A heat pump — like an air conditioner or refrigerator — moves heat from one place to another.
In the summer, a geothermal heat pump (GHP) operating in a cooling mode lowers indoor temperatures by transferring heat from inside a building to the ground outside or below it.
Unlike an air conditioner, though, a heat pump's process can be reversed.

In the winter, a GHP extracts heat from the ground and transfers it inside.
Also, the GHP can use waste heat from summer air-conditioning to provide virtually free hot-water heating.
The energy value of the heat moved is typically more than three times the electricity used in the transfer process.
GHPs are efficient and require no backup heat because the earth stays at a relatively moderate temperature throughout the year.

There are two main types of GHP systems.
The earth-coupled (or closed-loop) GHP uses sealed horizontal or vertical pipes as heat exchangers through which water, or water and antifreeze, transfer heat to or from the ground.
The second type, the water-source (or open-loop) GHP, pumps water from a well or other source to the heat exchanger, then back to the source.

Natural geothermal systems depend on three factors to produce energy: heat, water, and permeability.
While heat is present virtually everywhere at depth, water and permeability are less abundant.
Geothermal technology is an attractive renewable resource because it can provide a constant source of renewable baseload electricity.
While the sun and wind offer a large potential source of renewable energy that varies over time, geothermal technology is uninterruptible
and can provide a stable baseload form of energy while diversifying the nation’s renewable portfolio.

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