The building sector accounts for an astonishing 38% of all energy- and process-related carbon emissions worldwide. Decarbonizing buildings will require huge changes to our houses, offices, schools and hospitals — and the way that we live in them. 

Thibaut Abergel is co-leading the work on building energy technologies at the International Energy Agency (IEA) and co-authored the IEA’s Net-Zero by 2050 report. He spoke to BRINK about the changes that he expects to happen in this sector.

ABERGEL: Emissions from the building sector come from various sources. First, we’ve got direct emissions from the use of fossil fuels in buildings, such as coal, oil and natural gas. Together, the combustion of these fuels account for 9% of all global energy-related carbon dioxide emissions. 

On top of that, there are the indirect emissions from the use of electricity and commercial heat consumed in buildings, and these account for another 19% of all global energy-related carbon dioxide emissions. 

Then there are emissions related to the quarrying, manufacturing and transportation of construction materials, as well as building renovation and end-of-life. This “embodied carbon,” as we call it, is responsible for another 10% of global emissions. 

No More Fossil Fuel Boilers

We need to take a holistic approach and tackle each step of the building’s life cycle to reduce all of these emissions. In our report, we defined the zero-carbon ready requirements that all new worldwide buildings will need to comply with by 2030. And by 2050, we will need to have retrofitted almost all of the existing stock still standing to this zero-carbon ready level. 

Our roadmap to net zero emissions also highlights other targets, such as no more fossil fuel boiler sales after 2025, making today’s best-available electric appliances the new norm by 2035, or meeting 50% of heat demand with heat pumps by 2045.

BRINK: What is the most cost effective way of reducing carbon emissions in buildings that already exist?

ABERGEL: For buildings that have already been built, we need ambitious deep energy retrofit measures to reduce the buildings’ thermal needs, in concert with the changeover of heating and cooling equipment. 

For example, if we’re switching from a gas boiler to a heat pump, we can adjust the thermal insulation so that the new heating equipment meets no more than the resulting heating demand to avoid oversizing. By doing these in a holistic way, there’s a way to save costs.

It’s also very important that we just do them once, so that we wouldn’t need to do another renovation to achieve this level. Digitalization will have a strong role to play in identifying opportunities for standardization and mass production of renovation components and in improving product traceability for their reuse in a circular economy. There is a lot at stake: Around half of today’s building stock is likely still to be in use by 2050.

The Essential Role of Heat Pumps

BRINK: Can you explain what heat pumps are, as they seem to be a big part of the solution? 

ABERGEL: Heat pumps are equipment that can provide both heating or cooling by transferring calories from one source to another. 

Used in buildings in heating mode, they transfer heat from the outdoor environment to the indoor environment. In cooling mode, they do the exact contrary: taking calories from the inside to bring outside of the house. So instead of using fuel that we burn in a boiler to produce heat, the heat pump uses electricity to transfer heat from one place to another. 

While fossil fuel boilers or electric boilers have an efficiency that is at most at 100%, heat pumps will be able to achieve an efficiency of 350% in heating mode and 400% in cooling mode.

There’s also a second benefit: Heat pumps run on electricity, so that means they could be entirely decarbonized as the heat pump could be connected to solar PV on the roof, for example, or more generally to the electricity grid that could be decarbonized through utility-scale renewable sources.

You can take the calories from different sources. From the air, it will be an air-source heat pump. But you can also take the calories from the ground with geothermal heat pumps or ground-source heat pumps. 

BRINK: And is this heat transfer technology already developed and being widely used?

ABERGEL: It is very well-known under a different name: There are over two billion air-conditioners installed worldwide today. These are all heat pumps used in cooling mode.

Renovation consumes on average 40 to 80 times less materials in mass than construction — extending the lifetime of a building through a renovation will reduce embodied carbon quite significantly.

However, heat pumps currently only meet 7% of total heat demand in buildings. This needs to be 50% by 2045 in our net-zero by 2050 scenario. In the grand scheme of things, heat supply today is still dominated by fossil fuels, but heat pumps are on the rise. 

For example, in Europe, heat pumps have experienced a double-digit growth each year over the past five years. Heat pumps used for heating are very common in new construction. They are even the leading heating technology for new buildings in many countries, such as the United States, France or Germany. But for the replacement of equipment in existing buildings, heat pump sales are more lagging behind. We need strong incentives, awareness raising and innovative compact technologies to make them part of renovation strategies.

The Challenge of Air Conditioners

BRINK: Climate change is obviously causing a lot of countries to become hotter, and that’s increasing the demand, particularly in middle income countries, for air conditioning. Is that a problem?

ABERGEL: Indeed space cooling will be the fastest-growing building end-use: About four billion people will get access to cooling by 2050. It is good news as more people can live in healthier buildings, enjoy more comfortable living conditions and be more productive at work.

But with current construction practices and AC energy performance levels, it would also result in a tripling of electricity demand. More alarmingly, ACs will consume electricity at the same time — when it is very hot — that could generate high peaks in demand and threaten the electricity system stability.

But over the past 20 years, the average energy performance of air conditioners has increased by more than 30%. We need to accelerate that trend to achieve a 50% improvement over the next 10 years. 

BRINK: Is the heating and AC industry on board with all this? Are they investing in highly efficient technologies?

ABERGEL: The industry is taking some steps to increase the efficiency of the air conditioners. A lot of research has been done to understand: how to find new refrigeration cycles that could operate better and how to integrate them with rooftop solar PV and storage devices. High-end products are showcased as part of the Global Cooling Prize. 

Regulation will also be key to drive this momentum. Minimum energy performance standards are very effective to phase out inefficient products, and drive R&D spending on products at the top of the ladder. 

Right now, there are about 60 countries with minimum energy performance standards in place for air conditioners. We would need all countries on board and upgrading standards to keep up with and fuel technology progress.

Embodied Carbon: The Hardest to Eliminate?

BRINK: Ten percent of the total carbon emissions are in the manufacturing and transportation of building materials — how is this going to be reduced?

ABERGEL: Embodied carbon is typically harder to decarbonize because the solutions to produce low carbon cement and steel are still not mature. At least the capacity to produce low carbon cement and steel is not deployed at scale. 

A second lever is to switch towards other types of material — bio-sourced materials or wood construction, depending on locally available resources — that have obviously a much lower carbon footprint on a lifecycle basis than traditional buildings construction materials. 

Another opportunity for greatest savings: extending buildings’ lifetimes. We could do this by making buildings more modular so they can serve multiple purposes. In addition, renovation consumes on average 40 to 80 times less materials in mass than construction — extending the lifetime of a building through a renovation will reduce embodied carbon quite significantly.

There’s the recycling or reuse of building components at the end-of-life stage. For example, steel could be partially recycled, and the production of steel from secondary routes (that is using scrap) is much less carbon-intensive than the primary route using iron ore.