Carl Nielsen, a professor at The Ohio State University (OSU), built the first residential ground-water heat pump in 1948 at his residence in Columbus, Ohio. Nielsen devised a one-ton unit using common plumbing materials and by drilling a well in his back yard to a depth of 80 feet. The constant-temperature well water ran through a simple heat exchanger, regulating his home’s temperature for seven years with no problems. In 1955, Nielsen installed in a home a larger unit that ran for two decades with only a single, minor problem (Gannon, 1978).
Commercial ground-water heat pumps became more widespread in the 1950s and 1960s. One of the largest, early commercial installations was at Battelle Memorial Institute in Columbus. In 1958, Battelle began heating a 317,000-sf building by drilling five 16-inch wells to a depth of 50 feet in a sand-and-gravel aquifer and circulating the constant-temperature water through a series of large heat exchangers. Commercial ground-source heat pump installations increasingly are becoming a viable economic alternative in new or retrofitted commercial and institutional buildings. For instance, OSU will install a geothermal heating-and-cooling system in two new eleven-story dormitories and rehabilitate several older buildings beginning in 2011. The $4M closed-loop system will consist of 450 vertical wells drilled to a depth of 550 feet that will circulate fluids to an array of heat exchangers located in the basement of one of the new dormitories. An estimated 34 percent less energy will be needed for heating, cooling, and hot water, saving more than $200,000 annually compared to natural gas.
Residential ground-water heat pumps became more common after the large increase in energy prices in the 1970s. Residential ground-water heat pumps had to overcome several obstacles, including costs of well drilling, lack of experienced installers, fears about corrosion, and other operational or maintenance issues. Technological advances in heat pump efficiency, horizontal and vertical closed-loop systems development (ground-source heat pumps), and better site-specific planning led to more than 450,000 ground-source heat pumps being installed in the United States by the year 2000. Growth in the business has continued, with approximately 115,000 units installed nationwide during 2009. Ohio is a leader in the installation of geothermal heat pumps with approximately 10,000 installed during 2009 (EIA, 2010). ODNR Division of Geological Survey efforts include providing additional geotechnical data relevant to heat pumps.
Ultimately, coal-mining regions such as eastern Ohio may become a “Saudia Arabia” of geothermal energy, according to the National Energy Technology Laboratory (Ackman and Watzlaf, 2007). Not new, this concept has been executed abroad and is currently being studied in Pennsylvania and Indiana (see Schoonmaker, 2010). These large geothermal systems potentially are some of the most efficient and profitable, but exploitation has been limited in the past due to relatively low conventional-energy costs. The concept also takes advantage of abandoned and flooded mines by capturing mine water, using it in a heat exchange cycle, and then returning it to a mine. Because of Ohio's large number of closed underground mines, the ODNR Division of Geological Survey is taking an active interest in investigating their potential for geothermal heating and cooling and for off-peak energy storage.
Diagram illustrating use of water from flooded coal mine to heat and cool a district. The heat pump cycle uses refrigerant to extract heat from the mine water, which goes to the exchange plant that provides heat to the buildings. The process can be reversed to provide cooling during warmer periods of the year. Click image to enlarge.
- U.S. Department of Energy Geothermal Technologies Program—Extensive online resource for information about research efforts, funding opportunities, latest technologies, & more.
- GeoExchange.org—Site for the Geothermal Heat Pump Consortium, a non-profit trade association.
- Information Survival Kit for the Prospective Geothermal Heat Pump Owner—Oregon Institute of Technology, Geo-Heat Center.
- Use of abandoned mines in geothermal energy system:
- Coal Mines to be Converted to Geothermal Boilers—CalFinder.com blog article, Aug. 14, 2009.
- Eco Tech: Repurposed coal mine generates geothermal energy—EcoFriend.com article, Dec. 11, 2008.
- Abandoned Coal Mine Areas in Virginia with Geothermal Heat Pump Siting Potential—U.S. EPA map. [557 KB PDF]
- Closed Coal Mines Can Provide Clean Geothermal Energy—HeatingOil.com blog article, July 29, 2009.
- Mine water to be studied for ground source heating, cooling—Geothermal Digest blog article, Nov. 28, 2010.
- Geothermal energy from mining sources in the Zasavje region—Pre-investment study conducted as part of the ReSource project of Europe, Dec. 2010. [779 KB PDF]
- Geothermal energy recovery from abandoned mines—Renewable and Sustainable Energy Reviews article from February 2011. [251 KB PDF]
Ackman, T.E, and Watzlaf, George, 2007, U.S. mining regions—the Saudia Arabia of geothermal energy, in Electric Utilities Environmental Conference, 10th, Tuscon, Ariz., January 21–27, 2007: U.S. Department of Energy, National Energy Technology Laboratory.