Dehumidification Kiln Conditioning Without Steam

Techniques and equipment for producing a balanced environment inside your kiln. May 11, 2005

I am building two chambers for Nyle 200 dh units. I've read the archives and searched every book I can find for info on how to condition in a DH kiln without using steam. I think some very fine mist nozzles might be an option, like a car wash with high pressure. Nyle told me to use a crockpot. I laughed at the guy on the phone. They also said to just let the wood set out a couple of days and it would be fine, or let it cool in the kiln then bring it back up to temp quickly, causing the wood to sweat.

I would like to know something before I get too far along with the buildings. I have a broad customer base, from fine furniture makers to craft people that buy my wood, so I need to do it right and have the same wood quality every time. Most of the methods I have seen seem to be lacking this. I plan on taking red oak from the saw to the kiln. I will also be drying poplar and ash but I think they will have very little degrade with some air drying, so I don't think the conditioning will be a problem with these.

Forum Responses
From contributor D:
Nyle sells an atomizing kit for humidification with an L200. But you need running water or a pump at the kiln. If you don't have running water, some people do use a variety of ways and one is to use a Fry-Daddy or such to boil off about one gallon of water per hour per MBF.

From the original questioner:
I talked to Nyle about 3 weeks ago and they never mentioned the atomizing kit to me. Can you make a guess on the amount of pressure needed to make it work, or what size pump is needed? I still can't get over the Fry Daddy concept - it just seems like all we would be doing is adding water all the time. I guess I'm in the dark on the amount of water it would take to condition an average load of red oak. I will call Nyle about the kit.

I have one more question about the kiln chamber. I can't find in the books how much space to leave for airflow between the unit and the stack and from the stack to the other side wall. These are track loaded kilns with a door on the end. I understand the ends and top need to be baffled; it's just easier to do it right the first time than to go back later.

From contributor D:
During conditioning, you need to add 6-10 pounds (pints) of water per thousand board feet of lumber. If you use an atomizer, usually 30 psi is okay, but if you do use a pump, you can collect the water from the dehumidifier in a sump or tank under the floor. If you have enough storage for 10 hours of spraying, that is usually fine. So for a 4000 BF kiln, you would want 4X10X10 or 400 pounds, a little less than 50 gallons of water stored. If you have not built your kiln yet, you can put a sump in, drain the dh unit into the sump and then have it overflow to the outside. Buy a shallow well pump that will maintain about 60-100 psi and it will work well.

As for plenums, you need about 30" on the side where the L200 sits and 18" on the opposite side. Some people make these a little larger so they can get into the space and check the lumber. Don't overdo it because you are just adding surface that loses heat. But you do want to be able to examine the lumber while in the kiln from both sides.

From contributor C:
I air dry first, so I have very little case hardening, but when it does happen, I turn off the compressor at the end of the drying cycle and dump 10 to 15 gallons of water on the floor of the kiln, close the door and check for case hardening the next day. If there is still some, I'll do it again. Very low tech, but it works.

From Gene Wengert, forum technical advisor:
The best stress relief occurs when you add moisture back quickly at as warm a temperature as possible. When checking for stress, it is important not to have any moisture gradients, shell to core.

From contributor G:
I do exactly as contributor C does. Works surprisingly well with no moving parts to maintain.

From the original questioner:
Thanks for all the help. I'm interested in any other tips on the Nyle L200. We will be starting on the chamber next. We just finished the pad and put the tracks down in the concrete for our kiln carts. We will be using walk-in freezer panels 5 1/2" thick. I think the finished size will be 10' wide x 8' tall x 22' long, but we can change it as we go along, if needed. They are very easily adapted for almost any application.

From contributor B:
To minimize the drying stress, you should properly air dry first. The faster lumber is dried, the more stress in the lumber. Properly air dry for 60 to 90 days before kiln drying. At that point, the lumber should be well below 30% (fsp). Proper equalizing will also minimize stress (results in long kiln time) and to condition in an RH kiln, you can add moisture to the shell with a quality atomizer. This will work better then putting standing water on the floor because the atomizer is put into the air flow and will be taken by the lumber quicker. As Gene said, reintroduction of moisture to the shell as fast as possible, with as high of a temperature as possible, is critical. Be careful with atomizing - it's very easy to rewet the lumber. In the beginning, you will, in all odds, have to redry some lumber.

From contributor O:
Fry-Babies, crock pots, dumping water on the floor, letting the load cool and then quickly reheating to make the wood sweat are all a waste of your time (and money). Having run an L200 for 9 years, I can assure you that you need a misting system similar to what you see in a typical grocery produce section. It is very simple and inexpensive to set up.

From Gene Wengert, forum technical advisor:
You can relieve stress by adding moisture back to the surface of the lumber. Adding moisture quickly and at hot temperatures makes the process work better. So, adding steam is really fast. Misters work and so does water on the floor, but not as quickly as steam.