2021

Thermal cadaster of Lausanne’s subsurface urban heat island

Substantial amounts of waste heat are daily rejected in the urban subsurface due to anthropogenic activity, underground transport, and subsurface energy infrastructure. This waste heat contributes to subsurface urban heat islands and represents an untapped energy source that can be reutilized in buildings. For the first time, GEOEG assessed Lausanne’s subsurface heat island intensity by determining its sources and effects in order to propose sustainable retrofit interventions and an energy efficiency strategy at the urban scale. The work resorted to temperature measurements in the field and numerical simulations of the thermo-physical state of the subsurface.

An amount of thermal energy equivalent to the annual consumption of 7000 Minergie P buildings is yearly rejected into the underground of Lausanne

Analysis of a specific neighborhood expanded in the context of this project to the entire city of Lausanne. (a) Cadaster and aerial photograph of Saint Laurent neighborhood; (b) 3D finite element numerical model of the considered area; (c) Simulation of drinking water networks (blue) and district heating networks (red).
As a part of this project, a shallow subsurface thermal cadaster was developed for the city of Lausanne, considering both localized and diffused drivers of subsurface urban heat islands, including building basements, district heating networks, and sewer networks. Such cadaster was developed with due consideration of the building characteristics (method of construction,  insulation, age of the building, etc.) and the features of the local underground infrastructure systems (e.g., drinking water networks and district heating networks). Starting from the hearth of Lausanne, such a cadaster was extended citywide, allowing to determine that an amount of thermal energy equivalent to the annual consumption of 7000 Minergie P buildings is yearly rejected into the underground of Lausanne.
Temperature maps for Saint Laurent neighborhood. The figure shows the spatial variation of temperature around building basements considering different depths and the surrounding heat sources.
The project has set the stage for the development of an innovative urban planning strategy devoted to foster (i) technologies that can reutilize from the shallow subsurface significant waste heat emissions rejected by underground infrastructures in such environment or (ii) retrofit interventions that can support energy savings in buildings through more adequate thermal insulation of basements and other sources of waste heat in contact with the ground.

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