Vac kiln advantages?

[Dave Shepard]

I scrolled back about 15 pages and have been reading up on kilns and find many mentions of vac kilns. However I don't find much actual info on the advantages/disadvantages of them. Can someone give me a brief lesson on them? Thanks. I am researching kilns to dry mostly white pine, but we will have a lot of red oak 4/4 from a timber frame that I am going to be cutting and we would like to recover some of this as usable boards. Right now we are just ripping them into stickers. :( If we do set up a kiln, we would start to develop the hardwood end of the business, as we currently have no market for non KD hardwoods and we get a lot of side boards from timber projects.


Dave

[TeenSwinger]

Some of the advantages are;
dries wood much faster
dries wood with less heat required
is able to dry thicker lumber more throughly

Some of the disadvantages are;
cost to buy
cost to run
alot of models require that everything be loaded by hand

We do not own one, so if I have mistated anything someone please correct me.

[Den Socling]

The disadvantage of vacuum kilns is that they can't be scaled down to a couple hundred board feet. The smallest vacuum kiln cost the most when calculated by drying capacity. That's why I'm always trying to help someone here to build their own.

Vacuum kilns certainly are not all the same. Most will destroy difficult to dry species. But, if you have a good vacuum kiln and know how to use it, you can dry just about any thickness or species. There are two reasons. One is that you can control drying conditions perfectly. The second is due to the fact that vacuum kilns can remove water from down inside wood instead of only from the surface.

Because you are removing water from down inside, you can dry faster and thicker. Freshly cut 8/4 can be dried in 5 or 6 days.

Because the heat goes toward evaporating water and not heating a building, you need less. Also, you are not venting either heat or acidic vapor. If a vacuum kiln is correctly designed, it is the cheapest way to dry.

I used to sell vacuum kilns at a price close to cost. The idea was to prove the value in different markets. Then I started adding a small profit. Now, my company is part of a joint venture and they set prices by drying capacity. At least that is a guide. For example, if one of our kilns can dry a million board feet per year, then it is priced the same as a conventional kiln that can dry a million bf a year. That will make a 5000 or 10,000 bf chamber look expensive until you do the math.

We have built systems that load with vacuum grippers. We are currently designing a fully automatic system for the big operators on the west coast of the US. And, here at the R&D lab on the east coast, we are building a system that will allow one man with a joystick to drive a vacuum gripper around to load heating plates and wood.

[Dave Shepard]

Thanks for the replies. I like to build equipment. Not to save money, but to learn something while I am doing it. I will probably start with a "container" type kiln due to my lack of knowledge and the ready availability. We do have a kiln room in the barn that has been used to dry pine down to under 6% in a very short time, but it has been filled with junk and our heat source is defunct. I realize that is probably too low an MC, but this was with a very uncontrolled environment. I will endeavor to learn more about the vac kilns though. I don't know if red oak is a hard to dry species, I am guessing it is, but it would be nice to have a kiln system that would take say 500 feet of lumber or less at a shot. As I mentioned we have a lot of oak side boards from cutting timbers and it would be ideal to get them into a controlled environment asap. The short drying time would work well with a small batch system. I hope I make sense, I am just getting into the drying game. Fortunately it's not a rush, so I can get an education first.


Dave