Refrigeration Heat Pumps - Page 1 2 3 4 5 6


 

Coefficient of performance (COP)

 

This is used to define heat pump efficiency.

 

COP = T1 / ( T1 - T2 )

Where;

COP = coefficient of performance

T1 = condensing temperature (oK).

T2 = evaporating temperature (oK).

 

It is normal to express this coefficient as the ratio of energy output to energy input, rather than use temperatures, as shown below.

 

COP = Q / W

Where;

COP = coefficient of performance

Q = high grade energy output (kWh or kJ).

W = electrical or mechanical energy input (kWh or kJ).

 

 

Typically, a heat pump operating from a source temperature of 5C and designed for heating only would have a COP of about 3.0, whereas a reversible machine for the same conditions would have a COP of about 2.6.

 

The diagram below shows typical COPs for a heat pump.

It can be seen that the COP is increased with higher evaporating temperatures, this means that the higher the low grade energy source temperature the higher the COP.

In winter water sources can be at a higher temperature than outside air, these include; lakes, deep ponds and rivers.

Other sources of low grade energy are sub-soil, and waste products from industry such as effluent and power station waste water.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


In summary, the coefficient of performance (COP) is improved if the temperature of the cold side (heat source) is raised.

For this reason heat pumps can be seen as devices able to convert low grade thermal energy to useful heat.

 


Refrigeration - Heat Pumps - Page 1 2 3 4 5 6