The Forestry Forum is sponsored in part by:

iDRY Vacuum Kilns


Forestry Forum
Sponsored by:


TimberKing Sawmills



Toll Free 1-800-582-0470

LogRite Tools



Norwood Industries Inc.




Your source for Portable Sawmills, Edgers, Resaws, Sharpeners, Setters, Bandsaw Blades and Sawmill Parts

EZ Boardwalk Sawmills. More Saw For Less Money!

STIHLDealers.com sponsored by Northeast STIHL


Woodland Sawmills

Peterson Swingmills

 KASCO SharpTech WoodMaxx Blades

Turbosawmill

Sawmill Exchange

Michigan Firewood, your BRUTE FORCE Authorized Dealer

FARMA


Council Tool

Baker Products

ECHO-Bearcat

iDRY Wood Lumber Vacuum Drying for everyon

Baltic Abrasives Technologies Nyle Kiln Dry Systems




Author Topic: Solar kiln paint or not?  (Read 738 times)

0 Members and 1 Guest are viewing this topic.

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Solar kiln paint or not?
« on: March 27, 2019, 03:51:42 AM »
The question, which would create more heat? Or which would work best? Paint the inside of the kiln black or install a plenum painted black 6 or 8 inches off of the collector? I have some used aluminum roof panels with some nail holes to use for a plenum.  

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Re: Solar kiln paint or not?
« Reply #1 on: March 27, 2019, 06:37:40 PM »
Ok experts what do you say?

Offline YellowHammer

  • Senior Member x2
  • *****
  • Posts: 3888
  • Age: 54
  • Location: New Market, Alabama
  • Gender: Male
  • Take Steps to Save Steps
    • Share Post
    • Hobby Hardwood Alabama
Re: Solar kiln paint or not?
« Reply #2 on: March 27, 2019, 10:03:12 PM »
The entire kiln should be painted black, both inside and out.  Even though the walls are insultated, any temperature rise of the outside will help the inside.  Also, I lay black painted corrugated roofing tin on top of the wood stack,  which is under the black painted fan baffle, from which drops the black painted tarp.  In a solar kiln, if it isn’t black, it should be.    

HobbyHardwoodAlabama.com

Offline doc henderson

  • Senior Member x2
  • *****
  • Posts: 1308
  • Age: 58
  • Location: Hutchinson, Ks
  • Gender: Male
  • Evil Prevails when Good Men Standby and Do Nothing
    • Share Post
Re: Solar kiln paint or not?
« Reply #3 on: March 27, 2019, 10:18:19 PM »
in theory you would put a back on the collector esp if it were separate from the kiln.  you could do it on the VT plans and keep light from shining on and bleaching/degrading your wood.  The benefit is you can insulate the back and reduce night heat losses. esp if the top and bottom of the plenum had gates to stop airflow when the fans were off.  It would not be needed for a firewood kiln. Or you can keep it simple with no back on the collector but cover the wood stack with black metal or wood to shield it from UV.  The old style passive solar used the angle of the collector plenum like a chimney to move air with cold air return back to the bottom.  covering the underside of the collector rafters will help protect your polycarbonate or glazing.  should be flat black for the record  :)

Offline GeneWengert-WoodDoc

  • Senior Member x2
  • *****
  • Posts: 2565
  • Location: Bishop, GA
  • Gender: Male
  • Author of "Sawing Hardwood Lumber"
    • Share Post
    • Book on Sawing hardwood Lumber
Re: Solar kiln paint or not?
« Reply #4 on: March 27, 2019, 10:57:14 PM »
There is a fixed amount of energy coming through the collector covers. Once inside the kiln, we need it absorbed about 95% so that is done by using a black surface or surfaces. The easiest is to paint everything black.  A sepaate black absorber can be used but there is no overall advantage or disadvantage.  In the VT design, I went with the easiest idea...paint wall, fan shroud and pile cover black.
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

  • Senior Member x2
  • *****
  • Posts: 3888
  • Age: 54
  • Location: New Market, Alabama
  • Gender: Male
  • Take Steps to Save Steps
    • Share Post
    • Hobby Hardwood Alabama
Re: Solar kiln paint or not?
« Reply #5 on: March 28, 2019, 06:56:37 AM »
Since the entire kiln is considered a solar collector assembly, then everything in view of the aperture (the sun side) should be painted black, including the wood pile which should be covered or otherwise obscured with a black surface.   
HobbyHardwoodAlabama.com

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Re: Solar kiln paint or not?
« Reply #6 on: March 28, 2019, 08:07:34 AM »
OK I think......... But if I put tin behind the collector (painted black) I would not have to paint inside the kiln. I said plenum in my earlier post so my bad. The tin behind the collector would be 6-10" from the collector with a gap at top and bottom and the heat would have a chimney effect. So is what I meant to ask is would this heat the kiln better? Or forget this and just paint the inside? Or no difference? It will be insulated, I am in North-west Pa.  This collector would be on the lines of Pineywoods.

Offline doc henderson

  • Senior Member x2
  • *****
  • Posts: 1308
  • Age: 58
  • Location: Hutchinson, Ks
  • Gender: Male
  • Evil Prevails when Good Men Standby and Do Nothing
    • Share Post
Re: Solar kiln paint or not?
« Reply #7 on: March 28, 2019, 10:43:00 AM »
i think plenum was an ok description.  i the day boys life showed how to make a solar heater with plastic and wood and alum cans.  For a stand alone, you need a glazing, a hot air space and cold air return.  if the collector and kiln space are one, this is not needed.  The idea i had discussed at one point was to combine a solar kiln with a wood fired stove or outside forced are furnace to sterilize.  the problem is that the VT kiln does not hold heat well when outside temps drop due to losses through the large "window"  (solar collector)  as a roof.  so the collector in this application would need to be isolated from the wood space by airflow and insulation.  there are pros and cons.  For a firewood kiln no way I would spend the time and or money for a back on the collector.  For hardwood, you need to protect the wood in the kiln from UV.   If you put a back on the collector, you may need lights in the kiln.  as an example of pros and cons. so paint every thing exposed to sunlight, seal air leaks, insulate well, have fun.  looks like in may, there is a solar kiln seminar.

Offline pineywoods

  • Senior Member x2
  • *****
  • Posts: 5120
  • Age: 83
  • Location: Marion, Louisiana
  • Gender: Male
  • Engineering analysis-just sittin thinkin about it
    • Share Post
Re: Solar kiln paint or not?
« Reply #8 on: March 28, 2019, 11:03:39 AM »
 

YES YES paint everything black, cheap and will definitely help, but not nearly as much as a black metal collector plate..

Some further comments based on my experiences..
How hot... remember I live in the deep south
Couple of profs from Louisiana Tech forestry department instrumented my kiln with recording instruments. Hit 180 deg F on an overcast day
BUT...Thats an empty chamber with NO insulation in the floor and only 4 inch fiberglass batt insulation in the walls, 1 inch styrofoam in the doors. A load of wet wood will lower that due to evaporative cooling.
One local sawyer used plastic walmart fans..the blades melted and fell off. Another used small metal box fans, they all quit due to blown internal thermal  fuses...labeled 200 deg C...
About the black metal collector mounted under the glazing. 2 advantages.. The space between them acts as a plenum. There is a good bit of convective airflow up that plenum. (hot air rises) Allows me to cheat and use smaller fans. Black metal is much more efficient at converting infared radiation to heat, especially when it's perpendicular to the incoming radiatiom. . Plus this gives 2 sides of hot  metal exposed to the air. Effectively twice the heated air..ie I get acceptable performance despite a poorly constructed enclosure..

YES YES paint everything black, cheap and will definitely help, but not nearly as much as a black metal collector plate...

1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Offline GeneWengert-WoodDoc

  • Senior Member x2
  • *****
  • Posts: 2565
  • Location: Bishop, GA
  • Gender: Male
  • Author of "Sawing Hardwood Lumber"
    • Share Post
    • Book on Sawing hardwood Lumber
Re: Solar kiln paint or not?
« Reply #9 on: March 28, 2019, 01:26:28 PM »
A black plate, metal or wood, or a black painted inside kiln will both absorb the same amount of solar energy and therefore will generate the same amount of heat.  In either case, the sun will not "see" the lumber so only the top of the lumber pile needs a black cover.

In fact, if you use a black fan baffle that is flexible at the bottom, you can have the baffle go from the fans that are close to the rear wall to the front of the lumber pile.  Note that the difference from having a black plate versus a black kiln is that the plenum space in the black kiln is larger.  At the end of the day, both designs will have the same solar input, and the same efficiency of absorbing the solar energy, so the same amount of heat available for drying...assuming the same insulation in the walls, etc. and the same glazing.  Stated another way...the same energy comes in, the same is converted to heat, the same heat losses, and the same energy for evaporation.  A smaller absorber well get hotter but has less area, but the BTUs absorbed and released will be the same...a black absorber absorbs all the sunlight, so its shape, area, or location makes no difference.

The black fan shrouds, the black top of the lumber pile and the black walls will get hot and the hot air will rise and provide help for the fans...no difference.  At the end of the day, you will get the same amount of heating from using a collector plate directly under the clear glazing or with a black painted inside. In the VT kiln the fans blow to the South and then through the lumber pile.  If run the other direction, some of the newly collected heat will go out through the vents and not do any work or evaporation.  The collector area is same as the shadow that it casts at noon.  The VT kiln uses 10 BF of lumber for each square foot of collector area.  If you want hotter, increase the roof area or decrease the amount of lumber.

The VT kiln will get 200 F without any lumber in it.  The energy needed to heat air to 200 F is very small.  We can get close to that inside a closed car.  So, an empty kiln always needs to have the vents open wide to avoid damaging the kiln....maybe even run the fan too.  But once there is wet lumber in the kiln, the energy for evaporation will use the heat.  In fact, if the kiln heats very much with wet lumber, that is an indication that the heat is not being used for drying the wood very efficiently.

For new solar kiln people, one key feature when drying wet lumber green from the saw is that the kiln will cool at night and this 99% RH will relieve the drying stress, also called casehardening.  This same high RH also occurs in early morning in most of the US outside, so well air dried lumber is also free of stress.  Remember when using the prong test for measuring stress, it only works when there is no moisture gradient.

The average EMC in the VT kiln (low humidity when the sun is shining and the kiln is hot, and high humidity at night and early morning) is around 11 to 12% EMC.  So, if you run the fans 24/7, you will dry to about 11-12% MC.  To get drier, you need to run the fans only when the kiln is heated and is therefore drier.

I did write my master thesis on the energy balance for a solar kiln at Colorado State fifty years ago and took five graduate classes in mechanical engineering heat and mass transfer.  For technical people, it should be interesting reading.
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

  • Senior Member x2
  • *****
  • Posts: 3888
  • Age: 54
  • Location: New Market, Alabama
  • Gender: Male
  • Take Steps to Save Steps
    • Share Post
    • Hobby Hardwood Alabama
Re: Solar kiln paint or not?
« Reply #10 on: March 28, 2019, 03:11:34 PM »
Gene,
Isn’t that your 1967 paper “Energy Losses From a Solar Kiln Dryer”?

HobbyHardwoodAlabama.com

Offline GeneWengert-WoodDoc

  • Senior Member x2
  • *****
  • Posts: 2565
  • Location: Bishop, GA
  • Gender: Male
  • Author of "Sawing Hardwood Lumber"
    • Share Post
    • Book on Sawing hardwood Lumber
Re: Solar kiln paint or not?
« Reply #11 on: March 28, 2019, 03:35:43 PM »
The paper is based on the thesis, but there is more detail in the thesis, perhaps somewhat far removed from practical info.
Gene - Author of articles in Sawmill & Woodlot and books: Drying Hardwood Lumber; VA Tech Solar Kiln; Sawing Edging & Trimming Hardwood Lumber. And more

Offline doc henderson

  • Senior Member x2
  • *****
  • Posts: 1308
  • Age: 58
  • Location: Hutchinson, Ks
  • Gender: Male
  • Evil Prevails when Good Men Standby and Do Nothing
    • Share Post
Re: Solar kiln paint or not?
« Reply #12 on: March 28, 2019, 04:04:19 PM »
thanks Doc, i look forward to seeing you in a week or so in Georgia.  i would love a copy of your thesis or info on the paper.  learn something new everyday

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Re: Solar kiln paint or not?
« Reply #13 on: March 29, 2019, 07:53:04 AM »
  THANKS for the info and taking the time to point me in the right direction. This will be a lumber kiln. I did see the class in Va in May. I am about 8 hours from there so I will not be there. Hope to have my kiln done by then.

  My next thing is length, I was thinking 14' to handle 12' lumber. But now leaning 18' to take 16' or 2 packs of 8'. I plan to do this only once as I am out of room, to many trees and no flat ground. If I put shorter wood in a long kiln I will need to block off the ends. No other concerns right?

Offline YellowHammer

  • Senior Member x2
  • *****
  • Posts: 3888
  • Age: 54
  • Location: New Market, Alabama
  • Gender: Male
  • Take Steps to Save Steps
    • Share Post
    • Hobby Hardwood Alabama
Re: Solar kiln paint or not?
« Reply #14 on: March 29, 2019, 08:08:56 AM »
The main thing is to keep the ends baffled and stay within the guidelines of collector area to kiln load.  
HobbyHardwoodAlabama.com

Online btulloh

  • Senior Member x2
  • *****
  • Posts: 1643
  • Age: 67
  • Location: Midlothian, VA
  • Gender: Male
  • I never met an air conditioner I didn't like
    • Share Post
Re: Solar kiln paint or not?
« Reply #15 on: March 29, 2019, 08:13:55 AM »
If you short load it you MAY need to block off some of the collector area depending on the species.  You just don't want to exceed the maximum drying rate.  That would be necessary primarily for oak.  If it's air dried, you'd probably be ok anyway.  It's manageable.  Mine is limited to 12ft long lumber which works for me.  Never had a problem managing smaller loads and I've never had to cover the collector - yet.
HM126

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Re: Solar kiln paint or not?
« Reply #16 on: March 29, 2019, 08:18:18 AM »
Nice all day rain today so I need to make plans for this. Thanks

Offline doc henderson

  • Senior Member x2
  • *****
  • Posts: 1308
  • Age: 58
  • Location: Hutchinson, Ks
  • Gender: Male
  • Evil Prevails when Good Men Standby and Do Nothing
    • Share Post
Re: Solar kiln paint or not?
« Reply #17 on: March 29, 2019, 08:32:08 AM »
The real harm in making it longer is to your billfold. If you can swing it , I think 20 feet is good. My mill cuts up to 21 feet but have not done it.  If I do, it would be a beam and it would prob. be air dried or dry in place.  I think as well for 16 feet you need a little room on each end as well.  just a thought.  remember Nyle has plans based on how much lumber you want to dry.  if you look at the L of this page and go to  Nyle, look at the manuals for their dehumidifiers, and there is a chart on size vs. load.  might be helpful in you decision.

Offline pineywoods

  • Senior Member x2
  • *****
  • Posts: 5120
  • Age: 83
  • Location: Marion, Louisiana
  • Gender: Male
  • Engineering analysis-just sittin thinkin about it
    • Share Post
Re: Solar kiln paint or not?
« Reply #18 on: March 29, 2019, 08:40:11 AM »
The big mistake I made with my kiln was making it 14 feet long to handle 12 ft lumber. 12 ft is an odd length for lumber. Some guy showed up wanting 16 ft stuff right off the bat. I may yet build another one 18 ft..The only extra expense would be for 4 more feet of glazing, and maybe a little more on the doors..
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Offline tacks Y

  • Senior Member
  • ****
  • Posts: 353
  • Location: NW Pa
  • Gender: Male
  • I'm new!
    • Share Post
Re: Solar kiln paint or not?
« Reply #19 on: March 29, 2019, 09:21:14 AM »
I do not have plans to how much or often I use it. The kilns that dried for me one is gone and the other will no longer accept orders. The plan is hard wood floor in the house, carpet is 30 years old. I do have enough roof material already. It will be on steel skids, so they will need longer. Just need to keep wife and plants out of it when not in use.

Online btulloh

  • Senior Member x2
  • *****
  • Posts: 1643
  • Age: 67
  • Location: Midlothian, VA
  • Gender: Male
  • I never met an air conditioner I didn't like
    • Share Post
Re: Solar kiln paint or not?
« Reply #20 on: March 29, 2019, 09:37:03 AM »
Plants shouldn't be a problem.  After one day in an empty kiln, they should be dried up and dead.  

I've been wanting to cook a pork shoulder or a couple chickens in mine between loads, but I haven't gotten around to that.
HM126

Offline doc henderson

  • Senior Member x2
  • *****
  • Posts: 1308
  • Age: 58
  • Location: Hutchinson, Ks
  • Gender: Male
  • Evil Prevails when Good Men Standby and Do Nothing
    • Share Post
Re: Solar kiln paint or not?
« Reply #21 on: March 29, 2019, 09:43:43 AM »
can make jerky.  


Share via delicious Share via digg Share via facebook Share via linkedin Share via pinterest Share via reddit Share via stumble Share via tumblr Share via twitter

xx
Solar kiln interior paint?

Started by vfauto on Drying and Processing

3 Replies
537 Views
Last post September 14, 2017, 08:33:34 AM
by Kbeitz
xx
Mental Exercise! Hybrid kiln design (solar drying concept w/o solar heat)

Started by scsmith42 on Drying and Processing

11 Replies
1640 Views
Last post March 31, 2016, 10:51:46 PM
by GeneWengert-WoodDoc
xx
DC solar powered fans for Solar kiln

Started by Paddock Jack on Drying and Processing

8 Replies
1841 Views
Last post February 21, 2019, 09:21:24 PM
by longtime lurker
xx
Pre-build solar kiln questions(Photos of kiln building progress)

Started by caveman on Drying and Processing

58 Replies
8084 Views
Last post April 17, 2016, 06:35:35 PM
by caveman
 


Powered by EzPortal