CASE STUDY

Sustainable heat recovery in Infomaniak D4 data center

In Geneva, Switzerland, digital infrastructure turns into a local community asset: D4 recovers the heat generated by their servers and supplies it to the local district heating network - warming around 6,000 homes. Siemens provides the power distribution backbone for this large-scale energy reuse.

A sustainable data center in Geneva

Infomaniak developed the D4 data center in Geneva together with the La Bistoquette cooperative and Services Industriels de Genève (SIG). Built underground beneath a public park, the facility combines high-density computing with a sustainable urban energy concept. Instead of rejecting excess server heat, D4 captures it and feeds it into Geneva’s district heating network, supplying heating and hot water for around 6,000 homes. The project combines resilient IT infrastructure with energy-efficient operations and sustainable urban integration.

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Turning server waste heat into a community resource

D4 operates a closed-loop heat recovery system that reuses energy generated by IT operations. All electricity consumed by servers, inverters and cooling infrastructure is ultimately converted into heat at approximately 40–45°C. This heat is transferred via air-water heat exchangers and upgraded using heat pumps before being fed into Geneva’s district heating network. The cooled water, at around 28°C, is returned to the data center to regulate server temperatures, eliminating the need for conventional air conditioning. The system runs without water consumption and is powered entirely by renewable hydro and solar energy.

Measuring sustainability performance

D4 operates around 10,000 servers and reuses 95% of the energy consumed as heat. With 1.7 MW of recovered energy, it can supply heat to 6,000 energy-efficient homes in winter or 20,000 five-minute showers in summer daily - avoiding up to 3,600 tons of CO₂ emissions annually compared to natural gas.

1.09 Average PUE

0.95 Average ERF

1,7 MW Total utilized heat output

Resilient power distribution as the foundation

D4’s energy reuse concept depends on continuous, stable operation of its digital infrastructure. To support high availability requirements, Infomaniak implemented a redundant electrical architecture based on Siemens power distribution technology across its critical systems:

SIVACON S4 switchboards for the main power distribution system
SENTRON 3WA/3VA circuit breakers for seamless switching between grid, UPS, and backup generators
SIVACON 8PS busbar trunking for efficient power transmission with minimal energy losses

Together with redundant medium-voltage feeds, dual UPS systems and backup generation, the infrastructure provides the electrical resilience required for uninterrupted data center operations and stable system performance.

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Today, PUE is no longer enough in the face of the climate emergency. We must also consider new metrics such as ERE and ERF. Digital infrastructure should be a driver of the energy transition, not just a consumer of electricity.

Boris Siegenthaler, Founder & CSO at Infomaniak

A circular blueprint for digital infrastructure beyond PUE

D4 demonstrates how resilient electrical infrastructure, renewable energy and heat recovery can work together to create a more sustainable model for digital infrastructure that’s giving back to their surrounding communities.

Looking beyond traditional efficiency metrics, the project proves that data centers can make better use of the energy they consume while maintaining highly reliable operations. To encourage wider adoption, Infomaniak has published the D4 concept as an open-source project together with EPFL, IMD and the University of Lausanne as part of the E4S program on d4project.org.

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