1. J. Lund, B. Sanner, L. Rybach, R. Curtis, G. Hellström, Geothermal (ground–source) heat pumps. A world overview, Geo-Heat Center, Oregon Institute of Technology, Klamath Falls, OR, 2004, http://www.geoheat.oit.edu.
2. Geothermal Energy Utilization in the United States;Lund,2000
3. Field tests for ground thermal properties–methods and impact on ground–source heat pump design;Kavanaugh;ASHRAE Transactions,2000
4. Ground thermal conductivity testing-controlled site analysis;Kavanaugh;ASHRAE Transactions,2002
5. Comparison of the thermal performance of double U-pipe borehole heat exchangers measured in situ;Pahud;Energy and Buildings,2001