I’m struggling to understand how to construct schedules in FPL-118 and what is published in both FPL-118 and the Nyle manual for the L-35. Note, I did find some typos in the Nyle schedules and in FPL-118. Also provided Nyle that feedback. However, the real issues are understanding how to assemble a proper schedule per Page 77 in FPL-118 and the associated tables.

Second issue is temperature. The schedules appear to be all over the map and contradict each other. some white oak dry bulb temps start at 110 and some start at 90 degrees F.

For this discussion I am drying white oak (8/4 and 12/4). I’m attempting to construct schedules for green white oak for both thicknesses. I realize there are notes to Air dry to below FSP, but in my area, the climate is so variable that air drying produces surface checking for the thickness I am drying. I understand shade screens, sheds, etc., but the best environmental control is a kiln with automation. I do not care how long it is in there. My goal is little to no degrade. I want to start with green in the kiln.

There are many references to holding temp control to precise values, but there are references that start at 110 degree F (T3 in Table 7.5) and some that start as low as 90 degree F (dehumidification on page 95 and the Nyle schedules). So the thesis of maintaining tight temp control below FSP (~30 MC) seems to be false within this range of starting points. Both references in FPL-118 to white oak (8/4 and 12/4) use T3 which starts with 110 degree F. Yet there is a steam to DH comparison on page 95 that shows red oak starting at 110 and 90 respectively. This makes no sense as temp is temp regardless of what generates it. What is consistent on Page 95 is the RH for both steam and DH. Yet Nyle schedules raise the RH in the alternate schedules if the temp is raise by 10 degrees. This is not consistent and contrary to page 95 in FPL-118.

Since I am drying white oak from green with initial MC of 64%, I went into Table 7.6 and came up with a 9 step schedule (column E). That did not work. The resultant EMC values went crazy. I attempted a T1-E1 schedule. The EMC were: from 18.9 (normal) down to 0.2, but went back up to1.7 and 2.2. Notwithstanding, achieving 1% RH is not achievable and ridiculous.

On page 98, there is a reference to 12/4 white Oak, recommending T1-B1. I assembled that, and it was reasonable, but there is a slight typo. Step 4 should be 110 degrees F.

So how does one assemble a schedule from Green MC, which should be a 9 step schedule in Table 7.6. What am I missing here? How is B1 on page 98 chosen?

Finally, if heat helps extract the moisture from the core, should not thicker wood be better off with a higher temp of 110 verses 90 degree dry bulb at the beginning?

I can’t find a good or consistent reference to target RH for current load. Drying 12/4 white oak with probes showing 35% MC on wettest probe. Goal is average drop is 0.5 MC per day. Current RH is 60%, 110 degrees, 10.0 EMC, seems to have stalled. T1-B1 would call for 100 degrees and 86% RH or 17.4 EMC, which is crazy high. Nyle shows 110 degrees, 65% RH, and 10.9 EMC for the same MC state.

Any guidance is appreciated.
George

- You are correct in saying temperature (heat) is the same no matter what the sources.
- The reason for the note to keep tight control of the temperature is that small change in temperature within a step can change the RH or moisture control a large amount' which can cause higher degrade (checks). For example:You don't want the temperature to vary from 100F to 110F while keeping the wetbulb constant. This will cause drastic EMCs.
- Yes, higher temperatures will increase drying rate. But, the higher the temperature the weaker the wood is and thereby promote degrade (checks).
- the reason for increase in RH in some schedule and some steps within a schedule is that when these schedule were first developed there was a desire to maintain a constant wet bulb depression. At higher temperature a constant wet bulb depression causes increased RH. As a side note this late increase in RH produces a small "conditioning step" before the equalization step and this is beneficial for reducing stress in the final product.

Jim,
Thanks for the response. Was wondering if anyone would respond.

If that is what is meant by "precise temp control," then it makes total sense. I'm still a bit baffled by the starting point temperatures of some schedules verses others of the same load type. for example, the Nyle dehumidifier schedule starts at 90 degrees and finishes at 120. however, traditional schedules start at 110 and finish at 160 degree. My only guess is this is due to the limits of the dehumidifier to operate in higher than 120 temps (a compressor /system limitation). Therefore, if 110 is an acceptable starting point, it appears two initial steps can be eliminated. This assumes proper RH (EMC) is appropriate for the schedule. Certainly, that range of temps (up to 120) will not hurt the strength of the wood. A better approach is an EMC schedule.

For my other question about trying to use the FPL-118 process to derive a schedule for 4 inch which oak, it appears it can’t be used. One has to use experience and judgment to derive a suitable schedule. On my last load, I used Lignomat probes to measure the center (2 inch in from surface), another set a probes at 1 inch from surface, and controlled the EMC at the surface or in the kiln. Ultimately trying to keep the gradient between surface and core within reasonable limits.

As a side note, if I raised the temp and RH dropped too much, I just added more steam – actually the system added more steam automatically to keep the RH set point.

Bottom line: I believe there is a lot of latitude in the temperature as long as suitable EMC is maintained. I also deduced, FPL-118 can’t be used as a “cookie cutter process” to derive a suitable schedule for 4 inch white Oak from green, without using common sense.

I thought drying 12/4 white oak in a dehumidification kiln was impossible. I've seen enough poorly dried 8/4 white oak to believe this is true.

I have air dried 12/4 white oak in two years down to ~ 15% MC with a few very shallow surface checks. Have tried to kiln dry it though.

Rich,
To clarify my DH kiln, I also have a small steam generator controlled by a target humidity controller. And have a supplemental PTC heater. In the first part of the schedule I did not use the DH. My target humidity was 90 with initial temp at 90 for a target EMC of 20. Using the lignomat probes in center thickness and 1 inch in from surface, I logged and charted the differential. With an EMC of 20 at the surface and 60 percent MC in center, I could observe the rate of change or derivative. My goal was one half percent MC per day. You can do the math on how many days that is/was down to 9 percent MC. It was actual 5 months as some days the MC drop was flat or no change.
I did get some degrade - mostly twist. But that was my fault for not properly weighting or constraining the stack. There was no surface checks, but did presurface the load. Cutting off the ends with end coating. I did have one large internal check or honeycomb about 3 inches from the end on one board. Could have been my heat ramping schedule or inconsistent humidity control at the beginning. I replaced the faulty control unit early in the schedule. Who knows. It was an experiment. I learned a lot.