1. VDI 4640, Part 2. Thermal use of the underground–ground source heat pump systems; Verein Deutscher Ingenieure; Düsseldorf, Germany; 2001.
2. CO2 thermosyphons as heat source system for heat pumps — 4 years of market experience;Rieberer,2005
3. CO2 two-phase thermosyphon as heat source system for heat pumps;Rieberer,2004
4. Heat pipe science and technology;Faghri,1995
5. VDI Wärmeatlas, Berechnungsblätter für den Wärmeübergang; VDI Verlag GmbH, Düsseldorf, Germany; 1994.