How does geothermal heating and cooling work with the earth?

There are currently three ways that geothermal units connect with the earth. Two use a liquid and one does not. The two that use a liquid are called "Open Loop" and "Closed Loop". The other is called "DX". We'll address the open loop first.

Open loop uses the naturally occurring ground water we call well water as a "tap" to the natural energy of the earth. The water in the earth attains the same temperature as the earth itself. The open loop system uses a pump to move some of this water out of the earth and deliver it to the geothermal unit. There the geothermal unit either removes or adds BTU's to the water (depending on what needs to be done to the comfort level in the building) and releases that water back to the earth to again attain the temperature of the earth. This is a very simple system and in areas where the ground water is plentiful like northern Indiana, it is a very good way to heat and cool a building. In most cases, the same well that supplies domestic water to the building supplies the well water to the geothermal unit.

Closed loop is a system where a series of plastic piping loops are buried directly in the earth. An antifreeze solution is circulated through this series of loops and through the geothermal system. The geothermal unit again either adds or removes BTU's from the solution depending on what needs to be done to the comfort in the home. After leaving the geothermal unit, the solution flows through the loops and the earth tries to bring it back its natural temperature. The size and lengths of the loops determine how well the earth can get this job accomplished. Closed loop systems are mostly used in places where well water is not available or of poor quality.

DX geothermal is where a part of the geothermal unit is built directly in the earth. This system needs no water or solutions to tap the earth for it. The system does it directly, that's why it is called DX or "Direct Exchange". This system directly exchanges heat with the earth either adding or removing BTU's depending on the comfort of the building. DX is used because of its simplicity, greater reliability and higher efficiency than the liquid based systems.