Efficient use of Air conditioner

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Can not convince wife about two things. Just want to bring it here for a serious judgement:
1. Use Air conditioner for home at night: Temperature outside = 69F, Temp in home = 81F, Air conditioner trigger set to 75F
method A. With windows being open - My way method B. With windows being closed - Wife's way
Question: which one make house temp drop faster and which one costs less electricity?
2. Use AC for car in a hot summer day Temperature outside = 80F, Temp of a car parked in sun for one hour = very hot, don't know exact temp
After getting into the car Method A: open windows, drive for a moment then close the windows and start AC. - mine Method B: Start AC right away without opening windows. - wife's
Question: which one make car temp drop faster and which one costs less electricity?
Thanks!
-Tom
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1 - this depends upon the temperature Vs time profile, A and B are good strategies with certain profiles. you also need the humidity levels/profile, as air that is cooler but has a lot of moister causes the AC to run longer to remove the water. If you have 30% humidity, widows open, 80%, windows closed. Look up latent heat. 2.- Method A. Get that superheated air out (140F) and start with 80F
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micheal wrote:

Modified method A: Start the AC at the same time as you open the windows. The system will take a few moments to start producing cool air, so you might as well have it do the pre-cooling in parallel. Won't make much difference to the energy cost, and the total time to a cool car will be less.
After you've closed the windows, set the AC to recirculate for a while until the car has reached a comfortable temperature. Some climate control systems do this automatically.
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Method A is probably going to be moer efficient in both cases.
So what? The energy and money you save doing it your way would not offset the cost of a divorce. Do it your wife's way whenever she's around.
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So true! Don't waste your time and energy on this trivial crap.
Brigitte
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On Tue, 20 Jul 2004 16:08:35 GMT, "Brigitte"
snip

AND,,edit (snip) the drivel fro the posts ! BTZ
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It also has to do with air filtration.
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This is Turtle.
Would that filter be for the Shit coming his way also ?
TURTLE
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On Tue, 20 Jul 2004 20:15:05 -0500, "TURTLE"

or FOS...?
BTZ
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If there is no wind (or no fan blowing the cool air into your house), then neither method A nor method B will cool the house down more quickly. This is because the air return to the AC system is inside the house. The hot air will not get 'blown out' of the house. And there will be minimal air exchange through the windows.
As the wind increases, eventually method A will cool the house down more quickly. However, it will take a good sized wind or big windows to beat the AC. AC units typically cool the air about 20 degrees F. So the air coming out of the AC will be at 61 F (starting with 81 F), regardless of where the thermostat is set.
(Let your wife win on this one.)
If you want to save electricity, buy a window fan.

Method A here will cool the air inside the car faster. But the main source of heat in the car is not the air, but the roof, seats, floor, windows and dashboard. They've all been heated to uncomfortable levels, and the heat capacity of the air is minimal, compared to the rest.
Once the air has been blown out (which will take about 2 seconds), you can safely close the windows.
There is no electricity in a car AC system (except in an electric car)... the AC compressor runs off of an engine belt.
-- greywolf42 ubi dubium ibi libertas {remove planet for return e-mail}
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Actually, yes there is electricity in a car AC system. The clutch on the compressor takes electricity. There are often controls which turn the clutch off and on, which are electric. My GM vehicle has an electric low pressure cutout switch for the suction side.
--

Christopher A. Young
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tom wrote:

There are far too many variables to say one or the other.
I will say the one thing many people miss when they try to figure this out is the very high cost of removing the moisture that comes in from outside.
However I do have an answer. Real time test! Try it both ways several times. See what works best (more comfortable and less run time) Repeat several times on different days. Keep records and let us know the answer. (Local weather may provide degree days so you can adjust for different outside temps to some degree.

Most cars burn gas not electricity. ;-)
Generally I would guess opening the windows for the first quarter mile to exchange the hot inside air, then shutting it up. There have been a number of test that indicate that cars with A/C get better mileage using the A/C than by opening the windows because of all the wind resistance added by the open windows.

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Joseph E. Meehan

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That's a low cost, unless water vapor condenses inside the house.
Nick
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writes:

And just why do you think air conditioners have drip pans?
    John Briggs
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To remove liquid water from walls and furniture? :-)
Nick
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snipped-for-privacy@encompasserve.org writes:

Speaking of which, there is some potential cooling assist in the condensate. The condensate will be about the temp. of the evaporator when it's formed, that is, rather cool. There is cooling ability both in warming this water, and in re-evaporating it. Let's say you either use this water to cool the freon going into the condensor coil or that leaving the condensor. Which is more efficient (in amount of cooling per kWh)? The freon going into the condensor is hot, so maybe the water will re-evaporate, taking with it more heat. Or the condensate cools the freon leaving the condensor coil, cooling it even further, meaning the freon entering the evaporator coil will be cooler, meaning the A/C output is cooler, but it is less likely to evaporate. (Both the warmed condensate and evaporated condensate are dumped outside)
Any thoughts?
--
-Mike

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On Thu, 22 Jul 2004 21:30:56 +0000 (UTC), snipped-for-privacy@world.std.spaamtrap.com (Michael Moroney) wrote:

Very good.
Condensate is often slung into the condenser airstream, usually by friction drag. It mostly evaporates before ever reaching the condenser coil, thereby avoiding additional corrosion of the equipment.
-- -john wide-open at throttle dot info
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In sci.physics snipped-for-privacy@ece.villanova.edu wrote:
Ummm, don't think so.
Take a given volume of air at 90 F and 40%.
How much energy does it take to cool the air to say 72 F?
How much energy does it take to cool and condense enough water to get down to 40% at 72 F?
Let's assume the the air comes out of the heat exchanger at 40 F.
The 40 F air gets mixed with the warmer air until the overall temperature is 72.
The cooled and condensed water goes out the drip tube and contributes nothing to further cooling the enclosed area or condensing more water.
It's energy goes to cooling the bush growing under the drip tube.
Without running through the math, I would think getting the water vapor out is the energy expensive part.
--
Jim Pennino

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We were talking about a) ventilating a house at night vs b) keeping an AC running. I'm thinking a) is better, as long as we don't have condensation inside the house.

Why 90 F and 40%?

Depends on the volume :-)

Why 40%? Standard ASHRAE humans are comfy at 56% and 80.2 F.

Try math! If your 32x32x8' house has 6K Btu/F of fast capacitance and 400 Btu/h-F of thermal conductance, including 200 cfm of air leaks, and it's 78% and 71 F in the morning, and the outdoor temp hits 92 in the afternoon, with the morning humidity ratio, which is better, a) or b)?
Nick
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wrote re:

outside.
down
vapor
afternoon,
If you walk out on your back porch and don't have enough pancakes to build a fence True or False?
False because bicycles don't have hotdogs with flat sidewalks.
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