1. Heat conduction: with engineering, geological and other applications;Ingersoll,1954
2. Conduction of heat in solids;Carslaw,1959
3. Earth coupled heat transfer;Hart,1986
4. Design and installation standards, stillwater,1991
5. Hellstrom G. Ground heat storage. Thermal analysis of duct storage systems: part I. Theory. Doctoral Thesis, Department of Mathematical Physics, University of Lund, Sweden, 1991.