the hottest it's been is 75F....and mostly it's been cloudy and even raining!  WHAT!?!?!

I put a temp logger inside and every day I see water pooled around the hose (or a big wet spot anyway) so it's doing something and we'll just have to be patient to see how well this works.

My hope is that I can flatten out some of the badly warped slabs and at least use some of them and there is wood in there that didn't move much but WOW did I get a lot of movement in this English Walnut.  The logs were checked the moment they hit the ground though and were over 40% MC at the end grain so I'm guessing the stress and rapid drying had something to do with that (milled in Portland OR and bought to EA Washing to dry and use).

I've only dried a little lumber out here in the desert and it moved a ton then too so I thought that could happen again but this wood was on the more shaded side of the house with a roof over and lots of air movement around it but I'm guessing it was just too dry.

[OlJarhead]

Oh and my hope is to get this all down to 7% or lower since it's a dry climate.  Not sure this will work but if in 3 weeks it isn't dry enough I'll move it into the garage in the same kind of set up but with insulation and a heat source and I'll pour the heat to it for the last week (or at least hope I can).

[GullyBog]

Thanks for posting.  I'd like to do this myself and have learned a lot from your pictures.  Here in the humid east it would be a little different.  Good luck adding value to your wood.  "Read and you will succeed!"

[OlJarhead]

Thanks.  Bighest issue so far is the darn rain!  Usually only get 8 inches a year or so but lately it's been pretty steady (for us) and I didnt out much roof support in

[low_48]

I wouldn't think wind helps you much either. That structure would make a nice sail. I was surprised how quickly visqueen breaks down in sunlight and heat. I experimented with a warm air solar collector in the 80s. My collector made it through the winter, but broke down quickly with the spring sun angle and heat.

[mredden]

I'm planning to try this soon myself (without fan and de-humidifier) when I get some boards air dried down to EMC. BUT, EMC around here is 14%.

Next ten days forecast here in South Georgia  95+ degrees and morning humidity of 85% or higher and no rain/ Gonna have some afternoons when the humidity drops into the 40s though.

Please keep us updated

[OlJarhead]

Have to have those in the tent or it wouldn't work.  You have to have a way to get the moisture out.

After 1 1/2 weeks I am seeing very little moisture coming out of the hose.  Used to be several feet of wet pavement around the end, now just a small spot.  It's 75F today and might be like that the rest of the week so I'm hopeful I'm getting 100+ inside the tent/kiln because I'm guessing I need heat now to really get the last water out.

Plan is to open it again this weekend weather permitting.

[doc henderson]

thick slabs are going to "move"  all you can try is to weight them or strap them.. adjustable straps are best since after it shrinks/dries, the straps will be loose.  even though you are in the desert, if it is sealed up and with a dehumidifier, you should be able to replicate what ever environment you need.  although dependent on the sun for heat.  looks like you are having a good time.  the slabs that went through a branch point are going warp and twist no matter what.  use as rustic or mill it out.  best regards.

[doc henderson]

can you put a container under your dehumidifier hose to help quantify the water removed.  when the temp drops, the relative humidity goes up.  that is why it is called relative.  the dehumidifier will remove most water during the night, and may not be seen in the am as much.  I have been using the sensor push recommended by @YellowHammer .  it is cool to see the temp and humidity graph, they are just the inverse of each other.  I have mentioned on other threads that I have taking 5 gallons a day from my shop, after a month of no ac, and all the wood sucked up moisture.

[OlJarhead]

Thanks Doc.

I raised the dehumidifier today to get it off the ground though I don't what what that will do.

Inside the kiln at 12:30 today it was 102 and rising and the dehumidifier was report exhaust MC of 30%.  I found that odd but it may not have the oomph I need either.

However 1" slabs are showing 5% now!  Just the 2" stuff is dow. To 10% with some still showing higher. (13% even).

It will get hot in there today so we shall see.

[OlJarhead]

Another week to get down to 8% maybe?  But I still think below 7% is better for this climate.


Now I'm thinking I should remove the 1.25" stuff as it's obviously getting down to good range now.


Darn it!  I am surprised at how all over the place the readings are actually.



Interesting that it's showing 30% RH and so to is the dehumidifier.

2.25" slab showing 13.6% still....where is the scratching head emoticon?

[OlJarhead]

Hmmmmm.....it's 31%RH here today and 30% in the kiln with an exhaust of 30% on the dehumidifier....might be the lowest it can go???

[OlJarhead]

Incidentally, you might wonder why there is no weight on the wood slabs.  i was told it didn't move once below 16% and it all went in the kiln at about 12.5% so I figured I wouldn't need weight at this point.

Hope that isn't incorrect!?

[OlJarhead]

 

Less than two hours after I entered the kiln and raised the dehumidifier 6" or so and closed it all back up I see this   So water's coming out again.  I have to assume the heat (it's been hotter today finally!  Hit 79F) is working in my favor now.

[doc henderson]

the higher temps move water cause it is closer to the boiling point.  a home dehumidifier shuts off under 35%.  it is most efficient at higher humidity and that occurs at about 4 or 5 am.  if you add a container, you can quantify the overnight water volume loss.  during the day the RH will be low as the temp rises.  the center of a 2.5 inch slab has to be higher than a 1 inch board that started at the same MC.  the probes measure the surface moisture unless they a insulated except for the tip.  the heat raises the amount of water the air can hold.  at night it will condense unless removed by your dehumidifier.  your meter should be set for average density based on species, but any density variation in a board can give a false reading.  such as sap wood vs a knot.

[OlJarhead]

Ahhh good stuff.

I'll have to find a section of hose I can sacrifice and see what happens.  Was also thinking of sticking some finishing nails into a 2.25" piece and see how that reads from the middle.  I get much lower MC when checking the face (for obvious reasons mentioned above and something I do not do other than occasionally out of curiosity) but I check at the end grain and jam the meter in as far as it will go.  I get different readings that way (and higher ones).

[Fedge]

Checking your moisture content on the end grain will give you lower results than other area of the boards. The real moisture content is significantly higher than you believe.

[GeneWengert-WoodDoc]

When checking the MC during drying, the best method is to use insulated needles that have the tips uninsulated.  These are driven at a depth of 1/4 of the lumber's thickness to get an average MC, or into the core (1/2 thickness) to get the wettest.

The next best way is to use two shiny nails spaced one or two inches apart and driven 1/4 or 1/2 thickness.  These will read the wettest along their length, which is ok if the surface has not gained moisture.  Run wires from these nail heads to a moisture meter.

You can measure humidity by using a thin piece of wood or a thick piece of paper and put that on the pins of a moisture meter.  Some companies sell wafers for this purpose...Lignomat is one.  The reading from the meter in this case is EMC of the air which can be converted to RH.

[OlJarhead]

Checking your moisture content on the end grain will give you lower results than other area of the boards. The real moisture content is significantly higher than you believe.

Using the pin type meter (above) it gives me the higher reading then on the surface.   I'll be trying the nail method soon though.

[OlJarhead]

Tested with some small finishing nails nailed deep in the wood about 15" back from the end and saw MC readings at 14.5% +/- (had a hard time holding the meter pins on the wood and no clips and wires yet).  So this shows an increase of about 2-3% over what I'm seeing on the end grain.  Don't know if that's to be expected or what.

Still see readings all over the place but clearly the 5/4 stuff is much lower showing as low as 6.5% on the ends.

My temp logger showed only 6 days in the last two weeks with temps above 100F in the 'kiln' and the highest temp so far was 109F which is about a 30F increase over ambient air temps.  We've had a very cool summer (coldest in 20 years) and cool fall so I'm not confident I'll get many days over 70F now.

I have to pull the wood inside in a week or two as we're having a shed delivered and I need the driveway space it's in now to back the shed into place.  However, I'm thinking that will be fine as I can restack it inside the garage and rebuild the 'kiln' there perhaps (if I decide to bother).

When I pulled the logger it showed temps 20F above current outside air temps and humidity of 37% which is 5% lower than what the weather sites tell me we are here today (42% RH and 48F with overcast conditions vs 67.3F and 37% inside the 'kiln).

Interestingly enough I did find RH to be higher then temps where lower and only on the 10th day did I see RH of above 50% (which is today/this morning).  So I can only guess when it's been above 30% the dehumidifier should be removing that moisture.  What I'm wondering is if it would be worth placing a small heater on high inside the 'kiln' to keep it a bit warmer in there day and night with the obvious exception that it will shut off if the sun ever decides to come out and heat things up again.