Shallow geothermal systems in dense urban areas: The issue of thermal interference and long-term sustainability

Shallow geothermal systems, namely Ground Source Heat Pumps (GSHP) and Ground Water Heat Pumps (GWHP), are expected to give an increasing contribution to the decarbonization of the buildings climatization sector. A fully sustainable use should guarantee fair access to the shallow geothermal sources for new systems, given the potential thermal interference among neighbouring ones in dense urban areas, and address environmental concerns related to thermal pollution of ground and groundwater. In this paper the state of the art concerning environmental concerns, regulation approaches and sustainability metrics is firstly reported. Then, focusing on closed-loop systems, a simulation case study is developed to study the long-term thermal footprint in the ground. The Energy Imbalance indicator, summarizing the annual energy balance in the ground, drives the thermal drift produced by the bore-field and is therefore proposed as the main sustainability indicator. For given ground conditions, a maximum Energy Imbalance is identified, which limits the thermal perturbation distance to the borehole spacing and minimizes thermal interference with other systems.