DIY kiln question for smart people (I'm disqualfd)

[oldsaw]

Driving to work yesterday, I was struck by a sure sign of spring...my first garage sale sign.  Immediately I had flashbacks to last summer when I came across an inordinate number of really old crappy window AC units.

Anyway, yesterday, it struck me that it should be possible to build a kiln around one of these things as a temporary/portable setup.  I've seen DIY projects based on dehumidifiers and light bulbs or small heaters, but this seems like an "all in one solution".  You've got a lot of heat and DH capability by building some sort of simple heat (cold) exchanger to monitor drying.  Just throwing ideas out to the smarter people out there.

Any thoughts?

[Frank_Pender]

Your last sentence leaves me out, sorry.

[DanG]

I must disagree on one point, Oldsaw. You gotta be smart, 'cause you're thinkin' just like me!  You're also cheep!

I think it will work, but obviously not as well as a unit that is designed for the purpose.  The biggest argument I've been able to find against it, is that the acids will eat it up. That's not a big concern to me, 'cause I can get them so cheap.  I think some "creative" ductwork might be in order, to take advantage of the cold air vs. hot air that is generated.  The cold air could be blown through some kind of exchanger to enhance the moisture removal properties.

I have an old unit on hand that works well, so I think I'll try it. It will be interesting and educational enough to make the little project worthwhile. I'm thinking small, here, maybe 200-300bf, to start with.

[shopteacher]

Butch and I would have tried to respond, but due to restrictions beyond our control, found neither of us to be qualified.

[karl]

I know you asked for smart people- but I'm posting anyway My first "Kiln" was a house dehumidifier, a box fan, electric milkhouse heater, 6 mil poly draped over 2x4s on sawhorses in my shop- good thing the lumber wasn't valuable or a large amount, but it worked. I've heard that air conditioners/home dehumidfiers  won't last because of the acids too, it's prob'ly just a rumor started by those kiln manufacturers .
I like my old Nyle 150 hotrodded to 2 hp.
Maybe this is the push I need to try to post pics.. :-/

[Den Socling]

I think Woodhaven's post sounded pretty good. If Don replies, I think he'll say something about room air conditioners problems when run at 'high' temperature.

[Buzz-sawyer]

This is an exerpt from an article  By Andy Davenport

....... The heart of the equipment is an old 18,000 btu , 220 v window Air Conditioner. ( Gibson, I think....I dunno...I tore all the sheet metal and face plastic off ! ) The AC unit sit on a shelf in one corner of the inside of the kiln. Also use a small ( like 18" ) portable fan on sitting on the floor on the other end to help keep air moving and a small ( 1500 watt ) portable electric heater . I got the AC for free to haul off ( many people here convert to central air....there are a ton of these old dogs around ) , paid about $50 for the fan new ( Home Depot....Lifetime warranty....snicker/snicker ) and the little heater was garage sale $5. Beats EBAC at 20x that !
Running the Kiln
To run it, I load the kiln with 800 to 1000 bd ft of air dried lumber ( I've never tried green....I'm too cheap to spend the electric to do what nature will if you just wait a while ! ) The stack is on 6x6 sleepers on the floor, then stickers as a normal drying pile. I turn on the electric heater to start the room....after the room hits about 90 degrees ( like a day or so depending on startup temp ) , cut it off...the waste heat off the AC is plenty of heat. Start the AC at the same time, when the temp gets high enough, the AC thermostat will kick the compressor in, and you are in the dry kiln business. The waste heat off the AC will continue to build room temp over several days.....mine peaks at about 125. At 100 or so degrees, the water really starts coming off the wood and the room hits 100% relative humidity. This warm, humid air hits the cold coil on the AC and the drip pan fills and in my case, runs into a 5 gallon bucket underneath the shelf. It is hard to believe that it will pull 5 gallons a day off "dry" lumber ! ( YES...a real "engineer" would screw a fitting in the bottom of the drip pan and lead a hose outside, but I like the sauna and like to go in a pet my wood ! ) ( + so much to do...so little time ! )
Takes about 2-3 weeks for a 1000 bd ft load and runs about $50 in extra electricity here.....like a nickle a foot !  HOME DEPOT.....red oak is 1x12 at $6.60 a running foot..HA ! I figure I've got about $0.60 a foot in mine !
Now the question almost everybody asks: YES, the air conditioner is completely INSIDE the room..not a hole in the kiln wall....you WANT the waste heat inside....it is a LOT more than the cold that is coming off the evaporator ( cold )coil....don't think about it....just do it !
Mixing species in the same load seems to have no effect on drying time or anything......
Total costs for the kiln including construction of room, wiring, etc.....about $500 ( and WAY more than paid for on the first load...commercial kilns around here charge $0.50/ft IF they will even fool with your little bit )

A/C Unit - Important Note
Note about the AC unit: The first one tried was an old one a friend gave me...worked fine until the compressor mount gave way and vibrated a hole in it. The next one was also a freebie, but would only work for a short while when the temp got up in the 110 range before the internal thermal switch on the compressor would kick out, the compressor would cool a bit and then kick back in, run 5 minutes, kick out and so on....the problem was the R-22 gas in the last unit. If you get one with R-22, the pressure gets too high much past 100 degrees....they just weren't meant to operate in that range according to a refrigeration buddy of mine. He took out the 22 and replaced it with R-12 that will operate at a LOT less pressure ( and therefore load on the compressor ) in the same temp range. Works like a charm. So get a unit with R-12 or plan on getting it changed over. And I think the old, ineffecient AC dogs are better than a new one.....more waste heat and you want that.

[oldsaw]

So this could be really simple to moderately complex.  I can handle that.

My first thought was to put the whole unit inside and vent out the cold air.  Then the acid thing started getting to me, which brought up the heat exchanger thing, then it started getting more complex from there.  I had an idea that I was making this a lot harder than it had to be.  That still seems like a plan, (I really hate it when the first simple idea is good and I have to try to make it harder for myself).

The auxiliary heater is a good idea.  I bought two box fans last summer, one for a quasi-kiln idea (forced air drying, to fight the chance of molding more than anything), and the other for a paint booth thingie. (Cardboard, fan, furnace filter, and TV swivel platform).  

I really like you guys, you appeal to my cheaper side.  Woodhaven, I may bounce a couple of other ideas off of you down the road.  Now I have to start searching for an old AC unit.  

Anyway, the thinking was walls and top made of plywood, 2x4s insulation, and inside just a poly sheet (or styrofoam).  Put 3-4 T-nuts on each corner.  I've got some shingles for the roof, a basic floor, and I've got something I can knock down and store in the garage.

Wife's calling, gotta go.  Thanks again guys.

[Fla._Deadheader]

OK, this sounds pretty good. Can you set the pitch, in Pine, at 160° for 12 hours or so, and how??? Just add more heat, once the low MC is attained???

[Fla._Deadheader]

I been looking for that equation for years. Thanks, Richard

[shopteacher]

Woodhaven that is one good synopsis and very understandable.  Cold =absense of heat.
What would the consequences of changing the R22 to R12 as far as the compressor is concerned?  Could the new 134A be substituted?

[Fla._Deadheader]

There's a source for 25' Reefer boxes, down here, for $350.00. IF that includes the refrigeration unit, could a plenum be constructed over the exhausted hot air from the coils, and be blown right back into the box??? Seems as that is what Woodhaven is saying??? Have I got this right??? Sure would be an easy install for a kiln, until I get the vac unit working???

[oldsaw]

Yep, I understand the physics part of heat.  Explain that one to my wife all the time.  We had a heat spell a couple of years ago where it was above 100 for days on end.  The AC unit just couldn't keep up.  She got really mad when I told her about removing heat rather than making cold.  Thought I was making it up.  Then I told her there really scientifically was no such thing as cold, only a situation with less heat.  BTW, I was forgetting about the dry air part going back in.

Okay, it doesn't get much simpler than just putting the thing in the box, and drain the water.  Just, that's too simple for me, I'm not sure if I can handle it.  May just have to mod the unit...need complexity, must have complexity...

This is getting to be a really good thread.  A resource for cheapskates for years to come.

[shopteacher]

How warm does it usually get inside the kiln on a day to day basis?  Just wondering because of the talk of it being to warm inside for the AC.  I mean in areas like Phoenix it get above 100 deg. on a daily basis and they run the AC constantly, right? Just wondering.  Also I've heard the acid in some species will consume the aluminum fins of the evaporator. What do the factory kilns do to avoid this problem, if it is a problem.

[Buzz-sawyer]

Harold....that would work...dry low humidty air and heat...for 350

[DanG]

Thanks for the confirmation and the tutorial, Woodhaven.  That's pretty much what Mr Hootie's SIL, the refrigeration guy, was telling me, last week.

Some of the older, high-end, units had a lever that enabled you to either recycle the inside air, or exhaust the room air. Would it make a difference in a  closed system, like this?

Now, instead of removing the housing, I was thinking of using ductwork to direct the flow of air, to take advantage of the different outputs.  The hot air from the condensor would be blown directly through the lumber stack, obviously.  The output from the "cold air" vanes, would be ducted through a series of pipes, which would trap a certain amount of moisture on their surfaces, before being directed back into the intake filter. Do you think I would get enough of a "double whammy" on the DH level to make this extra step worthwhile?

FDH, you could install a heat exchanger to bring the temp up to sap-setting, bug-killing levels with a boiler unit. Just run the same chamber as a "conventional" kiln for a few hours after the wood is dry.

[Ianab]

Dang.. I think thats overly complicated
What the unit should have is 2 'radiators', one will get hot, one will get cold. (or is that 'get less hot')
What it seems you need is the humid air to be sucked into the cold radiator, the water will condense on the cold surface and run down to a drain or bucket or whatever. The now cooled dried air is blown out thru the hot radiator so it comes out as warm dry air. Blow that thru the wood stack and it should come out humid again...
repeat as required  
It all seems practical, knowing there are problems with corrosion, it wont be fast, and there will be all sorts of unexpected gremlins. But just cos people say it wont work is no reason not to do it  

Good Luck

Ian

[shopteacher]

Woodhaven:  Would it be better to start out with a separate unit like that in a reach-in cooler like in the convenience store? The kind of cooler you get milk or soda out of.  The units are already separated and I believe use the lower pressure R12.  The evaporator also has a separate fan to move air through the coil and the condensing units usually have adjustable high and low pressure controls as part of the unit.

[Fla._Deadheader]

I know where there is a "walk-in" cooler, that HAS to be moved. The Highway Dept. is widening the road, and will CRUSH it and haul it away??

 I'm looking at 6 acres, also. Hmmmmmmmmmmmmm

 Thanks, Richard. You put out a BUNCH of good info. Really appreciate it.

[Fla._Deadheader]

Also, I been thinkin about using 6" Galv. duct pipe, with them in-line fans inside the pipe. Being as how yer blowin dry air into the stack, that should help "Boost" the air along the length of the duct, for even distribution, EH