RF/vacuum kiln

[myxpykalix]

Has anyone dried wood using a RF/vacuum drying kiln? My searches don't yield any construction details only comparitive studies done. The only details i've gleaned is that some drying can be done in days as opposed to weeks or months.

One study showed a comparision of RF/vacuum drying of 88 hours compared to 60 days with less checking and splitting and internal movement.

But if we're talking about having to build a vacumn chamber the size of a shed and great expense for RF then it might be cost prohibitive.

[myxpykalix]

I did find this, although i haven't finished going thru it. This is a big operation but if you could downsize it...anyway back to reading:
http://www.fglco.com/preso/process/index.html

[nschlee]

I used to dry wood. We used a Nyle DH Kiln, worked great for birch. Would take a 2K BF load from green to 6-8% in 21 days. Before building a kiln with the Nyle unit I looked into the vacuum kilns and purchased some wood dried by this method. Although it is faster, the quality is not nearly as good. Too much case hardening, checking and twisted boards from drying too fast. I used a 20' insulated container, added the Nyle L200 unit, a fan wall, some vents and it's ready to go.

[myxpykalix]

What was the cost of the Nyle DH Kiln?

[fmihm]

Jack --

You might find this Nyle L200 DH Kiln thread of interest:
http://www.forestryforum.com/board/index.php?topic=5973.msg65459

[nschlee]

$4K 7 years ago, I think they're more like $5K now. Here's some pics. Most insulated containers have stainless walls and aluminum grate floors, and are insulated with 3.5" of urethane foam. There's an 18" space on the refer end where the refer was, I removed the refer unit and built a insulated end wall with 2 man doors aligned with each other, mounted the controller and other controls in the void between the doors. This way you can check the controls without actually opening the kiln. They are very efficient, if memory serves the cost to dry was 5-7 cents a BF and after you burn a few loads it takes very little babysitting, just a daily controller check, and most of the time no adjustment needed. I ran the moisture meter leads to the controller, just plug it and check, again without having to opening the kiln. I had about $8K in it, recently sold it.

Neal

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[rb99]

How much does it cost to run?

RB

[daski]

I built my own kiln. A big insulated box made of 2x6 and OSB, r20 in the walls and ceiling. left a space between the back wall and the stack just like the pics above. Put two furnaace fans blowing the air into that space through two holes in plywood stiing on top of the pile just like above. I used a large Sears dehudifier to dry the wood. The temp would climb to about 120 and I'd get about 5 gals of water per day until the free water was gone. Once we started removing the bound water the amount dropped to about a gal per day and the temp dropped off too. It took about 20 days to do 1500 board feet. As long as the ends are well sealed the checking was minimal. You know when the wood is dry because no more water is being collected. My meter would read 6-8%. I let it cool slowly for 3-4 days. It was a very good setup, unfortunately we had to move cross country and there's just no time for the fun things right now.

[nschlee]

Cost to run was 5-7 cents a board foot. It requires a 220v single phase 30 amp circuit. The unit has a pre-heater that only comes on at startup, after the inside temp reaches 80 degrees (4-6 hours) it shuts off, from then on the compressor and fans generate the heat. It runs at 110-120 degrees inside temp depending on species. Outside temp does not make much difference, we ran it from 20 below to 70 degrees, this with a tight insulated container.
After the load got to 6% we'd turn off the unit open the vents completely, let it sit for a day or 2, then fire it backup for 1-2 days and bring it back to 6 degrees. This helps condition the wood. When drying softwoods with this unit (110-120 degrees) you need to keep an eye out for mold, Nyles larger units cook to 160 plus degrees, less chance of mold formation at the higher temps. For the smaller operater this a great unit, takes a little longer than vac or higher temp kilns but less chance for mistakes and the quality is excellent. It's really a simple system that requires very little maintenance.

Neal

[nschlee]

Nyle supplies blue prints to build the kiln structure with unit purchase. Here in Alaska I could get the container cheaper than the materials to build the structure, makes it easy to move too.

Dave's way is good too.