Air Conditioner Question

N:dlzc D:aol T:com (dlzc) wrote:


David, I like this idea! It would be a great way to to cool a greenhouse or an indoor temperate rain forest exhibit! The waterfall would lower the ambient temperature while keeping the humidity high.
Unfortunately, this would be a poor way to cool and office or a house. The main benefit of air conditioning is that it removes humidity from the air. I don't know about you, but I'm more comfortable in warm dry environment than a cool damp environment.
I live in Virginia where hot, humid summers are the norm. Comfort is all about the dew point. ;-)
I wish I lived near Sante Fe, NM.
Paul D Oosterhout I work for SAIC
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It would *lower* the humidity. Where do you think the water comes from?
Don Kansas City
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On Sat, 20 May 2006 15:37:27 GMT, "Don A. Gilmore"

    It depends entirely on the temperature of the water, and the dew point of the air it interacts with.

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Dear .p.jm:

Yes. You could moderate the humidity in the room from as low a dew point as "40 deg F" (give or take) to as high as you wanted. And still cool the room, and filter the air.
Might be a bad thing to hear running water in the night though... makes some people have to pee. ;>)
In fact you could do this all in an enclosed chamber, spray the water "across" a forced air stream, and distribute the flow through the house. No air filters required, but you would have to treat (or refresh/blowdown) the water. If you were removing water from the air, like in Virginia or Florida, you'd also need a sewer connection (or send it to the yard).
David A. Smith
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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
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On Sat, 20 May 2006 20:25:48 GMT, "Don A. Gilmore"

    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.

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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
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On Sat, 20 May 2006 23:01:46 GMT, "Don A. Gilmore"

    I'me very happy for you.
    What in the fuck 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 ?

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huh?
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Try shoving the probe up your ass and see what it says.
Let us know!
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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
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On Sun, 21 May 2006 02:53:54 GMT, "Herman Family"

    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.

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Dear Herman Family:
wrote in message ...

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
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Chris W wrote:

I wouldn't really need to be that fancy. You can control the temperature of the evaporator coil by varying the amount of throttling. The compressor still chugs along merrily and the fan still runs at the same speed. There are all sorts of controllable expansion valves available.
Don Kansas City
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little
sure
ASHRAE has criterion for moving air when air conditioning - see the ASHRAE manuals.
If you move air too slowly, room air will stratify, and if you move it too rapidly, it will give you windchill :-)
15 FPM is the recommended flow rate for AC, 5 FPM for heating. (You can drop the size of an AC unit significantly by keeping air moving over 15FPM in rooms vs having it below 15FPM. ) Home units have AC on high speed, and heating on low speed fan settings.
Continuous running provides more even air and fewer complaints about comfort.
Running the fans 24/7 is the least costly, both from maintenance and from energy use, even when not even considering the savings from raising or lowering temperature from nominal by running 24/7. (think starting the entire mass of air in a building moving each time you start a fan vs just overcoming friction as it moves continuously - in a house test moving 25,000 cu ft continuous vs on demand, one month one way the next month the other, the difference was $20 per month lower for 24/7. Then think of the wear on a bronze bushing starting and stopping from dead stop dozens of times a day for years vs non-stop running wear. )
----- And as to vents - there are roughly 5-6 types for each size, for different applications and velocities.
If the air is moving too fast from the vents you have, get a vent that is more diffuse or one that can direct air off the workspace. (Normally, vents for AC are directed upward so the cold air it moves into the room drops gently through the room's exisitng warmer air, while heating vents are directed along the walls to warm them and directed down so the warm air rises through the room's exiith sting cooler air. In one of my rooms that is 25 feet long with lots of glass and wall vents, I had to change the vent types spring -cooling type- and fall -heating type- to get the comfort desired )
fwiw

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I've just installed an inverter-driven heat pump/AC unit (~ 1 kWe/3.5 kWth) that manages to run over a wide speed range from flat out when starting in a cold room to ticking over when things are up to temp - check out Panasonic. Mitsubishi and others.
Bruce.

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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
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