How do air source heat pumps work in freezing temperatures?

Air source heat pumps are an excellent alternative to traditional gas or oil boilers that are typically found in most UK homes. Air source heat pumps work by using natural heat found in the air surrounding your property. 

Experts claim that residential heating is responsible for nearly 20% of the UK’s carbon emissions. The use of fossil fuels to heat your home not only damages the planet but also increases your household bills, especially due to recent energy price hikes. By using the outside air to heat your property, you’re using a renewable source and reducing your need to use carbon-producing fossil fuels.

Despite their popularity in other countries, many people in the UK don’t believe that our climate is warm enough for air source heat pumps, especially places in the north of England and Scotland. Some of the biggest air source heat pump manufacturers state that their technology will work in temperatures as low as -20°C. The biggest question often asked is how can air source heat pumps produce heat when outside is below freezing point.

A quick introduction to Kelvin

When people think of temperature and how it’s measured, the most common scales are Celsius (°C), and Fahrenheit (°F). Most people are not aware of another temperature scale called Kelvin (K), which is a scale used mostly for scientific purposes. The Kelvin scale, named after Lord Kelvin a British physicist, very rarely makes an appearance in everyday life.

Also referred to as the absolute scale, or absolute zero, zero Kelvin is the absolute lowest temperature that can be reached, with no thermal energy left in the air. For example, there is no such thing as a below-zero Kelvin figure.

Molecules (or atoms) on earth move mostly because of heat, at zero Kelvin all particles stop moving completely. Zero Kelvin is the equivalent of -273.15°C or -459.67°F.

So, what does this mean?

Based on the Kelvin scale, claims that air source heat pumps can still produce heat at -20°C, are correct. At -20°C, there’s still more than enough heat in the air for the technology to generate heat at a comfortable and consistent level for use in the home.

To put things into perspective, Northern Europe has some of the coldest climates. In Finland, Norway and Sweden (where temperatures can reach as low as -30°C), over 40% of households have air source heat pumps installed, more than any other country in the world. Despite milder temperatures in the UK, less than 1% of the population have heat pumps installed, due to the lack of information, or in most cases, the misinformation they’ve heard or seen.

Is an air source heat pump still efficient in cold weather?

The efficiency of an air source heat pump is measured using the Coefficient of Performance, also referred to as CoP, and is calculated by comparing the energy input/output of the system. 

For example, when a heat pump uses one kW of electricity to operate, it produces four kW of heat, so the Coefficient of Performance is four. The higher the CoP the more efficient your system is.

Though air source heat pumps aren’t as efficient in colder climates, they still produce more than enough heat and hot water for your home.

The biggest thing to consider when installing an air source heat pump is the quality and quantity of your home’s insulation. A professional heat pump installer will always do a full survey, which includes accurate heat loss calculations, before installing a heat pump. The purpose of heat loss calculations is to determine how efficient and suitable a heat pump will be for your home.

In some cases, there is the need to upgrade your radiators for bigger ones, as heat pumps work at lower flow rates. Radiator temperatures generally sit between 35–50°C, and to heat your home, you need more surface area to reach the same temperatures. An alternative to radiators is underfloor heating.

If your home has insufficient insulation heat easily escapes through the roof and walls. This will make the heat pump work harder than it needs to (and likewise with a gas boiler), resulting in much higher electricity costs. To avoid the possibility of a heat pump inefficiently heating your home it’s crucial that your installer is fully registered and accredited by leading regulatory organisations. In addition to this, if you would like to take advantage of the Boiler Upgrade Scheme your installer must be MCS accredited.

At All Seasons Energy we have been installing air source heat pumps for nearly a decade. In this time, we have won many awards and have the accreditations to professionally install heat pumps, solar panels, and all types of home insulation. With over 650 genuine customer reviews, at an average rating of 4.7/5, we have built an excellent reputation in the renewable energy and energy saving industry.

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