The amount of heat within 10,000 metres of the earth's surface contains 50,000 times more energy than all the oil and natural gas resources in the world. This energy is derived from the 51% of solar radiation from the sun that is absorbed by land and water. Because this energy is retained at a more or less constant temperature just a few metres from the surface throughout the year it is a valuable source of renewable energy for heating and cooling

Capturing and Using Earth Energy

A heat pump is normally used to extract earth energy to provide heat for a building in winter and can be reversed to move heat out of the building and into the ground in the summer, thereby providing air conditioning. Other terms used to describe an earth energy systems are geo-exchange or ground source heat pumps. Earth energy is also often called a source of green heat along with solar thermal energy.

Two basic methods are used to bring the heat into a building. In a closed loop system a buried pipe (loop) circulates a fluid through the ground, a lake or a well. The fluid absorbs heat and transfers it into the building. In an open loop system, the lake or well water itself is pumped up into the building where the heat is extracted. In both cases, the heat pump transfers the energy to warm air (or warm water) and then distributes it throughout the building.

An earth energy heat pump still requires electricity to run the unit's compressor and circulate fluid through the open or closed loop. However, the power requirement is much lower than the energy that would be used by an equivalent gas or electric heating and cooling system. If electricity to power the heat pump is generated by another renewable energy source, such as wind or hydro, the system will have minimal environmental impacts.

Benefits

• Earth energy systems can significantly reduce heating and cooling costs (savings of 65% compared with electric furnaces).
• Little maintenance is required.
• Earth energy can provide heating in winter, cooling in summer and year-round hot water for home use.
• Earth energy systems can provide heat to one room and simultaneously provide cooling to an adjacent room. This is very useful for institutional buildings, for example, schools.
• According to the U.S. Environmental Protection Agency, these air conditioning systems are extremely energy efficient, environmentally clean (when electricity to power the heat pump is generated from a low- or zero -emissions source such as wind or hydro) and cost-effective.

Challenges

• As homes become more efficient, the heating and cooling load becomes too small to make an earth energy heat pump worth while. This challenge can be overcome by using a heat pump to heat a group of homes.
• Heat pumps have a high first cost compared with gas furnaces or electric heat and therefore innovative methods of financing are needed to pay for the heat pump from the long term savings in gas or electricity.

Global Status and Potential

Earth energy is used widely in northern Europe, especially in the Scandinavian countries, which have adopted the technology quickly. Earth energy is also becoming more common in the southern United States where it is used to cool buildings.

Canadian Status and Potential

More than 30,000 earth energy installations are in place in Canada for residential, commercial, institutional and industrial applications.

Links for more information

Organizations

• Canadian Association for Renewable Energies
• Canadian Geo Exchange Coalition
• Earth Energy Society of Canada
• Geothermal Education Office
• GreenHeat Partnership
• International Ground Source Heat Pump Association (IGSHPA)

• U.S. Geothermal Heat Pump Consortium (GHPC)

General Information

• Pollution Probe's Primer on the Technologies of Renewable Energy
• NRCan: About Earth and Geothermal Energy
• NRCan: Earth Energy Publications
• Residential Earth Energy System Guide (NRCan 2002)
• RETScreen — Ground Source Heat Pumps: pre-feasibility analysis and training modules