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Author Topic: Using the new solar kiln  (Read 427 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, BUT NEARLY CLOSED FOR OAK.

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.
1992 LT40HD

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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.