When choosing a heat source for your home’s central heating system, Heat pump is now a mainstream, and well-supported, technology. But, for some homeowners they are still not as well known or familiar as boilers.
And, while heat pumps are classified as a renewable energy type, they still require electricity which leaves homeowners wondering how much electricity will my heat pump use?
While each individual’s costs depend on a number of factors, not least the size of your home and how often you need heat, as energy expert, David Hilton explains there are ways to understand potential electricity costs.
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How does a heat pump use electricity?
Heat pumps have operational characteristics that differ from other heating technologies viz Gas boiler Or Oil fired central heating. Simply put, heat pumps don’t burn fossil fuels, they move heat from one place to another. A heat pump is usually named after the location from which it receives heat.
N Air-source heat pumps A heat pump derives its heat from the surrounding air, while a Ground source heat pumps Heat is extracted from a large network of pipes buried in the ground. The heat is absorbed by the refrigerant circuit and then boosted before being transferred to the central heating system.
The heat source (nature) may be free, but the transfer process uses energy, and that energy is electricity.
Why heat pump efficiency affects electricity use
A heat pump operates at an efficiency called a Coefficient of Performance (COP). This is the ratio of electricity used for heating to the energy delivered to the home. So, if a heat pump uses 1 unit of electricity to move 4 units of heat into a home, the COP will be 4 or 400%. The harder the heat pump works, the lower the COP.
So, what makes a heat pump work harder? Well, there are two main reasons for a heat pump to work hard. Cooler temperatures in the air or soil (source), or the need for higher temperatures in the home.
The ideal scenario for an efficient heat pump is a small temperature difference between the heat source and the required delivery temperature. If the air is 7°C and the required water temperature is 35°C, the temperature difference is only 28°C. In this case you can expect a COP of around 4.
But, if the air temperature outside is -7°C and the required water temperature is 55°C, the temperature difference is now 62°C – more than double the temperature rise, and therefore almost half the efficiency.
As the season changes and the required heat load changes, so will the COP. Therefore, it is common to use the Seasonal Coefficient of Performance (SCOP) which is the average COP over a year to get a better understanding of efficiency.
From these figures we can see that it is always best to let the heat pump run slowly. A common one Heat pump error A short start-stop cycle is intended to be used in the same way you would run a gas boiler. However, this method makes the heat pump work harder as it tries to reheat the water, and in doing so requires achieving a large temperature difference.
There are many other influencing factors, but to keep things simple, COP and SCOP are the main contributors to a heat pump’s efficiency – and subsequently how much electricity it will use.
Which heat pump is more efficient – ground source or air source?
When it comes to weighing its efficiency Air Source Heat Pump vs Ground Source Heat PumpThe efficiency of air source heat pumps is more variable than that of ground source heat pumps. This is because the air temperature can change very quickly and often, several times a day.
However a ground source heat pump derives its heat from the ground, where the temperature is more stable. At a depth of 1.5m the soil temperature may be about 10°C, and in dry soils this temperature may drop only a few degrees throughout the heating season.
A consistent source temperature may mean that ground source heat pumps are slightly more efficient than air source heat pumps, mainly due to the fact that the ground temperature will be higher than the average air temperature during the heating season, while Underfloor heating And radiators Will be used more often.
How much electricity will my heat pump use?
Given the variable nature of heat pump efficiency, determining how much electricity a heat pump uses depends on two main factors – how much heat the home needs, and what the actual heat pump efficiency is.
Suppose your house consumes 12000kWh of heat energy per year. If the heat pump operates at a COP of 4 you will use 3000kWh of electricity. But if the efficiency was closer to COP 2, you would use 6000kWh of electricity.
Then you might think that you just multiply the amount of electricity by the unit price, but that’s a very simple equation.
The exact amount of electricity used depends a lot on when the heat pump is running the most. The lion’s share of annual energy consumption will be in the heating season (mainly winter), and you may also have different electricity costs at different times, especially if you have an electric vehicle tariff or a special heat pump tariff.
however you wish Run your heat pump during cheaper off-peak timesIt is inevitable that it will also need to operate during more expensive peak times. On average your heat pump may have a COP of 3, meaning you will use around 4000kWh of electricity per year to produce 12000kWh of heat.
If we assume that 50% (and that is an optimistic estimate) of energy is used during off-peak hours, then 2000kWh will be charged around 8p (£160/year) And 2000kWh at 28p (£560/year).
That’s total £720/year. But, if you use only 25% of the energy in the cheap time, your cost goes up £920.
Please also note that these cost scenarios are based on an average COP of 3 and 12000kWh per year for heating energy, and do not include standing charges or any other electricity use in the home such as car charging, lighting, laundry, cooking or any other appliances. Different tariffs may also apply to different tariffs from different providers.
In summary, if you are looking for ways to ensure that your heat pump uses electricity efficiently, you need to manage energy use in particular, and try to target energy use at cheaper tariff times.
Solar PV panels and Solar battery systems Used with heat pumps By generating usable electricity, your heat pump can also help reduce electricity costs. And finally, don’t turn off the heat pump, make sure you stay on top Heat pump maintenance with annual service, and conducts regular checks on performance and Balancing your central heating system.
