POLITECNICO DI TORINO

ENERTUN – ENERGY TUNNEL SEGMENTAL LINING

The patent is an improved tunnel precast segmental lining (ENERTUN) equipped to exchange heat with the ground to heat and cool adjacent buildings. A circuit of pipes is installed in each segment in the factory before precasting and fluid circulates through them allowing for heat exchange with the ground. The tunnel segmental lining is to be used for tunnels constructed by TBM. The concrete segment can be equipped with different configurations: a single circuit of pipes on the ground side to exchange heat with the soil (ENERTUN GROUND), a single circuit of pipes on the tunnel side to exchange heat with the tunnel internal air (ENERTUN AIR) or a double system of pipes to exchange heat with both sides (ENERTUN AIR&GROUND). Each equipped segment is connected to the adjacent one through hydraulic connections to form a ring of the segmental lining. The system allows maximising the heat exchange and reducing the hydraulic head losses. The system can be used to extract heat from the ground to heat the adjacent buildings or inject heat into the ground to provide air conditioning (metro tunnels or tunnels in urban areas) or to reduce costs of cooling deep mountain tunnels.

Patent Status

SUBMITTED

Priority Number

102016000020821

Priority Data

29/02/2016

License

INTERNATIONAL

Market

ENERTUN can potentially be implemented in all future tunnels excavated through Tunnel Boring Machine (T.B.M.). The patent is of interest to construction companies involved in the tunnel industry and investors in public works. The potential market is also in the areas of energy stakeholders, such as companies managing district heating systems in an urban environment.
The additional market can be represented by the realisation of deep Alpine tunnels, as the high geothermal potential associated with the need of cooling the tunnels may open interests over the Enertun system.
The lifetime of the patent is related to the lifetime of the infrastructures that are in the range between 50 to 100 years.

Problem

It is estimated that 30-40% of the total energy consumption and global energy-related CO2 emissions in 2017 were used by the built environment. However, the environmental deterioration is related to the growing energy demand that can be satisfied by sustainable solutions, which rely on both decreasing the consumption of fossil fuel and developing technologies that harvest renewable energy sources. In this framework, the ground-coupled heat pump systems offer one way of providing renewable energy in an urban environment, where the ground immediately below a city can be used to exchange heat for covering the cooling and heating demand. A modern application of this technology is represented by the so-called energy geostructures. They couple the structural role of geotechnical structures to the low enthalpy geothermal principles, by integrating into the concrete elements a circuit of high-density polyethylene plastic pipes for ground heat exchange. The ENERTUN patent concerns the application of this technology in tunnel linings.

Current Technology Limits

Space heating is often operated by boilers (mainly natural gas fueled), district heating or heat pumps. Boilers produce heat by combustion of fossil fuels rather than biomass. Howeverr in both cases greenhouse gas emissions result from combustion.
District heating shows high efficiency by concentraring the energy production in large installations and then transporting the energy to the final user. Greenhouse gas emissions are only spatially moved to suburbs and energy transportation is related to energy losses.
Very few installations only provide heating in winter season and cooling in the summer season. Moreover district cooling is extremely uncommon. Heat pumps can be used for this purpose. These are based either on air-to-water or water-to-water installations.
Air Source Heat Pumps show large influence of external temperatures on the efficiency. These are extremely variable. On the contrary, Ground Source Heat Pumps, namely geothermal heat pumps employ resources that are highly stable from the thermal point of view.
Heat exchange with the ground usually requires deep and expensive drillings rather than large surfaces to be dedicated exclusively to this purpose. Energy Geostructures can overcome these issues.

Killer Application

A prototype of the technology has been installed and successfully tested in the tunnel of the South extension of the Turin metro line 1 (Italy). The system is installed between the Lingotto and the Bengasi stations. The experimental site includes two lining rings, which corresponds to three meters of tunnel length, entirely equipped with ENERTUN Ground&Air system. The segments are connected to a heat pump system and a secondary circuit for heat utilisation. The installation has been extensively monitored in operational conditions during the construction of the tunnel. The results, which were also published in scientific journals (Barla et al. 2019, A novel real-scale experimental prototype of energy tunnel, Tunnelling and Underground Space Technology 87, 1-14; Insana & Barla 2020, Experimental and numerical investigations on the energy performance of a thermo-active tunnel, Renewable Energy 152, 781-792), confirmed the energy potential of the ENERTUN technology. The prototype is now in the process of being upgraded to allow for the continuation of working also after the opening to service of this section of the metro line.

Our Technology and Solutions

The implementation of the Enertun technology into a tunnel will allow the implementation of a large low enthalpy geothermal system to be used as a means of heat exchange. The amount of energy exploitable is in the order of 0.5/1.5 MW each km of tunnel length, depending on the specific site conditions. The most appropriate application and the first target would be related to the construction of metro tunnels in urban areas by mechanised excavation. The attractiveness of this application is enhanced by the vicinity of the potential users of the heat collected by the tunnel exchangers. Users may be directly connected to the primary system (the tunnel) whereas an interesting alternative is that of connecting the energy tunnel to a low-temperature district heating system and adopting this to distribute the heat to the final users. This will simplify the commercial interaction with final users and allow for robustness and backups and the system. This specific solution is currently studied for a specific area in the North Eastern suburbs of the city of Torino (Italy) in cooperation with Iren, the company responsible for the district heating system in the city. From the economical point of view, the realisation and implementation of the ENERTUN segment do not represent a significant additional cost with respect to tunnel construction. The advantages obtained with the production of heat and cool for the whole duration of the life cycle of the infrastructure with limited maintenance and operating costs are particularly attractive from the cost/benefit point of view. It is worth mentioning once again that the energy provided by the proposed system is sustainable, green and local, perfectly according to the current policy of sustainable development.

Advantages

The concrete segment can be equipped with different configurations (see the figure): a single circuit of pipes on the ground side to exchange heat with the soil (ENERTUN GROUND), a single circuit of pipes on the tunnel side to exchange heat with the tunnel internal air (ENERTUN AIR) or a double system of pipes to exchange heat with both sides (ENERTUN AIR&GROUND). Each equipped segment is connected to the adjacent one through hydraulic connections to form a ring of the segmental lining. The system allows maximising the heat exchange and reducing the hydraulic head losses. The system can be used to extract heat from the ground to heat the adjacent buildings or inject heat into the ground to provide air conditioning (metro tunnels or tunnels in urban areas) or to reduce costs of cooling deep mountain tunnels.

Roadmap

Many expression of interest were recently received from national and international construction companies and institutions, representing a first step forward towards the commercialisation and industrial development of the patent. The Enertun technology was considered by:
– Systra & partners, among the feasibility study for the Metro Line 2 in Torino (Italy);
– Engie Solutions, among the feasibility study of the Ligne 15 Ouest of the Grand Paris Express, France;
– the municipality of Cluj Napoca (Roumania) for the new metropolitan line.
Future steps will therefore target the above stakeholders and companies. The most attractive one being the Metro Line 2 in Torino, because of the obvious logistic opportunities and because of the advanced stage of the project. The overall project involves 30 km of tunnels, most of which to be realised by mechanised excavation. The thermal activation by Enertun segments has been formally included, studied and assessed in the feasibility study of the line. Further investigations and identification of potential receivers for the heat were made in the North-Eastern area of the city, together with Iren SpA and may lead to commercial utilisation of the heat. Based on this, the inventors will both support the next design stage of the infrastructure as well as finalise the assessment of the marketing opportunities with Iren SpA.

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Il team

Alessandra Insana

Alessandra Insana is a research assistant at the Politecnico di Torino (Italy) since 2019. She got her Ph.D. in Civil and Environmental Engineering at Politecnico di Torino and Université Paris-Est in 2020, with a thesis on energy geostructures entitled “Thermal and structural performance of energy tunnels”. She is an expert in numerical modelling of Thermo-Hydro-Mechanical coupled problems and her current research activities are mainly devoted to thermoactive geostructures, with particular focus on energy tunnels. Recently, she also developed an interest in research related to adaptation to climate change of geostructures, tunnelling in difficult conditions and fiber optics monitoring of debris flows. Since two years she is also working as a consultant of Geosolving s.r.l., an engineering company in Torino, where she is active in energy geostructures design, numerical modelling for the solution of geotechnical problems and monitoring data interpretation. As of 2017 she is assistant for the course of Numerical Methods in Geotechnical Engineering. She is author of several scientific publications on international journals and on conference proceedings.

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Alice di Donna

Dr. Alice Di Donna is Assistant Professor at the University Grenoble-Alpes (France). Her main research activities are related to energy geotechnics and thermo-hydro-mechanical couplings in geomaterials, both from experimental and numerical point of view. She obtained her PhD at the EPFL (Lausanne, Switzerland) on the thermo-mechanical behavior of energy piles and was later on involved as a post-doc at the Politecnico di Torino in the development of the energy tunnels technology. She co-edited one book on energy geostructures (available in English, French and Chinese), authored over twenty scientific papers and co-inventor of the patent ENERTUN. She has been Italian delegate in the Management Committee and working group leader of the COST Action GABI TU 1405. She was the nominated delegate for Italy by the Italian Geotechnical Association (AGI), at the EYGEC 2016 (Sibiu, Romania) and she got the first runner up price at the DFI Educational Trust 2011 Student Paper Competition, Boston, MA, USA. More recently she was awarded with the French Kerisl Price, for her scientific developments in the geotechnical field. She also worked as structural and geotechnical engineer at the Teknema Progetti srl, a civil engineering society based in Torino (Italy).

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Marco Barla

Marco Barla is Associate Professor of Geotechnical Engineering at the Department of Structural, Geotechnical and Building Engineering (DISEG) of the Politecnico di Torino. He is the coordinator of a research group that carries out activities in the field of laboratory testing on soils and rocks, numerical modelling, tunnel excavation, slope stability, monitoring with ground-based radar and energy geostructures (www.rockmech.polito.it). He is the Editor in Chief of the ASCE International Journal of Geomechanics and a member of the Editorial Board of Tunnelling and Underground Space Technology and Soils and rocks, the President of ELGIP, European Large Geotechnical Institutes Platform, and Chair of the next Iacmag 2022 conference. He holds academic duties as the Rector's Advisor for sports activities, President of the University Sports Committee, member of the University Quality Control Center and member of the Department's Board. He is the Author of a book, conference proceedings, over 160 scientific papers and holds a patent of an energy tunnel segment (Enertun). He is the recipient of the “Excellent Contributions Award” of the IACMAG and the 'Telford Premium' from the Institution of Civil Engineers.

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