Our air-source heat pump often seems like magic.
Last winter, temperatures here in Oxford fell to -10 degrees Celsius. But this unremarkable-looking device, whirring quietly away on our outside back wall, was somehow extracting enough heat from the freezing air to comfortably heat our home. In the year since we installed the pump, our home energy use – and its carbon footprint – have both fallen by around 60 per cent.
Working like a refrigerator in reverse, heat pumps can draw stored-up solar or geothermal heat from the air, ground or water. They work in a highly efficient way, typically pumping out two to four units of heat for each unit of electricity they consume.
When combined with a renewable electricity grid, these pumps can deliver reliable heating without the need for fossil fuels, inefficient hydrogen production or locally polluting wood-burning stoves. The potential impact is huge: currently heating and hot water combined account for half of all energy used in buildings globally.
The world already runs 190 million heat pumps, but their distribution is patchy. Norway has one for every three people, and Sweden has been installing more than 100,000 per year for the past decade, in both cases boosted by government subsidies. Others like the UK are lagging behind, with only one pump per 177 people and one of the lowest installation rates in Western Europe.
But, across the world, heat pumps are becoming more popular and sales rose by 11 per cent in 2022 – although still not enough to meet global climate targets. Households can be put off by the high installation costs and space requirements, and many countries face a lack of qualified installation engineers. There are also concerns about extra pressure on national electricity supplies (especially when combined with the rise of electric vehicles).
Energy markets with outdated pricing mechanisms can also pose a barrier. In the UK, for example, electricity costs over three times as much as gas per unit, despite the rapid growth of cheap wind and solar power. In our house the heat pump has only reduced energy bills by 15 per cent, because the small amount of electricity used to run the pump is almost as expensive as the large amount of gas the pump has saved. Fairer electricity pricing to reflect the lower cost of renewables could make heat pumps affordable for many more households.
New government grants and subsidies are coming online in multiple countries, but even with increased support, pushing for individual heat pumps in every building may not be the most effective – or fair – way to create this change. District-level pumps to heat whole neighbourhoods can be far more efficient and affordable, especially when set up to draw waste heat from industrial sites.
An experimental project in Bristol, UK is using air-source heat pumps – powered by solar panels – to extract heat from the warm summer air and store it underground. That heat can then be accessed by a ground-source heat pump during the winter. These kinds of hybrid community-scale solutions might be a better bet for a rapid shift to low-carbon heating – rather than waiting for individual households who are lucky enough to have the resources to install one of these magic devices themselves.