why do we cool cold air?
why do we cool cold air?
(OP)
hat might be trivial question.
I wonder why in air conditioning system, in most cases, it cool the colder air from inside the room, even thought the air conditioner (the heat pump) have the highest efficiency if the air feed ed in to it has as high as possible temperature, or the differential between the cold side and the hot side of heat pump is as close as possible.
Why do we not pull the hot air from out side, cool down and then push in to the room? It look like logical looking on the heat pump characteristic.
I try to analyze my room windows air conditioner characteristic, and I get to conclusion that the highest efficiency it achieve when you just start the unit, when the room is really hot. Once the room cool down the efficiency of that air conditioner significantly drop down.
I wonder why in air conditioning system, in most cases, it cool the colder air from inside the room, even thought the air conditioner (the heat pump) have the highest efficiency if the air feed ed in to it has as high as possible temperature, or the differential between the cold side and the hot side of heat pump is as close as possible.
Why do we not pull the hot air from out side, cool down and then push in to the room? It look like logical looking on the heat pump characteristic.
I try to analyze my room windows air conditioner characteristic, and I get to conclusion that the highest efficiency it achieve when you just start the unit, when the room is really hot. Once the room cool down the efficiency of that air conditioner significantly drop down.





RE: why do we cool cold air?
90% efficiency with a 50º delta is worse power consumption than 75% efficiency with a 20º delta.
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RE: why do we cool cold air?
Efficiency of heat pump are measure in terms of ration of power use to "shovel" heat power from one place to another (usually from cold to worm space).
It little difficult express that in percentage because it will have to be 200% efficient for refrigerator and 350% and more for most air conditioners, which have no sense, heat pump is not over unity device if I am correct. So better stick with absolute ration.
Now the question is: do you "shovel" the heat down heel or up heel, if up heel what the slop grade is, steep or not. Your logic is correct between input of cold side and output of cold side, however it look different if you look the problem between input of cold side and output of worm side.
The "heel" have less gradient between that two sides of heat pump when temperatures are closer to each other.
RE: why do we cool cold air?
RE: why do we cool cold air?
The opposite is true of heating. You want to start with the warmest air possible to minimize the amount of power consumed. The fact that you have a lower efficiency is less relevant than the fact that you'll consume less power overall.
Qconsumed = ht*deltaT/eff
Start with a lower deltaT, you consume less energy.
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RE: why do we cool cold air?
coefhttp://w
The higher the delta t, the more energy required for cooling.
RE: why do we cool cold air?