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Efficiency of heat pump and refrigerator

by anizet
Tags: efficiency, heat, pump, refrigerator
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anizet
#1
Oct6-08, 02:30 PM
P: 11
I know the formulas for efficiencies e of heat pump (it is e<=Tmax/(Tmax-Tmin)) and refrigerator (e<=Tmin/(Tmax-Tmin)), where Tmax and Tmin are temperatures of warmer and colder (respectively) involved containers. These formulas make me puzzled, as efficiencies seem to be possibly bigger than 1. Is that correct? If yes, what does it mean?
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stewartcs
#2
Oct6-08, 02:49 PM
Sci Advisor
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P: 2,283
Quote Quote by anizet View Post
I know the formulas for efficiencies e of heat pump (it is e<=Tmax/(Tmax-Tmin)) and refrigerator (e<=Tmin/(Tmax-Tmin)), where Tmax and Tmin are temperatures of warmer and colder (respectively) involved containers. These formulas make me puzzled, as efficiencies seem to be possibly bigger than 1. Is that correct? If yes, what does it mean?
The COP (coefficient of performance) for heat pumps and refrigerators can be greater than 1 (and normally are). You are mixing the idea of thermal efficiency of a heat engine with COP. They are not the same thing.

CS
russ_watters
#3
Oct6-08, 05:07 PM
Mentor
P: 22,281
In a typical heat engine, you have a certain amount of thermal energy that is converted to mechanical energy. In a heat pump or refrigeration cycle, the working fluid is being circulated to move heat between a hot and cold well. There is no direct corellation between the energy required to circulate the working fluid and the energy it is carrying with it when you move it.


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