Heating installation that combines renewable energy sources

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EPFL recently put an innovative heating installation online and will soon connect it to a large data center. The plant will help the Ecublens campus to optimize its production and energy consumption, with the objective of carbon neutrality.

Seen from the metro, the design of the new structure is quite striking: red blocks entirely covered with solar panels. In reality, this is only the visible part of a vast underground network that stretches from Lake Geneva to the campus’ Parc de l’Innovation. Inaugurated this year, EPFL’s new thermal power station stands out for its aesthetics, its innovative approach and its energy-saving performance. It will be presented as part of CISBAT 2021, a conference on the energy and environmental efficiency of the built environment, to be held at EPFL from September 8 to 10.

Next to the building are two fireplaces connected to gas boilers. These supplied heat to the EPFL campus for two years while the plant was under construction. In the future, they will only be used in the event of a system failure. “The new plant was put to the test one weekend in February when the temperature fell below freezing. It went brilliantly, ”explains Pascal Gebhard, who is part of the Infrastructure group within the vice-presidency for operations (VPO). With his colleagues from the construction and operation teams, he has supervised the project since its start in 2014, and particularly since 2019, when the old boiler room was demolished.

There is a lot of interest in the new factory and we receive many requests for visits. Heat pump technology is gaining ground around Lake Geneva. In addition, the thermal recovery of waste makes it possible to close the loop and reuse the water several times. Less water is needed, less energy is required for pumping, and less water is released into the local stream.

Before the start of construction of the new factory, the campus buildings had been using water from the lake for their heating system since 1985. EPFL has indeed been a pioneer in this field since the end of the 1970s, when it started. built its first pumping station for cooling purposes. But meanwhile, two oil-fired turbines were used to supplement the heating needs, especially following an increase in the number of buildings on campus.

An innovative solution

When the time came to modernize the obsolete boiler room, EPFL’s Sustainable Development Unit – and in particular its former director Philippe Vollichard, now retired – lobbied for an innovative solution. Rather than opting for gas, which would save money in the short term, but at the cost of CO2 emissions, the decision was taken to build an integrated system combining several renewable energy sources.

The new pumping station draws water deeper into the lake at a constant temperature of 7 ° C. It is connected to new generation heat pumps which raise the water temperature to 50 ° C thanks to a thermodynamic process which involves compression, condensation, expansion and evaporation, thus offering significantly better energy performance.

The other major advance is that the plant uses thermal waste generated by a data center built on top, with server racks whose doors are designed to accommodate industrial filtered water cooled by lake water. . This solution is energy efficient but technically quite daring – normally it is best to keep the water and electronics away from each other.

Cooling the servers to heat the rest of the EPFL generates considerable electricity savings, especially compared to the classic approach of cooling servers with refrigeration units. In a standard system, 3.3 units of electricity are required to supply one unit of electricity to the servers. Here, after taking into account the heating savings, this figure is 1.3 units, a reduction of 60%.

What about plant waste?

The innovation doesn’t stop there. With solar panels covering the sides and roof of the building and ample space for pilot testing in the works, the plant could one day use a nearby composting facility, where plant waste from the parks and gardens of the nearby campus is deposited. A digester for food waste from campus cafeterias could be another step towards local small-scale biogas production.

However, the very small quantities of biogas produced would be insufficient to cover all of EPFL’s needs, according to David Gremaud, energy project manager at VP.

The main purpose of this facility is to process food waste locally rather than trucking it off site. In addition, it can be used by the university community for teaching and research purposes.

Energy savings

Switching from oil turbines to heat pumps will reduce EPFL’s CO emissions2 emissions of 1,800 tonnes per year. However, the energy savings of the solar panels will only be marginal, since they will generate in total only 160 kW, whereas a single heat pump requires 2000 kW. But according to Gianluca Paglia, energy systems and construction methods project manager at EPFL’s Sustainable Development Unit, having solar panels installed directly on the building that houses a boiler room is a rare and instructive example of photovoltaics integrated into the building – one of the subjects addressed to CISBAT.

The construction work itself has been repeatedly delayed due to COVID – but also due to infiltration of quagga mussels. These creatures, which live in the deep waters of Lake Geneva, colonized the pipes and other equipment of the heating system. Engineers had to thoroughly clean the equipment and install a new removable strainer that allows for easier cleaning of surfaces. They also introduced new filters.

Another issue to be addressed was the discharge of wastewater from the cooling system into the local stream. Engineers devised a mechanism to regulate the discharge valves in order to preserve the local biotope, paving the way for the township’s approval of the project’s environmental impact statement.

A new data center will soon be operational

The delays in the new boiler room also affected the new EPFL data center, still under construction. Project managers are now awaiting delivery of the server racks. “We operate on a tight schedule,” explains Aristide Boisseau, head of data center operations at EPFL. The new boiler room will be connected to a 1,000 m² data center which will eventually house 12 rows of servers, including one for the University of Lausanne. Server racks used in the data center will be slightly taller than conventional models and will have water-cooled doors. It is a design that is already in use in other buildings, but so far only for cooling purposes. It is planned to recycle the heat generated by the servers in the boiler room which should start up this winter. This will increase the campus data storage and processing capacity, first to half the capacity to 2 MW, then to 4 MW.

We don’t want to put all of our eggs in one basket. We plan to slightly reduce the number of small data centers we have – currently around 30 – and keep the two large ones in the MA and INJ buildings. –

Space for pilot tests

The last big advantage – and not the least – of the new boiler room is that it will have a large raised surface for carrying out pilot tests. This space will be the size of six badminton courts and will span one side of the factory building. Here, engineers will be able to perform all kinds of experiments and demonstrations. “Before Philippe left, we made a preselection of possible projects in the fields of education and research,” explains François Maréchal, chemical engineer and professor of mechanical engineering at EPFL.

This is because the field lends itself to educational purposes in a variety of ways, such as explaining system design and comparison, tracking operating data, reconciling measurements, improving process control, and generating forecasts. It also opens the door to many synergies between EPFL laboratories, particularly within the Faculty of Engineers. For example, Maréchal’s colleague Jan van Herle, senior researcher at EPFL’s Energetic Materials Group (GEM) in Sion, is working on a fuel cell that can be installed in the heating plant to convert the biogas produced to from organic waste into heat and electricity. . Jürg Schiffmann, associate professor at EPFL’s Applied Mechanical Design Laboratory, has developed a new type of compressor for heat pumps, and Professor Mario Paolone of EPFL’s Distributed Electrical Systems Laboratory has found a way to integrate the central heating system in the intelligent system system used to manage campus electricity consumption.

The design of heating systems is a very promising area for the future, and Maréchal is encouraged by the evolution of EPFL’s own heating plant over the years.

The technology used in our heating plant is not necessarily complicated. What makes our factory innovative is the way the different systems are integrated with each other. It stood out when it was built 50 years ago and still does today, making the EPFL campus a benchmark in terms of sustainable development.

Another promising development is the growing number of students enrolling in the Marshal course on Optimizing Energy Systems. In this class, which has grown from 15 to 60 students in just a few years, Maréchal takes the new EPFL boiler room as a case study. “Any engineer involved in energy systems must have an eye on the energy transition. It is a crucial and very motivating issue for engineering students. While it takes a lot of work, it also shows students how important it is to analyze systemic ways to incorporate renewable energy into their designs. At the end of the day, they’re pretty proud of what they accomplish.


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