A: The temperature of shallow ground water in the U.S. ranges from 44°F in the north central areas to approximately 80°F in Florida and southern Texas. In North America, geothermal heat pumps can operate efficiently at ground water temperatures as low as 39°F, or even lower, with equipment currently being constructed. Higher temperature ground water will, of course, put less demand on the system and make it more efficient
In the extreme South, where the cooling cycle predominates, ground water temperatures average about 72°F. It leaves the geothermal heat pump at about 85°F. Geothermal heat pumps have been used for many years in Florida.
In the North, where the heating cycle is crucial, ground water temperatures average about 52°F. There is less flexibility available in severe northern climates for lowering the ground water temperature before freezing occurs. Some geothermal heat pumps are designed to operate with a very small temperature drop in the water to avoid freezing damage.
While there is a small potential risk of changing the ambient temperature of the aquifer where recharge or aquifer volume is limited, a geothermal heat pump usually raises the temperature of the water by no more than 10°F, so the water is usually returned to the original aquifer with no change in water quality and only a modest temperature difference.