How do heat pumps work in cold climates?

A heat pump can be an excellent alternative to a gas or oil boiler, however you may be worried that this type of system won’t heat your home efficiently if you live in a cold climate. In fact, this isn’t the case.

Heat pumps  work by using natural heat that can be found in the ground, air or groundwater that surrounds your home. Therefore, unlike other heating appliances, they do not use fossil fuels to warm up your home and can lower CO2 emissions that may otherwise harm the environment. This is making them increasingly popular among homeowners who are conscious of the ecosystem and want to use more renewable energy sources.

But what if you live in a cold climate? In the UK, the temperature can drop to around   -10 °C in winter. You may be thinking, how is there enough warmth in the ground or surrounding air to heat your home?   We’ve answered this question and many more in this helpful article, so read on to find out more.  

How a heat pump works

Heat pumps use the heat in the air  or the ground around them as their main source of energy. They use a small amount of electricity to pull this energy out of the surroundings and into a heat exchanger, sometimes known as an evaporator. Within this heat exchanger, the heat is absorbed by a refrigerant, which evaporates and becomes a gas. The refrigerant can absorb heat even in extremely low temperatures of   -20 °C, which is why heat pumps are able to work in cold climates.

This evaporated refrigerant is then compressed, which increases the temperature further. The gas can then transfer its heat into your home’s central heating system. When this happens, the refrigerant gradually cools down until it condenses to become a liquid again. This occurs in a second heat exchanger, otherwise known as the condenser. Within the condenser, cooler water from the central heating system can continue to absorb any heat, which is then pumped around your home through any radiators or underfloor heating. Alternatively, it can be used to provide your taps with hot water via a cylinder.  

Finally, the cooler refrigerant passes through an expansion valve. The pressure decreases and the refrigerant returns to the evaporator for the whole process to begin again.  

How good are heat pumps in cold weather?

Now that you know how a heat pump works, you may still be wondering how the system can take heat from the ground or air when it is below zero degrees.

In the UK, the temperature of the ground doesn’t usually fall below 10 °C. Although this may not feel warm to us, there is still some heat that the heat pump can take to warm up your home. Even with an  air source heat pump, there is ambient heat available that can be used. Remember that celsius is a man-made scale and zero degrees doesn’t mean that there is no heat in the air at all. If there was zero heat, the earth would have reached a temperature of   -273.

Your heat pump will continue to work in cold weather, as long as you purchase the right one. Every heat pump is different and you will need the right equipment in order to make sure that your home can be heated throughout winter. For the UK’s temperatures, this may not be as big a problem as it could be for some places, such as Canada or North America, where temperatures can drop to   -30 °C. As a German manufacturer, Viessmann have tested their heat pumps in the harsh German winter and elsewhere in Europe.  

How efficient is a heat pump in cold weather?

Your heat pump won’t be as efficient in cold temperatures as it would be in milder conditions. More electricity may be required to remove the heat from the air, which can result in a lower efficiency.

Heat pump efficiency  is measured using Coefficient of Performance (CoP). This is calculated by comparing the amount of input to the amount of output. For example, if an air source heat pump uses one kW of electricity to produce three kW of heat, the CoP is three. The higher the CoP, the better, as it shows your heat pump is more efficient.

If you do live in a very cold climate, you may benefit more from a  ground source heat pump. This is because the ground temperature tends to be warmer than the air temperature. Therefore, a ground source heat pump could require less electricity to run and it could produce a greater amount of heat.

With an outdoor temperature of 8.3 °C, your heat pump could achieve around 3.8 CoP. However, if the temperature drops to around -8.3 °C, your heat pump’s efficiency could drop to around 2.3 CoP. If the outdoor temperature drops too low for your heat pump to produce any heat, a backup may be required. This is unlikely to occur in the UK, however, heat pumps in countries such as Canada may need to rely on a backup. This can become expensive,so if you live in an extremely cold climate, a heat pump may not be the most efficient way to heat your home.

Your heat pump will remain efficient for longer if you look after it. You should ensure that your system is serviced every 12 months. Not only does this make sure that everything is running safely, but you’ll also feel happier knowing that your heat pump will be able to warm your home throughout the winter. If you have an air source heat pump, you should clear any debris from the area to prevent the airflow from becoming blocked. This could reduce the heat pump’s efficiency. You may also want to regularly check the filter and change it if needed, any maintenance is best carried out by a qualified engineer.