iDRY Vacuum Kilns

Sponsors:

Starting to build the solar kiln

Started by btulloh, May 31, 2017, 05:14:28 PM

Previous topic - Next topic

0 Members and 1 Guest are viewing this topic.

grouch

Someday, I'm going to have enough lumber ahead to use Jim_Rogers' system of palletized stacking. That looks to be good from mill to air dry to kiln to storage.
Find something to do that interests you.

btulloh

Grouch, if you have 9 or 10 boards and you're gonna use them tomorrow, you need a pallet.  You would be surprised how much the pallets improve your life whether you're storing lumber or just moving from the mill to where you're building.  If you sit one next to the saw, you can stack and sticker right off the mill and be done with it.  If you're sawing pine here in VA you can't wait til tomorrow or you'll be growing mold already.  Even if I'm putting up siding green, I sticker the siding on the pallet and then it's easy to move and won't grow the green stuff while I'm looking for my glasses.  It takes an hour to build one, so it's not a big investment in time and it pays that back pretty quick.  I can't remember how Jim's are, but I run three boards across the bottom as well and nail the stickers in place on top.  With the boards on the bottom the thing is almost a torsion box, so it doesn't want to rack or twist.  If I set a loaded pallet down on uneven ground I just stick some wedges here and there to take the load.  (That's for short term only.)

HM126

btulloh

Fans.

I also notice I forgot an important little item:  I need to close off the space between the rafters above the fan mounting boards otherwise I'm going to short-circuit my air flow.



  

  

  

 
HM126

grouch

It's looking neat.

Naturally, you'll be losing some 'steampunk' charm by not doing the lineshaft, flat belts and lignum vitae bearings. You could make up for that with some gauges, valves and pipes on the outside. They don't have to do anything.
Find something to do that interests you.

GeneWengert-WoodDoc

I am impressed with the fans. They have all the correct features
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

btulloh

'Bout time.  Cookin' some wood.  Finally got it finished enough to operate.



 

Getting the pallet in went ok, all things considered.  It was kind of like a night carrier landing in rough seas.  With a swarm of yellow jackets in the cockpit.  But no fatalities.  I opted for a small pallet of EWP that was around 19%.  About 300 bf.  It was a good choice to start with an easy one.  My joystick has an interesting personality and it can make life interesting at times.  I need to get the slop out of it one of these days.  All that weight on bucket forks is tricky anyway, even with a light pallet.

The air flow is pretty good and uniform, even with a lot of openings on the sides and under that pallet.  I plan to plug those up, but I ran out of time and enthusiasm today.  Air flow seemed pretty good anyway.  If I tighten up the holes I can probably reduce fan speed or maybe even run on one fan.  We'll see.  125 lfpm is 1.8 mph (if my math is right) so it's not exactly a hurricane coming through the stack when it's right.  I don't know if 1.8 mph will even move a small anemometer, but it felt about right.  I'm still going to plug up the holes in the morning.

The temp got up pretty good considering I closed the doors about 2:30.  I opened a lower vent and stuck my hand in about 6pm and it was pretty warm and moist.  110F coming out of the stack even at 6pm.  I'm not measuring humidity right now, other than feel, but it was pretty humid.  I opened up the vents some more and let the fans run for a while.  When it gets down below 90F I'll cut the fans off.  (I'm just guessing about how to operate this thing, plus what I've read here on FF.)  Riding the bike is different from reading about the bike though.

Don't anybody stress out about my sleepers not lining up with the stickers yet.  It's just 300 bf of EWP at 19%, so it's pretty light.  WE'll get all that done better on the next go round.

It's a good day in kiln-ville and I'm glad to get this thing running, even though I've got some exterior items to finish up.  Thanks for everybody's input up to this stage.  The hard part is just getting under way. 

Now I get to go watch the Hokies play their first game of the season.  I hear they are starting 20 freshmen tonight.  That'll be interesting. 

7:30 ABC
HM126

grouch

Good job!

Well, except for those misaligned 'sleepers'.
And not getting exact temp readings.
And not getting exact airflow.
And running off to watch a football game instead of turning on some lights and getting that work done.

;D

Hey, I'll be glad to tell you the score when it's done. Game's been on in the garage and now it's in the house while I eat and you're right, it has been interesting!
Find something to do that interests you.

btulloh

Quote from: grouch on September 02, 2017, 06:50:33 PM
It's looking neat.

Naturally, you'll be losing some 'steampunk' charm by not doing the lineshaft, flat belts and lignum vitae bearings. You could make up for that with some gauges, valves and pipes on the outside. They don't have to do anything.

Good plan.  I could make it look like something out the old movie "Metropolis".  I have a couple old art deco boiler gauges I could start with:



      
HM126

btulloh

Now that I'm trying to operate this thing, I read back through some of the threads and it cleared up a couple things for me.  Basically more humidity, more vent.  Makes sense.  Now I'm wondering if it would be possible to use a thermostat on the fans.  Is it an absolute temperature where they should be on/off or is it the differential between inside and outside temps?  I can see where some degree of automatic control would be a benefit for me in case I'm not around in the evening.
HM126

WDH

I believe the fans should run during the day when the sun is shining, and be turned off at night.  A timer may be more valuable than a thermostat. 
Woodmizer LT40HDD35, John Deere 2155, Kubota M5-111, Kubota L2501, Nyle L53 Dehumidification Kiln, and a passion for all things with leafs, twigs, and bark.  hamsleyhardwood.com

btulloh

First day of all-day drying with full sun.  This thing seems to be working well.  The temp probe that's measuring the air as it comes out the stack was reading 126F.  I had all the vents about half open.

Someone loaned me this nifty little device that is pretty useful.  It measures air speed, temp, RH, wet bulb, dew point, barometric pressure, and altitude. 



 

I used it to check the air flow through the stack at various points and was able to confirm that the air flow is pretty consistent and the at right desired velocity.  FWIW, the RH of the air coming out of the stack was 36%.  Not sure what that means, but I bet Gene will. 
HM126

btulloh

The temperature of the air coming from the stack was 103f at 8pm.  I let the fans run a little longer, until it got down close to 90f.  Not sure when it's ok to turn the fans off.
HM126

btulloh

Today I have the vents open only about 10%.  Air temp coming out of the stack is 140F and 23% rh.  This morning the lumber was showing 12% mc on average. 

One note on the fans.  Before the sun got involved this morning I was taking checking air flow with the Kestrel to see if it was uniform.  It's fairly uniform throughout the stack, but I tried various combinations of fans and fan speeds to see what effects that had on air flow.  The 16" greenhouse fan seems to be doing all the work.  There was adequate airflow with just the 16" fan (which is the greenhouse fan).  The HD fan didn't really contribute.  With only the HD fan running, at any of the three speeds, there was zero or close to zero airflow.  I don't think it likes static pressure.  Today I have it on low just to help bring air from behind the fan board.  I'm not quite sure what to make of that.  At any rate, the air flow is even, and perhaps a little too fast.  I only took a reading at one spot because I didn't want to open the doors, but it was showing a little over 200 lfpm, which I think I've heard is too much.
HM126

grouch

Thanks for posting the picture of that Kestrel. I've been wondering what to use for measuring all the variables that need to be juggled.

At 23% RH, that should be sucking moisture out of the lumber. You'll have shrivelled up toothpicks with 0.1% MC in a day or two.  ;D

I've had 80% to >90% RH in my 'kiln' ever since the plastic covering the ridge broke open. No telling how much rain dumped inside during the 6 inch deluge we had that night.

That HD fan sounds like it's all show and no flow.
Find something to do that interests you.

YellowHammer

200 fpm is OK for hardwoods.   600 fpm or more is preferred for softwoods.
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

btulloh

Cool rainy day yesterday.  The kiln had the day off.

Today was nice and bright, and it only got up to around 78f.  Nice day.  We have 3 more of those coming, then Irma comes to town.  It'll be somewhat milder by the time it gets here, tropical storm at worst or maybe just some rain.

Today I had the vents open about 10% and the air out of the stack was 140f @23%rh.  I'm hoping someone will tell me what to think about that.  Yesterday the lumber looked to be about 12%mc on average.  I'm thinking today will get it to the finish line.  I opened up the vents to 50% about 5:30.  We're at about 74f 53% rh outside right now.  I'll let the fans run until the temp gets down below 90.  That's been around 9pm the last couple days.  The vents are open more now, so we'll see.

If all goes well, I'll take this load out tomorrow and put in another load of SYP that's been air dried to 20%.  Film at 11:00.

HM126

YellowHammer

YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

btulloh

Hmmmm. Thanks.  Where do I find this information?
HM126

btulloh

I've still got a little more work to do on the outside of the kiln, but that can wait a few days while I catch up on a lot of things I've neglected around here.  While that's happening, there's another load of SYP in the kiln that should be ready in two or three days.

I'm going to start a new thread on using the kiln.  I'm already starting to find out what I don't know about operating this thing.
HM126

grouch

Quote from: btulloh on September 08, 2017, 07:18:12 AM
Hmmmm. Thanks.  Where do I find this information?

I want it, too!

I don't see how measuring the RH of air being forced through the stack can tell you the moisture content of the wood. It looks to me like that would be measuring somewhere between the potential for the air to absorb moisture and the amount of moisture available for it to absorb.
Find something to do that interests you.

YellowHammer

Grouch, you are correct.  The EMC value is the moisture level when given enough time, the wood will have reached an equilibrium with its environment and is no longer gaining or losing moisture.  In some species of wood, such as pine which looses moisture very quickly, the wood will rapidly approach EMC, however, in some species, such as white oak, the drop in moisture content is very slow.  However, given enough time, they will all reach it. 

The important thing about Btullohs number is that he has achieved, during a heating cycle, an EMC value which is lower than the actual wood moisture content, so the wood will dry.  Manipulation of the vents will allow this to be controlled to some degree.     

There are calculators and tables on the web for computing the EMC of wood at or below the fiber saturation point (about 30% moisture content) given the temperature and relative humidity.  Here one:  http://www.csgnetwork.com/emctablecalc.html

The difference between the current moisture content of the wood and the EMC value is used to determine, or in the case of conventional kilns, regulate how much moisture the wood will loose in a certain period of time.  These chamber conditions are manipulated in a predetermined "schedule" to safely dry the wood in a fast but safe manner.  I have printed out an EMC table and have copies at each kiln for quick reference.

For example, in an air conditioned house of 70° F and 40% RH, the EMC value will be 7.7%, so given enough time, all the wood in the house will come to equilibrium at that value.  A good way to do a sanity check on a moisture meter is to check wood moisture values in a stable, air conditioned or heated house, especially where the thermostat displays RH and Temp. 


YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

grouch

Find something to do that interests you.

btulloh

I'm taking this to a new topic:  "Using the new solar kiln"  https://forestryforum.com/board/index.php/topic,97731.0.html

(Grouch, posted a neat way to do these links, but I didn't use it at the time, and now I've forgotten the procedure.  That never happened to me when I was younger. ;D)
HM126

GeneWengert-WoodDoc

I agree that a timer is likely most useful.  But, technically, we would not run the fans unless the kiln is 20 F warmer than outside.

MORE TECHNICAL INFO:  in general, the humidity is the key variable as it allows us to consider how fast wetter wood is drying and how low the final MC will be.

Here is info from another posting about air dried wood going into a solar kiln:
The key for your low MC lumber is the average humidity for the day, not a peak value in the afternoon, etc.

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 truth, 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 initially, but there would be some if we drain the liquid.

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.  Lower MC if the fans are not run when the kiln and outside temperature are nearly the same.

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

btulloh

Thanks again for the help, Gene.



One note to anyone building one if these: I have to say that the lexan twinwall is a good choice for glazing.  I am amazed by how much of thermal barrier that quarter inch gap provides.  When the kiln was at 140F on the air leaving the stack, I put my hand on the outside of the lexan and it did not even feel warm.  It actually felt cooler than the ambient air.  All in all it seems to be a good solution.  Compared to double layers of the corrugated stuff it's a lot easier to install and about the same price. 
HM126

Thank You Sponsors!