Fans Size and Drying Kiln Dimensions
Considerations regarding fan capacity, kiln size, and lumber pile size in a dehumidfying kiln. January 25, 2010
Question
I am putting in a Nyle L200 for 4000 bdf. I read here that the two 16" circulating fans would not be enough air flow for this amount of bft. Does anybody have experience with 4000bft with only two fans? My kiln is 12' x 18' and I want two four packs 4' wide x 8' long. 74" h.
Forum Responses
(Sawing and Drying Forum)
From Professor Gene Wengert, forum technical advisor:
A word of caution: Packs that are only 4' wide become quite unstable after about 48" high. You should probably consider using a 4x4 for every 36" in height. Even then, be careful, as the piles do tip slightly in normal drying.
Regarding the fans, are you thinking of a load that is 8' x 16' x 74"? What species? What will the entering MC be? What is your sticker thickness?
If you are drying a wood like oak that is air dried first and using 3/4" stickers and there are two adjacent piles so the air flow path is 8' long, you will have an air flow channel that is 3/4" high, 16' long. There will be 40 of these in your load. You should have about 200 fpm air velocity. Note: 3/4" is 3/48 feet. So, 3/48 x 16 x 40 x 200 = 8000 cfm. Add 50% for air losses and this means you need fans that can provide 12,000 cfm.
From the original questioner:
My plans are to stack 8 ft wide x 16 long with 1" x 1" stickers. I will dry 4 quarter #1 com red oak, right off the mill. I have 4" spray foam insulation in interior covered with plywood. You mentioned I would have 50% air loss; can you explain?
From Professor Gene Wengert, forum technical advisor:
I suggest that you plane your stickers (dry, I hope) to 3/4. The air losses are due to air sneaking under, over and around the piles and not going through them.
From contributor J:
I have a L200 Nyle and have five 1/2 hp 16" fans in my drier. Three of them run on a speed rheostat together and the other two on a separate switch for more air flow with softwoods. I have an air flow meter to let me know how many cubic feet of air per minute is going through the stacks. For 4000 feet of hardwoods I use three fans most of the time with 450-500 cubic feet of flow. Pine needs all five and I don't put more than 3000 board feet of pine in at a charge when MC is over 60% or your pine will mold with the L200. If your pine has been air drying for awhile, more than 3500 is okay.
From contributor S:
My experience with an L200 for green oak is, keep your stack no wider than 6' by 16' long, using 3 fans, keep your temp at 95 deg with kiln cycle at 100%. When your charge is at 40% moisture kick the heat to 120 and run it out. I never dry green oak. Let nature do the work for you. We always air dry for at least 1 month.
From the original questioner:
If you air dry 4/4 red oak for a month off the mill, what is your MC at that point? I also put three fans in the kiln, and stacked 6' wide, 40 layers high. My intentions are to always have a kiln load air drying while there is a load in the kiln, 4/4 RO. I have my kiln inside another building, so the lumber air drying will be under roof, with wind blowing through the open doors east to west. I am in Southeastern Pa, where we don't get a lot of humid air for long periods of time. So, my question is what MC do you lose in 30 days during the months of March through Oct. (4/4 red oak)?
