Climate-friendly heating and cooling with water from Lake Zurich

Lake Zurich is a popular recreational area for people living in and around the city. At the same time, it also serves as a sustainable energy source. We supply properties around the Zurich lake basin with climate-friendly heating and cooling drawn from the lake water.

Environmentally friendly

The use of lake water is ecologically sound and sustainable for a variety of reasons. The energy is produced locally and consumed in the area within the energy network. Long transport routes for fossil primary energy sources such as oil or gas are rendered unnecessary. If a heating network using lake or river water replaces a fossil heating system, carbon emissions can be reduced by an average of 80 per cent. No water is taken from the body of water; only heat of up to about 3 kelvin is extracted or added. The thermal energy stored in the lake – including low temperatures of around 5 degrees in winter – is harnessed by efficient heat pumps. In relation to the volume of the lake as a whole, the heat extraction is so minimal that it has hardly any effect. Eawag, the Swiss federal institute for water research, has investigated the effects of lake water installations on the ecosystem. The experts conclude that in general, a slight cooling of a body of water caused by heating in winter does not adversely affect ecosystems. Even if the water temperature dropped slightly, it would be ecologically sound and would even counteract global warming.

Hotspot Lake Zurich

The Zurich lake basin offers ideal conditions for lake heat networks. As many properties with heating and cooling requirements are located in a small space, only short lines are required to connect neighbourhoods near the lake. Since 2003, we have put the Escherwiese, Fraumünster and Falkenstrasse networks into operation around the Zurich lake basin. The Seefeld heating network is currently under construction, and with the CoolCity and Enge networks, other major projects are in the works. In this way, we supply heating and cooling to many buildings around the Zurich lake basin sustainably and cost-effectively. These include the Zurich Stadthaus, Convention Center, Park Hyatt hotel, NZZ buildings and various office and residential buildings. The connected properties are interconnected in energy networks, which are designed in such a way that additional properties can be connected and sub-areas developed.

Functioning of a lake heat network

Connected properties are supplied with heating and cooling via lines from the central system or have their own heating system. The lake water is collected with a sieve and transported to the central lake water system using pumps. In winter, we use a heat exchanger to extract heat from the water circulating in a primary circuit. This heat serves as an energy source for the heat pump. This raises the carrier medium to the required temperature level (approximately 40 to 65°C). Distribution in the buildings takes place via a secondary circuit. In summer, the system works in reverse: with free cooling, the lake water can be used directly for room cooling instead of electricity-powered air-conditioning.  At the end, the lake water removed is returned to the lake without any chemical changes around 150 metres from the shore and the cycle begins again.

Enormous potential

In order to meet Switzerland’s climate targets and reduce CO₂ emissions, fossil fuels will have to be replaced by renewable ones in future. Swiss waters hold a lot of unused thermal energy that can be used to cool or heat buildings near lakes or rivers. This can make a significant contribution to covering energy consumption in Switzerland – without damaging the environment. Until now, thermal energy from lakes and rivers has not been used much, even though the proximity of many Swiss towns and cities to water makes it suitable for heating and cooling, the technology is well known and CO₂ emissions could be significantly reduced.

A study carried out by the water research institute Eawag and supported by the Federal Office for the Environment (FOEN) shows that the potential of Switzerland’s main lakes and rivers is ‘remarkably high, often far above regional demand’. This thermal energy is particularly suitable for larger neighbourhoods, large companies and industrial areas. According to estimates by Eawag, the potential for heat extraction in the 25 largest Swiss lakes is 97 TWh and that of the five largest Swiss rivers is 24 TWh. So Switzerland’s lakes and rivers could become a significant source of thermal energy in the near future.

Swiss Life has several properties around Lake Zurich. Four of these are connected to the Falkenstrasse lake heat network and seven to the Escherwiese network. How did this come about?

In the course of ongoing maintenance works and the resulting replacement investments for heating installations, we are constantly evaluating various alternative options, which is how we found out about ewz’s lake heat networks. Sustainability, preservation of the climate, economic aspects, reliability and round-the-clock service were particularly important to us. The lake heat network supplies our properties with environmentally friendly heating and cooling in a cost-effective way. Being connected to the various lake heat networks meets our requirements perfectly: it provides us with a plentiful supply of carbon-free energy and uses Lake Zurich, which is right on our doorstep, as an environmentally friendly source of energy. In economic terms the system is comparable with market offers involving other technologies. It’s important to us that the system runs smoothly. Working together with ewz as contractor for our heating and cooling solutions gives us the assurance that the facilities are being professionally managed and efficiently operated around the clock. We’re happy to be connected to these innovative networks.