An experimental platform dedicated to surface geothermal heat exchangers

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D2Grids Project

3455 Last modified by the author on 02/07/2020 - 12:45
An experimental platform dedicated to surface geothermal heat exchangers

In line with the challenges of the energy transition and its innovation approach, BRGM has set up an experimental platform that is unique in France, dedicated to research and development of surface geothermal exchangers. This project is part of the process of setting up a European energy efficiency cluster in the Centre-Val de Loire region. It is co-financed by the Centre-Val de Loire Region and the ERDF (European Regional Development Fund).

This laboratory site celebrated its tenth anniversary in 2019. It is experimenting in real conditions with all types of surface geothermal exchangers - commercial and other more innovative ones - in order to optimise their energy and environmental performance. It enables the performance of different techniques to be compared for uses such as heat and cooling production, heat storage or the solar/geothermal energy mix and heating networks.

The platform meets four important needs for the development of geothermal energy in France and Europe:

  • Experimentally validate the numerical models of innovative geothermal exchangers
  • Upgrading and testing underground heat storage devices
  • Assessing geothermal cooling systems
  • Testing tools for diagnosing the quality of geothermal installations

In addition, the geothermal platform is a showcase for market technologies, which makes it a privileged partner for professionals in the sector with a didactic and pedagogical purpose, for public authorities, large industries, but also for students and schoolchildren. It makes it possible to promote techniques that are not very visible, because most of them are located in the subsoil.

Over the past ten years, more than fifteen scientific projects have made it possible to test all types of surface geothermal exchangers on the platform: horizontal or vertical exchangers, geothermal baskets, Canadian wells. State-of-the-art metrology allows precise analysis of the impact of various parameters (meteorological, geological, hydrogeological, geometric, thermal, etc.) on the performance of the exchangers. Three piezometers and a complete meteorological station, including temperature and soil moisture measurements to a depth of 1.5 metres, have been installed on the site. In addition, 12 km of fibre optics were deployed along all the exchangers, allowing soil temperature measurements every metre. Thus, almost 12,000 ground temperature values can be measured every minute. These measurements enable experts to precisely analyse the thermal behaviour of the ground and the quality of heat transfer between the heat transfer fluid and the ground. They provide a detailed understanding of the physical phenomena involved, with a precision that also enables the validation and improvement of the various modelling tools developed in parallel by BRGM.

Compact heat exchanger

The cooling of buildings by using the coolness of the subsoil is one of the main areas of research on the platform. The GEOCOOLVERT project, funded by an APR IR from the Centre-Val-de-Loire region, currently aims to improve performance and extend the possible coverage of geocooling in this region. Geocooling is a passive cooling technique where the heat extracted from the building is directly exchanged with the ground. The energy efficiency of this technique is very important, but it is also sensitive to the thermal performance of the materials composing the system, as well as to the control strategy used. The project therefore aims to improve these two points, firstly through dynamic modelling adapted to the conditions of the Centre region, and then through experimental deployment on the site of the geothermal platform.

As part of an intelligent heat network, underground heat storage makes it possible to match heat production and demand over periods of time ranging from a few hours (daily storage) to a few months (seasonal storage). The ABC Storage project, in conjunction with the start-up Accenta and the ARMINES Energy Efficiency Centre, supported by ADEME's APED, has enabled BRGM's geothermal platform to be equipped with a field of thirteen vertical geothermal probes for the study and development of this method of storage. In this project, the site's thermodynamic machinery plays a major role by simulating storage loading and unloading cycles over several months, corresponding to the operation of a heating network with several different heat production and consumption units.

Installation of the vertical geothermal probe field

The site's thermodynamic machinery was completely renovated in 2019, in line with the ramp-up and expansion of the platform's testing capacity. A thermo-fridge-pump that can deliver 200 kW of heat and 150 kW of cold, at temperatures between -8 and +55°C, supplies up to 8 regulation circuits in parallel. These circuits serve the various geothermal exchangers installed on the site. The machinery thus allows simultaneous and completely decoupled measurement campaigns on several different exchangers. It simulates heat exchanges at the level of the surface energy system, such as a geothermal heat pump, or a heat network, at temperature levels between 10 and 55°C. The study of fifth-generation heat networks, which are the subject of the D2Grids project, fits therefore perfectly into the testing possibilities of BRGM's geothermal platform.

Thermodynamic machinery

By developing this experimental platform dedicated to research and support for the surface geothermal energy sector, in close conjunction with its expertise in modelling energy systems including the exploitation of underground resources, BRGM intends to be a leading player in the national strategy for energy transition towards sustainable development (French law). The test resources and metrology used on the geothermal platform make it possible to provide a precise and relevant response to a wide variety of research projects in this field, and to contribute in particular to the development of the intelligent heating networks of the future.

An article from BRGM


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