Green RO, KD time?

[Don P]

I've never done a load green from the saw. We closed the doors on a small load of 4/4RO, initial mc was reading around 60%, it is hitting the high 40's now. It was short but not short enough to double stack, we got about 1000' in the L200. We turned it on Saturday. Moving cows and then sawing the next load today. Any rough ideas on when we'll be able to pull it and reload?

[K-Guy]

It will take about 5-6 weeks, watch the moisture loss, you only can pulll 3.8% per day and that has close to stressing the wood. I would aim for 3%.

[Don P]

Thanks Stan, it sounds like we are running a little too fast. We are at 120/95 now, should I raise the wet bulb 5°?

[K-Guy]

Use this Don, it's the group 3 schedule.
                     DB    WB
Above 45%    90° F 86° F
45% - 35%   100° F 96° F
35% - 25%   110° F 98° F
25% - Final   120° F 98°F 

[Don P]

Whoa, we had a communication breakdown somewhere... I just called DB, he's turning it down now. Thanks... hope we didn't burn the cookies!

[scsmith42]

Yup, typically 4 - 5 weeks for green 4/4 oak.

Try to keep it under 90F until it's below 35% MC.

[Larry]

I've always air dried before going to the kiln but for the last year or so I've been drying green oak.  I knew going in with green wood that it would require lots more attention to produce quality lumber.  Did some studying and read some of @YellowHammer posts about oven drying kiln samples.

With green lumber my normal procedure is every morning I weigh my two or three kiln samples and see how much they come down.  When its less than Nyle's guidelines I'll crank it up a degree or two.  Too fast and I'll back off.  Much like watching the speedometer on your car.

Kiln drying from green is giving me a higher quality product but their are advantages to air drying first.

[YellowHammer]

Green red oak in the kiln is bad to surface check, so stay as cool as possible while hitting 3% per day for 4/4 RO.  The kiln schedules are broad suggestions, use real life data to fine tune your set points.  A 10° depression is used for preventing sticker stain in white woods, not a problem in red oak.  

In green RO it's easy to hit 7% per day moisture loss, and really cause problems so you generally have to slow things down in the beginning.  However, as it starts to dry it will be much easier to control. I like the oven dry method vs a moisture meter for green wood because the margin for error is very low and most moisture meters can't hold the accuracy required over 30%, which is where the danger zone is.  For example, 2% per day is too slow and will take a long time in the kiln,  while 4% will crack the wood.  So a 1% error on either side of 3% and even a Delmhorst won't be accurate to within 1% over 30% mc, even with their super 60% one.

Only start raising temps when you can't hit you moisture removal goal of 3% for 4/4 with a 10° depression. There is no need to raise it early because warmer wood is much weaker, and more prone to cracking.  Also you don't have to jump 10 ° increments from 100 to 110 to 120.  You can do any you want, even 108/98 or whatever feels right.   

[Ianab]

but their are advantages to air drying first

Main advantage is you can get maybe 4 times more wood though a finite kiln space if it's 3/4 way dry when you put it in. Kiln drying from green should give the best results if you carefully nurse the wood dry under perfect conditions. If you try and rush it, bad things will of course happen. 

So if you can finish an air dried load (<20%) in maybe a week, it means you have to have maybe 10 kiln loads lined up pre-drying for a couple of months. But it should mean a load a week out the kiln, vs a load a month. In an ideal world you would just have more kiln space, but sometimes you just need to make the best use of what you have. 

[Don P]

We just shut it down yesterday morning leaving the fans on, still too hot and in this ambient temp it wasn't coming down. I'll go check it today and probably restart. This is why I'm a woodworker, there's always designer kindling   :.

[Larry]

The daily grind, pictures from this morning.

Check and empty the water bucket.
Check temperatures.
Weigh my two samples.



It's hot in there!!!!
Look for drying defects on the lumber pack.



This is a load of 4/4 green white oak.  Weighing my two samples told me I'm at 18.3 moisture content.  Also told me I lost 1.8% MC in the last day.  Maximum safe lose is 2.5% so I'm good.  I'm at 120 DB and 98 WB so I can't speed it up at this point.  I guess just be patient.  

Below 20% both my J-2000 and Wagner pinless read very close to my samples.  Above 20% they are not that close with the Wagner showing the most error.

With the lumber going in green its still bright and clean.  Doesn't have the defects seen in air drying.  When I air dry its in the yard with a cap on the stack but I still get wind blown rain in the stack that causes defects.  The biggest customer (ME) wants the highest quality possible out of the kiln and doesn't care much if it takes longer.

[scsmith42]

I have a very simple trick for "fire and forget" drying of 4/4 and 5/4 green oak in an L200, and that is to simply load the kiln to full capacity, and don't allow the temps to exceed 90F for the first 2.5 - 3 weeks.

The compressor cannot remove enough water to dry the wood too quickly if you max out the kiln load.  So you don't have to worry about daily testing, oven dry boards, etc.  Simply load 4,500 - 5K of bd ft in an L200 and you're good to go.  Temp operated automatic vents are nice too.

When I dry 8/4 from green, I do the same thing but also set the RH% fo 95% and keep it there via a high pressure fogging system.  Takes around 4 months for a load of 8/4 QS oak from green, with no internal checking.  

I prefer to dry oak from green in the fall, winter and spring though when I don't have to worry as much about temps climbing too high in the kiln.

[Larry]

With more experience I should be able to get to the "fire and forget" stage with my L53.  I'm keeping records and can see a trend now.

[GBar]

There are three concepts in the thread of this post: drying environment, Control, and Measurement.

Agree with Yellow Hammer that published kiln schedules are guides. However, those guides must be take in consideration the controls or the ability to control the environment, and be reasonable.  The attached picture of Excel data is derived from the Nyle schedules in the L-53 manual.  There are a few mistakes that I have provided to Nyle...for their next revision.  first the Group 3 second step raises the EMC.  Whatever the values are, subsequent steps in the schedule should not increase moisture.  it should be a linear decline.  What is more erroneous is Group 4 (8/4) is more aggressive than Group 3 (4/4).
In Gene's Drying Oak Webinar, he cites a 3 degree depression at the start of a Green Oak (red or white) 8/4 schedule and 4 degree depression for 4/4 Oak.

Temperature.  There is a wealth of documentation out there that temps can begin at 100, 110, or 120 (historically). I discount the claim of starting at 90 degrees. Gene's perfect schedule starts at 105 degrees. But the environment has to be right (already cited a 3 degree depression). The use of higher heat is fine, but the EMC has to be high enough to not cause excessive degrade.  Consider the gradient from the core to the surface. Green Core is around 70 MC.  Yet a 100 degree F with 3 degree depression will yield 90 RH and 19.3 EMC.  That is a large gradient between 70 and 19.3. The conditions have to be controlled precisely...not just the temp.

Control.  As scsmith42 mentioned, a good way to control environment is to have a large load of wood giving off enough moisture that results in a high stable EMC.  I'm not a fan of air drying oak.  But i do understand it is wise for production efficiency.  Air drying in my area produces variable results - mostly severe degrade (radically changing conditions). Of course there are measures to combat the outside, but the kiln is best controlled environment.  So I'm a fan of Green Oak in the kiln.

One way I control drying rate is by changing the air velocity.  Variable speed fans help.  Too high of air velocity drys the surface too fast and increases the effective gradient to the core MC.  I also use a steam generator on a humidity control mechanism.

Measurement.  Instrumentation has come along way lately.  There are humidity instruments that are more accurate (less variable) than DB/WB, where WB is subject to the variables of wick moisture and air velocity.
Although a historical practice of weighing kiln samples, I'm suspect of the accurate representation of small piece of wood in the kiln drying at the same rate of the larger boards - even with end coating on the small sample.  Those small pieces are going to emit MC much faster.  Unless you cut the small sample from the center of the board prior to each measurement. The best method.

I use Lignomat PK probes.  Have verified them at multiple stages of MC by sample weight. Suitably accurate for rate of change measurements.  Since the probes measure the core, and I know the EMC, the overall gradient is known.  This is done outside the kiln with the moisture meter.  I can run up to 10 separate probe pairs to get a good sampling.  Steps functions in the schedule are done at the wettest reading.

All of this is a guide.  Once you have your schedule, it is repeatable with good control mechanisms.

[K-Guy]

Our schedules are not the fastest but as safe as we can make them to get a good result. Since wood is a natural product there will always be variances from load to load. In drying experience is the best teacher.

[GBar]

Concur Stan that experience is the best teacher.  But do you concur there is a typo in your Group 4 schedule first step?  Whereas your Group 3 (4/4) has a beginning 4 degree depression (DB to WB), the Group 4 (8/4) uses a 5 degree depression.  It should be either the same as Group 3 or more conservative as Gene documents in his briefs, who has more experience than all of us.

I believe it is a simple typo that propagated the schedule.  There are other Nyle published schedule documents that do not match what is in the L53.  Why would those other Nyle documents NOT match?  Whatever the reference value listed (based on experience or whatever), it should be consistent with the other published documents.

Q.E.D.