Practical Efficiency or COP

The work of Carnot and Kelvin tells us the maximum possible Coefficient of Performance.
COP = T0/(T1 - T0)    What's this Equation?
This is called the Carnot COP. This ideal efficiency can never be attained with a vapour compression cycle and because in practice there are many other losses we arrive at realistic COP values which are achievable by best practice systems today.

Application Temperature
Lift
Carnot
COP
Practical
COP
Freezing
-35°C to +30°C
3.7
1.5
Cooling
-10°C to +30°C
6.6
3.5
Air Conditioning
+5°C to +30°C
11.1
6.0
heating
-5°C to +50°C
5.9
3.0

Temperature Lift
This is simply the span of temperature through which the heat must be lifted. The larger the lift, the more energy has to be used to drive the heat "uphill", and so the COP is lower.

Practical COP
This is the ratio of heat extracted to power input:
COP = heat extracted/power input

For heating applications, COP is expressed in terms of the useful heat delivered:
COP = heat delivered/power input


Note that the units of Heat and Power must be the same. The normal unit is kilowatt (kW).

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