[D2grids] Residential-office buildings: combining high-performance renovation and decarbonated heating networks

Rather than opposing them, high-performance renovation of buildings should be combined with the deployment of heating networks, in order to achieve the energy transition objectives that France has set out to achieve.

A long way to go for the energy transition in the residential-tertiary sector

There is still a long way to go to comply with the Paris Agreements and effectively fight global warming. In France, the government has translated its commitments through various objectives in the energy-climate law that aims to :

• Carbon neutrality by 2050, which requires a 6 to 9-fold reduction in greenhouse gas (GHG) emissions compared to 1990;
• A 40% reduction in the primary energy consumption of fossil fuels in 2030 compared to 2012;
• An increase of 32% in the share of renewable energies in gross final consumption in 2030, 38% in final heat consumption and 40% in electricity production;
• A 50% reduction in final energy consumption in 2050 compared to 2012 (-7% in 2023, -20% in 2030).

The challenge is particularly great for the residential-tertiary sector, which is the largest energy consumer and the second largest emitter of GHGs. In 2017, housing and tertiary buildings were responsible for 46% of final energy consumption (29% for residential and 17% for tertiary) and 22% of GHG emissions in Metropolitan France.

In 2015, more than one household in two was heated mainly by fossil fuels (39% gas, 12% oil and 1% LPG). However, gas and fuel oil emit up to 2.8 times more GHGs than electricity or heating networks1.

In addition, 21.5% of dwellings are thermal sieves (energy label F or G). On this point, the challenge is twofold: France still has a lot of work to do to reduce its impact on global warming, but the performance of the French housing stock also threatens the solvency of households. Indeed, in 2017, 11.6% of households spent more than 8% of their income on energy in their accommodation. This share will increase further, with the rise in energy prices observed in recent years and expected in the coming years, as well as the modest rate of improvement in housing performance.

Heating networks: a decarbonised solution to be deployed

Heating networks are one of the solutions that can help decarbonize our heat production if their rate of renewable energies (biomass, geothermal) and recovery (heat from waste-to-energy plants, industrial processes, biogas, data centers, wastewater, etc.) remains high or increases, as it has been since the end of the 2000s. In fact, 56% of the 761 heating networks in France are supplied by renewable and recuperated energy sources.

The main renewable energies used to supply the heating networks come from biomass or waste incineration, which means that more than three out of four heating networks have a high rate of renewable energies (>50% green energy). On average, heating networks thus include a higher share of renewable and recovery energy than the electricity network (18.4% in 2017) and the gas network (less than 1%).

However, other renewable energy sources are underused in the current heating networks. This is due to the fact that a poorly performing dwelling cannot be connected to all types of heating networks. Indeed, it requires a fluid at high temperature, which can be delivered by fuels (gas, fuel oil and wood) and some renewable energies (deep geothermal, biomass, solar thermal). On the contrary, ultra-low-energy geothermal and most recovery energies do not allow these high temperature levels to be reached. However, biomass, for example, can raise issues of conflict of use with the timber or the pulp industries. It is therefore preferable to diversify renewable energy sources further.

The same issue of resource potential arises for recovery energy. In a world that is going to reduce its waste production, particularly of some high calorific value waste such as plastic, heating networks will have to rethink their energy mix to continue to reduce their share of fossil fuel use.

Another challenge is the evolution of the economic model of heating networks. It is necessary to increasingly reduce the "subscription" share of their final price to users, as too high a share makes energy efficiency actions unprofitable. The cost of heat from heating networks must remain affordable in renovated housing, otherwise it will encourage buildings to disconnect from them.

Combining renovation and decarbonised heating networks

All means to decarbonise the energy supply of our buildings must be mobilised and they must not be opposed. The challenge today is to think about the right combination so that we no longer have to choose between one or the other, but add them together. In the same way that our electricity and gas mix must become greener, it is key to work to make heating networks even more efficient and less carbon-intensive, and to think about more integrated approaches to adapt them to future developments in terms of flexibility and energy efficiency. The D2Grids project aims to achieve this very goal.

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It is particularly interesting to consider the relevant heating network solutions to be integrated for new construction projects of passive buildings, or energy-efficient renovation projects such as EnergieSprong, which aim for a " zero energy " level. The latter offer a drastic reduction in energy consumption (label DPE A or B), with local energy production that compensates for the rest to be provided.

The performance of these renovations is guaranteed over the long term (30 years), which is a guarantee of the quality of the work carried out, and significantly and sustainably reduces household energy bills. The local production of renewable energies, with the installation of photovoltaic panels for example, makes it possible to supply part of the electricity consumed by the building or the operation of the heat pumps of a low-temperature heat network. This type of demand-reducing project also raises the question of extending existing heating networks at the time of these renovation operations, in order to make it possible to use the network's energy supply capacity in more homes.

The democratisation of this very high-performance renovation system, combined with low-temperature heating networks and the acceleration of their deployment, will help to achieve the objectives that France has set to reduce consumption, develop renewable energies and reduce energy insecurity. Let's be creative to combine these solutions in an innovative way!

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1 Average based on the 553 heating networks for which greenhouse gas emission data (between 0.001 and 0.384 kgCO2/kWh) are available on the greenhouse gas balance resource centre - www.bilans-ges.ademe.fr.

Article translated from French, published on Good Future

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