Types of heat pumps
Geothermal (or ground-source) heat pumps use the natural heat storage capacity of the ground, rock, or groundwater instead of the outside air, to provide heating, cooling or even domestic hot water.
Parts of Geothermal Heat Pumps
Geothermal (ground) heat pumps systems are very similar to air-source heat pumps. The main difference is that they use they interact with the ground instead of interacting with the outside air like air-source pumps. To perform it, geothermal heat pumps use a set of pipes (or loop) buried in the ground.
The other components of the system are the indoor heat pump equipment and a flow unit to connect the indoor and outdoor equipment.
The indoor unit, commonly called an air handler, contains a large blower and a filter just like conventional air conditioners and air-source heat-pumps. The heated (or cooled) air is distributed around the house via ductwork (and the blower).
Energy efficiency
Temperatures below ground surface are relatively constant year round, well above the freezing point, even in freezing climates, allowing geothermal heat pumps to be very energy-efficient in all weather conditions and climates.
Closed and Open Loop Heat Pumps; DX (Direct Expansion) Heat Pumps
A Closed Loop Heat Pump involves a system of pipes buried in the ground. The heat transfer fluid is permanently contained in that closed pipe system. Common ground heat pumps are closed loop systems.
A Open Loop Heat Pump system involves a lake, a well or other water body. The heat transfer fluid is the body of water.
A Direct Expansion (DX) Heat Pump is a system in which the refrigerant is circulated in pipes buried in the ground (rather than using a heat transfer fluid like water bodies or antifreeze solutions in a separate closed loop).
ground, water and rock heat pumps
Ground heat pump
In this more common variant, the heat pump uses a pipe-loop buried about a meter below ground. The length of loop pipe varies with the soil type, configuration and intended pump capacity. Loop lengths between 250 and 1,000 feet (75m and 300m) per ton of capacity are common.
Water/GroundWater heat pumps
(Open loop Heat Pumps) 
A groundwater heat pump is a variant of the geothermal heat pump. This system uses a hose on a lake floor, weel or another water source instead of a pipe buried below ground. In groundwater heat pumps (also called open loop systems) the loop pumps water from the lake or another water body into a heat exchanger inside the heat pump.
Images credit: Danfoss
Rock heat humps
A rock heat pump is another variant of geothermal heat pumps, and a very common one. The system uses the energy stored in the rock shelf and the loop is lowered into a 300-500 feet (100–150 m) bore hole in the rock.
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