Evaluating the geothermal potential of a metro station considering its airflow conditions

• This work presents numerical simulations of a geothermally activated metro station. • Computational fluid dynamics is used to evaluate air domain considerations. • Geothermal potential is assessed for a variety of realistic airflow scenarios. • Average heat transfer coefficient use is validated for time-varying boundary conditions. • Interaction effects between geothermally activated sections are identified. This study examines the influence of the internal air environment on the geothermal potential of a metro station in Bucharest with a standard design commonly found in metro stations. It addresses the challenges posed by factors such as train movement on air circulation and braking, passenger flow, and technical infrastructure on temperature patterns within the station respectively. The aim is to evaluate the feasibility of utilizing energy geostructures within the station considering the influence of waste heat, with the objective of improving cooling and ventilation systems and reducing the impact on the surrounding underground climate change. This aspect is evaluated using three-dimensional numerical modelling. A novel modelling approach is used to account for the air domains in the metro station due to its complex geometry. Convective heat transfer boundary conditions are implemented based on computational fluid dynamics simulations of the full air domain, accounting for the variation in airflow conditions caused by the passing of metro trains. This allows assessing the variation in geothermal potential caused by variations in airflow conditions, soil temperatures and representative air temperatures inside the station, which is a core aspect of the design of energy geostructures. The work demonstrates the possibility of working with an equivalent wall heat transfer coefficient to represent the variation in airflow conditions over time caused by the passing of metros. Furthermore, the influence of interaction effects between different geothermally activated sections is evaluated. This is an essential aspect to consider during the design phase for the determination of geothermal potential. Through these factors, the study contributes to improving the understanding of the physical mechanisms relevant for geothermal activation of metro stations and presents a novel approach to account for the airflow conditions in these underground infrastructures in the assessment of geothermal potential.