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Geothermal heating

(Redirected fromGeothermal heat)
This article is about direct uses of geothermal heat. For electricity generation, seegeothermal power.For 'geothermal' heat pump, seeground source heat pump.

Geothermal heatingis the direct use ofgeothermal energyfor some 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 270PJof geothermal heating in 2004. As of 2007, 28GWof geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.[1]Thermal efficiencyis high since no energy conversion is needed, butcapacity factorstend to be low (around 20%) since the heat is mostly needed in the winter.

Geothermal heating

Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, fromradioactive decayof minerals, and fromsolar energyabsorbed at the surface.[2]Most high temperature geothermal heat is harvested in regions close totectonic plate boundarieswhere 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. Below 6 metres (20 ft), the undisturbed ground temperature is consistently at the mean annual air temperature,[3]and this heat can be extracted with aground source heat pump.

Applications

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Top countries using the most geothermal heating in 2005[4]
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
Direct use of geothermal heat by category in 2015 as adapted from John W. Lund[5]
Category GWh/year
Geothermal heat pumps 90,293
Bathing and swimming 33,164
Space heating 24,508
Greenhouse heating 7,407
Aquaculture pond heating 3,322
Industrial uses 2,904
Cooling/snow melting 722
Agriculture drying 564
Others 403
Total 163,287

There are a wide variety of applications for cheap geothermal heat including heating of houses, greenhouses, bathing and swimming or industrial uses. Most applications use geothermal in the form of hot fluids between 50 °C (122 °F) and 150 °C (302 °F). The suitable temperature varies for the different applications. For direct use of geothermal heat, the temperature range for the agricultural sector lies between 25 °C (77 °F) and 90 °C (194 °F), for space heating lies between 50 °C (122 °F) to 100 °C (212 °F).[4]Heat pipes extend the temperature range down to 5 °C (41 °F) as they extract and "amplify" the heat. Geothermal heat exceeding 150 °C (302 °F) is typically used forgeothermal powergeneration.[6]

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 ofReykjavíkandAkureyripipe hot water from geothermal plants under roads and pavements to melt snow.Geothermal desalinationhas been demonstrated.

Geothermal systems tend to benefit fromeconomies 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 asReykjavík,Iceland;[7]Boise,Idaho;[8]andKlamath Falls,Oregon;[9]is known asdistrict heating.[10]

In Europe alone 280 geothermal district heating plants were in operation in 2016 according to the European Geothermal Energy Council (EGEC) with a total capacity of approximately 4.9 GWth.[11]

Extraction

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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.[12]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 naturalhot springsand piped directly intoradiatorsorheat exchangers.Alternatively, the heat may come fromwaste heatsupplied byco-generationfrom 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 throughearth tubesordownhole heat exchangerswhich act as heat exchangers with the ground.

Steam under pressurefrom deep geothermal resources is also used to generate electricity from geothermal power. TheIceland Deep Drilling Projectstruck a pocket of magma at 2,100m. A cemented steelcase was constructed in the hole with a perforation at the bottom close to the magma. The high temperatures and pressure of the magma steam were used to generate 36MW of electricity, making IDDP-1 the world's first magma-enhanced geothermal system.[13]

In areas where the shallow ground is too cold to provide comfort directly, it is still warmer than the winter air. Thethermal inertiaof 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.[10]Geothermal heat pumps are economically viable essentially anywhere in the world.

In theory, geothermal energy (usually cooling) can also be extracted from existing infrastructure, such as municipal water pipes.[14]

Ground-source heat pumps

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Main article:Geothermal heat pump

In regions without any high temperature geothermal resources, aground-source heat pump(GSHP) can provide space heating and space cooling. Like a refrigerator or air conditioner, these systems use a heat pump to force the transfer of heat from the ground to the building. 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 or 50–54 °F) as a source of heat, thus taking advantage of its seasonally moderate temperatures.[15]In contrast, anair source heat pumpdraws heat from the air (colder outside air) and thus requires more energy.

GSHPs circulate a carrier fluid (usually a mixture of water and small amounts of antifreeze) through closed pipe loops buried in the ground. Single-home systems can be "vertical loop field" systems with bore holes 50–400 feet (15–120 m) deep or,[16]if adequate land is available for extensive trenches, a "horizontal loop field" is installed approximately six feet subsurface. As the fluid circulates underground it absorbs heat from the ground and, on its return, the warmed fluid passes through the heat pump which uses electricity to extract heat from the fluid. The re-chilled fluid is sent back into 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 significantly more heat can be transferred to a building 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 relatively cooler ground (or groundwater) rather than delivering it to the hot outside air as an air conditioner does. As a result, the heat is pumped across a larger temperature difference and this leads to higher efficiency and lower energy use.[15]

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

History

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

Hot springshave been used for bathing at least since Paleolithic times.[17]The oldest known spa is a stone pool onChina'sMount Libuilt in theQin dynastyin the 3rd century BC, at the same site where theHuaqing Chipalace was later built. Geothermal energy supplied channeleddistrict heatingfor baths and houses inPompeiiaround 0 AD.[18]In the first century AD, Romans conqueredAquae Sulisin England and used the hot springs there to feedpublic bathsandunderfloor heating.[19]The admission fees for these baths probably represents the first commercial use of geothermal power. A 1,000-year-old hot tub has been located inIceland,where it was built by one of the island's original settlers.[20]The world's oldest working geothermal district heating system inChaudes-Aigues,France, has been operating since the 14th century.[4]The earliest industrial exploitation began in 1827 with the use of geyser steam to extractboric acidfrom volcanic mud inLarderello,Italy.

In 1892, America's first district heating system inBoise, Idaho,was powered directly by geothermal energy, and was soon copied inKlamath Falls, Oregonin 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland and Tuscany at about the same time.[21]Charlie Lieb developed the firstdownhole heat exchangerin 1930 to heat his house. Steam and hot water from the geysers began to be used to heat homes in Iceland in 1943.

By this time,Lord Kelvinhad already invented theheat pumpin 1852, andHeinrich Zoellyhad patented the idea of using it to draw heat from the ground in 1912.[22]But it was not until the late 1940s that the geothermal heat pump was successfully implemented. The earliest one was probably Robert C. Webber's home-made 2.2 kW direct-exchange system, but sources disagree as to the exact timeline of his invention.[22]J. Donald Kroeker designed the first commercial geothermal heat pump to heat theCommonwealth Building (Portland, Oregon)and demonstrated it in 1946.[23][24]Professor Carl Nielsen ofOhio State Universitybuilt the first residential open loop version in his home in 1948.[25]The technology became popular in Sweden as a result of the1973 oil crisis,and has been growing slowly in worldwide acceptance since then. The 1979 development ofpolybutylenepipe greatly augmented the heat pump's economic viability.[23]Since 2000, a compelling body of research has been dedicated to numerically evidence the advantages and efficiency of using CO2, alternative to water, as heat transmission fluid for geothermal energy recovery from enhanced geothermal systems (EGS) where the permeability of the underground source is enhanced by hydrofracturing.[26][27]As of 2004, there are over one million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.[28]Each year, about 80,000 units are installed in the US and 27,000 in Sweden.[28]

Economics

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Geothermal drill machine

Geothermal energy is a type ofrenewable energythat encourages conservation of natural resources. According to the USEnvironmental Protection Agency,geo-exchangesystems save homeowners 30–70 percent in heating costs, and 20–50 percent in cooling costs, compared to conventional systems.[29]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.

Some utilities, such asKansas City Power and Light,offer special, lower winter rates for geothermal customers, offering even more savings.[15]

Geothermal drilling risks

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Cracks at the historic Town Hall ofStaufen im Breisgaupresumed due to damage from geothermal drilling

In geothermal heating projects the underground is penetrated by trenches or drillholes. As with all underground work, projects may cause problems if the geology of the area is poorly understood.

In the spring of 2007 an exploratory geothermal drilling operation was conducted to provide geothermal heat to the town hall ofStaufen im Breisgau.After initially sinking a few millimeters, a process calledsubsidence,[30]the city center has started to rise gradually[31]causing considerable damage to buildings in the city center, affecting numerous historic houses including the town hall. It is hypothesized that the drilling perforated ananhydritelayer bringing high-pressuregroundwaterto come into contact with the anhydrite, which then began to expand. Currently no end to the rising process is in sight.[32][33][34]Data from theTerraSAR-Xradar satellite before and after the changes confirmed the localised nature of the situation:

A geochemical process calledanhydriteswelling has been confirmed as the cause of theseuplifts.This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) intogypsum(hydrous calcium sulphate). A pre-condition for this transformation is that the anhydrite is in contact with water, which is then stored in its crystalline structure.[35] There are other sources of potential risks, i.e.: cave enlargement or worsening of stability conditions, quality or quantity degradation of groundwater resources, Specific hazard worsening in the case of landslide-prone areas, worsening of rocky mechanical characteristics, soil and water pollution (i.e. due to antifreeze additives or polluting constructive and boring material).[36]The design defined on the base of site-specific geological, hydrogeological and environmental knowledge prevent all these potential risks.

See also

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References

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  1. ^abcFridleifsson, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11)."The possible role and contribution of geothermal energy to the mitigation of climate change"(PDF).In O. Hohmeyer; T. Trittin (eds.).Proceedings of the IPCC Scoping Meeting on Renewable Energy Sources.Luebeck, Germany. pp. 59–80. Archived fromthe original(PDF)on 2017-08-08.
  2. ^Heat Pumps, Energy Management and Conservation Handbook, 2008,pp. 9–3
  3. ^Mean Annual Air Temperature
  4. ^abcLund, 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. 1–9,ISSN0276-1084,archived fromthe original(PDF)on 2010-06-17,retrieved2009-04-16
  5. ^Lund, John W. (2015-06-05)."Geothermal Resources Worldwide, Direct Heat Utilization of".Encyclopedia of Sustainability and Technology:1–29.doi:10.1007/978-1-4939-2493-6_305-3.ISBN978-1-4939-2493-6.
  6. ^Hanania, Jordan; Sheardown, Ashley; Stenhouse, Kailyn; Donev, Jason."Geothermal district heating".Energy education by Prof. Jason Donev and students, University of Calgary.Retrieved2020-09-18.
  7. ^"History of the utilization of geothermal sources of energy in Iceland".University of Rochester.Archived fromthe originalon 2012-02-06.
  8. ^"District Heating Systems in Idaho".Idaho Department of Water Resources.Archived fromthe originalon 2007-01-21.
  9. ^Brown, Brian.Klamath Falls Geothermal District Heating SystemsArchived2008-01-19 at theWayback Machine
  10. ^ab"Geothermal Basics Overview".Office of Energy Efficiency and Renewable Energy. Archived fromthe originalon 2008-10-04.Retrieved2008-10-01.
  11. ^"EGEC Geothermal Market Report 2016 Key Findings (Sixth Edition, May 2017)"(PDF).egec.org.EGEC - European Geothermal Energy Council. 2017-12-13. p. 9.
  12. ^What is Geothermal?ArchivedOctober 5, 2013, at theWayback Machine
  13. ^Wilfred Allan Elders, Guðmundur Ómar Friðleifsson and Bjarni Pálsson (2014).Geothermics Magazine, Vol. 49 (January 2014).Elsevier Ltd.
  14. ^Tadayon, Saied; Tadayon, Bijan; Martin, David (2012-10-11)."Patent US20120255706 - Heat Exchange Using Underground Water System".
  15. ^abcGoswami, Yogi D.,Kreith, Frank,Johnson, Katherine (2008), p. 9-4.
  16. ^"Geothermal Heating and Cooling Systems".Well Management.Minnesota Department of Health.Archived fromthe originalon 2014-02-03.Retrieved2012-08-25.
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  19. ^"A History of Geothermal Energy in the United States".US Department of Energy, Geothermal Technologies Program. Archived fromthe originalon 2007-09-04.Retrieved2007-09-10.
  20. ^"One Hot Island: Iceland's Renewable Geothermal Power".Scientific American.
  21. ^Dickson, Mary H.; Fanelli, Mario (February 2004)."What is Geothermal Energy?".Pisa, Italy: Istituto di Geoscienze e Georisorse. Archived fromthe originalon 2009-10-09.Retrieved2009-10-13.
  22. ^abZogg, M. (20–22 May 2008).History of Heat Pumps: Swiss Contributions and International Milestones(PDF).Zürich, Switzerland: 9th International IEA Heat Pump Conference.
  23. ^abBloomquist, R. Gordon (December 1999)."Geothermal Heat Pumps, Four Plus Decades of Experience"(PDF).Geo-Heat Centre Quarterly Bulletin.20(4): 13–18.ISSN0276-1084.Archived fromthe original(PDF)on 2012-10-31.Retrieved2009-03-21.
  24. ^Kroeker, J. Donald; Chewning, Ray C. (February 1948). "A Heat Pump in an Office Building".ASHVE Transactions.54:221–238.
  25. ^Gannon, Robert (February 1978)."Ground-Water Heat Pumps – Home Heating and Cooling from Your Own Well".Popular Science.212(2): 78–82.ISSN0161-7370.Retrieved2009-11-01.
  26. ^Brown, D.W. (January 2000)."A Hot Dry Rock Geothermal Energy Concept Utilizing Supercritical CO2 Instead of Water"(PDF).Proceedings of Twenty-Fifth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 24-26, 2000:233–238.
  27. ^Atrens, A.D.; Gurgenci, H.; Rudolph, V. (2009). "CO2 Thermosiphon for Competitive Geothermal Power Generation".Energy Fuels.23(1): 553–557.doi:10.1021/ef800601z.
  28. ^abLund, 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.25(3): 1–10.ISSN0276-1084.Archived fromthe original(PDF)on 2014-02-01.Retrieved2009-03-21.
  29. ^"Geothermal Heat Pump Consortium, Inc".Retrieved2008-04-27.
  30. ^The Telegraph: Geothermal probe sinks German city (March 31, 2008)
  31. ^Lubbadeh, Jens (15 November 2008)."Eine Stadt zerreißt"[A town rips up].Spiegel Wissenschaft(in German).Partial translation.
  32. ^Sass, Ingo; Burbaum, Ulrich (2010)."Damage to the historic town of Staufen (Germany) caused by geothermal drillings through anhydrite-bearing formations".Acta Carsologica.39(2): 233.doi:10.3986/ac.v39i2.96.
  33. ^Butscher, Christoph; Huggenberger, Peter; Auckenthaler, Adrian; Bänninger, Dominik (2010)."Risikoorientierte Bewilligung von Erdwärmesonden"(PDF).Grundwasser.16(1): 13–24.Bibcode:2011Grund..16...13B.doi:10.1007/s00767-010-0154-5.S2CID129598890.
  34. ^Goldscheider, Nico; Bechtel, Timothy D. (2009)."Editors' message: The housing crisis from underground—damage to a historic town by geothermal drillings through anhydrite, Staufen, Germany".Hydrogeology Journal.17(3): 491–493.Bibcode:2009HydJ...17..491G.doi:10.1007/s10040-009-0458-7.
  35. ^"TerraSAR-X Image Of The Month: Ground Uplift Under Staufen's Old Town".spacemart.SpaceDaily. 2009-10-22.Retrieved2009-10-23.
  36. ^De Giorgio, Giorgio; Chieco, Michele; Limoni, Pier Paolo; Zuffianò, Livia Emanuela; Dragone, Vittoria; Romanazzi, Annarita; Pagliarulo, Rossella; Musicco, Giuseppe; Polemio, Maurizio (2020-10-19)."Improving Regulation and the Role of Natural Risk Knowledge to Promote Sustainable Low Enthalpy Geothermal Energy Utilization".Water.12(10): 2925.doi:10.3390/w12102925.ISSN2073-4441.
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