Abstract

A heat exchanger is connected via an insulated flow pipe (26) to a pump (28) arranged in a borehole. The flow pipe and the pump are surrounded in the borehole by a protective tube (34) open at the bottom adjacent to a return region (38) which extends radially outward to the wall of the borehole. The return region communicates with the interior of the protective tube. A return line (42) from the energy exchanger contains at least one return pipe (40) which extends approximately to the bottom of the borehole and is subdivided along its length by a plurality of transverse plugs (44). At the transverse plugs, the return water flows through passages arranged on either side of the transverse plugs and penetrates the porous filling (48) surrounding the return pipe. After the transverse plugs, the return water flows out of the porous filling and back through the passages into the return pipe. This results in reliable guiding of the return water and optimal heat uptake by the water from the return region and from the wall of the drilled hole.