Issy CĹ“ur de Ville is an eco-neighbourhood located in Issy-les-Moulineaux. Covering approximately 100,000m2, this mixed-use, pedestrianised development aims to provide residents with a connected and environmentally responsible lifestyle.
Issy-les-Moulineaux is one of the closest cities to Paris, part of the first inner suburb and not far from the Eiffel Tower. This medium-sized city is one of the major digital districts for its region and the whole country, testified by its 72,000 jobs, which exceeds its inhabitants (about 70,000). Due to its location and economic vitality, Issy needs to be responsive and smart if it wants to fight against climate change.
The Issy Cœur de Ville neighbourhood has been under construction since 2019, fully integrating Issy-les-Moulineaux’s highly committed pro-environment policy, with the objective to receive the highest certifications for energy, biodiversity, health and well-being.
Geothermal energy as a solution
Geothermal energy is essential to the energy network of the neighbourhood of Issy Coeur de Ville in Issy-les-Moulineaux. Currently, 78% of the neighbourhood’s energy needs are covered by geothermal energy. On average, the neighbourhood has saved 600 tonnes of CO2 per year compared to the use of natural gas.
Here’s how it works: water from the water table, captured at a depth of 35m and at a constant temperature, supplies two loops (hot water and chilled water, thanks to an innovative ice cooling system) serving all buildings for heating, domestic hot water, and cooling. While heat networks are common in France, urban cold networks are less numerous. Nevertheless, they are in full development and constitute an effective – and above all – positive response to climate change.
Just like conventional air conditioners, the installation also uses refrigerants. In gaseous form, these fluids are powerful greenhouse gases and can escape during construction, maintenance, or due to leaks. They are the biggest contributors to air conditioner pollution. With this system, the neighbourhood uses 90% less refrigerants, which halves the CO2 emissions. These fluids are used in small balls which constitute the main innovation of the site: placed in a large 130m3 tank, they are used to store cold items (like reusable ice cubes), in order to meet the strong demands for freshness during the summer.
The buildings connected to the heating and cooling network are:
- 627 housing units
- More than 40,000m² of offices that will house the future headquarters of CNP Assurances
- Cinema with seven screens
- Shops
- Public facilities (school, nursery, community hall)
Key figures
- 4 wells
- 180m3/h geothermal flow
- 8km network
- 1,159 tonnes of CO2 avoided
- 2.5x fewer CO2 emissions compared to conventional AC systems for cold
- 18 substations at the foot of the building
- 15.8°C water table temperature
- 75% hot renewable energy rate
- 70% cold renewable energy rate
Key drivers
Environmental: Due to natural reserves, France has been developing geothermal energy for many years, with direct use operations taking place in the Paris sedimentary basin since 1969. The Multi-Year Energy Programme 2028 sets the objective of 3TWh of cold delivery over the next eight years in France. This objective aims to respond to the growing phenomena of heat islands and heatwaves, in a context of an aging population. An urban cold network is an effective and sustainable solution to meet this ambitious objective. This is the purpose of the geothermal energy deployed in Issy-Les-Moulineaux by the ENGIE Solutions teams.
“Since 2005, the City has recorded a 26% drop in its greenhouse gas emissions thanks to the restructuring of buildings driven by the Municipality.” André Santini, Mayor of Issy-les-Moulineaux
Governance and policy: The 2028 national geothermal energy target represents a 50% increase relative to 2020. The 2050 target of 100TWh is a 10-fold increase on the 2028 targets, with the work is supported by a Governmental Action Plan and a Geothermal Energy Roadmap that have been co-developed with the French geothermal industry.
Altarea, ENGIE, the national French government, ADEME, and the local council of Issy were the main actors developing this project. The Issy Coeur de Ville project received a subsidy from ADEME of €532,000 out of a total budget of around €8 million for all energy investments. The municipality sold the site to ENGIE for a symbolic €1 to manage the construction over a 20-year contract, and ENGIE and Alterea worked together to supply the energy infrastructure, equipment, and substations.
Social: In Issy Coeur de Ville, 25% of residential units are dedicated to social housing. When it comes to the cooling system, given that the past years have been the hottest in the past century, air conditioning in homes is becoming a real necessity, particularly for the elderly. The innovative cooling technology was developed and provided in all new buildings to avoid inhabitants from buying their own air conditioning units which are detrimental to the environment.
Challenges
Infrastructure: The main challenge with geothermal energy is to build the infrastructure in existing buildings, as it requires connecting the buildings to an underground heat source, cooling materials, and the appropriate piping to each dwelling unit. In Issy’s case, the buildings were built new, including the appropriate infrastructure needed to supply the energy. The cost of renovating existing buildings was deemed too high, and the strategy focuses solely on new developments.
Ingredients for replicability and lessons learnt
Environmental: Of course, groundwater sources are required. Many French cities and others in countries like Germany, Italy, Portugal, Iceland, and Turkey already utilise geothermal energy. However, ground freshwater is much easier than sea water, which can cause issues with the pipes and lead to higher maintenance costs.
Initiatives of this type can prevent the proliferation of individual air conditioning systems that will doubtless increase given the rate of heatwaves. Unlike air conditioning systems, the cold network limits heat islands. With low greenhouse gas emissions, it also makes it possible to promote local energy thanks to a supply mainly provided by renewable energy.
Another significant advantage of geothermal energy is that residents' energy bills will be insulated from the taxes, price increases, and shocks that come with fossil fuels.
Social: Issy-les-Moulineaux has pushed for all buildings in the neighbourhood to be connected to geothermal heating and cooling systems. In ensuring that social housing is included, it ensures that most vulnerable citizens are protected from extreme heat in the summer while also avoiding that they buy polluting single-unit cooling systems. In providing this service already in the building design, Issy is able to reduce its overall emissions.
Governance: Overall, Issy-Les-Moulineaux has been developing geothermal energy districts for more than 12 years, the first one being The Digital Fort. By using an incremental approach, and learning from each iteration, Issy has learnt from their past challenges to innovate the system further with their stakeholders.
The municipality knew that it could not develop such a neighbourhood on its own. Through public-private partnerships, working with ENGIE Solutions and Alterea, they gave responsibility to private developers to develop the site as part of the city and national wider environmental vision.