Resource: Geothermal Heating & Cooling
Title: Geothermal Heating & Cooling
Resource type: Product
Topics: Buildings, Business, Energy
Keywords: energy efficiency, efficient energy, hydronic, natural gas alternative
Audience: All
Region: Minnesota Statewide, Outside Minnesota
Summary: Geothermal (or ground-source) heat pumps (or heat exchangers) are a dependable technology that uses the earth as a free heat source and as a heat sink.
Content: Technically the term "geothermal" refers to capturing heat energy from hot springs and other very hot places in the earth's crust. In Minnesota the term geothermal, or ground source heat pump, refers to using the stable temperatures (42 - 55 degrees, depending on location) in the Earth's shallow surface (6 feet to hundreds of feet).

Rather than creating heated and cooled air and associated air pollutants, as conventional furnaces and air chillers do, heat pumps use small amounts of electricity to move existing heat from the ground into buildings during the winter, and heat from buildings into the ground during the summer. Systems use an antifreeze mixture or water in closed loop systems or water in open loop systems in plastic pipes to move heat. An emerging system runs water from utility mains through heat pumps.

While more expensive than conventional heating/cooling systems to install (excavation or drilled wells are needed except for the utility systems), geothermal systems are cheap to maintain and operate. Efficiencies exceed 300%, compared to 96% for the highest efficiency furnaces and around 150% for air-source heat pumps.

The upper Midwest has a number of installed geothermal systems. The heat pump at the 80,000-sq. ft. elementary school in Onamia, MN extracts 1.75 million BTU from the earth in its heating mode and 230 tons of cooling during the summer. [See http://www.cleanenergyresourceteams.org/files/CS_EEschool_onamia.pdf for details.] Fangmann Service Center in Garnavillo, IA installed a geothermal system and in-floor heating (also called radiant heat) which cuts utility costs (compared to similar area service stations) in half and cuts insurance costs (no risk of furnace fires). The American Lung Association of Minnesota (651/227-8014) spent about $8,000 to install a heat pump in its 1996 Health House in Lake Elmo, MN (3,100-sq. ft.) that costs $580/yr. to heat and $210/yr. to cool.

Minnesota has one geothermal system manufacturer (ECONAR: www.econar.com), over two dozen installers, and utilities that promote geothermal systems.
Although a variety of heat pumps are available in MN, a horizontal closed loop ground source heat pump appears to be the most practical for MN. Despite the fact that geothermal systems reduce reliance on imported natural gas, a Minnesota Office of Energy Security study from the mid-2000s concluded that systems in residential settings currently increase greenhouse gas emissions by 40% over conventional high efficiency natural gas furnaces due the higher CO2 emissions from coal-fired electricity that runs the geothermal pump. These GHG emissions can be cut completely by Minnesotans purchasing renewably generated electricity from their electricity supplier.

In August 2008 the MN DNR published a fact sheet on how these systems work and what some of the permit requirements are for the involved water agencies (DNR, MDH and PCA). See http://files.dnr.state.mn.us/publications/waters/geothermal_systems.pdf

For more information contact the Geothermal Heat Pump Consortium in Washington, D.C. at http://www.geoexchange.org/ or the federal Department of Energy's Office of Energy Efficiency and Renewable Energy at http://www1.eere.energy.gov/geothermal/

Suggested by: Philipp Muessig
Added: 12/15/00
Updated: 05/2/11