Ground Exchange - This type of heat pump uses the grounds current heat and exchanges it with the temperatures in your home. If you plan to have a ground sourced heat pump then you will need a heat exchanger which sits against either ground or ground water to make the pump function properly.

Direct Exchange - Instead of using a circulating refrigerant the direct exchange geothermal heat pump works by using a SINGLE loop refrigerant in direct thermal contact with the ground.

Closed loop - The typical system uses two loops on the ground side and one loop located in the appliance cabinet which exchanges temperatures with the loop which is pulling the temperatures from the ground. Closed loop systems have much longer and larger pipes implemented into the ground for better accuracy and also have an extra loop located in between the refrigerant loop and the water loop, pumping in both loops.

Closed loops come in two different types themselves one being the vertical closed loop and the other is the horizontal closed loop. The difference between the two being the vertical closed pump has pipes which run vertical through the ground while the horizontal closed loops have pipes running horizontally through the ground.

Pond - Pond based heat pumps are not commonly used due to the need to be close to an external source of water. Pond based heat pumps are more preferred and recommended for people who want to use a pump but have bad quality water, or a low heat source currently containable by a standard heat pump. The Pond based heat pump gets its name from the fact that the loop dragging in the heat is located underneath a large body of water, for example a pond.

Open Loop - An open loop is a heat pump which draws in water from an external source stores it in the main refrigerant where heat is extracted from the water source and the water is then returned to the external source.

Standing column well - A standing column well heat pump is much like an open loop heat pump except it is designed to pull in water from deep within a well and exchange it for heat in the main refrigerant where it is then returned back into the well while traveling down it exchanges heat with the bedrock.
 

Source: Heat Pump   Ground Source Heat Pump