Connor Dacquay introduces ground-source heat pumps in this session from MIT's IAP course RES.ENV-007, Geothermal Energy Networks: Transforming Our Thermal Energy System, taught with HEET. He explains how the stable temperature of the earth a few feet underground can be tapped for heating and cooling buildings, walking through the basic engineering of a ground-source heat pump system: boreholes, circulating fluid, and the heat exchange that lets the system move warmth into a building in winter and out of it in summer. The talk frames geothermal heat pumps as a practical piece of decarbonizing building heat, connecting the physics of underground temperature to the networked systems HEET is piloting in Massachusetts neighborhoods. It is a short, focused primer rather than a deep technical derivation, suited to someone encountering ground-source heat pumps for the first time.