Foolproof relative humidity for drying/not wrecking red oak?

[Don P]

I did some rooting through the pile here. The schedule you asked about is from a class handout from Dr Wengert/Nyle's "Introduction to Kiln Drying" class. The other guys are talking from experience, I'm just acting as a librarian here.

more stuff while digging around;
("Drying Hdwd Lbr")
Air velocity is as important as temperature and RH for controlling
the drying process. The velocity of air when the
wood is above 40% MC (approximately) affects the rate of
drying. Higher velocities result in faster drying (Fig. 2.3),
more uniform RH within the pile, and more uniform drying
within the pile. Of course, faster drying can increase the risk
of checking, but conversely it can decrease the amount of
warp. (The curves in Figure 2.3 vary with lumber thickness,
species, specific gravity, and other variables. The intent of
presenting this information is to illustrate the general affect
of velocity on drying rates.)
Below 20% MC, velocity has very little effect on the rate or
quality of drying. That is, the relationship between velocity
and drying rate is nearly a horizontal line at 20% MC
(Fig. 2.3). Velocity has an insignificant effect because at low
MCs, the drying speed is controlled by the rate at which
water can move within the wood rather than the rate at which
the air can carry the moisture away from the surface. Between
40% and 20% MC, the effect of velocity decreases
proportionally (Fig. 2.3).

There is a direct relationship at high MCs between air velocity
and RH. That is, if the velocity is decreased, which will
slow drying, then the RH can be decreased, which will increase
the rate of drying. In other words, many combinations
of velocity and RH can provide the desired drying rate.
Pages 58 and 95 from "Drying Hardwood Lumber" has some more info and is a good book for the reading list also;
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr118.pdf

This came out of one of them;
Dehumidification Kilns
For DH kilns, use the same RH, but lower the temperature to the typical operating temperature for the compressor; raise temperature to steam values when convenient and possible.

[james04]

Hi Tom,

I have seen 3.8% mc loss per day in several references. However I would like to keep my loss at around 3.5% to be on the safe side. After 3 days of slow drying I was happy to get the 3.66 as I have some white mold growing. Will the higher temps slow or stop this?

BBTom,

Thank you for digging that up. Funny I could have sworn that I have read that PDF. I must have let that pass under my nose without noticing the Red Oak DH schedule.

I currently have two 1600 cfm fans in the kiln. The kiln is 8'x11.5'. I have purchased one more fan to add. Do you think 3 1600cfm fans will be enough. Some of the plans I have seen on the net had 4 12" inch fans and advised two would be ok. Well I figured since mine are 14" that two would be ok. Any thoughts on this?

James

James

[Handy Andy]

  Just noticed this is an old thread, but wondered how that tar worked for IndyIan when you saw into that log.  Or maybe he put it on after the logs were sawed into boards.  Basement waterproofing would be a cheap log sealer.