When water from Lake Geneva becomes the air conditioning of tomorrow

Can water from Lake Geneva be used to heat or cool buildings? 

This is the challenge that the Services Industriels de Genève (SIG) have taken on, by developing their colossal underground hydrothermal project GeniLac. On 4 August, 2022, Heidi.news visited the construction site of the largest ecological thermal network in the canton of Geneva.

What it’s about

The structure that’s coming up under the feet of Genevans resembles a real spider's web. GeniLac, a 30-kilometre-long underground and hydrothermal network, will extend from the city centre to the Etang district, in Vernier, connecting the airport and the municipalities of Bellevue, Prégny-Chambésy and from Meyrin. On the left side, it will also stretch to the (Praille Acacias Vernets district  and the Geneva University Hospitals.  The project is expected to be completed by 2024 for a total outlay of around CHF 800 million. 

The network is expected to reduce the amount of energy used to cool buildings that are connected to it by 80 per cent while reducing CO2 emissions from heating systems by 80 per cent. 

“GeniLac is an infrastructure to address global warming. It will allow the canton to save energy while reducing its dependence on fossil fuels,” said Vincent Collignon, executive director of GIS, speaking to journalists in front of the Palais des Nations. . 

How it works

At Vengeron, on a beach parched by the heatwave, four pipes are assembled in a gaping hole. “The Vengeron pumping station, the heart of GeniLac, will be built here,” noted Véronique Tanerg, spokesperson for SIG. 

The pipes will be submerged at a depth of 45 metres, from where water will be taken directly to be routed into the network. 

“At this depth, the water temperature remains constant, between 7 to 8°C all year round,” Collignon said. Water from the lake will not enter the drains of the buildings. A device called a heat exchanger will transfer thermal energy from the lake to a closed circuit in the buildings, without the two liquids coming into contact. 

GeniLac currently has 68 customers. By 2045, up to 350 buildings could be connected to the network. This would save up70 GWh per year – the equivalent of the annual consumption of 27,000 households – and reduce the canton’s carbon emissions by 70,000 tonnes per year.

Palais des Nations pioneers the energy transition

GeniLac’s story began in the 2000s first with a cooling water distribution system  named the Geneva-Lac-Nations (GLN) network. Since 2008, the UN, GLN’s first client, has been using the technology to cool the conference rooms of the Palais des Nations as well as two other buildings.

“This makes the Palais des Nations one of the most energy-efficient UN complexes in the world,” said Clemens Adams, director of the division of administration at the UN. In all, 25 per cent of the Palace’s surface is air-conditioned in an eco friendly way. 

“The next step will be to use the water from Lake Geneva to heat the buildings in a sustainable way, by equipping our system with heat pumps from 2025 onwards,” he added. 

Other international organisations such as the World Health Organization (WHO), the World Meteorological Organization (WMO) and the World Trade Organization (WTO) have followed suit.

Unlike GeniLac, water from the GLN network is, until now, being drawn from a depth of 30 metres. The issue, as Vincent Collignon explained, is that the winter breeze could cause a reversal of the lake's thermal layers, increasing the temperature of water to 18ºC at 30 metres deep. This prompted the firm to choose to pump water at a greater depth of 45 metres. 

Who benefits?

The population of Geneva greenlighted GIS developing the thermal network during a vote in February 2022, which accelerated the work. But who will benefit from this eco friendly air conditioning?

“In Geneva, the law prohibits air conditioning in housing, so it will have tobe administrative buildings, offices and shops,” Tanerg noted.

Impact on the lake? 

At the end of the cycle, the cold water drawn from the bottom of the lake will be discharged onto its surface, or into the Rhône, at a temperature of around 12°C. Is there not a risk of warming up the of Lake Geneva, which has already increased by 2°C in 50 years? “We pay particular attention to the preservation of water resources. State monitoring makes it possible to verify that the impact is neutral on the environment,” Charlotte Génot, development manager, replied.

In its 2021-2030 action plan, the International Commission for the Protection of the Waters of Lake Geneva (CIPEL) confirmed that, according to the studies carried out, the GeniLac facilities, as a sole entity, should not have a significant impact on the temperature of the lake and on its ecosystems. It is rather the cumulative effect of similar installations that worries the organisation, which considers that a complete overview is needed. 

In a 2018 report,he Federal Institute for Aquatic Studies (Eawag) pointed out that “large-scale thermal use could in theory cause impacts on a larger scale, such as a disturbance of the winter mixing (in lakes) or fish migration (in rivers)”.

Another environmental obstacle

To prevent quagga mussels from clogging the pumping pipes, chlorine is injected into the heating/cooling system. Won’t this powerful oxidant be harmful to wildlife when it is discharged into the waters of the lake and the Rhône? “Chlorine concentrations are well below the standards set by the federal ordinance on the protection of water (OEaux),” Tanerg answered. “We are currently studying the possibility of integrating a pipe cleaning system to do without chlorine.”