The Veillon neighborhood in Bussigny, Switzerland, rises on a site formerly occupied by the Veillon VPC house. Lively, urban, and innovative, it will accommodate housing, a hotel, offices, but also shops, local services, and leisure activities. Close to public transport, this new district will respond to contemporary habits of work, accommodation, travel, and consumption. For this project, GEOEG performed the detailed design of more than 200 vertical geothermal boreholes of 300 m in length and performed a thermal response test (TRT) on a test borehole. The thermal response test performed on site allowed to characterize the response of the underground to the operation of the designed geothermal technologies and validate their design. Such a design was performed via 3-D time-dependent thermo-hydraulic finite element simulations lasting 50 years, which allowed to reproduce thermal interaction effects among boreholes and the building operation with accuracy.