I just watched a video here on WOODWEB by green-dri kilns. They say they use Nobel Prize winning technology from Japan. They also say they can dry mixed species and mixed thicknesses. They state that the specially designed walls remove the moisture (which appear to be wood boards) and show a fan in an upper corner and a good sized vent open in the top of the unit. Is anyone familiar with this kiln? I am curious as to how it actually works.
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
I hope they install a kiln so we all can see how dry wood walls will absorb moisture from wet wood and achieve 7% MC. The Nobel Prize stuff is about living cells from Johnís Hopkins. I cannot see the application to drying, but maybe we will learn.
I am just using my healthy dose of skepticism regarding any "new drying technology" because they seem to come and go. I hope they are the real deal because the claims they're making make it an attractive alternative for many species. What makes me think it might actually work as advertised, is if you look at it, it works essentially like a solar kiln but instead of using the sun they use infrared, and instead of trapping the heat and moisture and slowly venting it out, their unit allows it to slowly migrate out through the wall membranes. I wonder how the wood walls will perform long term, when species that need high temps to kill bugs are given a good dose of 130ļ plus supplemental heat for four to six hours?
I don't know how significant it is, but they make the clear distinction that their product is not a wood kiln, but a wood drier. Maybe that's what they're saying - that their unit is not intended to kill bugs, just dry species that aren't prone to infestation? Because they also note in their third party testing that Japanese cedar is termite and bug resistant.
I was not having luck finding someone that owned one. I was interested in the Greenstone statement that some of the dry times could be faster and with less heat. They stated that the wood will dry stronger and with less stress.
I am a one man Woodmizer saw mill and drying operation and I sell my rescued lumber from Florida retail. I also have a Lucas slabbing mill. I normally mill 3" table top slabs from oaks and maples and a few others. My dry time is between two and three years per slab. I wanted to speed up the drying time as cost effective as I could so I was looking for another method to dry and Vacuum kiln was too costly for my small business.
Last year I came across Greenstone lumber drier. It took some time to buy in on the process but after much discussion with the owner and some isolated testing on my own I decided to buy one of their units. My unit is 8' deep x 8' high and about 16' in length. My first load was a mix of big yellow pine timbers (10) 6"x 12" and 10' in length and on top of the timbers I placed (2) 3" x 42" wide and 100" in length laurel oak slabs that had been air dried for several months. I started the unit and in about three weeks I was getting exterior shell readings on my Lignomat moisture at 3 percent on the pine and oak. The pine was showing surface cracks and the oak was drying fine. I was satisfied that this lumber slabs was in good enough shape to work with. The pine i cut off 12" off the end to check the interior. I found the interior to be from 18mc to 30mc. my average was around 18mc was ok as I was taking the wood to be pressure treated. I did not cut the slabs in half to check the interior.
I have just finished a small load of about 500 bf of 4/4 live and laurel oak. After 18 days in the drier my eight sample boards were indicating that they were at 8 mc. I am really happy about what seems like express drying but uneasy that all is evenly dried. I decided to cut the live oak in half and check the core. I found the core to be at 12-15 percent. The exterior was indicating generally 9 to 12 mc. I am still testing with meters and I am milling some of the lumber to see how it works. Sorry this is so long, but I felt most of the story was important enough to mention. I do feel like this drier really works but canít seem to get a hold on what is happening on the inside.
Here is my question: If the kiln has a temperature and relative humidity cycle that dries wood more quickly than a standard schedule, why not use these new settings with a DH kiln? If this kiln dries using air a certain temperature, RH and air flow, we should be able to use the same settings in a more conventional kiln and get the same results. Is it possible that the faster drying reported is merely because a faster drying schedule is used? This modified schedule often is possible with many kilns, if you check the drying manuals, as the basic schedule is conservative as it must work for all sorts of variations in wood quality, equipment variations, and operator skill. Schedule acceleration is encouraged.
If there's something special about the Green Dry kiln that allows faster drying with no more defects than any kind of conventional drying, I fail to see where it's explained anywhere. The drying time for those thick slabs seems to be very fast to me, faster than anything other than vacuum drying which is sort of its own animal in my mind