The role of numerical modelling in the design of open-loop shallow geothermal systems

Open-loop shallow geothermal systems have emerged as a low-carbon solution for covering heating and cooling needs of buildings. The operation of these systems, however, produces hydraulic and thermal alterations of the aquifers exploited, which must be addressed in the design phase and monitored during the operation phase. This paper reviews the role of numerical codes for flow and heat transfer modelling in porous media in the design and evaluation of open-loop shallow geothermal systems, addressing key design issues like drawdown and level rise around abstraction and reinjection wells, thermal plume propagation, and thermal recycling. Various modelling codes are discussed, among which FEFLOW, MODFLOW, and COMSOL Multiphysics, each offering specific capabilities. A short review is provided for modelling techniques to address thermal recycling and the propagation of thermal plumes, which are two essential aspects, respectively, for the design of single installations and for the management of their co-existence in urban areas.