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Author Topic: Using the new solar kiln  (Read 1416 times)

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Offline btulloh

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Using the new solar kiln
« on: September 09, 2017, 07:02:03 pm »
(New thread.  See http://www.forestryforum.com/board/index.php/topic,96418.0.html for the thread leading up to this.)

Today was the first full day with the second load in the kiln (SYP).  Cool for this time of year (75f 50%RH) and occasional clouds.  The vents were all open about 50% and the air coming out of the stack was 120f @ 40%RH mid afternoon.  This load has been air dried and averages around 18% MC when I put it in yesterday around 2 pm.

Thanks to YellowHammer for posting this link http://www.csgnetwork.com/emctablecalc.html in the other thread showing the relationship between temp / rh / EMC.

I assume that this means that given a certain kiln condition, a load of lumber will at some point reach the emc found in the table.  I can see how to apply that in a DH or other type of kiln and I can see how it would be helpful with the solar kiln.  Basically I can open or close vents to affect the conditions inside the kiln.  These are supposed to be forgiving - I hope so.  After a couple more loads I have some air-dried WO to run, so the price of poker will go up. 

Right now I'm concerned about running too hot with too little humditiy in the kiln for something like WO.  Should I be worried?  Does the overnight cooling remove all the potential issues?

I know this is supposed to be simple in the solar kiln, but right now I am not quite sure about these things.

My first load of EWP where I ran the temp up for the last day came out a little crispy, but it bounced back to about what I was looking for - 10% on average.

All comments and insults are welcome.

HM126

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #1 on: September 09, 2017, 09:45:05 pm »
You are a bit too worried about instantaneous readings.  The key for your low MC lumber is the average humidity.

The VT kiln is design to achieve 7% final MC with the vents 95% closed, but with a few leaks.  This will indeed happen.

If the kiln building were perfectly sealed and vents were tightly closed, the MC average would never change...water could not get out.  However, if there were a few wetter pieces, they would loose MC and the drier ones would come up in MC.

In practice, the air would heat and get to 100% RH in the afternoon.  The kiln would then cool as the sun goes down, so we would see the moisture in the air condense on the walls, floor and collector.  Hopefully the liquid can drain out of the kiln.  This cycling would occur everyday.  The average RH would be very high, so we would not see much drying, but there would be some loss if we drain the liquid.  Note the around three gallons = 1% MC loss from 1000 BF, so we would have to drain a lot of water.

For pine, we want no drier than 10% MC.  We know that if the vents were wide open and the fans were run 24/7, then the lowest MC in most of the USA would be 11 to 12% MC.

So, you need to use a setting between these two extremes...VENTS OPEN PRETTY WIDE FOR PINE (10% final MC), BUT NEARLY CLOSED FOR OAK (7% final MC).

Note that you cannot damage well air dried material no matter what you do.  So we run the kiln to achieve the correct final MC.

Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline Darrel

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Re: Using the new solar kiln
« Reply #2 on: September 11, 2017, 12:08:58 am »
Glad to see that you got your kiln up and running. I will be interested to hear how it works out for you.
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Offline btulloh

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Re: Using the new solar kiln
« Reply #3 on: September 12, 2017, 07:43:04 pm »
Cloudy the last couple days.  Still have a load of SYP in the kiln nearly dry.  I am surprised at how much energy comes through the cloud layer.  Averaging about 25 degrees above ambient on completely cloudy day.  Some decent drying is happening.  I'd like to get a good full-sun day to finish off this load, so I could get to sterilization temp.

I found on the first load that the pitch got set to some degree, although I understand it's not like running 160F for 24 hours.  I checked some pitch pockets and they were hard as a rock.  Even though the pitch didn't officially get set, it's a step in the right direction and makes the lumber easier to work with.
HM126

Offline btulloh

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Re: Using the new solar kiln
« Reply #4 on: September 12, 2017, 07:46:48 pm »
Thanks for the info Gene.  It really helps my learning process.  I see a lot of different information around but I don't have a comprehensive understanding so that I can process it all.  I'm learning though, thanks to all the help here.
HM126

Offline btulloh

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Re: Using the new solar kiln
« Reply #5 on: September 18, 2017, 08:43:57 am »
Third load of SYP in the kiln now.  Everything is going well and the kiln works great.  We've had a lot of partially cloudy and cloudy days here, so the last load took a week to go from 20% to 10% mc.  All good.

One thing I have to do is add some automatic control to the fans.  The kiln is holding its heat so well that the temp stays well above the 20 degree above ambient until very late.  Sometimes I open the vents at dark to get the cooler air into the kiln.  Not sure if that's the best way to deal with it.  The last couple nights the kiln was still at 91F at 11:30pm and the outside temp was 66F.  I'm looking around for a low-cost differential controller, or maybe I'll make one.  I don't need another project so I hope to find something.  There are plenty of industrial controls around if I wanted to spend the money, but I don't.  I may just put a timer on the fans for the short term.

The bottom line is that the kiln is working as it's supposed to and lumber is getting dried.  I have one more load of SYP to dry after this one and then I will dry some more difficult loads.  I have some air-dried WO to run, and then I will try some air dried 8/4 RO slabs.

Offline fishfighter

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Re: Using the new solar kiln
« Reply #6 on: September 29, 2017, 06:28:19 am »
Good to hear things are working for you. Keep us up dated. I will start to build mine some time this winter.

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #7 on: September 29, 2017, 07:02:14 am »
There was an article in Sawmill & Woodlot magazine that provided more details about solar design and operation...summer 2016 I believe.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline WDH

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Re: Using the new solar kiln
« Reply #8 on: September 29, 2017, 07:59:22 am »
That WO will test your resolve and fortitude   ;D
Woodmizer LT40HDD35, John Deere 2155, Kubota M5640SU, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

Offline btulloh

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Re: Using the new solar kiln
« Reply #9 on: September 29, 2017, 09:24:25 am »
WDH, I am thinking you're right about that.  I have one pallet of low-grade WO shorts that have been air dried for a year that I'm going to try first.  The kiln has been sitting empty all week waiting on me to load it.  Maybe today. 

I have run 3 loads of SYP and one load of EWP so far and I'm pleased with the results.  Some of this is for paneling and I test-planed a couple pieces.  I hate running any pine through my planer, but it has to be done.  The pitch got set to some degree, even though I never really reached the magic number for that.  I planed enough 5/4 for porch boards on my little cabin and installed it this week.  The porch boards really didn't need to be kiln dried, but I'm glad I did it.  I put some clear deck oil on it and it came out great.  The kiln drying really changes the nature of this VA Pine.  Goes without saying I guess, but experiencing it is whole nother thing.  I'm going to use the same stuff for flooring, I just have to saw enough high-grade to use.

One note of caution to pass along with regard to dust and mold.  Some of this SYP had a little mold here and there and even though it had been through the kiln, it seemed to have enough mojo to give a bit of an infection after breathing it.  It really took me out for a few days.  Clearly I should have been using better breathing gear, but I kind of left that out of the equation.  After dusting the lumber, trimming, planing, I kicked up enough spores to cause a problem.  Sometimes managing eye, ear, and nose protection, I skip over the breathing protection, which is not a good idea. 

FF, one thing is for sure.  It's better to build a solar kiln in the winter.  I'd be careful about letting it get rained on during construction though.   I used store-bought materials so I wouldn't have to worry about closing up a bunch of wet lumber and insulation and creating a black mold generator. 

All is going well and I'm really pleased with this thing.  I'll keep you updated as I get into more difficult loads.  At some point I'll put some air-dried RO slabs in the kiln.  I'm quite nervous about that.
HM126

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #10 on: September 30, 2017, 07:23:55 am »
Once lumber is under 25% MC, it is next to impossible to damage it.  The main quality factor is achieving the correct final MC.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline YellowHammer

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Re: Using the new solar kiln
« Reply #11 on: September 30, 2017, 08:45:33 am »
It really won't matter what species you put in, if it is air dried, it will just take longer with some species than others, there won't be any risk.

If you put green white wood, like poplar, basswood, or soft maple in the solar kiln, and put in enough to overload it, then it will cause gray and sticker stain.  If you have to do this, use the solar kiln as a modified fan shed, keep the temps down and the airflow up.  Basically open the doors to remove moisture.

The solar kiln excels at drying slow hardwoods, such as red and white oaks; you can put a full load of green in and no worries, it will just take awhile.

It will give you time to build your second one.  :D   
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Re: Using the new solar kiln
« Reply #12 on: October 01, 2017, 07:39:13 am »
There was an article in Sawmill & Woodlot magazine that provided more details about solar design and operation...summer 2016 I believe.

Is it on the web? Thanks

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #13 on: October 02, 2017, 02:47:38 pm »
I doubt it.  Just in the magazine.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline btulloh

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Re: Using the new solar kiln
« Reply #14 on: October 03, 2017, 05:32:32 pm »
Put a load of WO in yesterday.  It was little heavy for my bucket forks.  Had to remove the top 5 layers and the re-sticker after I put the stack in the kiln.  Not fun but necessary.  Kiln is running well and the oak is drying. 

This kiln works well.  Wish I hadn't waited so long to build it.

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Re: Using the new solar kiln
« Reply #15 on: October 04, 2017, 12:32:29 pm »
I forgot did you automate anything or is it all still manual? vents and fans.
I knew what I thought I meant.

Offline btulloh

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Re: Using the new solar kiln
« Reply #16 on: October 04, 2017, 06:42:55 pm »
All manual at this point.
HM126

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #17 on: October 04, 2017, 08:44:41 pm »
The first automation is to put a clock or timer on the fans. In VA at this time of year, probably turn on at 9 AM and off around 7PM
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline btulloh

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Re: Using the new solar kiln
« Reply #18 on: October 05, 2017, 05:45:26 pm »
I plan to do something with the fans so I don't have to stay on top of it.  Even running with the all the vents half open, the thing doesn't get down below 90f until around 11pm, even this time of year (sunset at 7:00 pm-ish).

Today was typical of the weather lately, mostly clear all day, high around 85f.  The temp out of the stack was about 126f around 2pm.  Down to 120f at 5pm. 

Here's the instrumentation I'm using:

 

 

Probe temp is on the left.  Target temp is on the right.  This instrument didn't have a setting for WHITE OAK, so I used the BEEF setting.  Every time I check the temperature I get hungry, for some reason.

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #19 on: October 06, 2017, 08:15:13 am »
OPERATION OF FANS AT LOWER MCs.   We want to run the fans only when the humidity in the kiln is low enough.  For wet, check-prone woods like oak, that might be 95% RH. For ďalmost dryĒ hardwoods that we want 7% final MC, under 50% RH.  If we run the fans at 24/7, we can dry to around 11% MC in most of the US, but no drier.  For softwoods that target 10% final MC, under 70% RH.

As the wood gets drier and drier, the vents need to be closed more and more to maximize heating, which also will get the lower humidities required to get the lower MCs.

At night when the kiln begins to cool, the humidity will quickly increase with this cooling.  So even though we have heat above outdoors, we need to turn the fans off to avoid adding moisture to the dry wood.  The kiln will be more humid than outside and hotter.  Active venting will exhaust the excess moisture, but unless you have separate vent fans, we cannot vent without also blowing moist air through the lumber pile.  So, fans need to be shut off early.

Fans are turned on in the morning when we start to get good heating inside the kiln.  In mid summer, the sun rises in the northeast, so we get very little light into the south-facing roof until the sun moves upward in a few hours.  Of course, the sun also sets in the summer in the NW, so we lose heating in the kiln before the sun sets.  So, that is why we can use a clock timer to turn fans on and off...on maybe 9AM and off at 7PM, but fine tune these numbers for daylight time, where you are in the time zone, final target MC, etc.  Use common sense!  These ideas also include the idea of using expensive electricity for the fans only when the lumber will dry.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline btulloh

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Re: Using the new solar kiln
« Reply #20 on: October 06, 2017, 06:07:49 pm »
Good info, Gene, thanks.  Iím really just trying to get a handle on this.  Keep in mind that I just report some of the data to get this kind of feedback.  Hopefully I will gain a better understanding of the machine as time goes on.  While Iím waiting for that to happen, I am actually getting good results.  The load of WO has been in for 4 full days now and has dropped from 18.5%mc to 12.5% this morning (which would be three days).  Today I ran the heat up and had the vents closed about 95% all day, and I will check the mc in the morning.  After tomorrow the sun is going to disappear for a few days. 

I started checking the rh in the kiln again today just to try and get a better understanding of whatís going on.  I will turn the fans off earlier this evening as you suggest.  Iím also going to monitor the RH in the kiln through the evening and see when the rh starts to go up.

Just FYI, my kiln is situated with some tall trees to the east side, so it doesnít get full sun until 10:30 am. Consequently I donít get a good jump on the morning heat.  This placement was a compromise.  Itís not always possible to get things in the ideal location, but Iím getting decent results in spite of the late start on sunshine.  At some point, I plan to move the kiln to a better location, but proximity to power forced me into this location.

Noon Ė 126f 36%rh 
2:00 pm Ė 136f 29%rh
3:00pm Ė 138f 26%rh
5:30pm Ė 136f 20%rh
Iíll update the kiln readings later this evening during the cool down period.
HM126

Offline btulloh

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Re: Using the new solar kiln
« Reply #21 on: October 06, 2017, 10:44:32 pm »
Evening data:

6:30pm 122f @22%rh
7:30pm 118f @24%rh
8:30pm 111f @34%rh
9:30pm 106f @37%rh
10:30pm 97f @40%rh

temp and rh readings are taken inside lower vent on air leaving the stack
HM126

Offline GeneWengert-WoodDoc

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Re: Using the new solar kiln
« Reply #22 on: October 07, 2017, 12:24:17 am »
If your humidity readings are correct, no need to shut then fans until 10PM.

Your data shows the effect of heating the air, as I assume you are venting as he kiln cools, so you are bringing in outside air! Which is then heated, which drops the humidity.  Foggy air heat around 25 degrees F will drop the humidity to 30% RH.   
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline btulloh

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Re: Using the new solar kiln
« Reply #23 on: October 07, 2017, 03:11:12 pm »
Thanks for the info.  Humidity readings are pretty accurate, or at least I'm using an accurate device (Kestrel 3500).  I suppose there's always a way to take a bad reading.  I put the instrument just outside the stack and let it settle.

Today turned overcast from about noon on.  Not much sunshine expected until later in the week.  MC readings were 11.3% this morning.  I expected a bit lower, but then again I don't really know what to expect.  It'll be done when it's done.

3pm  109f @41%rh
ambient is 81f @79%rh (overcast)

Fans are running for now.
HM126

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Re: Using the new solar kiln
« Reply #24 on: October 10, 2017, 11:38:16 am »
We're in a bad weather period for solar kilns.  85degr, 90% rh, mostly cloudy, and no rain to show for it.

Yesterday there were a few periods of sunshine but mostly cloudy.  Kiln got to 108f, but internal humidity was still at 50%.  A couple more days of this and then maybe back to sunshine.  Load of WO holding at 12%mc.  I think I've heard that getting from 12 to 7 or 8%mc can be a slow trip.  As soon as I get that big heater in the sky back to work, I'll find out.

On another note, bow season opened last Saturday.  I sure don't like hot weather  for hunting.  Waiting for a cooler spell.
HM126