Gianluca Fardo
The energy consumption of cities is of high importance in the implementation of the European climate targets. The huge demand of fossil energy sources for heating and cooling must be reduced and replaced to a large extent by renewable energies. Challenges present itself in the increasing demand of cooling or process cooling. However, opportunities open up in areas in which a large heating demand from residential buildings is met with a similar-sized cooling demand. With so-called “anergy networks”, heating and cooling demands can be connected and synergies exploited. For this essay I investigated the potential of this promising technology based on two examples in the city of Zurich.
The importance of low-carbon heating and cooling alternatives
As visible in the diagram below, heating and cooling are responsible for over half of all consumed final energy in Europe.
Figure 1, Total heating and cooling demand as share of Europe’s final energy consumption. (EASE, 2017)
In Europe, as much as 85 percent of the demanded energy for heating and cooling are covered by fossil fuels. 45 percent of the total energy used for heating and cooling are demanded by the residential sector, 37 percent by the industry and only 18 percent in services. To achieve carbon-neutral societies, it is therefore crucial to investigate low-carbon alternatives. That smart heating and cooling concepts play a central role in Europe’s energy transition has been recognized by scientific and industrial communities a long time ago, which is why technologies have been invented to bring these goals to realization. One of these technologies is called Anergy Network (EASE, 2017).
Anergy networks: Functionality explained based on two concrete examples
In thermodynamics two forms of energies can be distinguished, anergy an exergy. Whereas exergy is organized energy, which can be exported and is able to execute work, anergy is diluted and cannot be transformed into work. Often lost in the process of transformation, anergy networks make use – as it’s name suggests – of anergy. The networks consist of a combination of pumping stations, heat exchangers, a network of pipelines and heat pumps with which energy in water can be used for heating and cooling (Roger, 2020).
One example where this technology finds application is at the ETH Zürich, at Campus Hönggerberg. At Hönggerberg over 30 buildings are occupied by 12’000 students and staff, consuming a total of 77 gigawatt hours of energy (electricity and heat) per year, which is almost as much as a small Swiss town (ETH, 2021). Of this total energy consumption, 22 gigawatt hours are for heating and cooling alone. To meet their target of a 50 percent reduction of the campus’s CO2 emissions by 2020, ETH decided in 2006 to make use of their so far unused waste heat from the servers and other heat emitting devices. The so-called anergy grid is a dynamic underground storage system, which is in operation since 2013. It stores excess heat in 150-200 meters in the ground with the help of water-filled geothermal probes (ETH, 2021). The stored heat can then be extracted again in cool months and used to heat the buildings of the campus. This network therefore avoids generating new energy and instead makes use of the existing supply in the area. This reduces emissions, but requires energy-efficient buildings that can be heated with relatively low temperatures (32°C). According to Wolfgang Seifert, energy appointee at ETH Zürich, the campus at Hönggerberg has very different requirements then a housing complex. “For us, cooling goes further than keeping classrooms at a comfortable 22 degrees in summer. Countless server rooms, laboratories and other research facilities need to be cooled all year round” (Seifert, 2021). He explains, that this is an advantage for the anergy network. “When cooling and heating requirements are roughly balanced, the system is most efficient. In conventional residential or office buildings, the demand for heat is significantly higher than for cooling” (Scheiderer, 2021).
By 2018 the system covered 81% of the useful heat (Nutzwärme) and 78% of the useful cold (Nutzkälte) of the connected buildings. Nevertheless of the 33 existing buildings at the campus in 2018, only 14 were connected. The goal is to achieve a coverage rate of 90% for the whole campus and with that to substantially contribute to the goal of reducing at least 80 per cent of C02 emissions per year by 2040 (in regards the base year of 2006, Scheiderer, 2021). With further planned expansions of the campus both the total cooling and heating demand will rise, which is ideal for dynamically operated networks (Real Estate Management, 2020).
Another example is the Anergy network of the family cooperative at Friesenberg, Zürich. The so-called FGZ decided in 2011 to cover a large part of its heating requirements by means of an anergy network. It is planned to expand the network in several construction phases up to 2030. The project will supply energy for around 2’300 residential properties, 5 500 residents, a total heated floor area of 185 000 m2 with a heating requirement of 35 gigawatt hours per year. This energy is provided by mainly two waste heat suppliers – the Swisscom and Credit Suisse data centers. The waste heat potential in the given area amounts to approx. 80 GWh, which exceeds the heat demand of the cooperative by far (Ruesch, 2018). In summer, excess waste heat is stored by 330 geothermal probes and thus extracted again in winter, enabling a significant reduction in greenhouse gas emissions of primary energy demand (Heatpumpingtechnologies, 2020). According to the official website of this project, half of the 2’300 residential properties are currently using the waste heat via the anergy network – with new ones being added every year. However, because the network is not able to cover peak energy demands for heating and cooling, oil and gas are still in use (Anex Ingenieure Ag, 2022).
Figure 2, Plan of the neighborhood Friesenberg with its anergy network. The points represent decentralized heat pumps. (heatpumpingtechnologies, 2020)
Anergy network: Potential
To completely abandon fossil energy sources by introducing anergy grids seems very unlikely. In February 2018, Energy Switzerland published a paper with nine case studies, including the ETH energy network at Hönggerberg and the FGZ energy network at Friesenberg. In the section “lessons learned”, Energy Switzerland stated that it is economically questionable in some cases to design the grids for peak power requires. It is suggested to cover peak power demands with decentralized fossil energy sources. In this case the anergy network would still decrease the demand of fossil energy sources to large extent, however it could not entirely quit non-renewable energy sources (Ruesch, 2018).
Furthermore, anergy networks also create dependencies. For example most of the networks depend on a seasonal balance between im- and exported heat. If this balance isn’t given the risk exists of heating or cooling the soil too much, which would have a large impact on the efficiency of the anergy grid (Ruesch, 2018).
This technology in its present development stage is not suited to heat and cool whole cities by itself. As these areas tend to be densely populated, geothermal probes would be placed too close by each other and therefore draw heat from the ground and cool the rock in the long term. Geothermal probes that are placed too close by each other would therefore require an active regeneration. One way of doing that is by cooling the house in summer by directing the excess heat down into the probe. However this technique is not very effective and therefore is not seen as a possible way of regenerating the geothermal probes. Another possible way to achieve regeneration is with solar collectors on the roof of the houses. Nonetheless the required solar collector area in densely built-up cities quickly becomes too large, which makes this solution as well unsuitable. It is therefore essential that new and better solutions have to be designed, otherwise anergy grids can never actually be applied on a large scale to densely populated areas (Wieland, 2017).
References
Anex Ingenieure Ag. (2022). Anergienetz Friesenberg, Zürich | Anex Ingenieure. Abgerufen 10. April 2022, von https://www.anex.ch/de/projekte/anergienetz-friesenberg/
EASE. (2017). Thermal Storage Position Paper. In The European Association for Storage of Energy (EASE). Abgerufen von http://europa.eu/rapid/press-release_MEMO-16-311_en.htm
ETH. (2021). Anergy grid | ETH Zurich. Abgerufen 10. April 2022, von https://ethz.ch/en/the-eth-zurich/sustainability/campus/environment/energy/anergy-grid.html
Heatpumpingtechnologies. (2020). ANERGY NETWORK FRIESENBERG OF THE FAMILY CORPORATION ZURICH – SWITZERLAND Anergienetz Friesenberg der Familienheim-Genossenschaft Zürich (FGZ) – HPT – Heat Pumping Technologies. In IEA Technology Collaboration Programme on Heat Pumping Technologies. Abgerufen von https://heatpumpingtechnologies.org/publications/anergy-network-friesenberg-of-the-family-corporation-zurich-switzerlandanergienetz-friesenberg-der-familienheim-genossenschaft-zurich-fgz/
Real Estate Management, E. Z. (2020). The energy of tomorrow Anergy Grid Campus Hönggerberg-a dynamic underground storage system Real Estate Management.
Roger, S. (2020). Anergy networks with ductile iron pipes. Abgerufen 13. April 2022, von https://eadips.org/anergy-networks-with-ductile-iron-pipes/?lang=en
Ruesch, F. (2018). Anergienetze als Chance zur Dekarbonisierung der Energiesysteme. Nachhaltige Technologien, 01(Fernwärme der Zukunft). Abgerufen von https://www.aee.at/netzgebundene-waermeversorgung/89-zeitschrift/zeitschriften/2018-01/1035-anergienetze-als-chance-zur-dekarbonisierung-der-energiesysteme
Scheiderer, L. (2021). Wie die ETH Zürich sich selbst mit Energie versorgt | BFE-Magazin energeiaplus | Energiemagazin des Bundesamtes für Energie. Polarstern. Abgerufen von https://energeiaplus.com/2021/04/19/wie-die-eth-zuerich-sich-selbst-mit-energie-versorgt/?translateto=de
Seifert, W. (2021). Interview mit Wolfgang Seifert: Wie die ETH Zürich sich selbst mit Energie versorgt | BFE-Magazin energeiaplus | Energiemagazin des Bundesamtes für Energie. Abgerufen von https://energeiaplus.com/2021/04/19/wie-die-eth-zuerich-sich-selbst-mit-energie-versorgt/?translateto=de
Wieland, U. (2017). Erdwärmespeicher für unsere Städte | ETH Zürich. Abgerufen 10. April 2022, von https://ethz.ch/de/news-und-veranstaltungen/eth-news/news/2017/01/erdwaermespeicher-fuer-unsere-staedte.html