running dehumidifier with central a/c, yes or no?

ok. i live in georgia. fairly hot and humid summers. i have central a/c. it;s old but it works ok.
i have some dehumidifiers i could also run in the house.
i know that would a. help the a/c by drying the air but b. not help it, by heating the air up as it is dried.
so my question is, for the same degree of comfort in the house, would it use more energy, in a month, to run a dehumidifier or not?
what about more than one?
[these are plain-jane, cheap, garden variety home depot or sears type units, with the fan, humidity control, etc]
wle.
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If your intention is to control the humidity, then yes run your de-humidifiers. The trade off is more money. The heat added by the de-humidifiers will cause the a/c to run longer and help with humidity control. You are trying to gain something over and above what you have already got so it is going to cost you more to get more. (simple math)
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Wrong, wrong, wrong. Just let the AC filter get dirty.
Nick
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snipped-for-privacy@ece.villanova.edu wrote in message wrote:

Well, it is wrong, but filters isn't the answer. (Although they may help with the constant volume problem.)
I don't think his intention is to control humidity, I think it is to save energy.
But it would be a more interesting question if that were his intention. Normal household AC does not control humidity. It controls temperature, and reduces humidity by happy thermodynamic accident. There is no humidistat in the usual control system, and the AC neither knows nor cares what the humidity is. It measures and controls temperature. If the unit is sized very well, and infiltration isn't too bad (no pressurization available), and outside conditions favorable, you sometimes get pretty good humidity reduction. But not control.
One way to get better control is to use a humidistat and add reheat. A dehumidifier could sort of function that way. I think you would want to change your basic AC parameters if you wanted to do that though.
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The heat is bad news, in summertime.

To reduce the airflow over the cold side...

I disagree. (What's the "constant volume problem"?)

We might use night air for cooling, with AC mainly for dehumidification.

It's no accident. If C cfm of 70 F air at 50% RH with Pa = 0.374" Hg enters a box with a 20 ft^2 40 F coil and mixes well before leaving, we might have something like this (viewed in a fixed font):
1/C 1/40 70 ---www-------www--- 40 | T = exit air temp = 40+30C/(C+40).
cfm T RH@70F = 100e^(17.863-9621/(T+460))/(2x0.374)
100 61.4 50% 50 56.7 50% 20 50.0 49% | 10 46.0 42% | dirty filter 5 43.3 38% |

Reheat is bad news, in summertime.

We might add a freezestat...
Nick
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snipped-for-privacy@ece.villanova.edu wrote in message = 100e^(17.863-9621/(T+460))/(2x0.374)

Your system is designed to have variable air volume by adding resistance to the filter section. Bad idea for two reasons: The way you want to vary the CFM is by a variable speed fan. Also, you can't turn airflow down to 5% on a DX coil, you'll freeze it solid.

No, there's nothing wrong with reheat, IF you have capacity. And you always do, at part load. At full load, your reheat doesn't run. It doesn't need to, you have (usually) sufficient humidity control.

Tim
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On 20 Jul 2004 03:27:11 -0700, snipped-for-privacy@aol.com (TimR) wrote:

Yeah, with any cheap commercial, cap-metered unit with no ORI (EPR) valve. Unless you can cycle the pump and keep it from short-cycling.
Ane evap cpil will ice up, if the compressor runs too long, regardless of airflow, UNLESS there is a good EPR downstream in the suction line.
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Hi ~^Johnny^~, hope you are having a nice day
On 21-Aug-04 At About 14:36:13, ~^Johnny^~ wrote to All Subject: Re: running dehumidifier with central a/c, yes or no?
~> Ane evap cpil will ice up, if the compressor runs too long, ~> regardless of airflow, UNLESS there is a good EPR downstream in the ~> suction line.
Just so eveyone is clear this is not true. if the air flow and temp are high enough you could run the compressor as long as you want and it would not freeze. but if you let the air flow rate, or temp, drop too low it will freeze in no time flat.
-=> HvacTech2 <=-
.. *IT IS* documented, look under "For Internal Use Only."
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