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Started by Fla._Deadheader, April 03, 2004, 11:00:12 AM

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Fla._Deadheader

Eggzacktly, how does a de-humidifier work???

  If ya got an old air conditioner, and it doesn't get cold, will it still take moisture out of the air???  If it will blow warm air, instead of cold, why would it not dry wood, in a tightly closed environment???
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

Tom

I canT talk like a book but here goes........

Warm air holds more water than cold air
Cold air gives up water the colder it gets

A tightly enclosed space has no way of getting rid of the water even if you get it out of the wood.

So, Here's kinda what you do.
Heat the wood and the air so that the air can become saturated with water.

Take the saturated air to another place and cool it.  The cool air will drop the water.

Get rid of the water and send the dry air back in there where the wood is to be warmed back up so it can carry the water out again.  (A DH might work in an enclosed area if you can get rid of the water.)

A stack of wood is hard to get the water out of because it's hard to move the air inside of the stack.  You have to get rid of that water-saturated air from inside of the stack.  That's why you stack wood in fairly narrow stacks in the open or move the air with fans in a kiln.

Now somebody that really knows will come along and give you some formulas :D :D

Fla._Deadheader

  By tightly closed, I MEANT ;D set the A/C up, as you would a de-humdinger. Ain't they about the same thing??? A de-humdinger don't have cold air, right ??? ??? ???
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

tawilson

Sounds like your old air conditioner is broke. So no cooling or dehumification. A dehumidifier cools and heats the air to get the moisture out and send it out at the same temp. So a functioning air conditioner could work.
Tom
2017 LT40HDG35 WIDE
BMS250 and BMT250 sharpener/setter
Woodmaster 725

woodhaven

Tom,
 You did a right good job at that. I would never have gotten that far down to earth.

FD,
Be a little more specific and I will give it a shot.

Here is a couple of things to consider.
Water boils at 212 Degrees
The Refrigerant in a window unit boils at -20 degrees
Technically speaking cold is -460 degrees
There is still heat in the air down to -459 degrees

You are right in the fact that a dehumidifier or air conditioner doesn't have cold air.
It does have air that the heat has been removed from. It may seem the same but there is a big differance.
Richard

Fla._Deadheader

 I just got back from a visit with Ole Jeeves. He says that there IS a cold coil in a de-humdinger, that condenses the water from the air ::) Guess my idea wasn't so dangerous after all ::) ::)
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

woodhaven

You are zactly right. The cold coil is the evaperator and containes the refrigerant with the -20 degree boiling point.
That is exactly the same coil that is in front of a window unit.
The one that sweats. If you had -20 degree blood in your body you would sweat at a low temp too.
Richard

Fla._Deadheader

Then, can ya reverse the fan on a A/C and get a BIG de-humdinger ::) ::) ;D
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

woodhaven

Richard

Ianab

Okies...
I'll have a go at explaining how it works
Here's my simple DH unit with the covers taken off  ;)



The components in a DH and an airconditioner are basically similar, but the air flows thru the DH in one path. In an Aircon you have your inside air thru one radiator, and the outside air thru the other one.
Does that make sense  ??? :)

Ian
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

tawilson

A picture is worth a thousand words.
Tom
2017 LT40HDG35 WIDE
BMS250 and BMT250 sharpener/setter
Woodmaster 725

woodhaven

FD,
Got any questions about Ianab's picture? It's perfect. There is one missing component which wouldn't mean much to you at this point.
If you stuck a fan between his two coils and had the air blowing forward out of the cold coil you would have turned it back into a AC unit.
Richard

Fla._Deadheader

  I think I's got it !!!!!!!!!!!!!!!!
All truth passes through three stages:
   First, it is ridiculed;
   Second, it is violently opposed; and
   Third, it is accepted as self-evident.

-- Arthur Schopenhauer (1788-1860)

LeeB

So if you reverse the fan in an a.c. you get a dehumidifier? LeeB
'98 LT40HDD/Lombardini, Case 580L, Cat D4C, JD 3032 tractor, JD 5410 tractor, Husky 346, 372 and 562XP's. Stihl MS180 and MS361, 1998 and 2006 3/4 Ton 5.9 Cummins 4x4's, 1989 Dodge D100 w/ 318, and a 1966 Chevy C60 w/ dump bed.

woodhaven

Nope, Not at all.
If you reversed the fan what you would get is little to no air flow.
The fan blade pitch is directional. Changing that would do nothing.
Richard

Don_Lewis

There is a difference in the pressures of the two coils. In a DH kiln, depending in the refrigerant, the fluid is boiling off at about 40 PSIG. In order to boil anything, water or refrigerant you have to add heat. In a boiler, the heat comes from the fire. In a DH unit, the heat comes from the air. This causes the air to be cooled and when cool enough, the water in the air condenses. Then the refrigerant pressure is raised by the compressor to about 300 PSIG, the condenser does just what a steam coil does, condenses the gas to a liquid giving up heat to the air. The heat given up is the total of the heat removed by the evaporator plus the energy put in at the compressor. You have all had the experience of using a spray can and haing it get cold as you spray. That is the refrigerant boiling off just like in an evaporator. If that refrigerant could be collected at the spray nozzle, and pumped up and put back in the can, you would have a refrigeration system and the sweating on the side of the can would be dehumdification.

woodhaven

Don is also right.
If you could take a glass of refrigerant and pour it out it would disapear before it ever hit the floor. Back before ozone became such a big issure I could do all kinds of things with refrigerant. Not anymore nowdays you can go to jail for stuff I did. Anytime I had a part that needed to be shrinked to fit I just spray some Freon on it. A lot quicked than leaving it in the freezer overnight. If any of you have ever changed piston sleeves in a engine you know what I mean.
Richard

rs1626

so if you unhook the fan in the a/c unit and connect a fan to
the front of the unit will it work to dry lumber?

Buzz-sawyer

simple question ;
simple answer;
 put old inefficient ac window unit on a table in the middle of a closed room, and it will both heat, and dehumidify at the same time
answer, YES
    HEAR THAT BLADE SING!

tawilson

That's if it is still functional. Fla_Deadheader started out by saying he had "an old air conditioner, and it doesn't get cold", so I took that to mean it was broke, so no cooling or dehumidifying.
Tom
2017 LT40HDG35 WIDE
BMS250 and BMT250 sharpener/setter
Woodmaster 725

woodhaven

Thats right,
I would hate to see some of you guys try this and then say we are crazy because it didn't work. You need a good AC not a piece of junk.
The first 40% of what any AC unit does anyway is dehumidify your house then it starts to cool.
When I do a heat loss and heat gain calculation on any structure you would be surprised at the unit size if it were not for moisture removal.
Richard

Buzz-sawyer

Right Guys... :D
It can be a 1965 model with no plastic left on it ....but it HAS to be a functional a/c unit....it must dehumidify and heat....that all there is to it
plain ...simple ;) ;)
    HEAR THAT BLADE SING!

Don_Lewis

It will work as a dryer as long as the system is still functional. There are two main problems. It won't last long because corrosion form the acid in wood will eat up the wet surfaces quickly and it can't function at high enough temperatures to be effective. The airflows are designed for around 70F so when you raise the temperature it becomes less efficient and may not even take water out of the air when you get down to 30% RH, which you need at the end of the cycle to get to 6%. But people do it and you can dry wood that way just not very well.

Ianab

QuoteBut people do it and you can dry wood that way just not very well.

Very true, you aren't going to make a $10,000 DH kiln with a $200 second hand aircon unit. But to dry small quantities of timber, or get your 20% airdried wood down to 10%, it is practical. You wont have killed all possible bugs, you wont have set pitch, it wont be fast.... Just be aware of the limitations and if you can work with them go for it.
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Buzz-sawyer

I hold a slightly different opinion :) .....in that I got the a/c unit for free ( and most old r-12 units can be had for $50-$100 or free) and I feel it works exceptionally well,(in light of the cost to to usefullness ratio)
as far as corroding and dissintigrating into pieces ...havent seen that happen.....if it does after 5 or 10 1000 bdft loads SO? visit another garage sale and set another one in there , right, Harold!
and the OLD r-12 units do function fairly efficiently at higher end of cycle (as discussed in previous thread.... ;) 8) 8)

     regardless it is satisfying to me personally to collect the parts and make something for free that can turn 1000 feet of air dried into6-8% lumber essentialy for the cost of electricity ($50).....results may vary , but the fun of DOIN it doesnt....
Keep those projecs flowin....good fun guys good input all...
Don
    HEAR THAT BLADE SING!

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