Air Conditioner Question

No, it works just like your refrigerator or your car's windshield defogger. It dehumidifies the air by condensing water out on the cold surface, just like an evaporator. It would seem like the colder interior air would approach the dew point causing a higher relative humidity (that is, if no water were removed), but it doesn't work that way. The evaporator condenses more water out than the dew point can keep up with, or than will re-evaporate back into the air from the evaporator catch pan. Vapor compression refrigeration always *lowers* the RH of the contained air. This drying effect often has to be taken into account when designing such systems.

Don Kansas City

WTF are you talking about ?

No shit. Now explain how a refrigerator and a windshield defogger work in the same way ??????

Wrong. Utterly totally wrong.

Here, study this :

A room is at

DB 80.0 F WB 60.2 F Dew 45.8 F RH 30.0 %

I run an evaporator at 50 % F coil temp.

Think about what happens. To room gets cooler, the RH goes ** UP **. ** NO ** moisture is removed from the air.

Before you say 'this is some kind of theoretical example that never happens in real life', go study the weather in Phoenix AZ.

You need to back to school, first year, and start with the basics. Learn about something called 'psychrometrics'.

After you save up some, you can maybe afford to purchase one of the programs I wrote on the subject.

Then try to study the advanced concept of 'chilled water DEhumidification, which was the topic here.

Heh, calm down, kid. Nobody's talking about your mother.

I just did a little experiment for you. I have a digital hygrometer. I put it on the table here and it says that the humidity in this room is 40% at a temperature of 78 degrees (I have the windows open today). That agrees with what the weather service says for Kansas City. I put the same hygrometer in my refrigerator for five minutes. When I take it out it reads 11% humidity and 41 deg. F, just as I would have expected.

Try it yourself sometime.

Don Kansas City

I'me very happy for you.

What in the f*ck does that have to do with anything I said, or anything in this thread ? Other than perhaps your own incorrect statements, for which you have now provided a non-proof ?

I agree with the idea that the humidity will drop. If the room is going to be cooled by the waterfall, then the waterfall is at a lower temperature than the room. It will enforce a relative humidity of 100 percent next to it, but the actuall grains of water per cubic foot will be much lower, and hence the maximum partial pressure of water will be less there. Since the water vapor in the room will diffuse to maintain the same partial pressure, more vapor will be drawn to the area near the waterfall, where it will condense (because it exceeds the carrying capacity of cold air). The net effect is that the room loses humidity. Pretty nifty.

Michael

Yep. If the water is above the dewpoint in the room, humidity will rise. If it's colder than that dewpoint, room air moisture condenses out in the chilled water stream, and humidity is lowered.

The mositure in the air doesn't know or care WHAT it's condensing on, only the temperature and heat transfer capacity.

In fact, there are test chambers I've worked on that work entirely on that principle. Instead of the air being blow across a coil, it is blown through a saturation water spray chamber. By controlling the water temperature, humidy is easily raised or lowered on command.

Dear Herman Family:

A little more fun than a "standard" room dehumidifier, which uses both the evaporator (to condense the water from the air) and the condensor (to warm the dried air back up) on the same air stream...

David A. Smith

Try shoving the probe up your ass and see what it says.

Let us know!

Thermodynamically I assumed that you meant to insulate the outer walls of the building. Insulating the inner walls would make no sense. If you are running the cooling loop inside the wall, then you are depending on conductivity of the inner wall to get a cold surface to the room.

First, the cooling coils of a refrigerator have forced air passing over them, so they remain more or less dry. The inside of the wall would not, which would allow liquid water to form from condensation. Second, non-sterlie liquid water entrapped in a closed space will quickly form mold and mildew on any growth medium present, and there is lots of growth medium available on a house. The metal coils of a refrigerator do not support mold growth even if they are wet. There are lots of sick people around right now because of mold growth in houses, and don't even mention New Orleans. Down there the authorities won't even let workers into some abandoned houses because of toxic mold contamination, unless the workers are wearing full Hazmat suits.

Dear Harry Andreas:

Then there would be no condensation on the outside, nor would there be condensation in the emtpy space between the walls (I've done this in equipment with no outside air exchange).

No they do not. I have moisture condensing and dripping off my evaporator coils.

Again, I have standing water under my evaporator coils, and they are wet. I have no such growth.

Because they are metal, and tend to suppress most biogrowth (especially at cold temps). The collector pan is not metal.

Too bad they don't just blow some air-fed ozone in there for about 30 minutes...

David A. Smith

huh?

Oops. Not a bad idea except you would have to keep the fluid in the walls above the dewpoint in temp. Which in a house would be impossible. This system is used in europe with chilled beam ceilings.

Air is blown from a main AHU across a chilled beam and diffuses into the room. However we dehumidifi the air coming into the building to around 40 % RH this way the extract dew point temp rarely gets above 12 DegC.

Bye.

Dear Guido:

It would be possible. I have a "wetwall" in my shower. It would simply be "ugly" to have a huge wall with a floor drain. In every room.

Thanks. In Russia, they do a similar thing, only with heating... so condensation is never a problem.

David A. Smith

VERY doable in some places.

Bret Cahill

It might not be all that expensive ONCE IT WAS DESIGNED but the problem is most engineers are quite happy to find ONE design point that is efficient so it is easier to just shut the thing on and off than screw around with an INFINITE number of design points.

Bret Cahill

Very dewable :-) in others.