Heat pumps are largely considered the most relevant technology to decarbonize our heating systems. Organizations such as the International Energy Agency forecast them to meet most of our energy needs in the future. However, heat pumps have long been questioned for not being very effective in cold climates, which is in fact not true.
A study from Oxford University and the Regulatory Assistance Project, an NGO, found heat pumps are two to three times more efficient (meaning they use less energy per heating) than oil and gas heating systems in temperatures ranging from 10C to -20C. The researchers gathered performance data from studies done across Europe and North America.
Duncan Gibb, study author and senior adviser with the Regulatory Assistance Project, told the National Observer that while heat pumps have to work harder during sub-zero temperatures, they are more efficient than other sources of heat. Gibb said the fossil industry regularly tries to disqualify heat pumps by claiming they are not efficient.
“Even though heat pump efficiency declines during the extreme cold and backup heating may be required, air-source heat pumps can still provide significant energy system efficiency benefits on an instantaneous and annual basis compared with alternatives,” the researchers wrote in their study, published in the journal Joule.
The more efficient choice
Heat pumps work on the same principle as refrigerators and air conditioners: they move heat from one place to another. Instead of generating heat directly like a furnace, heat pumps use a small amount of external power to move heat from a cooler area to a warmer space, making the cool space cooler and the warm space warmer. This process can be used for both heating and cooling purposes. The basic mechanism behind a heat pump involves a cycle of evaporating and condensing a refrigerant.
Although heat pump sales were initially lackluster, heat pumps are now expanding fast. About three million were installed last year, up 38% compared to 2021. In Europe, their use is concentrated in countries with colder climates. Norway has 60 heat pumps installed per 100 households, followed closely by Sweden and Finland (around 45 each).
But a common misconception still lingers: that in cold climates, heat pumps are less efficient.
In their study, the researchers contradict that myth. They collected raw performance data from seven different field studies, focusing on heat pump efficiency in mild cold climates. The datasets represent a range of climatic zones, heat pump models, and heat pump configurations from Switzerland, the US, China, Germany, the UK, and Canada, they write.
The blue dots in the graph below, included in the study, represent data from the studies collected by the researchers. They show the average coefficient performance (how efficient the heat pump is) and the average outside temperature of different kinds of heat pumps.
The measurement goes from 100% efficient to 600% efficient. Because heat pumps use the electricity put into the system to concentrate available heat energy from the air in the surrounding environment, they can transfer way more energy than the electricity required to power it.
While heating based on fossil fuels can be up to 98% efficient, heat pumps can get up to 540%, depending on the outside temperature, the study showed. They are two to three times more efficient than fossil fuel alternatives in places that reach up to -10C, while under colder climates (up to -30C) they are 1.5 to two times more efficient.
“Our view is that the widespread rollout of air-source heat pumps around the world as part of decarbonization efforts can be successful with existing technology in most areas that have space heating demand. Ground-source heat pumps and hybrid air-source systems may have significant value in the coldest climates,” the researcher wrote.