Abstract: The invention relates to a heat source or a heat sink unit with thermal ground coupling, comprising at least one ground probe arranged in the earth, whereby each earth probe is a probe tube made from several pile tube segments. An open dip tube or a U-shaped tube loop is arranged in the probe tube at the open lower end thereof. Said unit is characterized in that each pile tub segment is made from ductile cast iron, the pile tube segments re embodied such as to plug into each other at the ends thereof and each pile tube segment comprises, at the one end thereof, a conical outer circumference and, at the other end thereof, a sleeve embodied with a shoulder stop having a matching conical internal circumference, whereby the diameter thereof and the cone angle are such that on driving in the pile tube segments a positive and sealed connection between the pile tube segments is generated.