Thermal balance of the water table
Inventory of groundwater use for heating and cooling in Sion, implementation of a temperature monitoring network.
Groundwater is an important energy resource. It can be used to generate heat and cooling throughout the year. The groundwater table in the Rhône plain is often the focus of particular attention from planners, due to its high exploitation potential and proximity to the surface.
There are around 150 installations in operation in the Sion area. Groundwater is used to meet the energy needs of a wide range of buildings: villas, apartment blocks, industrial halls, public infrastructures (hospitals, schools, etc.). The introduction of the Minergie and Minergie-P labels in the late 2000s(SIA standard 380/1) contributed to a significant and steady increase in demand(Sonney & Dubois 2013, CREALP 2021). While the initial trend was towards geocooling, heat production is gradually taking on greater importance. Today, the balance between heat production(11.6 MW) and cooling production(14.1 MW) is practically balanced.

As the number of installations continues to grow, some areas are currently saturated in terms of thermal groundwater exploitation potential. Without comprehensive, sustainable management of concessions, the following risks could arise:
- Risk of thermal interference between the discharge wells of a given facility and the pumping wells of another facility located downstream of the underground flows.
- Risk of thermal imbalance: tendency for the water table to warm up or cool down in relation to its natural temperature, downstream of areas with a high density of concessions.

Based on this observation and these potential risks, the City of Sion, OIKEN and the Environment Service(SEN) of the Canton of Valais have assessed the need to reinforce the monitoring of groundwater temperatures, by means of a secondary network(thermES) which would be added to the already operational networks of piezometers of the SEN and the Natural Hazards Service (Rhôn and Léman section). The data collected in this way will enable better planning and sustainable management of concessions granted or renewed.
Information
Project manager: Dr Romain Sonney
Project duration: 2020 – 2022
Project leader: OIKEN
Further information
Sonney, R., & Dubois, P. (2013). Groundwater potential in Sion. Geothermie.ch

CREALP (2021). Thermal balance of the Rhône water table. Axe 1 Monitoring – Inventory of groundwater use for heat and cold production in Sion, proposal for a temperature monitoring network. Unpublished report, May 25, 2021.