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Geothermal heating

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This article is about direct uses of geothermal heat. For electricity generation, see geothermal power.
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Renewable energy

Geothermal heating is the direct use of geothermal power for heating applications. Humans have taken advantage of geothermal heat this way since the paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.[1] Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter.

Geothermal energy originates from the heat retained within the Earth's core since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.[2] Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application. However, even cold ground contains heat, and it may be extracted with a geothermal heat pump. Due to recent advances in heat pump performance, this is now a rapidly growing market.

Applications

File:Sherman geothermal infographic pq.jpg
Geothermal Lake Technology
Top countries using the most geothermal heating in 2005[3]
Country Production
PJ/yr		 Capacity
GW		 Capacity
Factor		 Dominant
applications
China 45.38 3.69 39% bathing
Sweden 43.2 4.2 33% heat pumps
USA 31.24 7.82 13% heat pumps
Turkey 24.84 1.5 53% district heating
Iceland 24.5 1.84 42% district heating
Japan 10.3 0.82 40% bathing (onsens)
Hungary 7.94 0.69 36% spas/greenhouses
Italy 7.55 0.61 39% spas/space heating
New Zealand 7.09 0.31 73% industrial uses
63 others 71 6.8
Total 273 28 31% space heating

There are a wide variety of applications for cheap geothermal heat. In 2004 more than half of direct geothermal heat was used for space heating, and a third was used for spas.[1] The remainder was used for a variety of industrial processes, desalination, domestic hot water, and agricultural applications. The cities of Reykjavík and Akureyri pipe hot water from geothermal plants under roads and pavements to melt snow. Geothermal desalination has been demonstrated.

Geothermal systems tend to benefit from economies of scale, so space heating power is often distributed to multiple buildings, sometimes whole communities. This technique, long practiced throughout the world in locations such as Reykjavik, Iceland,[4] Boise, Idaho,[5] and Klamath Falls, Oregon [6] is known as district heating.[7]

Extraction

Main article: Ground-coupled heat exchanger

Some parts of the world, including substantial portions of the western USA, are underlain by relatively shallow geothermal resources.[8] Similar conditions exist in Iceland, parts of Japan, and other geothermal hot spots around the world. In these areas, water or steam may be captured from natural hot springs and piped directly into radiators or heat exchangers. Alternatively, the heat may come from waste heat supplied by co-generation from a geothermal electrical plant or from deep wells into hot aquifers. Direct geothermal heating is far more efficient than geothermal electricity generation and has less demanding temperature requirements, so it is viable over a large geographical range. If the shallow ground is hot but dry, air or water may be circulated through earth tubes or downhole heat exchangers which act as heat exchangers with the ground.

In areas where the shallow ground is too cold to provide comfort directly, it is still warmer than the winter air. The thermal inertia of the shallow ground retains solar energy accumulated in the summertime, and seasonal variations in ground temperature disappear completely below 10m of depth. That heat can be extracted with a geothermal heat pump more efficiently than it can be generated by conventional furnaces.[7] Geothermal heat pumps are economically viable essentially anywhere in the world. One geothermal district heating system at Drake Landing enhances storage of solar energy in the ground to such an extent that no heat pumps are needed.

Geothermal heat pumps

Main article: Geothermal heat pump

Even in regions without large high temperature geothermal resources, a geothermal heat pump can still provide space heating and air conditioning. Like a refrigerator or air conditioner, these systems use a heat pump to force the transfer of heat from the ground to the application. In theory, heat can be extracted from any source, no matter how cold, but a warmer source allows higher efficiency. A ground-source heat pump uses the shallow ground or ground water (typically starting at 10-12°C, 50-54°F) as a source of heat, thus taking advantage of its seasonally moderate temperatures.[9] In contrast, an air-source heat pump draws heat from the colder outside air and thus requires more energy.

Closed loop geothermal heat pumps circulate a carrier fluid (usually a water/antifreeze mix) through pipes buried in the ground. As the fluid circulates underground it absorbs heat from the ground and, on its return, the now warmer fluid passes through the heat pump which uses electricity to extract the heat from the fluid. The re-chilled fluid is sent back through the ground thus continuing the cycle. The heat extracted and that generated by the heat pump appliance as a byproduct is used to heat the house. The addition of the ground heating loop in the energy equation means that more heat is generated than if electricity alone had been used directly for heating. Switching the direction of heat flow, the same system can be used to circulate the cooled water through the house for cooling in the summer months. The heat is exhausted to the same relatively cool soil (or groundwater) rather than delivering it to the hot outside air as an air conditioner does. As a result, the heat is pumped over a greater temperature difference and this leads to higher efficiency and lower energy use.[9]

This technology makes geothermal heating economically viable in any geographical location. In 2004, an estimated million geothermal heat pumps with a total capacity of 15 GW extracted 88 PJ of geothermal energy for space heating. Global geothermal heat pump capacity is growing by 10% annually.[1]

History

The oldest known pool fed by a hot spring, built in the Qin dynasty in the 3rd century BC.

Hot springs have been used for bathing at least since paleolithic times. The oldest known spa is a stone pool on Lisan mountain built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. In the first century AD, Romans conquered Aquae Sulis and used the hot springs there to feed public baths and underfloor heating.[10] The admission fees for these baths probably represents the first commercial use of geothermal power. The world's oldest geothermal district heating system in Chaudes-Aigues, France, has been operating since the 14th century.[3] The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy.

In 1892, America's first district heating system in Boise, Idaho was powered directly by geothermal energy, and was soon copied in Klamath Falls, Oregon in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland at about the same time.[11] Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from the geysers began to be used to heat homes in Iceland in 1943.

At this point, the heat pump had long ago been invented by Lord Kelvin in 1852, and the idea of using it to draw heat from the ground had been patented in Switzerland in 1912.[12] But it was not until 1940's that the idea was successfully implemented. The first commercial geothermal heat pump was designed by J.D. Krocker to heat the Commonwealth Building (Portland, Oregon) in 1946, and Professor Carl Nielsen of Ohio State University built the first residential heat pump two years later.[10] The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The development of polybutylene pipe in 1979 greatly augmented its economic viability.[13] As of 2004, there are over a million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.[14] Each year, about 80,000 units are installed in the USA and 27,000 in Sweden.[14]

Economics

Geothermal energy is a type of renewable energy that encourages conservation of natural resources. According to the U.S. Environmental Protection Agency, geo-exchange systems save homeowners 30-70 percent in heating costs, and 20-50 percent in cooling costs, compared to conventional systems.[15] Geo-exchange systems also save money because they require much less maintenance. In addition to being highly reliable they are built to last for decades and can add considerably the resale value of a structure.

Some utilities, such as Kansas City Power and Light, offer special, lower winter rates for geothermal customers, offering even more savings.[9]

Subsidence

In geothermal heating projects the underground is penetrated by trenches or drillholes. Large projects may cause problems if the geology of the area is poorly understood as with all underground work. In connection with a geothermal heating project for the historical city hall of Staufen im Breisgau, Germany, subsidence of the ground up to eight millimeters has occurred while other areas have been uplifted by a few millimeters. A relation to the geothermal wells is suspected. The subsidence has caused considerable damage to buildings in the city center.[16]

References

  1. ^ a b c Fridleifsson,, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11). O. Hohmeyer and T. Trittin (ed.). "The possible role and contribution of geothermal energy to the mitigation of climate change" (pdf). Luebeck, Germany: 59–80. Retrieved 2009-04-06. {{cite journal}}: Cite journal requires |journal= (help); Unknown parameter |conference= ignored (help)CS1 maint: extra punctuation (link)
  2. ^ Heat Pumps, Energy Management and Conservation Handbook, 2008. pp. 9–3.
  3. ^ a b Lund, John W. (June 2007), "Characteristics, Development and utilization of geothermal resources" (PDF), Geo-Heat Centre Quarterly Bulletin, vol. 28, no. 2, Klamath Falls, Oregon: Oregon Institute of Technology, pp. pp 1-9, ISSN 0276-1084, retrieved 2009-04-16 {{citation}}: |pages= has extra text (help)
  4. ^ University of Rochester - History of the utilization of geothermal sources of energy in Iceland, http://www.energy.rochester.edu/is/reyk/history.htm.
  5. ^ District Heating Systems in Idaho, http://www.idwr.state.id.us/energy/alternative_fuels/geothermal/detailed_district.htm.
  6. ^ Klamath Falls Geothermal District Heating Systems
  7. ^ a b "Geothermal Basics Overview". Office of Energy Efficiency and Renewable Energy. Retrieved 2008-10-01.
  8. ^ What is Geothermal?
  9. ^ a b c Goswami, Yogi D., Kreith, Frank, Johnson, Katherine (2008), p. 9-4. Cite error: The named reference "heatpumps9-4" was defined multiple times with different content (see the help page).
  10. ^ a b "A History of Geothermal Energy in the United States". U.S. Department of Energy, Geothermal Technologies Program. Retrieved 2007-09-10.
  11. ^ Geysers and Energy american.edu Retrieved on 2008-04-12
  12. ^ [A History of Geothermal]
  13. ^ Bloomquist, R. Gordon (December 1999), "Geothermal Heat Pumps, Four Plus Decades of Experience" (PDF), Geo-Heat Centre Quarterly Bulletin, vol. 20, no. 4, Klamath Falls, Oregon: Oregon Institute of Technology, pp. pp 13-18, ISSN 0276-1084, retrieved 2009-03-21 {{citation}}: |pages= has extra text (help)
  14. ^ a b Lund, J.; Sanner, B.; Rybach, L.; Curtis, R.; Hellström, G. (September 2004), "Geothermal (Ground Source) Heat Pumps, A World Overview" (PDF), Geo-Heat Centre Quarterly Bulletin, vol. 25, no. 3, Klamath Falls, Oregon: Oregon Institute of Technology, pp. pp. 1-10, ISSN 0276-1084, retrieved 2009-03-21 {{citation}}: |pages= has extra text (help)
  15. ^ "Geothermal Heat Pump Consortium, Inc". Retrieved 2008-04-27.
  16. ^ Waffel, Mark (March 19, 2008). "Buildings Crack Up as Black Forest Town Subsides". Spiegel Online International. Der Spiegel. Retrieved 2009-02-24.

See also

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