B. Nordell, IEA ECES ANNEX8 Final Report, www.ltu.se/polopoly_fs/1.5013!ax8slutrapport.pdf (2000).
B. Sanner, New Trends and technology for under ground thermal storage (UTES), Proceedings of 7th International Conference of Thermal Energy Storage (MEGASTOCK ‘97)(1997)677-684.
C. H. Corgan: Heat pump tests provide basic data on ground coil system, Electric power and light, 26(1949)169-176.