What Is A Geothermal System And How Does It Work?

GeoExchange systems are the most cost effective HVAC systems for buildings.  They have the lowest life-cycle costs and the smallest carbon footprint.  They recover solar energy stored in the earth and transfer in into buildings.  They can be also be used to cool buildings by transferring heat from the building to the earth.  Because the earth’s temperature is very stable, they operate at extremely high efficiencies.

Every day, the earth absorbs over half of the sun’s energy. GeoExchange (also known as or Earth Energy) systems rely primarily on this stored solar energy to heat or cool a building and provide domestic hot water.  Electricity provides the power required to extract heat from the earth.  For every kW of electricity used by a geo system, anywhere from 3 to 6 kW of heat energy are pulled from the earth.

The link with the earth is done in two basic ways: open loops and closed loops. In open loop systems, water is pumped from a well.  Issues here include water quality, water management, and sustainability.  Closed loop systems are most common, and are often preferred for their reliability and low maintenance.

Closed loops use a network of High Density Polyethylene (HDPE) pipes to transfer heat to and from the earth. The pipes can be inserted into vertical boreholes, buried in horizontal trenches, or submerged in the ocean, lakes, or rivers.

The magic in the system is the ground source heat pump, which concentrates heat from the earth and transfer it into a building. The system can be reversible to provide cooling.  This isn’t new technology; the first GeoExchange system was installed over 50 years ago!  A common example of a heat pump is a refrigerator, where heat is transferred from the inside of the fridge to the room through the black grill on the back.

By transferring thermal energy rather than creating it through combustion or electrical resistance, GeoExchange systems achieve very high efficiencies. For each unit of electrical energy consumed by a heat pump, three to four units of heat energy are moved from the earth to your building.