A geothermal heat exchange unit, which can be placed in ground or in water, having a hollow sleeve about which a helical winding of thermally conductive tubing is wound and a return length of thermally conductive tubing along the central axis of the sleeve separated from the inner wall of the sleeve...http://www.google.fr/patents/US5623986?utm_source=gb-gplus-shareBrevet US5623986 - Advanced in-ground/in-water heat exchange unit
