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How do heat pumps work?



Heat pumps are hailed as our collective route to help reach Net Zero carbon emissions and many homeowners are turning to them to save on cash and carbon. But how do they actually work? The technology isn’t that complicated, which is also why they are low maintenance. In fact they work a bit like a refrigerator, but in reverse. Keep reading below, where we explore how the two main types of heat pump, ground source and air source, work and how their performance is measured.

How do heat pumps work?


In the simplest terms a heat pump moves heat from the environment outside (in the ground or the air), boosts its temperature, moves it inside and releases it through your central heating system. Heat pumps use electricity to do this, but will produce two to three times more heat output than is required to power it – which is why they are so energy efficient. And because they do not burn any fuel to generate the heat, they don’t emit any carbon emissions. 


Air source heat pumps explained


An air source heat pump extracts heat from the outside air by using a special fluid – a refrigerant. The fluid is compressed, making it hotter and turning it into vapour. The super hot gas is transported into your home and released to be used in your central heating system – for hot water and in your radiators or underfloor heating system. During this step the vapour transforms back into a liquid, which passes through a special valve, rapidly cooling it down to prepare it for repeating the cycle and absorbing more heat from the air outside. Air conditioners do the same, but in reverse, and some air source heat pumps can function as air conditioners, taking hot air from inside and releasing it outside – to cool your property. 


Ground source heat pumps explained


A ground-source heat pump absorbs heat from the earth by pumping a mixture of water and refrigerant through a network of underground pipes. That’s why ground source heat pumps require you to have enough outdoor space and suitable ground to install the pipes – which can be installed vertically or more commonly, in horizontal trenches. The water mixture is compressed and goes through a heat exchanger, which extracts the heat and transfers it to the heat pump. The heat is then transferred to your home heating system.


How is heat pump performance measured?


As we’ve already mentioned, the output of energy, in the form of heat, that a heat pump generates is several times greater than the energy required to power it. The measurement for energy output versus energy input is termed Coefficient of Performance (CoP). So for example, the CoP for a typical household heat pump is around four. That means the energy output is four times greater than the electrical energy used to run it. 


The CoP will have been measured at a single point in time, under test conditions and every heat pump has a published datasheet telling you what its measured CoP is. However, because any heat pump will experience temperature variations throughout the year due to air and ground temperatures rising and falling, the CoP isn’t necessarily going to help you to understand what the cost of running the heat pump will be, or its ‘real world’ efficiency over the course of a year.


Instead, the Seasonal Coefficient of Performance (SCoP) or Seasonal Performance Factor (SPF) is used to show the efficiency of the heat pump across the whole year. As a certified heat pump installer, we can calculate the SPF of your proposed system. SCoP demonstrates how the heat pump should perform given the average temperatures where you live and other variables such as the size of your radiators. This figure will give you a better indication of what to expect in terms of running costs and efficiency than the CoP figure.  


If you’re considering installing a heat pump, but you’re not sure which route to go or whether you home is suitable, then let us help you. We’re more than happy to answer any questions you might have and we can send one of our heat pump engineers out to assess your property, as well as your eligibility for the £7,500 grant. Get in touch today!