Anergy Grid

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Moving toward a carbon neutral campus:
An anergy grid replaces fossil fuels

While the technology is by no means new, the project size and complexity are unparalleled. ETH Zurich is building a dynamic underground storage system at ETH Hönggerberg in an effort to achieve virtually CO2-free heat­ing and cooling for the campus by 2025. This innovative construction proj­ect was acclaimed in 2012 as “exemplary” by the International Sustainable Campus Network (ISCN).

Schematic overview of the anergy grid on the campus Hönggerberg.
Schematic overview of the anergy grid on the campus Hönggerberg.

Only a few meters below the sur­face, one is able to traverse the Hönggerberg Campus in a multi­tude of seemingly endless corri­dors. Along the walls and above one’s head hang hefty, synthetic water pipes, arranged side by side or, in some places, on top of each other. With space being scarce, every meter is thoughtfully utilized and planned with painstaking preci­sion. “The mere configuration of this system posed a formidable challenge”, recalled Reto Hassler-Pause during a tour through the project. “Something of this scale and complexity is not to be found elsewhere in Switzerland”. Hassler-Pause is the ETH project coordina­tor responsible for planning and operation of the dynamic under­ground storage system, also re­ferred to as the “anergy grid”. An­ergy is a term to describe low-grade energy. The new ETH Zurich energy concept includes plans for deploy­ing as much anergy for heating and cooling purposes as possible through the use of geothermal energy and waste heat.

As Simple as Ingenious

What, however, makes this dynamic underground storage system − which is essentially based on con­ventional technologies such as heat pumps − a flagship project? The principle behind the dynamic under­ground storage system is as simple as it is ingenious; the subterranean storage fields function like a battery which, depending on the season and building use, is either charged or discharged. While some buildings are heated during winter others, such as those housing servers, tend to emit heat throughout the year. To date, the heat generated by the latter type of buildings simply van­ished. However, with the implemen­tation of the underground dynamic storage system along with the water-filled earth probe fields, this otherwise wasted heat is stored 150-200 meters below ground level for the purpose of heating in the winter. As buildings are heated during the cold months, heat is extracted from the storage and the temperature of the water drops. The process subsequently provides cool water to buildings in the summer.

Dynamic System

The system is thus considered a “dynamic” system because it provides both heating and cooling. Jeanette Maurer-Hartmann, acting on behalf of the ETH Building and Constructions Infrastructure Division as the Building Owners’ Representative, explains the exact function of the underground storage system: “The heart of the underground energy storage system is the vast energy channel – a central circuit ring. Attached to this are substations enabling the ‘refinement’ of the low-grade energy. In other words, the water temperature is altered in such a way that it may be used directly for heating or cooling. The energy is directed from the substations either to connected buildings, or back into the circuit ring. The substations as well as the earth probe fields are interconnected via this ring.”

Major Challenge: Growing Campus

At this point in time, the project is in the process of being deployed and optimized. Project coordinator, Reto Hassler-Pause, is under significant pressure: “The underground energy storage system must function as an interlocking whole.” In particular the hydraulics of the many pumps in this complex system poses a major challenge. Final completion of the circuit ring, substations and earth probes will, for the most part, likely occur prior to 2025. However, the campus is growing and, as such, each substa­tion is designed to service several buildings (called clusters) some of which have yet to be built or still require renovations. For example, in the short term, new student resi­dential buildings are expected to be connected to the anergy grid. The primary challenge of the project lies in ensuring a synchronized expan­sion of the subterranean energy storage system with the aboveg­round campus.

Lower Energy Costs, Less CO2

The underground energy storage project will cost 37 million CHF, spread over 15 years. Thereof, only approximately 17 million CHF is considered an additional investment resulting for the anergy project. This is due to the fact that ETH Zurich would have needed to reno­vate the existing heating system regardless of the approach. Antici­pated energy cost savings due to the innovative underground storage system are estimated at 1 million CHF annually. Hence the additional costs are likely to be amortized by approximately 2030. It is also antici­pated that CO2 emissions will be reduced by half by 2020.

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