How efficient are ground source heat pumps?

Ground source heat pumps are the most efficient heating system available, and can – in ideal conditions – produce up to six times the amount of energy as they use.

What are COP and SCOP?

You may see heat pumps described by their COP or SCOP. COP (Coefficient of Performance) and SCOP (Seasonal Coefficient of Performance) are two terms used in the heating industry to describe the efficiency of heating systems. COP is a measure for the amount of useable heat generated from one unit of electricity at a given moment. So, a COP of 4 is telling you that for every 1kw of electricity a heat pump uses it produces 4kw in useable energy for heat. SCOP is similar to COP but measures the efficiency of a heating system over an entire year.

What determines the efficiency of a heat pump?

Heat pumps efficiency is not set in stone; their performance depends on many variables. The most significant variable is the temperature difference between where the heat comes from (the heat source) and what it needs to be delivered as for useable heating. Typically the smaller this gap, the higher the efficiency. This is why ground source heat pumps are so much more efficient than air source heat pumps. When the outside air gets colder during winter, the temperature in the ground remains stable.

Other factors include how well your home is insulated, the size of the rooms you need to heat and your distribution system. Underfloor heating and larger radiators (e.g. K2/K3)  can deliver heat with much lower flow temperatures again supporting higher heat pump system efficiency.

The quality of a heat pump unit itself also makes a difference. Kensa’s Heat Pumps are highly efficient – you can Kensa Heat Pumpsread more about them here.

So how efficient are ground source heat pumps?

Professionally installed ground source heat pumps can achieve – in ideal conditions - a SCOP of up to 5.96 (Kensa Evo 7, with 10oC inlet and 35 oC flow temperature), meaning that across the year they deliver nearly six times the amount of energy they use. That compares to a SCOP of about 2.5 to 3.5 for air source heat pumps – and less than 1 for a gas boiler. Direct electric heating has a SCOP of 1.

Why are ground source heat pumps so efficient?

Ground source heat pumps are so efficient because they use the energy from the ground, which stays at a stable temperature all year round. In the UK, a metre below the ground the temperature is typically 8-12°C, even when the air temperature is below freezing. That means even in cold weather the heat pump has to do much less work than other heating systems to produce useable heat in the home.

By comparison, gas and oil boilers have to burn fuel to heat water, while direct electric heating systems have to use large amounts of electricity to heat up radiators. Air source heat pumps - though still an efficient technology - rely on thermal energy from the air, even when it is cold outside, so they also use more electricity to deliver adequate heating and hot water.

In the summer, ground source heat pumps can be used for cooling when the ground is much cooler than the air temperature. Again, since the temperature of the ground is already about 8-12°C, they can bring the air in a home to a comfortable ambient temperature. It should be noted that this can add potentially significant expense to a project.

Why is heat pump efficiency important?

The more efficient your heating system, the lower your energy bill. That makes ground source heat pumps the lowest cost heating option you can choose. Over the lifetime of a ground source heat pump, it can save you tens of thousands of pounds compared to an air source heat pump.

The other key benefit of ground source heat pumps’ efficiency is their sustainability. Ground source heat pumps emit no carbon themselves, and because they run on electricity that is getting greener over time, their carbon impact is incredibly low. And since the electricity they require is so low, they take much less from the grid than other heating systems.