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July 21st 2023

Why heat pumps are so energy-efficient

Everything around us contains thermal energy, or as it’s better known, heat. Heat naturally flows from a warmer place to a colder place. So, providing heat to a home when the outdoor temperatures are colder, means that we need heat to flow in the other direction, which is a difficult, and often highly expensive task. So how does a heat pump do it for so much less energy? We’ll tell you.

How do heat pumps work?

When the pressure of a gas increases, the temperature also increases. When the pressure decreases, the temperature decreases. This relationship between pressure and temperature is the key to how a heat pump works so efficiently.

The gas within a heat pump is called a ‘refrigerant’ and the pump uses electricity to compress this refrigerant, increasing the pressure and therefore the temperature. As the refrigerant’s heat is transferred through to the heat exchanger it cools down a little. Then, the refrigerant expands so that it cools even further meaning it is now cold enough to absorb more heat from outside and begin the process again.

But what about the heat? Well, the heat delivered to the heat exchanger when the refrigerant is compressed can then be used to heat your home. This would normally be done using a central heating system, i.e. radiators or underfloor heating. Or provide domestic hot water using the heat from the heat pump to heat a hot water cylinder.

How efficient are heat pumps?

Heat pumps are more efficient than other heating systems because the amount of heat production is significantly more than the amount of electricity they use. The amount of heat produced for every unit of electricity used is known as the Coefficient of Performance (CoP). So, if a heat pump has a CoP of 3.0, then it will give out three units of heat for every unit of electricity consumed. 

But what about seasonal differences? Well, the Seasonal Coefficient of Performance (SCoP) is used to show the efficiency of the heat pump across the whole year. Heat pump installers  calculate the SCoP based on their system design for your home. This calculation demonstrates how the heat pump should perform given the average temperatures at your location and other details such as the size of your radiators. The installer will then share this calculation with you before beginning any work. The SCoP will give you a better indication of what to expect in terms of running costs and efficiency than the CoP figure.  

Will installing a heat pump help save money on my heating bills?

While the compressor and pumps need electricity to work, they use less than the quantity of heat they move from outside to inside. The amount of heat energy moved versus the amount of electrical energy used does also depend on the source temperature and the output temperature. This means it varies constantly throughout the year as outside temperatures change.

How this will affect your energy bill will depend on several factors, including:

  • What fuel you are replacing and how much it costs
  • Your electricity tariff
  • Which type of heat pump you install and how efficient it is
  • The design of your central heating system
  • Your location and its average air or ground temperatures throughout the year 

Operating your heat pump system

The compressor in a heat pump works much harder when there is a larger temperature difference between the outside source temperature and the temperature needed for your radiators or underfloor heating. The less the compressor needs to work, the less electricity the heat pump uses.

While we can’t control the outdoor source temperature, it’s possible to design heating systems that use low temperatures indoors, meaning the heat pump can use less electricity and still heat your home comfortably. By using radiators with a larger surface area, or underfloor heating, more heat can be delivered into the room without increasing the temperature. 

That being said, when using underfloor heating the finished floor surface can make a massive difference and some surfaces are better at transferring heat than others. We always recommend avoiding using wood finishes on floors, That being said, when using underfloor heating the finished floor surface can make a massive difference and some surfaces are better at transferring heat than others. We always recommend avoiding using wood finishes on floors, although they can still be heated, as they require a higher flow temperature which would decrease the efficiency of the system overall.

The aim of a well-designed system is to reduce the heating temperature as much as possible. The closer the required temperature is to the source temperature (ie the outside air or ground temperature), the more efficient the heat pump will be, and therefore the lower the running costs.

What kind of heat pump is right for me?

Air source heat pumps are the most common type of domestic heat pump in the UK and are suitable for many types of home. However, if you have a garden or large outdoor space, ground source heat pumps are more cost effective to run and can be more reliable over time due to less components to fail within the products.

You can find more information on the differences between ASHPs and GSHPs in our blog. Or to find out more, fill out our contact form and we’ll get back to you as soon as we can.