Does cooling require more BTU/hr than heating to maintain same temp difference?

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wrote:

the
at
the
http://www.compactappliance.com/xq/JSP.detailmain/itemID.4600/itemType.PRODU CT/iMainCat.23/iSubCat.39/iProductID.4600/showTab.EnergyGuide/qx/shopping/pr oduct/product.htm
HWC05XCB Haier 5000 BTU Window AC
a.. Energy requirements: 115 Volts/ 60 Hz, 515 Watts, 4.5 Amps a.. EER: 9.7
--
SVL


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wrote:

while
http://www.compactappliance.com/xq/JSP.detailmain/itemID.4600/itemType.PRODU
CT/iMainCat.23/iSubCat.39/iProductID.4600/showTab.EnergyGuide/qx/shopping/pr
Question -- when it says 5k BTU does that mean it moves 5k BTU/HOUR from the house to the outside?

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wrote:

Even
conditioner.
of
http://www.compactappliance.com/xq/JSP.detailmain/itemID.4600/itemType.PRODU
CT/iMainCat.23/iSubCat.39/iProductID.4600/showTab.EnergyGuide/qx/shopping/pr
the
Yes.
The "H" on the end is commonly dropped, much the same as it is when discussing "KWH"
A BTU is the total amount of heat energy required to raise the temperature of one pound of water by one degree F.
And so it follows, one btu is also the total amount of heat energy that must be rejected in order to cool a pound of water in temperature by one degree F.
In practical application, this heat is added or removed over a period of time--hence, a 5000 btu unit has the ability to reject an amount of heat sufficient to raise the temperature of 5000 pounds of water by one degree, if operated for one hours time.
--
SVL



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On Mon, 26 Jul 2004 15:26:03 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:
snipT

/me bows
Thank you again Doug :-)
I begin low level introduction with the line: "There is no such *thing* as cold. Show me some Cold"
Its a difficult concept to convey. Some get it,, some prefer denial and argument. That's the nature of it ('ooman nature),,problem is there is no scientific credos for Cold.
cYa
BTZ
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On Mon, 26 Jul 2004 13:15:17 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

..thank you Doug,, well put. Worth waiting for :- )
BTZ
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snipped-for-privacy@milmac.com (Doug Miller) wrote:

Wrong again, by a factor of 3.
Nick
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On 26 Jul 2004 19:50:37 -0400, snipped-for-privacy@ece.villanova.edu wrote:

..yeah,, roight :-/
U keep right on factoring away. I am sure your misconstrued theorems will resolve to have us all choking for oxygen whilst treading the streets in galoshes/wellingtons/ gumboots..!
BTZ
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X-No-Archive: Yes
Doug Miller wrote:

All energy is conserved, therefore an air conditioner is like an outdoor heater with output being equal to that of power input. The heat output from refrigeration cycle is zero in thermodynamic perspective since it is simply being pumped outside.
Heat pump is also no more efficient than resistive heater at creating heat, because all it's doing is adding the thermal output of compressor + heat taken from outside.
Heat pumps and air conditioners are more efficient than resistive heaters in practical purpose however.
For every one watt of power you put into air conditioner, it can remove about three watts of heat and pumps out four watts of heat. This means that to get 15,000 BTU heat removal capacity, you only need about 5,000 BTU energy input.
For a resistive heater, you need one watt for every watt of heating desired.

Heat transfers into room in summer just like heat transfer out of room in winter.
It's a given that air conditioner works against temperature gradient and this is why it's called a thermal pump. Even then, it has a C.O.P of about 3.

Oops my bad.
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You should feel fortunate that little unit can maintain that temp differential. It must be working hard. I know you like to experiment so put an amp meter on it to see. Compare with cooler outside temps. John

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Think about how your space heater works vs how an air conditioner works. The space heater: Electricity in - Heat out. The amount of heat generated is independent of the outside temperature. So the space heater only has to make up losses. The amount of heat generated is only due to the electricity coming in.
The Air Conditioner. This little device doesn't "generate cold". What it does is move heat from one location to another. But heat only goes from hotter to colder. So if it's 100 degrees outside and you want it to be 75 degrees inside, you have a problem. You need to make something colder than 75 degrees inside and make something hotter than 100 degrees outside. The air conditioner works as follows: 1. Compress the refrigerant gas. Some high school physics will show you that you now have made the gas hotter. In an ideal world, if you now released the pressure on this compressed gas, you then get some uncompressed gas at its original temperature. But that isn't what's done. 2. Pass the hot compresses gas through a heat exchanger. This heat exchanger is outside and the hot gas becomes cooler. Note: The rate of cooling of this hot gas is dependent on the temperature difference between the hot gas and the outside temperature. If it is very hot outside, then the hot compressed refrigerant isn't cooled as efficiently as if it's colder outside. 3. Now take the cooled refrigerant which is now a liquid and allow it to boil under a lower pressure. This "boiling" takes heat from the environment. This happens in another heat exchanger inside the house. 4. Go back to step 1 with the low pressure refrigerant gas.
The key thing to note is that the process become less efficient when the outside temperature rises. The air conditioner is effectively attempting to heat up the outside air. So when the temperature rises, two bad things happen: 1. The air conditioner has to do more work due to heat gain from the outside to the inside of the house. 2. The actual process becomes less efficient because the outside heat exchanger can't work as well because the temperature difference between the hot compressed refrigerant gas and the outside air is less.
For your space heater however, when it gets colder the problem is: 1. The space heater has to do more work due to heat loss from the inside to the outside (the same as problem 1 for the air conditioner except in reverse). But, the space heater doesn't lose efficiency just because it's cold outside.
Hope this helps explain things, John Cochran
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Hi John, hope you are having a nice day
On 25-Jul-04 At About 21:40:00, John Cochran wrote to All Subject: Re: Does cooling require more BTU/hr than heating to maintain same t
JC> From: snipped-for-privacy@smof.fiawol.org (John Cochran)
JC> The Air Conditioner. This little device doesn't "generate cold". What JC> it does is move heat from one location to another.
Ok this is correct. but the rest of your explanation is not quite as correct. an a/c maintains a constant " delta T" even when it is hot outside. it would be quite a long explanation to go through how it works but just to let everyone know, your explanation is not correct.
-=> HvacTech2 <=-
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It's been such a long time since I had a course in thermodynamics, and even then I didn't really understand it.
So what I say here might be totally wrong ...
Above, given an ideal world (no friction, everything done super-slowly, etc), are you saying that you could compress a gas, then let it escape (through a small hole?), and you'd be back to where you started?
Especially, that if you could get that escaping gas to do some "work", like drive a turbine or piston or something, that it'd all net out to zero?
Probably you're not saying that -- but if you are, or if someone thinks you are, then I have a dim recollection of something called a "carnot engine" or something like that, and there's some inherent max efficiency you can get, and never any more -- some work done to compress the gas is just plain lost, gone, unrecoverable for useful work.
Again, I never did really understand this stuff -- maybe someone who does can expand on it, or maybe even show that I'm just plain wrong.
David
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snipped-for-privacy@panix.com (David Combs) wrote in

The perfect heat engine utilizes the Carnot Cycle (you can't do any better than that for heat engine efficiency):
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html

Here's a page that describes it in fairly simple terms: http://oak.cats.ohiou.edu/~piccard/phys202/carnot/carnot.html
At the end, it also shows how heat pump efficiency is calculated if the Carnot cycle is used -- notice that the COP (Coefficient of Performance) depends strongly on the temperatures involved. Given the right temperatures, a heat pump is the most efficient way to heat or cool a space.
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