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General Forestry => Drying and Processing => Topic started by: Glenn1 on August 18, 2014, 08:46:35 PM

Title: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 18, 2014, 08:46:35 PM

Hello,

I have been reading many posts but this is my first post.  Over the weekend, I went to Virginia  and picked up 400 bf of 5/4 walnut.  It is beautiful wood and it looks to be over 95% heartwood.  This is my first attempt starting with green lumber.  According to the sawmill owner, the logs were cut a while ago and the ends were not sealed.  There is some checking but it looks manageable.  I realize that my use of AnchorSeal 2 is probably too late but I used it anyway.  It is now stickered and has a corrugated metal roof on to help protect against rain and too much sun.  I live amongst many trees so it should not be overly sunny.  I just hope that I can get enough air circulation.

I am conflicted to build a dehumidification kiln or a solar kiln on my property.  My initial thought was a DH kiln in my workshop (heated and air conditioned) but then I read about the chance of fire.  I found some plans on building a DH kiln in FWW using a dehumidifier and a humidifier.  I also found plans in American Woodworker using similar equipment.  I travel a couple of days each week but I thought my wife would monitor the amount of liquid that came from the unit.  I am also using a Lignomat DX/C with probes inserted into the wood on 12' cables. 

I was planning on a small kiln that would handle at most 400 bf.  I understand the downside of using a solar kiln in the winter but just don't know which style of kiln will give me the best chance of quality lumber.  I am doing this strictly for myself.  I'd rather not wait a full year to get the lumber down to 7-8% but I'm not trying to make a living on it either.  I am a hobbyist. 

Based on plans that I have been evaluating, it looks more difficult and more expensive to build a solar kiln. I am trying to keep my cost down since it will not be used for a business venture.   I am here to get any and all thoughts about my dilemma.  Thank you!
Title: Re: Which to build? Solar or DH Kiln
Post by: WDH on August 18, 2014, 09:24:26 PM
I have the Nyle L53 and love it.  It is a little wood drying beast.
Title: Re: Which to build? Solar or DH Kiln
Post by: Compensation on August 18, 2014, 10:08:01 PM
Welcome Glenn! I am just a novice to the kiln stuff, but what I learned after I built my solar kiln makes me even more happy that I built it. I found out that a solar kiln cannot drop below 6% I believe. You can store your dry lumber in there without problems. If set up with solar panels and batteries it's free to run and operate. They can kill all your plants when you try to use it as a greenhouse. :D There is an abundance of pros here that will help you like they did for me.
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 18, 2014, 10:14:31 PM
Quote from: WDH on August 18, 2014, 09:24:26 PM
I have the Nyle L53 and love it.  It is a little wood drying beast.

Are you using it strictly as a hobbyist or do you use it for income?  I worry that a Nyle may be more costly than I can justify for a couple of hundred bf per year. 
Title: Re: Which to build? Solar or DH Kiln
Post by: mikeb1079 on August 18, 2014, 10:34:23 PM
i think pineywoods built a solar kiln while also using a small dh as well, kind of a hybrid system if you will.  there's a couple of threads on it here i think, lemme look....

here's planman's version:

https://forestryforum.com/board/index.php/topic,50281.0.html

more related:

https://forestryforum.com/board/index.php/topic,68153.msg1066993.html#msg1066993
Title: Re: Which to build? Solar or DH Kiln
Post by: Ianab on August 19, 2014, 04:08:16 AM
For the hobbyist I would think a solar unit would be the way to go.  Low cost, easy to operate, low maintenance etc.

For a commercial operation it's not as clear cut. Then you need to be able to get your wood dry on some sort of reliable schedule. Waiting 4 months for the winter load to dry is a problem if you have clients waiting. For a hobby guy, no big deal.

Ian
Title: Re: Which to build? Solar or DH Kiln
Post by: jdtuttle on August 19, 2014, 06:26:33 AM
Take a look at Sauno DH kiln made by Logosol. Mine has an 800 BF chamber & does a good job for me. I'm building a 3000 BF Nyle now. If money isn't a problem start with a small Nyle.
Good Luck
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 19, 2014, 08:50:10 PM
For someone that needs to dry 5000 BF per year or less, the solar kiln is the way to go.  As you get larger, you are betting the business on whether the sun will shine.  Further, you will not get very much drying during the wintertime.  I favor the Virginia Tech design for simplicity and very low operating costs, with no casehardening stress and the low final MC that is desired for most hardwood lumber.  The key to the VT design is one square foot of collector (measured perpendicular to the sun at noon) per 10 BF of lumber.
Title: Re: Which to build? Solar or DH Kiln
Post by: red oaks lumber on August 19, 2014, 09:01:25 PM
which ever setup you go with, fire threat in a dh is a non issue. i dont have a working knowledge of solar kilns but, i would think the initial start up costs would be alot less.
Title: Re: Which to build? Solar or DH Kiln
Post by: YellowHammer on August 19, 2014, 11:02:46 PM
Quote from: Glenn1 on August 18, 2014, 08:46:35 PM
but just don't know which style of kiln will give me the best chance of quality lumber.
All three styles of kilns, whether solar, solar+DH, pure DH, will yield excellent, very high quality lumber.  I've used all three for a number of years and each has its advantages and disadvantageous.  The pure solar is more forgiving but doesn't sterilize consistently throughout the year, and can finish a load in a reasonable time in the summer, but is painfully slow the winter.  The solar+Homeowner DH can be a little more complicated and stressful to the lumber, but will easily finish air dried hardwood in 3 weeks or less.  The pure DH kiln like a Nyle will finish out an air dried load every 5-10 days depending on species.

Quote from: Glenn1 on August 18, 2014, 08:46:35 PM
I'd rather not wait a full year to get the lumber down to 7-8%
Air drying will only get you down so far based on your local seasonal conditions, no matter how long lumber is air dried.  You can do an internet search for what can be expected in your area.  Around here, in North Alabama, 12% is the norm.

Quote from: Glenn1 on August 18, 2014, 08:46:35 PM
Based on plans that I have been evaluating, it looks more difficult and more expensive to build a solar kiln.
Nah, in its most basic form, a solar kiln is just a small, well insulated shed with a couple fans and a slanted sunroof facing South.  ;D.  I built mine out of sawmill wood and Wal Mart box fans in a couple weekends, and I can pick it up with my forklift and move it wherever I want.  If I can build one, anyone can. Logs of very knowledgeable people here on the Forum who can help you out.

Good luck which ever method you choose. 
YH
(https://forestryforum.com/gallery/albums/userpics/21488/3758/263.jpg)
Title: Re: Which to build? Solar or DH Kiln
Post by: pineywoods on August 19, 2014, 11:50:28 PM
YH covers  it nicely, it mostly depends on your needs..Sounds like for your operation, solar/dh of appropriate size would fill your needs. The pineywoods design is a bit different from textbook solar units, even dis-regarding the dehumidifier. It is the result of a lot of trial and error and a bit of heartache. Would you believe it can actually RAIN in a kiln? I have no doubt it could be improved. I'd like to see how well or if at all it would work with NO fans...
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 20, 2014, 08:43:56 AM



Thank you Professor Wengert, YellowHammer, WDH, Compensation, Ianab, Pineywoods, mikeb1079, jdtuttle, and Red Oaks Lumber.  From your posts and my low volume of lumber that is needed, I can see that I am being steered towards a solar unit.

Before coming to this site, my research took my to two articles pertaining to making a home made DH unit.  One was from FWW in issue #91 and the other was in an issue of American Woodworker published in 2002.  I am concerned about sterilizing the lumber since my projects will end up in my home.  Are there negatives to building a DH in this manner?  It uses a home DH unit (may last 1-2 years), a small heating unit (they used light bulbs) and a humidifying unit to condition the wood at the end of the process. I believe that it suggests a maximum temperature of 120 through most of the process although I could crank it up at the end for sterilization.  I have room in my shop to build a boxed unit and the shop has heat and an AC unit.

I am not questioning anyone's suggestions and I hope you know that I am very appreciative for  your comments.  If you could point out the negatives to building such a unit, I would be thankful.  Obviously, I do not want to chance a fire but I don't want bugs in my wood either. 

Thank you,
Glenn
Title: Re: Which to build? Solar or DH Kiln
Post by: LeeB on August 20, 2014, 08:53:21 AM
I don't see why you couldn't dry it in a solar kiln and the steralize it in a hot box afterward, but then I have no experiance with a kiln.
Title: Re: Which to build? Solar or DH Kiln
Post by: pineywoods on August 20, 2014, 09:45:25 AM
Glenn, with the pineywoods setup, not enough heat to sterilize is not a problem. We have documented 180 degrees more than a few times. The only downside I have seen in a few years of operation, is, it is possible to get some light case hardening, and LeroyC's melted the plastic blades on the fans.. ;D Be aware that trying to make a solar kiln behave like a conventional is an exersize in frustration. They are different.
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 20, 2014, 04:15:12 PM
Quote from: pineywoods on August 20, 2014, 09:45:25 AM
Glenn, with the pineywoods setup, not enough heat to sterilize is not a problem. We have documented 180 degrees more than a few times. The only downside I have seen in a few years of operation, is, it is possible to get some light case hardening, and LeroyC's melted the plastic blades on the fans.. ;D Be aware that trying to make a solar kiln behave like a conventional is an exersize in frustration. They are different.

Can you tell me where I can get information on your pineywoods setup?  All I know is that it is basically a solar kiln with a DH unit.  I am sure that this is an  over simplification.  With the DH unit operational, do I run the risk of increased case hardening?
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 22, 2014, 12:45:28 AM
With any kiln, the temperature achieved depends on the energy input and the energy loss.  The greater the difference between these two numbers, the more energy available for heating.  The advantage of solar is that it is free after you have a collector. 

You can get a kiln hotter by increasing the solar collector size or by putting in energy from an outside source such as electricity, propane, etc.

You can get a kiln hotter by reducing heat losses through the walls and floor by using lots of insulation and maybe caulk.  You can reduce solar collector losses by using triple layer of clear material, by moving the black absorber further away, and by using a heat reflecting material such as glass.  You can reduce heat losses by reducing the amount of water to be evaporated...less wood in the kiln or air drying first.

The VT design will achieve 50 F above outside when the lumber is fairly dry.  When really dry or when no lumber is in the kiln or when the fans are off, the temperature near the roof will exceed 200 F on a sunny, warm day.

You can also consider having a cover for the clear solar collector, so you can cover the kiln's main heat loss item on a cloudy day or cold day when losses can exceed energy input.  This is especially helpful when there is an outside source of heat or is a DH unit.

With a DH unit, the electric costs can be large.  Check the current draw of the compressor and its fan.  If your electric bill has a total cost of $.20 per kW, a 110v. unit with 8 amp draw, running 20 hours day will use 0.88 kW or $ 0.18 and hour.  Then x 20 hours is $3.60 a day.  This is true if the unit is for lumber drying, a basement, or other use.รจ

Regarding the AW kiln, I was involved with this kiln.  It does present a fire danger, as it does not have safety controls or features found in other kilns, such as a DH.  The light bulbs are really hot.  I suggest that putting it in your shop or home is not the best idea.  There are a fair number of house fires reported from small DH units that fail, overheat, etc.  The small units are not that safe especially in a small kiln chamber.

Note that if you air dry first, then casehardening stress will not be an issue in a solar, solar-DH, or straight DH kiln.
Title: Re: Which to build? Solar or DH Kiln
Post by: LeeB on August 22, 2014, 02:11:47 AM
Gene,
Would case hardening be an issue if you solar dried first and then used a 'hot box' simular to the AWW idea for a final sterilizing?
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 22, 2014, 10:38:14 AM
Dr, Wengert,

I have been looking at the VT solar kiln and I am not able to see black absorber that you mentioned.    In an earlier post, I read that it should be wood that is painted black.  Can you give me a little more detail on that piece of wood.  Can it just be plywood and how far should it be set back from the collector? 

I also found a smaller version online at this site:  http://www.americanwoodworker.com/blogs/projects/archive/2009/09/29/solar-kiln.aspx

In this article, the gentleman speaks about downsizing the VT kiln that you designed.  Again, I can not see any wood mounted below the corrugated roofing material. 

When you speak about a triple layer of clear material to enhance the heating process, would corrugated
roofing material be acceptable?  Can the 3 units be put directly on top of each other or do I need some airspace?

Your thoughts would be greatly appreciated.  Thank you
Title: Re: Which to build? Solar or DH Kiln
Post by: pineywoods on August 22, 2014, 11:22:15 AM
Glenn, go here https://forestryforum.com/board/index.php/topic,50281.0.html

Lots of pics and good write-up. Some additional tidbits

The transparent roof glazing needs to be transparent to infra-red radiation, in    other words greenhouse quality.
The actual collector is old corrugated metal roofing painted flat black and fastened to the bottom of the rafters
Leave a 6 inch gap at the top and bottom of the collector, in other words the collector is a foot shorter than the glazing. Otherwise, you will probably melt your plastic glazing.
Shut off the dh unit during the day, most of them will have a high temp shutdown somewhere around 100 degrees. residential Dh units don't work very well at high temps.
Yes, the interior of the kiln will cool down at night. Downside to that is extended drying time. Upside is cool down allows the wood to stabilize, fewer defects. The efficiency of the dh goes up dramatically as the temp drops.
Don't get hung up on optimizing everything. Every specification is a compromise, it ain't exactly rocket science  ;D 
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 22, 2014, 11:40:30 AM
I gotcha.....thanks for your suggestions.     :D
Title: Re: Which to build? Solar or DH Kiln
Post by: giant splinter on August 22, 2014, 12:18:46 PM
 http://www.americanwoodworker.com/blogs/projects/archive/2009/09/29/solar-kiln.aspx
Glenn that link is very helpful and for the most part just about covers the solar kiln, the other links and photos are also very helpful so I suspect this will be a good winter project for many of us and thanks goes out to all the others for their input also is very important.
Great Posts and an informative effort on everyones part ..... Thank You Glenn for starting this one off in the right direction. ;D
Title: Re: Which to build? Solar or DH Kiln
Post by: Bill Gaiche on August 22, 2014, 01:22:18 PM
Here is a little info for you to check out. bg
http://www.solarkilninfo.com/solar-kiln-resources-on-the-internet/links-to-plans-for-building-a-solar-kiln
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 22, 2014, 03:43:12 PM
Casehardening develops when the lumber is over 50% MC...early in the drying process.  Actually the outside is not harder than the inside, so the name is not very descriptive.
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 22, 2014, 03:56:58 PM
You have all given me great information and I think that I can now build a viable solar kiln.  One more dilemma.  I live on 7 acres that is virtually all trees.  There is one location near my shop that can get direct sun from approximately 11am to 2 pm in the summer.  In the winter, it should not be a problem.  Is that enough sun to make this cook?  There are tall trees to the east and also the west and my wife loves her trees just as they are.    I tried to download photos but they are in jpeg format so I guess they are not accepted that way.  Any suggestions?
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 22, 2014, 04:12:26 PM
The black absorber is more effective if it is far from the collector' sclera cover.  So, in the VT design, the interior walls and the fan baffle are black as well as the top of the lumber pile.  Plywood is fine, but plastic is ok too.  Avoid metal if possible as its heat properties are not as good as wood.

A collector cover should transmit as much solar energy as possible.  So, it should be clear.  On the other hand, if it is clear but breaks, tears or degrades quickly, it is not so good.  Hence many people do not use glass, but use corrugated fiberglass.  It transmits about 85% of the solar.  The loss of 10% over glass means that drying will take 10% longer! but what is three or four more days in a solar kiln?

Once the solar is in the kiln, it must be converted to heat.  That is what the black collector is for. 

Once you have heat, the collector will lose energy by conduction (hotter on the inside and cooler on the outside) and by infrared radiation.  To reduce the heat on the immediate inside of the cover, move the collector further away.  Second, use two layers which forms an insulating effect.  With three layers the insulating is even greater, but the solar transmission is further reduced.

The ideal cover for controlling the transmission of infrared through the cover to the outside will reflect the infrared heat.  (To reduce emission of infrared heat in glass windows, the glass can be coated to make "low e" glass.). Some materials like glass reflect a lot already.  Some films also do this, although some so-called solar films do not do it well, but these products are stabilized to avoid uv degradation and that is why they are used for solar.  Interestingly, glass that has a green hue on the edge does not reflect as well as non- green on the edge glass.  Again, with low e glass being expensive and the risk of glass breakage and the weight of glass, fiberglass and plastic films that are uv stabilized are used.

Overall, It is a compromise between the best energy product and the cost and the durability and ease of installation.  For some people, the best might be some old thermo pane windows.  Other might even use some old sliding patio doors which gives two layers and an insulated space...thermo pane.  For others, fiberglass corrugated on the outside and a solar film on the inside to make two layers.

Note that when the sun is not shining, the collector becomes 100% a loser of heat.   With the huge heat losses in the cool or cold winter when even on a sunny day the solar input is small (sun angle low and sunny hours few), a totally insulated collector is best, which points to 100% DH or 100% hot water kiln.

Note that the amount of solar energy into a kiln of any design is controlled or limited by the size of the collector at noon perpendicular to the sun.  Another way to say this, is that it is the shadow area that the collector makes at noon perpendicular to the sun.  For this reason, most good solar kilns use the 1 sq ft to 10 BF ratio.  That gives a good amount of energy for drying reasonably fast, but not too fast.

Questions?
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 22, 2014, 04:14:49 PM
Let's say your wooded location gives you 2/3 of the open location.  So, instead of 45 days to dry green oak, it will take you 67...that is, 50% longer.
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 25, 2014, 07:16:51 PM
Here is a hypothetical sizing question.  If I build a kiln that is 8 feet high in the back by 8 feet deep and 12 feet in length, I come up with approximately 132 sq feet for the collector.  Based on the 10 bf of wood to 1 sq ft of collector, I should be able to dry upwards to 1300 bf at a time.(I think)   Now what would happen to the wood if I only put 300 bf into the kiln either as green wood or air dried wood?  Would the heat from the kiln  overpower the 300bf of wood and cause all kinds of problems or would it work fine for any amount smaller than the maximum?
Title: Re: Which to build? Solar or DH Kiln
Post by: WDH on August 25, 2014, 08:48:25 PM
For many species drying from green, the answer is Yes.

With very fast drying species like most softwoods and some soft hardwoods, you might get away with it.  With green oak or other slower drying species, that would wreck it. 

Air dried wood would tolerate it better. 
Title: Re: Which to build? Solar or DH Kiln
Post by: GeneWengert-WoodDoc on August 26, 2014, 12:44:26 AM
With thicker wood, slower drying is required.
Title: Re: Which to build? Solar or DH Kiln
Post by: Ianab on August 26, 2014, 01:52:52 AM
You can always rig up a removable cover for part of the collector. Couple of sheets of tin and some studs and wing nuts to hold it in place. Cover 2/3 of the collector area and your ratio is sensible again. Of course if you are drying softwoods, then just let it cook.

Ian
Title: Re: Which to build? Solar or DH Kiln
Post by: Glenn1 on August 26, 2014, 07:43:30 AM
Quote from: Ianab on August 26, 2014, 01:52:52 AM
You can always rig up a removable cover for part of the collector. Couple of sheets of tin and some studs and wing nuts to hold it in place. Cover 2/3 of the collector area and your ratio is sensible again. Of course if you are drying softwoods, then just let it cook.

Ian


Hello Ian,
So you are saying  to put the tin cover on the outside of the clear collection plate to block the sun? Possibly, I can find the same corrugated sizing so the tin cover fits right on top of the clear top.  Since the cubic footage of the larger kiln will be considerably larger than the stack of lumber, I am guessing that it will be a trial and error scenario adding coverage until I get the correct temperature.    Would that be a correct assessment?
Title: Re: Which to build? Solar or DH Kiln
Post by: Ianab on August 26, 2014, 04:12:03 PM
Yeah, it's not an exact thing. But the collector sizing doesn't need to be exact, you have quite a margin between too fast and too slow. Covering part of the collector is just a way of "throttling" the solar power.

Ian