The Coefficient of Performance explained

Posted by Andi

Home heating

Here at Greener Living, we are trying our best to tell the world about Air Source Heat Pumps and show how they are the key to lowering the world’s carbon emissions. However, what’s not always properly explained are some of the more technical terms and phrases that you may come across while researching Heat Pumps. One of the main terms you will come across in your research is the ‘Coefficient of Performance’ or COP for short. In essence, the Coefficient of Performance is a way of measuring a system’s efficiency in transferring energy.

Energy generation…

Coefficient of Performance

The efficiency of any machine or system can be calculated as the ratio of the amount of work done by the machine to the amount of work given to the machine. In the context of an Air Source Heat Pump, the COP ratio represents how much heat energy an Air Source Heat Pump can generate in relation to how much electricity the Air Source Heat Pump Consumes. An example of this would be, if an Air Source Heat Pump has a COP rating of 3 then for every 1kW of electricity it consumes it would generate the equivalent of 3kW’s of thermal energy.

Energy transfer…

As some of you may remember, the first law of thermodynamics tells us that energy can neither be created nor destroyed, it can only be transferred. So surely, the best a Heat Pump could accomplish is to simply transfer all the electrical energy into thermal energy without wasting any? Wrong. While it is true that an Air Source Heat Pump is powered by electricity, it doesn’t use that electricity directly to generate the heat. It does this by using the energy in the outside air instead of converting electricity directly into heat as an electric space heater does. By using the heat energy stored in the air and combining it with the electricity used to power the Air Source Heat Pump it can output more thermal energy than the energy required to power it.

Coefficient of Performance…

For our more technical readers, the COP is written as Q/W, where Q is the thermal energy generated and W is the power used. Let’s look at this formula in action using a hypothetical situation, an Air Source Heat Pump requires 2kW of electricity to function and it operates in an environment where there are 4 kW of thermal energy in the outside air meaning it outputs 6kW of thermal energy. If we divide the Air Source Heat Pumps output by the Electrical energy used to power the heat pump we get the following –

6kW/2kW = 3.0

This means that the Coefficient of Performance for this hypothetical Air Source Heat Pump is 3.0. As you can tell, the COP rating of any Air Source Heat Pump is very important as it determines how efficient it will be in heating your home and saving you money, the higher the rating, the more heat it can generate for the electricity used to power it.