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Air source heat pumps are becoming more popular. They are a highly energy-efficient method of heating your home, and they help to reduce both your energy bills and your carbon footprint. They work by extracting the heat from the outside air, compressing it, and then using the resulting heat to heat the property. In the UK, the winter months can have much colder temperatures, and you might be wondering how your heat pump would perform under those conditions. The good news is that it will still work, although it might be slightly less efficient. Let's take a look in more detail.
Air-source heat pumps are one of the most efficient ways of heating a home and its water. They work quite differently from other methods of heating, such as gas boilers or electric resistance heating.
An air source heat pump works by extracting the heat present in the outside air, using the principle that warm air always moves towards cool air. The warmer air outside is drawn in and blown over a heat exchange surface to a heat pump evaporator, which causes the refrigerant liquid present inside to heat up to the point that it evaporates into a gas. The heated refrigerant gas is then compressed, which raises the temperature even further.
The heated gas is taken to a heat exchanger which transfers the heat into the property's heating system. This system could be fans that blow heated air directly into the room, or it could connect to the wet heating system and heat via radiators or underfloor heating. It can also be used to heat the hot water that comes through the taps.
It is clear immediately why there might be an issue of efficiency in the winter months. When the outside temperature drops, the heat pump will need to work harder to extract heat.
Learn more: How Does An Air Source Heat Pump Work
The efficiency of an air source heat pump is usually measured using the coefficient of performance (CoP). This is calculated by dividing the heat output of the pump by the amount of electricity used to power it. The higher the CoP value, the more efficient the system is.
The average CoP of an air source heat pump is 3 to 4. This translates to it having an efficiency of 300% to 400%. So for every 1 unit of electricity used to power the unit, it will provide 3 to 4 units of heat energy.
Perhaps more useful for looking at seasonal variations is the seasonal performance factor (SPF). This seasonal coefficient takes into account changes across the year when calculating the coefficient of performance.
It is the ratio of the total output of the heat pump over an entire heating season to the total electrical energy used by the heat pump during the same period. Using this calculation, we can compare different heating systems' efficiency rates.
The average SPF for air source heat pumps is 2.5 to 4.0.
The CoP of air-source heat pumps is much higher than many other heating systems.
Ground source heat pumps use the same method as air source heat pumps, but instead of extracting heat from the air, they extract it from underneath the ground. They have an SPF of 3.0 to 4.5.
It can be hard to believe but even on a very cold day, there is still heat present in the air. And air source heat pumps will still be able to extract it.
The heat in the air is generated by the movement of molecules and atoms, and these don't stop moving until the temperature drops to actual zero, which is far, far below freezing at -273.15 °C.
The majority of heat pumps will still work at -10°C, and some of the more advanced models can go as low as -25°C. These units exploit variable speed compressors and defrost mode to continue running even at extremely low temperatures.
If you live in the UK, none of this will affect how your heat pump operates. The average winter temperature in the UK is above freezing, between 2°C and 7°C. In 2023, a village in the highlands of Scotland recorded the lowest temperature of the year at -16°C, but most places will never get close to that.
In fact, air-source heat pumps are much more widely used in countries that have far lower temperatures than the UK. For example, in Norway, the average winter temperature is -6.8°C and yet one in four people owns air source heat pumps.
Uncover more: Can Air Source Heat Pumps Cool
We know that your air source heat pump will work throughout the winter, but the cold weather will affect its efficiency. While there is still heat present in cold air, the heat pump will need to use more electricity to extract it so it can maintain the desired temperature in the house.
Thankfully, the efficiency is only affected by a relatively small amount. And your air source heat pump will still be many times more efficient than a gas boiler, even in cold weather.
For example, the CoP of an air source heat pump when the air temperature is 15°C is 4.3. When the air temperature is 2 degrees, it is 3.1, and when the air temperature is -4°C, it is 2.6.
The average UK winter temperature is between 2°C and 7°C, so this will translate to a CoP for your air source heat pump of between 3.1 and 3.7 during the coldest months.
Some people opt for a ground-source heat pump, rather than an air-source heat pump, because they are better able to handle cold weather. The air temperature changes a lot, depending on the season and other factors. The ground temperature is less susceptible to changes because it is protected by the earth's thermal energy.
Even during the coldest winter months, the temperature in the ground will remain constant. On average, this will be between 8°C and 12°C. So a ground source heat pump won't need to work as hard in winter as an air source heat pump.
With that being said, because the temperature in the UK doesn't tend to reach very cold temperatures, the difference is less stark than it would be for very cold climates.
Explore in-depth: How Does A Ground Source Heat Pump Work
You don't usually need to worry about your air source heat pump freezing, even though it is located outside. In most heat pumps, there is a defrost mode. When the heat pump system recognises that the temperature is reaching freezing, it will temporarily reverse the refrigeration. Instead of extracting heat from the air and bringing it inside, it extracts heat from the outside and sends it to the outdoor unit.
Defrost mode will reduce the heat pump's efficiency while it is running, but it doesn't last for very long.
We've established that the efficiency of your air source heat pump will drop slightly during the winter (although it is still many times more efficient than traditional heating systems). There are ways that you can increase its efficiency to counteract this.
The most important step you could take to improve your air source heat pump's efficiency is to effectively insulate your home. Poor insulation means that warm air will leave your home, which then means that your heat pump will have to generate more heat to keep the house at a constant temperature.
Good insulation will improve the energy efficiency of your heat pump and lower your energy bills, and it is usually fairly inexpensive to install.
There are two main types of air-source heat pumps: air-to-air heat pumps and air-to-water heat pumps. An air-to-air heat pump will blow warm air directly into rooms using fans.
An air-to-water heat pump, on the other hand, will connect directly to your central heating system. So it will heat rooms using radiators. But radiators are not the most efficient way of heating your home with an air source heat pump.
Underfloor heating uses a network of pipes under the floor to distribute heat. This larger surface area means that they are better able to disperse heat evenly than a radiator. And they require less work from the heat pump to reach the desired temperature.
If you don't want underfloor heating, replacing your radiators with larger ones, which have a bigger surface area, will also help improve the energy efficiency of your heat pump.
Discover more: Can Air Source Heat Pumps Work With Existing Radiators
Just like any other complicated machinery, your air source heat pump will benefit from regular maintenance and servicing. There are many separate parts in the system that need to work at their highest level to ensure the best efficiency. And over time, certain parts will get worn out and stop working as they should.
It is often a good idea to get your air source heat pump checked and serviced before every winter, in preparation for the cold UK weather. That way, you will be sure that you are saving as much energy as possible during the period when your air source heat pump has to work its hardest.
Keeping your thermostat at a constant temperature will help to improve your heat pump's efficiency. Air source heat pumps are designed to run constantly at low power, rather than cycling on and off. It can be tempting to turn the thermostat up and down as and when it is needed, but this will prevent your heat pump from being as efficient as it could be.
If you're considering an air-source heat pump for your heating system, we can help. We understand how important it is to have the most effective and efficient heating for your home, and we will work closely with you to ensure that your air source heat pump installation is right for you.
Our team of highly trained and experienced installers will first come out to assess your property. They will find the best spot for placing the outdoor unit, determine whether new insulation might help your air source heat pump be more efficient, look at your current heating system to see if anything needs to be modified, and other factors. They will then discuss these with you to determine the best type of air source heat pump and the best way of installing it.
Once your air source heat pump is installed and running, we will always be on hand for maintenance, servicing, and repair, to help it stay at its highest efficiency.
Air source heat pumps work exactly like a fridge but in reverse. They extract heat from the outside air, use it to heat a refrigerant liquid, and then use that heat for the property's heating system. When the air outside is colder, it does make the heat pump less efficient because it has to use more energy to extract the heat. However, in the UK, the air temperature doesn't drop low enough for this to have too much of an impact. Air source heat pumps are still very popular even in countries with cold climates that have much lower temperatures than the UK.
