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Solar dry kiln construction

Started by Planman1954, April 13, 2011, 07:44:01 PM

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doc henderson

My understanding is having a black metal under the glaze combined to make a "collector is no better than having all the surfaces flat black that will receive sunlight.  However, the idea that super heating (relative) the wall that is next to the outside temps. seems to make sese there may competing losses out the wall through that insulation.  heat transfer is based on temp gradient vs. insulation.  so, heating a metal "pan" sheet metal under the glaze, and radiate heat to the interior from both sides makes some sense.  If it is fastened to the underneath side of the studs, it can make a plenum and can have convection forces, and well as indirect or direct forced air.  There are plans/ideas where with a plenum, the collector can be turned on and off to decrease losses after the sun goes down.  I recall one where there is a large (made from board foam) flap that creates a one-way valve that is pushed open by the fan that circulates air through the plenum/ducting.  

The best option for a DH is to go all out and get a Nyle DH.  The home ones are ok for a while (especially if used intermittently) to maintain moisture in dry lumber, or to finish off relatively dry (air dried to 12% here) lumber in say a container.  I have used the same Walmart DH (70 L a day rating) for 5 years, but it mostly gets turned on for a few days a month to maintain dry wood in a container.  Home model will also not have the capacity to move lots of water (usually rated in pints or liters) as a pro model.  It gets more complex when you try to do the hybrid style kiln.  As an example, if you will use added heat, a solar kiln loses lot via the plastic glaze.  you could cover at night with insulated moving blankets as an example. or close off the solar heat chamber, but then the underside of the metal pan must be insulated.  Most forms of drying will take some energy and therefore money.  all have advantages and disadvantages.  I would break it down by what you are investing in.  

For the heat component, you need good seals and insulation.  used to mobilize water from the interior of the wood and to lower the relative humidity of the air in the kiln.  Plastic glaze will increase losses when the outside temp is less than the kiln temp.  Heat can come from solar, or a heater that can be electric, gas, or any carbon fuel including wood scraps.  you need heat if you want to treat wood for bugs (sterilization).

Dehumidification requires electricity and good seals to control WB depression or relative humidity.  You could get one to run on LP gas like for a camper, but it would be more expensive up front.  It may have to be a system designed and constructed as a one off by a heating and air guy.  a commercial DH has coils coated to handle the chemical laden condensation it deals with.  you can measure losses via the water output.  It dries the air, so you also need air circulation to allow the dry air to reach the wood surface and change the liquid water to a gas (water vapor).  At over 100% it will rain inside your kiln, and on cooler surfaces like glaze at night you will get condensation.

air circulation is needed for all kilns to prevent mold and facilitate water coming off the boards.  also need good stickering and baffling.  It requires electricity (solar, wind, grid, generator and therefore fuel).  air drying uses the weather.  do you get much wind?

solar kiln is the cheapest and requires little energy input.  If you buy a Nyle dehumidifier, you may as well just build a regular container and skip the solar.  If you have to run a generator for electricity the combined/hybrid, then that cost is also a consideration.  I think your local weather is unique, and I invite anyone else to chime in.  I think the hybrid is good to help with the high relative humidity.  Even though the measured relative humidity is "relative" based on temp., the water content of the air remains the same unless you vent and bring in dryer air.  a DH removes water content and drops the RH.  With a hybrid solar/DH the RH will go up at night when it is cooler and may increase the efficiency of the DH although its capacity could be exceeded.

as far as the gap, it depends on if you want the "duct" effect to force air over the surface.  If you fasten it to the bottom of the collector studs/rafters, then you have to eliminate the bridging, or make it smaller dimension.  you could just suspend it below the rafter to receive the suns energy and let the overall air movement of the kiln take on the heat.  I will stop here, and I hope I addressed other questions you have.  I hope others will chime in.  I do not have a solar kiln, but have studied them for prob. 15 years now, and love the concept.  
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

there are many good articles about wood drying.  I think that Gene mentioned that if you can raise temp in the kiln, by 10 to 20°F, you will get a lower RH that will be enough to dry wood.  there is a national hardwood lumber ass. (NHLA) that Gene has webinars on that you can watch.  you will need to vent at night, or your kiln interior will be soaked in the am.  puddles of water on the floor, and leaking under walls and doors, is not good for a wood constructed kiln.  thus, good vapor barrier and sealing wood components, is important.  Is it cloudy most of the time?  I see in the rainy season, it rains every day, if only for an hour.  In December, it is the dry season, but the temp and relative humidity stays about the same, but at least I assume you have more sunlight.  I would guess that your kiln RH will exceed 100% almost each night without venting or the DH.  Do you have cheap electricity on site?  If not, I think a straight solar kiln would be good.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

teakwood

Quote from: doc henderson on December 11, 2022, 10:15:37 AM



this is from Limon, that's in the Caribbean, i live in the pacific north, it's warmer here (80, 28celcius average) and it rains less 70% average humidity.  January-May is dry season, very windy and hot, up to 105, 36 celcius with a 60% humidity, it's when you can air dry 1" boards in 2-3 month, the kiln will shine in this conditions. the question is how will it preform in the rain season with warm humid wether, it gets pretty cloudy too   
National Stihl Timbersports Champion Costa Rica 2018

teakwood

Quote from: doc henderson on December 11, 2022, 10:45:43 AMI would guess that your kiln RH will exceed 100% almost each night without venting or the DH.  Do you have cheap electricity on site?  If not, I think a straight solar kiln would be good.


The DH will be a must i imagine, good fans at the day and DH at night or 24/7. we have relatively good electrics, i have good conections to the grid, i have 3 services, it's not actually cheap but it's more or less a stable network (10-20 cents/kwh, depends on your consumption) the electricity doesn't concern me, it's just fans and a DH. I make money of this lumber and the kiln will increase productivity and my income so the costs are absorbed.
i have a solar equipment dealing friend, so in the future i could go that route. 
National Stihl Timbersports Champion Costa Rica 2018

YellowHammer

Quote from: doc henderson on December 11, 2022, 10:15:37 AMhe question is how will it preform in the rain season with warm humid wether, it gets pretty cloudy too  
It won't.

Solar kilns need solar to work.  When they get direct sun, they work OK, when they don't they are no better than an air drying shed with fans.

Solar kilns don't work in the rain.
They don't work at night.  
Under cloudy skies, it depends how much infrared radiation is getting through the clouds to the ground, but if the air is already humid and warm, then it will only be marginally better than an air drying shed.

If you want to see how it would work, run a simple test.  Put a black piece of sheet metal outside, protect it from the rain, and see if it gets enough solar radiation to heat up.  If it doesn't heat up, a solar kiln won't either.
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

doc henderson

I would guess shipping would be high, but a nyle DH would be first class.  I think solar Heat) could add to the process but is slower and no heat at night.  sounds like you have good air-drying conditions other than humidity and the rainy season.  can you get containers easily?  going with the container and a nyle system would set up fast, and prob be faster overall.  I think at your temps the DH would heat the kiln.  you might have a call with Stan (Kguy) and see what he thinks.  I have no personal gain from that.  good luck, it has been a fun discussion.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

as I was typing the prev., I had to hit post twice as YH was also typing.  He has solar kilns and Nyle stuff.  A solar might be ok, but the hybrid requires lots of thought (what we have been doing), More complex design, and the solar has net losses at night.  If it is affordable, it may be ahead to go straight DH.  The design by Dr. Gene Weingert is great for the hobby guy and even professionals like yourself.  Nyle has plans for a stick-built kiln for their DH also.  see the sight at the left of course.   :)   I have been watching the 200 level units, and even thought about getting the premade kiln box.  
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

doc henderson

If you go to the Nyle site.  click on resources, then manuals, then pick a DH like the L200.  it shows detailed drawing and speaks to design.  they can also tell electric use for a load to dome degree so you can be sure that it makes financial sense.  Of course, you got the quarry going so you seem to do well with these decisions.  good luck.  solar is still a neat way to go, but adds complexity, and may slow you down.  As YH mentioned, may not add that much to the process.  You could also do both separately.  
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

teakwood

Thanks a lot for all the help, i did the math for a container and a woodmizer 250, same as Nyle 200, it comes to at least 18-20k, that's too steep for me.
have seen a guy here with a 40foot container and a 250 in it and does aprox 4000bft in 22 days, but 500$ electricity bill.
thats too big for me, i can't keep up with felling, sawing, drying, processing, selling and the quarry. i will never have a 4000bft load. if i can get 1000bft per load in a solar that's enough, the rest is airdrying and waiting for the kiln.


you say DH like the Nyle200 but in my understanding they also heat. i just need a dehumidifier for the solar so the water goes out. if i need to add heat in the rain season i do some kind of firewood stove.

but i would love to have a more industrial dehumidifier, nothing big 
National Stihl Timbersports Champion Costa Rica 2018

doc henderson

decisions only you can make.  good luck.  Nyle has an L53, but they have not been available for some now, unless that has changed.  but that may be better than a homeowner one.  Mine is a 70 L per day from Walmart and was about 300 bucks.
Timber king 2000, 277c track loader, PJ 32 foot gooseneck, 1976 F700 state dump truck, JD 850 tractor.  2007 Chevy 3500HD dually, home built log splitter 18 horse 28 gpm with 5 inch cylinder and 32 inch split range with conveyor powered by a 12 volt tarp motor

wkf94025

I have two solar kilns with ~1500bf capacity each, based on VT design, with temp-triggered (or phone app triggered) louvered exhaust fans on east and west ends.  I use Honeywell residential DH's, about $350 each.  If your lumber economics are as solid as they appear, going through one or two of those a year doesn't break the bank.  They can wring a LOT of water out of the kiln in the early drying, circa 5-10 gallons per day per DH.  Their operations also throw off heat, which is beneficial, right?  I also use a linear array of 5" computer fans to recirc internally.  Check my other posts for graphs and details on the performance.
Lucas 7-23 swing arm mill, DIY solar kilns (5k BF), Skidsteer T76 w/ log grapple, F350 Powerstroke CCSB 4x4, Big Tex 14LP and Diamond C LPX20 trailers, Stihl saws, Minimax CU300, various Powermatic, Laguna, Oneida, DeWalt, etc.  Focused on Doug Fir, Redwood, white and red oak, Claro walnut.

Crusarius

wkf94025 that sure would be a kool build to see. Any chance you can do a build thread on your kiln setup?

teakwood

Kiln heat controller in Drying and Processing

I'm getting the plans together for the solar kiln. I like this gizmo so I can program by which temperature the fans start. What else do I need? Power vents for exhaust air or just manual? Could be controlled by this controller depending on humidity

https://www.ebay.com/itm/114884966273
National Stihl Timbersports Champion Costa Rica 2018

YellowHammer

No controller necessary for a solar kiln.  The vents are separated, 2 generally on the pressure side, 2 on the vent side, so 4 total with 2 mounted high and 2 mounted low.  I used plastic $20 foundation vents that slide open and closed.  There is no need to do anything other than make manual adjustments.  A solar kiln is the Easy Bake Oven of the kiln world.  If the inside is real hot and muggy, then you are not venting enough moisture so open the louvers a little more, if the inside is cool or only warm then close them a little.  If the inside is hot and dry, then the load is done.  That's pretty much it.  Don't let it get so hot inside that you burn the plastic roofing material, that's about 160F.  Been there done that.  

Once you get the feel for your consistent load size, then the vents need not be adjusted for weeks if not seasonal.  The fans I use are 2 Wal Mart box fans, $20 each, set on high.  There is no need for a vent controller or a temperature controller, a solar kiln isn't rocket science, it's too easy.  It just works, if you have sun.  I've told Gene this, it's one if the most elegant and simple designs possible, and it just works.  It like a bowling ball, it's simple, it works, don't overcomplicate it.  

Remember that a DH kiln works 24/7 and are being used to dry wood right on the maximum allowable drying rate curve, so controllers are necessary.  A solar kiln only works during the daytime so it's duty cycle is already cut in half, and at night the temp drops and the humidity comes up and the wood equalizes and cools.  That eliminates the issues of case hardening, stress relieving and pretty much anything else.  Just copy the Gene's Va Tech design and it will work.  2 layers of transparent plastic for the roof, one outside, one inside.  Paint everything flat black, inside and outside so the kiln itself become a solar collector. Use a plastic tarp dropped down on the wood stack as a baffle.  I use a couple sheets of corrugated roofing metal, painted flat black, laid right on the wood stacks.  Put the wood in it, put the metal on the wood, close the door, crack the vents, and walk away.

During the rainy season, close all the vents and put a $160, 60 quart Wal Mart dehumidifier inside, and set it for continuous on with a drain hose.  I used to put mine right on the lumber stack and plug it in.  It will last a couple years and die, so get the 2 year replacement service contract for it.

Don't get me wrong, you can make a solar kiln very complicated, but Gene designed it for simplicity. I've been running one for 15 years, 24/7.  Well 15 years, 12/7 anyway, unless there is a bright moon.

Seriously, it's no more than a black car parked in the Mall parking lot in the summer heat with a load of wood in it.  So crack the windows a little.  That's pretty much it.....  
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

caveman

As I think I previously mentioned, our kiln does not get as hot now as it did when the poly panels were new and clean/clear but it still does a good job drying wood.  We don't have any vents in ours but when the wood has high moisture content, we leave the doors slightly open.  When the MC gets lower, we close it up and let the moisture get out through the leaks and I generally open the doors for a few minutes in the heat of the day to purge the moist air.  

This afternoon around 5:15 it was still 80° in the kiln and the load of cypress that was put in about two weeks ago is considerable drier. 

  I took this picture after opening both doors for a short time.  The doors are still slightly open, maybe 1/8" gap.  On this load of cypress, we have been running fans continuously.  
Caveman

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