Documentation:
Heating and Cooling Efficiency of Geothermal Heat Pumps
https://www.energy.gov/energysaver/choosing-and-installing-geothermal-heat-pump-system
Community Geothermal Heating and Cooling Design and Deployment
https://www.energy.gov/eere/geothermal/community-geothermal-heating-and-cooling-design-and-deployment
Geothermal Basics
https://www.energy.gov/eere/geothermal/geothermal-basics
Geothermal Heat Pump Fact Sheet
https://www.energy.gov/eere/geothermal/articles/geothermal-heat-pump-fact-sheet
GHP Information for Consumers
https://www.energy.gov/eere/geothermal/geothermal-heat-pumps
Low Temperature & Coproduced Resources
https://www.energy.gov/eere/geothermal/low-temperature-coproduced-resources
Geothermal Everywhere
https://www.energy.gov/eere/geothermal/geothermal-everywhere
Ground source heat pump
https://en.wikipedia.org/wiki/Ground_source_heat_pump