Advanced Drying Topics

[GeneWengert-WoodDoc]

I have a question.  What drying topics would you like to learn more about?  As you might know, I wrote a column on drying in Sawmill & Woodlot, teach at advanced drying seminars (like the one at North Central Community College in August here in WI) and give short talks at shows like the Paul Bunyan show in Ohio this fall.  So, if you were to read or attend a class, what would you like to hear, see, or learn more about..specific or more general?  Thanks.

[jdtuttle]

I would like to learn more about hardwood drying schedules in a dehumidification kiln. Building a 3000 bf Nyle kiln now & hope to be running by this fall.
Jim

[Den Socling]

It always amazes me , Gene, that you can patiently answer the same questions over and over and over! Finding topics to speak and write about must be quite difficult when you are looking for a "fresh" subject.

[longtime lurker]

Advanced drying?
I'd like to see a real world cost/benefit analysis of presurfacing. Installation costs, mill flow issues, vs energy savings and value increase kinda thing. Has anyone ever looked at this with commercial numbers thrown at it? Has anyone ever looked at it apart from drying red oak? (Please Gene, tell me one of those papers you wrote had a little sample of eucalypt timber in one corner no-one mentioned) ;D

[redprospector]

I'd like to know if I'm crazy?  :D
I've been looking at solar kilns for a long time, and the thing that bothers me is temperature loss at night. I've devised myself a plan,  8) there is a place about 50 miles from a property I own, that is covered in black volcanic rock. I'm thinking that if I build the collection chamber with a couple of feet of volcanic rock in the bottom, and the actual lumber drying area beside it, would the extra cubic footage of the kiln eliminate any heat storage I could gain in this design?
In short, do ya recon it would be worth the effort to try to retain heat with volcanic rock?

Andy

[GeneWengert-WoodDoc]

Thanks for all the comments so far.  They are helpful indeed.

Special note to RedProspector.  My approach was to use all the heat that came in essentially right away.  Over 24 hours you will have the same heat input, so why not use it right away?  If you have a second collector to collect and then store, this would add quite a bit to the cost.  Most importantly is that the heat loss cools AND increases the RH high enough at night to relieve drying stresses (also called casehardening).  This stress relief is very important benefit.  Overall, if you want to dry twice as fast, but in half the amount of lumber and then build a second kiln if you need more annual capacity...cheaper than storage.

[longtime lurker]

I'd like to know if I'm crazy?  :D
I've been looking at solar kilns for a long time, and the thing that bothers me is temperature loss at night. I've devised myself a plan,  8) there is a place about 50 miles from a property I own, that is covered in black volcanic rock. I'm thinking that if I build the collection chamber with a couple of feet of volcanic rock in the bottom, and the actual lumber drying area beside it, would the extra cubic footage of the kiln eliminate any heat storage I could gain in this design?
In short, do ya recon it would be worth the effort to try to retain heat with volcanic rock?

Hi Andy,
Have a look online for Solar Dryers Australia. They do a modified solar kiln,utilising solar hot water systems so the hot water tanks act as a heat sink. There's a guy down the roads got one and they are pretty dammed good. Overpriced but... it wouldn't be that hard to make one yourself from off the shelf component

[GeneWengert-WoodDoc]

Note to LongTimeLurker...
I did do a complete analysis for and with a company, but cannot share specific cost data...part of the agreement.  It was positive benefit for 5/4 red oak.

I have not looked at other species...sorry.

[GeneWengert-WoodDoc]

Storage of solar heat using water is quite popular in the solar field, but is very expensive, with special concerns when freezing temperatures or snow occur.  In some cases, the overall efficiency of the collector is about half of what is calculated and designed.

Does it work?  Yes.  Is it cost effective in the case of wood drying.  Probably not, unless there is a government grant or substantial tax benefit.

[redprospector]

Thanks for all the comments so far.  They are helpful indeed.

Special note to RedProspector.  My approach was to use all the heat that came in essentially right away.  Over 24 hours you will have the same heat input, so why not use it right away?  If you have a second collector to collect and then store, this would add quite a bit to the cost.  Most importantly is that the heat loss cools AND increases the RH high enough at night to relieve drying stresses (also called casehardening).  This stress relief is very important benefit.  Overall, if you want to dry twice as fast, but in half the amount of lumber and then build a second kiln if you need more annual capacity...cheaper than storage.

Thanks Gene,
The property I intend to build the kiln(s) on is in Tularosa, NM. It is in the desert, during mid summer temps. can reach well over 100 degrees. I'm concerned that it could reach over 200 inside the kiln without a separate collector. How hot is too hot?

Andy

[Left Coast Chris]

Gene, thanks for considering some topics.  Here are some potential topics:

1)  Small scale specialty drying.  I turn bowls and mostly rough out to triple thickness then wrap in newspapers, put in a paper grocery bag  and put on the shelf for 4-6 months.  I live in the northern Sacramento Valley which is very hot with a lot of low humidity in the summer.  I generally try to avoid handling and air drying in the summer. But.... there is always that wet piece that shows up I have to handle.     So, some mini kiln ideas and operation basics would be good along with considerations for difficult woods such as apple, apricot, cherry, cottonwood burl, pistachio etc.  Some of these may take peg or a miracle.... not sure.  If there have been successes; that would be good to know about.   I just had to rough out some camphor wood.  It handled like it may shrink a lot.  Have it in double paper bags now since we have been having high heat up to 116 degrees.  If a small kiln could handle better it could be a significant help.

2)  Plans for a solar or dehumidification kiln based on salvaged or common off the shelf parts.

3)  Drying resource list:    Shrinkage data for different woods,  kiln plan sources along with matching operation guidelines, parts sources, storage sources, moisture meter recommendations -- what type is best.....

4)  Steam bending and shaping methods and apparatus.  Recommended wood for bending.

I realize it may take a book to cover some of these subjects but thanks for offering to provide info.

[trim4u2nv]

Like to know how to better spot green wood defects that become serious defects after drying.  I.e. small splits that become full length.  Lumber that is prone to collapse (currently can smell in red oak).  Or sometimes we have a board sawn perfectly flat when green and  dried it looks like a wrinkled bedspread or puckered.  In other words how to prevent junk wood from entering the kiln in the first place.  Maybe some of these boards would benefit from slower drying also.

[GeneWengert-WoodDoc]

Andy,
Probably makes most sense to air dry using shade-Dri cloth and then finish in the kiln.  Once air dried, you cannot heat it too hot if fans are running and vents are opened, as needed.