The coefficient of performance or COP (sometimes CP or CoP) of a heat pump, refrigerator or air conditioning system is a ratio of useful heating or cooling provided to work (energy) required.
When one is interested in how well a machine cools, the COP is the ratio of the heat taken up from the cold reservoir to input work.
[8] Similarly, the COP of a refrigerator or air conditioner operating at maximum theoretical efficiency,
Measured values for actual systems will always be significantly less than these theoretical maxima.
In Europe, the standard test conditions for ground source heat pump units use 308 K (35 °C; 95 °F) for
According to the above formula, the maximum theoretical COPs would be Test results of the best systems are around 4.5.
The EU standard test conditions for an air source heat pump is at dry-bulb temperature of 20 °C (68 °F) for
[9] Given sub-zero European winter temperatures, real world heating performance is significantly poorer than such standard COP figures imply.
As the formula shows, the COP of a heat pump system can be improved by reducing the temperature gap
For a heating system this would mean two things: Accurately determining thermal conductivity will allow for much more precise ground loop[11] or borehole sizing,[12] resulting in higher return temperatures and a more efficient system.
For both systems, also increasing the size of pipes and air canals would help to reduce noise and the energy consumption of pumps (and ventilators) by decreasing the speed of the fluid, which in turn lowers the Reynolds number and hence the turbulence (and noise) and the head loss (see hydraulic head).
The heat pump itself can be improved by increasing the size of the internal heat exchangers, which in turn increases the efficiency (and the cost) relative to the power of the compressor, and also by reducing the system's internal temperature gap over the compressor.
Obviously, this latter measure makes some heat pumps unsuitable to produce high temperatures, which means that a separate machine is needed for producing, e.g., hot tap water.
Seasonal energy efficiency ratio (SEER) is mostly used for air conditioning.
SCOP is a new methodology which gives a better indication of expected real-life performance of heat pump technology.