Reading a past post of window unit AC to make DH

[brdmkr]

I was reading past posts and come across a thread that talked about using a widow AC unit to build a DH kiln.  I plan on building several small solar kilns (500-1000 bdf capacity), but the idea of building a small kiln using a window unit sounds kind of interesting.  So, how many of you are doing this?  Have there been any mods that might be useful?  How long can you expect the AC to work before the acids in the wood takes a toll?  Any way to eliminate or reduce acid damage?  What size AC unit would be needed to handle 500 or so bdft?

Thanks in advance.

Mike

[Daren]

Mike
I hate to let this one lay, but I am afraid I don't have any answers. I have though about this myself. From what I have read you want an older a/c unit (the freon runs at higher temp so the compressor lasts longer than a new one that is designed to run cooler- I think) plus you can always pick them up for $25-$50. I didn't read the past treads, but you are talking about having the unit totally in the kiln? So the heat from the unit is used to free moisture that is removed by the condensing coil and drianed away. If it is cool you need additional heat to get it going. I don't know the btu's, but alot of units have thermostats, a guy could get a big one and just turn it down. Then air flow through the stack to get the moist air between the boards equal to the humidity level in the chamber.

Daren

[brdmkr]

The old post I was looking at suggested that the entire AC unit should be placed in the kiln.  I suppose a drain hose could be rigged up to take the condensed water off of the coil to the outside.  I remember that the older freon units were suggested.  Now that you mention it, it seems that someone indicated that they used a heater to get the temp up first and a fan to keep the air flowing.  I was hoping that someone who was using this type of setup would chime in with some of their experiences.  I would like to give this a try, but if I have to give 25 - 30 bucks for an old AC unit, I'd like to dry a more than one or two batches before the AC quits due to acids.  I never got a good indication of what kind of life could be expeced out of the AC in the acid environment.  I also don't remember any suggested BTU.  Oh well, thanks for keeping the thread alive.  Maybe someone will help out.

[whitey]

  Brdmkr   I used  a dehumidifer  that we used for moisture removale on wood floors . sticker the wood put a fan on one side  dh unit on the other and cover with plastic not real fast  but it works .  I built a electric 500 bdft kiln using a old electric furnace can  dry from 20% to 8% in about 4 days  Irun it up to 160 fh to set pitch and kill bugs (western juniper) run about $20 a load  don't know any thing other than that and pine. hope this helps.  that is a room dh unit free standing.

[woodhaven]

brdmkr,
A DH unit and a AC are basically the same thing. The only differance is minor.
I personlly would not put the unit inside the kiln.

[brdmkr]

So, would you just run cold air with the unit mounted just like it were in a window?  I suppose you could put a heater inside as well to keep the AC running.  Anyone tried this?

[DanG]

Well, I got some thoughts on this, but I ain't sure any of them are right. :  Basically, a window a/c and a dehumidifier are the same thing.  They are built differently to accomodate their purpose.  As I understand it, an a/c unit will cause wood to dry by removing the moisture from the air surrounding it.  The main problem with this seems, from what I've been told, to be one of controlling the drying rate.  A secondary problem is that of deterioration of the unit, itself.  Don Lewis and Den Socling, two of the leading experts on the drying of wood have freely shared their hard earned knowledge with us, and they don't seem to think much of the idea.  That being said, I am tempted to try it anyway.  I can't come up with the capital to purchase a factory unit right now, but I can put a second-hand a/c in a box with some semi-OK lumber that's gonna go to waste if I don't do something.

I can't see any advantage to putting the unit outside, then adding a heater.  The caustic air is going to circulate through the unit, anyway, and will probably ruin it in a short time.  Why not take advantage of the heat the unit produces?

I wouldn't want to put any high value wood in a kiln of this sort.  You would probably make more money selling it green, than trying to peddle it after you have ruined it.  It would be fun, though, to experiment with some low value stuff, just to see how it turn's out. ;D

For the more valuable stuff, a well-designed solar kiln is probably the way to go for us small-timers.  If your scrounging skills are up to par, and you put some thought and research into it, you should be able to build one for very little $ outlay.

[brdmkr]

DanG

I am thinking I can get my hands on a used AC for little of nothing.  That is why I am interested.  I was thinking of trying some pine just to see how it might work.  The old post that got me to thinking about this suggested that the entire AC unit be placed in the kiln.  I suppose that if I can get an AC for free, it really wouldn't matter how long it lasts, but I don't want to be wasteful.

[woodhaven]

Dang,
There are at least a dozen reasons NOT to put the unit inside the kiln. The heat that is blowen off by the unit is still used I don't mean it is wasted. Any refrigeration unit is the same to the degree that they all have the same basic componets. Evaperator,Condenser,Compressor and metering device. No matter if it is a AC the size of a truck  or a window unit or a DH or a household refrigerator. The only basic differance is the placement of componets. After working these units for over 30 years they are all the same to me. A little differant wiring and componets at a differant place but the same old same old.

If you wanted to you could take a DH unit and make a air conditioner.

[IndyIan]

One thing you have to account for is that if you have the whole AC unit inside the machine can't turn itself off, the more it runs the hotter it gets.  You need a seperate thermostat to turn off the AC unit at a specific temperature or a timer. 
I have an old beast of a window unit and left it running inside to dry out the house we are building.  It would pull about 8 gallons of water out of the air and drop the humidity from 80+% down to %40 for a 1000 sq. ft room with 300 bd.ft  of wet red oak in it overnight.
Ian

[brdmkr]

Maybe I should just pick up an old AC unit, mount it in an insulated box and let it run with the outside of the AC to the outside of the box.  I suppse that since I am just trying to learn about the only thing I would be wasting was time.   Or, better yet, I could try both approaches and just see what works best.

 

[slowzuki]

Letting the heat go out side will cool like a how you normally use AC, leaving inside just makes it a dehumidifier.  It is wasteful to let that heat go if you are paying for some other form of heat to make up for it.

For kicks we'll say your AC moves 2 kw of heat to the hot side for every kw of power you put in.  You leave it inside and you have a 1 kw heater and dehumidifier in one.

Poke it outside you have to pay for 2 kw of heat plus 1 kw of AC to get the same effect plus you now need a heater and the AC unit.

The bad part is the loss of separate controls over temp and humidity.

We have several dehumdifiers people put in basements, they seem to remove about 4 L a day in the summer.  I wonder how they would last in a kiln.

[woodhaven]

brdmkr.
slowzuki is on the right thought. You don't won't to blow that hot air outside you want it blown back in the kiln. I think is why some people just  set the whole unit inside the kiln there is no extra work.

But don't let me misguide you. You still have to monitor just as if it were a store bought unit. There are also other things to watch for and plan for. It is easy for me but maybe not as easy as it sounds. There is more to it than just throwing a window ac in a box and waiting. Properly done it is just as good as any store bought in fact it is the same thing.

I am not throwing off on any unit I think they are all good. I just perfere to build my oun stuff.

[Buzz-sawyer]

I believe I made the post you all are refering to .
The article I quoted was written by a member (NOW) here.
He has used it repeatedly and suffered no degrade or acidic failure on his $20 dollar a/c.....and as I said then .so what if it fails after 10-20k bdft..get another!

[Charles]

My thoughts on a a/c vs DH
DH units work very well inside a small kiln and are readily available and cheaper and less trouble that a a/c unit. a/c will work for big loads but gor small loads the a/c is way overkill. The unit a/c or DH must have R12 refrigerant or equilvilant. The R12 can still work in temps of 100-110f. The new units a/c or  DH have R134A in them and they have a shut off switch that kicks in at 100f, makes them useless for a kiln.
I built this small kiln that sits the basement of my shop. It holds 200bf and uses a DH unit for drying, and there are two doors to seal the kiln. I have dryed about 20 loads of AD'd  and am on my second DH unit. I might still be on the first but I dried a load of fresh red oak and it rotted everthing off the DH unit that was metal.

just as general info,

The kiln has the DH in the center top with 2 fans on a 45 angle at the sides. Air moves down and through the lumber and up the back of the kiln past the DH unit. The fans are on a Rheostat  to controll air movement. Lights up top help the initial warm up then are shut off, the heat from the DH unit keeps the temp at 105f with some venting, near the end of drying DH runs all the time. Water is collected and measured with a pail at the right side. The DH unit is cycled with the help of a small inexpensive PLC unit to maintain proper daily water extraction. The black box on the electrical panel is a temp readout from a internal probe so constant temp is maintained in bottom of kiln. Two little windows on right side of kiln allow you see a moisture meter in the inside of kiln in lower chamber and also the back of kiln to make sure proper air flow is occurring through the lumber. The average amount of water that is taken on about 150 BF of oak is only 16 pints a dayto start, so that is why a a/c unit is much over kill
There is also another temp readout not shown in which the probe is inserted between the condensing coils of the DH unit so the coil temp can compared to the inside air temp to make sure the DH is working.
The total cost was under $700 and the cost to dry is about half of what I was paying.  I built the kiln because I like to dry small amounts for myself and it was getting difficult to find anyone to do small quantities
Maybe this may shed a little more light I hope.

My thoughts
charlie

[brdmkr]

That looks nice!  The reason I was asking about AC is that I can probably come accross one of those for near nothing or free.   I suppose I should be on the lookout for an older DH unit that uses R12.   How long does it take to dry a load of AD oak (on average)?  What MC do you start with and where are you ending up?

[Charles]

a lot depends on the MC of the AD wood but it is usually around 15 to 20% .
I like to AD first cause the first % of drying costs nothing. From 20% to 6% it would take about 18-20 days or so. It takes a couple of days to get going then you drop about a % or better each day. After the drying I equalize the lumber by steaming about a gal of water back into the chamber, I really don't think I would have to do this but if it isn't broke don't fix it. Now these figures are just me. Alot of guys do this a whole lot faster, but I don't have to. I buy a tree or a log when ever I can and my neighbor has a mill and then it gets stickered and stored in my inlaw's barn upstairs. Stays there till I need some lumber, then I pull 150BF and dry it. Store the rest in the basement of the shop to keep it at 6%. Buying whenever there's a deal keeps up the inventory. Last fall I happened to be at the right place right time and picked this baby up for $180 over 400 hundred years old, white oak. I counted the rings and got lost at over 400 I had to cut it down too. The log was about 44" by 8' or so and I got about 700 bf from it.

[carl]

HI CHARLES
MY NAME IS CARL    IM FROM WINNIPEG; I WOUD BE INTERESTED IN INFO ON HOW  YOU ARE CONTROLLING THE DRYING  WITH THE PLC  AND DH UNIT.  ID TURN  BOWLS AND AM LOOKING TO FIND A
BETTER WAY OF DRYING OTHER THAN 6-10 MONTHS AIR DRYING    ANY INFO WOULD BE APPRECIATED
THANKS    CARL

[Charles]

Carl

The PLC is a PM4H-W Dual Timer 1.5 amp.
This is the base cause the PLC is transferable to different stations



The PLC itself is programable on and off to sec, min, hrs and 10x hrs. So you could have any combo of on off times such as 29 min on and 75 hrs off or 10 min. on and 33 min off. The lower corners adjust the hrs, min, sec for on, off. The red and green arrows allow for easy setting of on, off times.




Because the PLC is a 1.5 amp unit I installed a 15 amp mechanical switch that is wired to the DH unit and PLC, that allows the PLC to trigger the switch without blowing itself out, cause the load from the DH is more than 1.5 amps It is not a really good picture but they are big and when they switch they go clunk.



So end result is the DH is timed to a on, off time to allow for proper water extraction

I hope this helps. I think we have sort off gotten of the brdmkr's topic so if you want more info email me.

charlie

[Tom]

Charles,
Be careful about calling yourself Charlie.   My little brother is a member of this board and goes by the name Charlie as his UserId.   You sure don't want to be mistaken for that litlle @#$%^&*()_+!!

He's like a prickly pear thorn stuck under a saddle blanket.  :D :D

[Buzz-sawyer]

Dont be so shy about it man....topics are fluid IF they are incorporated into interesting discussions..that is the great thing about this forum ;)

[DanG]

Yeah.  Keep on posting this stuff for all of us to see.  I can assure you that brdmkr is hanging on every word and pic, along with everybody else.  We like innovative ideas. We Really like people who bring them into reality.  We really REALLY like people who bring them into reality with PICS! ;D ;D

[Buzz-sawyer]

By the way Charles what kind of saw cut this????

http://www.cyg.net/~charlesk/Milling%20log.jpg

[Charles]

Well taken won't happen again
signing off
charles

[Buzz-sawyer]

Charles so ...my point was lets keep talkin about it :D :D :D :D