Various geo-exchanger designs for equivalent efficiency
Various geo-exchanger costs for equivalent efficiency
Deep boreholes provide higher temperatures for lower operating costs
These are general rules of thumb for average designs that are on the border line between a system that runs safely above freezing and does not require any antifreeze in the water and systems that do require an antifreeze solution. We prefer to design all of our systems for 38F minimum return water temperature to not need any antifreeze. Systems designed warmer to not need antifreeze save cost in not adding the chemicals and cost less to operate at higher operating efficiency COP's. They also pose less risk to the environment.