View source for Physics:Geothermal heating

{{short description|Use of geothermal energy for heating}}
{{About|direct uses of geothermal heat|electricity generation|geothermal power|'geothermal' heat pump|
ground source heat pump}}

[[File:Geothermal heating.jpg|thumb|upright=1.7|Geothermal heating]]
{{Sustainable energy}}

'''Geothermal heating''' is the direct use of [[Earth:Geothermal energy|geothermal energy]] for 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 270 PJ of geothermal heating in 2004. As of 2007, 28 [[Gigawatt|GW]] of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.<ref name="IPCC" /> [[Physics:Thermal efficiency|Thermal efficiency]] is high since no energy conversion is needed, but [[Engineering:Capacity factor|capacity factor]]s tend to be low (around 20%) since the heat is mostly needed in the winter.

[[Earth:Geothermal energy|Geothermal energy]] originates from the heat retained within the Earth since the original formation of the planet, from [[Physics:Radioactive decay|radioactive decay]] of minerals, and from [[Physics:Solar energy|solar energy]] absorbed at the surface.<ref name="heatpumps9-3">{{Citation |title=Heat Pumps, Energy Management and Conservation Handbook, 2008|pages=9–3}}</ref> 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. Below {{convert|6|m}}, the undisturbed ground temperature is consistently at the mean annual air temperature,<ref>[http://www.icax.co.uk/Mean_Annual_Air_Temperature.html Mean Annual Air Temperature]</ref> and this heat can be extracted with a [[Physics:Ground source heat pump|ground source heat pump]].

== Applications ==

{| class="wikitable sortable" style="text-align:right;"
|+ Top countries using the most geothermal heating in 2005<ref name="utilization">{{Citation | last =Lund | first =John W. | date =June 2007 | title =Characteristics, Development and utilization of geothermal resources | periodical =Geo-Heat Centre Quarterly Bulletin | location =Klamath Falls, Oregon | publisher =Oregon Institute of Technology | volume =28 | issue =2 | pages =1–9 | url =http://geoheat.oit.edu/bulletin/bull28-2/art1.pdf | issn =0276-1084 | access-date =2009-04-16 | archive-date =2010-06-17 | archive-url =https://web.archive.org/web/20100617215822/http://geoheat.oit.edu/bulletin/bull28-2/art1.pdf | url-status =dead}}</ref>
|-
! scope="col"| Country
! scope="col"| Production<br />PJ/yr
! scope="col"| Capacity<br />GW
! scope="col"| Capacity<br />factor
! scope="col"| Dominant<br />applications
|-
! scope="row"| China
| 45.38
| 3.69
| 39%
| style="text-align:left;"| bathing
|-
! scope="row"| Sweden
| 43.2
| 4.2
| 33%
| style="text-align:left;"| heat pumps
|-
! scope="row"| USA
| 31.24
| 7.82
| 13%
| style="text-align:left;"| heat pumps
|-
! scope="row"| Turkey
| 24.84
| 1.5
| 53%
| style="text-align:left;"| [[Physics:District heating|district heating]]
|-
! scope="row"| Iceland
| 24.5
| 1.84
| 42%
| style="text-align:left;"| [[Physics:District heating|district heating]]
|-
! scope="row"| Japan
| 10.3
| 0.82
| 40%
| style="text-align:left;"| bathing (onsens)
|-
! scope="row"| Hungary
| 7.94
| 0.69
| 36%
| style="text-align:left;"| spas/greenhouses
|-
! scope="row"| Italy
| 7.55
| 0.61
| 39%
| style="text-align:left;"| spas/space heating
|-
! scope="row"| New Zealand
| 7.09
| 0.31
| 73%
| style="text-align:left;"| industrial uses
|-
! scope="row"| 63 others
| 71
| 6.8
|
|
|-
! scope="row" style="font-weight:bold;"| Total 
| style="font-weight:bold;"| 273
| style="font-weight:bold;"| 28
| style="font-weight:bold;"| 31%
| style="font-weight:bold; text-align:left;"| space heating
|}
{| class="wikitable" style="text-align:right;"
|+Direct use of geothermal heat by category in 2015 as adapted from John W. Lund <ref>{{Cite journal|last=Lund|first=John W.|date=2015-06-05 |title=Geothermal Resources Worldwide, Direct Heat Utilization of|url=https://link.springer.com/referenceworkentry/10.1007%2F978-1-4939-2493-6_305-3 |journal=Encyclopedia of Sustainability and Technology |pages= 1–29|doi=10.1007/978-1-4939-2493-6_305-3|isbn=978-1-4939-2493-6}}</ref>
|-
! scope="col"| Category
! scope="col"| GWh/year
|-
! scope="row"| Geothermal heat pumps
| 90,293
|-
! scope="row"| Bathing and swimming
| 33,164
|-
! scope="row"| Space heating
| 24,508
|-
! scope="row"| Greenhouse heating
| 7,407
|-
! scope="row"| Aquaculture pond heating
| 3,322
|-
! scope="row"| Industrial uses
| 2,904
|-
! scope="row"| Cooling/snow melting
| 722
|-
! scope="row"| Agriculture drying
| 564
|-
! scope="row"| Others
| 403
|-
! scope="row" style="font-weight:bold;"| Total
| style="font-weight:bold;"| 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&nbsp;°C (122&nbsp;°F) and 150&nbsp;°C (302&nbsp;°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&nbsp;°C (77&nbsp;°F) and 90&nbsp;°C (194&nbsp;°F), for space heating lies between 50&nbsp;°C (122&nbsp;°F) to 100&nbsp;°C (212&nbsp;°F).<ref name="utilization" /> Heat pipes extend the temperature range down to 5&nbsp;°C (41&nbsp;°F) as they extract and "amplify" the heat. Geothermal heat exceeding 150&nbsp;°C (302&nbsp;°F) is typically used for [[Earth:Geothermal power|geothermal power]] generation.<ref>{{cite web|last1=Hanania |first1=Jordan |last2=Sheardown |first2=Ashley |last3=Stenhouse |first3=Kailyn |last4=Donev |first4=Jason |title=Geothermal district heating|url=https://energyeducation.ca/encyclopedia/Geothermal_district_heating#cite_note-ot-4|access-date=2020-09-18 |website=Energy education by Prof. Jason Donev and students, University of Calgary}}</ref>

In 2004 more than half of direct geothermal heat was used for space heating, and a third was used for spas.<ref name="IPCC">{{cite conference|first1=Ingvar B. |last1=Fridleifsson |first2=Ruggero |last2=Bertani |first3=Ernst |last3=Huenges |first4=John W. |last4=Lund |first5=Arni |last5=Ragnarsson |first6=Ladislaus |last6=Rybach |date=2008-02-11 |title=The possible role and contribution of geothermal energy to the mitigation of climate change|book-title=Proceedings of the IPCC Scoping Meeting on Renewable Energy Sources |editor1=O. Hohmeyer |editor2=T. Trittin |location=Luebeck, Germany |pages=59–80 |url=http://grsj.gr.jp/iga/iga-files/Fridleifsson_et_al_IPCC_Geothermal_paper_2008.pdf |archive-url=https://web.archive.org/web/20170808204637/http://grsj.gr.jp/iga/iga-files/Fridleifsson_et_al_IPCC_Geothermal_paper_2008.pdf |archive-date=2017-08-08}}</ref> The remainder was used for a variety of industrial processes, desalination, domestic hot water, and agricultural applications. The cities of [[Place:Reykjavík|Reykjavík]] and Akureyri pipe hot water from geothermal plants under roads and pavements to melt snow. [[Earth:Geothermal desalination|Geothermal desalination]] has been demonstrated.

Geothermal systems tend to benefit from [[Finance:Economies of scale|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 [[Place:Reykjavík|Reykjavík]], Iceland;<ref>{{cite web|title=History of the utilization of geothermal sources of energy in Iceland |url=http://www.energy.rochester.edu/is/reyk/history.htm |publisher=[[Organization:University of Rochester|University of Rochester]] |url-status=dead |archive-url=https://web.archive.org/web/20120206010822/http://www.energy.rochester.edu/is/reyk/history.htm |archive-date= 2012-02-06}}</ref> Boise, Idaho;<ref>{{cite web|title=District Heating Systems in Idaho |url=http://www.idwr.state.id.us/energy/alternative_fuels/geothermal/detailed_district.htm |website=Idaho Department of Water Resources |url-status=dead |archive-url=https://web.archive.org/web/20070121104017/http://www.idwr.state.id.us/energy/alternative_fuels/geothermal/detailed_district.htm |archive-date=2007-01-21}}</ref> and Klamath Falls, Oregon;<ref>Brown, Brian.[http://www.geothermie.de/egec-geothernet/ci_prof/america/usa/klamath_falls_geothermal_distric.htm Klamath Falls Geothermal District Heating Systems] {{webarchive|url=https://web.archive.org/web/20080119025405/http://www.geothermie.de/egec-geothernet/ci_prof/america/usa/klamath_falls_geothermal_distric.htm |date=2008-01-19}}</ref> is known as [[Physics:District heating|district heating]].<ref name="EERE1" />

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.<ref>{{cite web |title=EGEC Geothermal Market Report 2016 Key Findings (Sixth Edition, May 2017) |url=https://www.egec.org/wp-content/uploads/2017/05/EGEC-Geothermal-Market-Report_KF_final_web.pdf |website=www.egec.org |publisher=EGEC - European Geothermal Energy Council |page=9 |date=2017-12-13}}</ref>

== Extraction ==
{{Main|Engineering:Ground-coupled heat exchanger}}

Some parts of the world, including substantial portions of the western USA, are underlain by relatively shallow geothermal resources.<ref>[http://www.geothermal.org/what.html What is Geothermal?] {{webarchive |url=https://web.archive.org/web/20131005004048/http://www.geothermal.org/what.html |date=October 5, 2013}}</ref> 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 [[Physics:Heat exchanger|heat exchanger]]s. Alternatively, the heat may come from [[Astronomy:Waste heat|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 [[Engineering:Downhole heat exchanger|downhole heat exchanger]]s which act as heat exchangers with the ground.

[[Physics:Supercritical fluid|Steam under pressure]] from deep geothermal resources is also used to generate electricity from geothermal power. The [[Engineering:Iceland Deep Drilling Project|Iceland Deep Drilling Project]] struck 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.<ref name="Geothermics Magazine, Vol. 49 (January 2014)">{{cite book |title=Geothermics Magazine, Vol. 49 (January 2014)|author=Wilfred Allan Elders, Guðmundur Ómar Friðleifsson and Bjarni Pálsson|url=http://www.sciencedirect.com/science/journal/03756505/49/supp/C |year=2014 |publisher=Elsevier Ltd.}}</ref>

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<!--article is about geothermal, not 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.<ref name="EERE1">{{cite web |url=http://www1.eere.energy.gov/geothermal/geothermal_basics.html |title=Geothermal Basics Overview |publisher=Office of Energy Efficiency and Renewable Energy |access-date=2008-10-01 |url-status=dead |archive-url=https://web.archive.org/web/20081004020606/http://www1.eere.energy.gov/geothermal/geothermal_basics.html |archive-date=2008-10-04}}</ref> 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.<ref name="Google Books 2012">{{cite web | last1=Tadayon | first1=Saied | last2=Tadayon | first2=Bijan | last3=Martin | first3=David | title=Patent US20120255706 - Heat Exchange Using Underground Water System | date=2012-10-11 | url=https://www.google.com/patents/US20120255706}}</ref>

== Ground-source heat pumps ==
{{Main|Physics:Geothermal heat pump}}
In regions without any high temperature geothermal resources, a [[Physics:Geothermal heat pump|ground-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 {{convert|10|-|12|C|F|disp=or}}) as a source of heat, thus taking advantage of its seasonally moderate temperatures.<ref name="heatpumps9-4">Goswami, Yogi D., Kreith, Frank, Johnson, Katherine (2008), p. 9-4.</ref> In contrast, an [[Physics:Air source heat pump|air source heat pump]] draws 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 {{convert|50|-|400|ft|m|sigfig=2}} deep or,<ref>{{Cite web |url=http://www.health.state.mn.us/divs/eh/wells/geothermal.html |department=Well Management |title=Geothermal Heating and Cooling Systems |website=Minnesota Department of Health |access-date=2012-08-25 |archive-url=https://web.archive.org/web/20140203060622/http://www.health.state.mn.us/divs/eh/wells/geothermal.html |archive-date=2014-02-03 |url-status=dead}}</ref> 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.<ref name="heatpumps9-4"/>

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.<ref name="IPCC" />

== History ==
[[Image:Oldest geothermal.jpg|thumb|right|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.<ref>{{Cite journal | last =Cataldi | first =Raffaele | date =August 1993 | title =Review of historiographic aspects of geothermal energy in the Mediterranean and Mesoamerican areas prior to the Modern Age | journal =Geo-Heat Centre Quarterly Bulletin | volume =15 | issue =1 | pages =13–16 | url =http://geoheat.oit.edu/pdf/bulletin/bi046.pdf | issn =0276-1084 | access-date =2009-11-01 | archive-date =2010-06-18 | archive-url =https://web.archive.org/web/20100618001239/http://geoheat.oit.edu/pdf/bulletin/bi046.pdf | url-status =dead}}</ref> The oldest known spa is a stone pool on {{wipe|China}}'s Mount Li built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. Geothermal energy supplied channeled [[Physics:District heating|district heating]] for baths and houses in Pompeii around 0 AD.<ref>{{cite conference |first=R. Gordon |last=Bloomquist |title=Geothermal District Energy System Analysis, Design, and Development |publisher=International Geothermal Association |conference=International Summer School |year=2001 |access-date=November 28, 2015 |quote=During Roman times, warm water was circulated through open trenches to provide heating for buildings and baths in Pompeii. |url=http://www.geothermal-energy.org/pdf/IGAstandard/ISS/2001Romania/bloomquist_dh.pdf |page=213(1)}}
*Alternate copy: {{cite web |title=Geothermal District Energy System Analysis, Design, and Development |type=Abstract |website=Stanford University |url=https://pangea.stanford.edu/ERE/db/IGAstandard/record_detail.php?id=5313}}</ref> In the first century AD, Romans conquered Aquae Sulis in England and used the hot springs there to feed public baths and [[Engineering:Hypocaust|underfloor heating]].<ref name="eere">{{cite web |url=http://www1.eere.energy.gov/geothermal/history.html |title=A History of Geothermal Energy in the United States |access-date=2007-09-10 |publisher=US Department of Energy, Geothermal Technologies Program |url-status=dead |archive-url=https://web.archive.org/web/20070904230627/http://www1.eere.energy.gov/geothermal/history.html |archive-date=2007-09-04}}</ref> 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 in Iceland, where it was built by one of the island's original settlers.<ref>{{Cite web|url=http://www.scientificamerican.com/article.cfm?id=iceland-geothermal-power|title = One Hot Island: Iceland's Renewable Geothermal Power| website=Scientific American}}</ref> The world's oldest working geothermal district heating system in Chaudes-Aigues, France, has been operating since the 14th century.<ref name="utilization" /> The earliest industrial exploitation began in 1827 with the use of geyser steam to extract [[Chemistry:Boric acid|boric acid]] from volcanic mud in [[Earth:Larderello|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 and Tuscany at about the same time.<ref name="Dickson">{{Cite web|last1=Dickson |first1=Mary H. |last2=Fanelli |first2=Mario |date=February 2004 |title=What is Geothermal Energy? |publisher=Istituto di Geoscienze e Georisorse |location=Pisa, Italy |url=http://iga.igg.cnr.it/index.php |access-date=2009-10-13 |url-status=dead |archive-url=https://web.archive.org/web/20091009080651/http://iga.igg.cnr.it/index.php |archive-date=2009-10-09}}</ref> Charlie Lieb developed the first [[Engineering:Downhole heat exchanger|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.

By this time, [[Biography:Lord Kelvin|Lord Kelvin]] had already invented the [[Physics:Heat pump|heat pump]] in 1852, and Heinrich Zoelly had patented the idea of using it to draw heat from the ground in 1912.<ref name="zogg">{{Cite conference | first = M. | last = Zogg | url = http://www.zogg-engineering.ch/Publi/IEA_HPC08_Zogg.pdf | title = History of Heat Pumps: Swiss Contributions and International Milestones | publisher = 9th International IEA Heat Pump Conference | date = 20–22 May 2008 | location = Zürich, Switzerland}}</ref> 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&nbsp;kW direct-exchange system, but sources disagree as to the exact timeline of his invention.<ref name="zogg" /> J. Donald Kroeker designed the first commercial geothermal heat pump to heat the Commonwealth Building (Portland, Oregon) and demonstrated it in 1946.<ref name="bloomquist" /><ref>{{Cite journal |last1 = Kroeker |first1 = J. Donald |last2 = Chewning |first2 = Ray C. |title = A Heat Pump in an Office Building |journal = ASHVE Transactions |volume = 54 |pages = 221–238 |date=February 1948}}</ref> Professor Carl Nielsen of [[Organization:Ohio State University|Ohio State University]] built the first residential open loop version in his home in 1948.<ref>{{Cite journal | last = Gannon |first = Robert |title = Ground-Water Heat Pumps – Home Heating and Cooling from Your Own Well | journal = Popular Science |pages = 78–82 |date = February 1978 |volume = 212 |issue = 2 |issn = 0161-7370 |url = https://books.google.com/books?id=qQAAAAAAMBAJ |access-date = 2009-11-01}}</ref> The technology became popular in Sweden as a result of the [[Finance:1973 oil crisis|1973 oil crisis]], and has been growing slowly in worldwide acceptance since then. The 1979 development of [[Chemistry:Polybutylene|polybutylene]] pipe greatly augmented the heat pump's economic viability.<ref name="bloomquist">{{Cite journal | last =Bloomquist | first =R. Gordon | date =December 1999 | title =Geothermal Heat Pumps, Four Plus Decades of Experience | journal =Geo-Heat Centre Quarterly Bulletin | volume =20 | issue =4 | pages =13–18 | url =http://geoheat.oit.edu/bulletin/bull20-4/art3.pdf | issn =0276-1084 | access-date =2009-03-21 | archive-date =2012-10-31 | archive-url =https://web.archive.org/web/20121031190555/http://geoheat.oit.edu/bulletin/bull20-4/art3.pdf | url-status =dead}}</ref> 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.<ref>{{Cite journal| last=Brown |first=D.W. |date=January 2000 |title=A Hot Dry Rock Geothermal Energy Concept Utilizing Supercritical CO2 Instead of Water |url=https://pangea.stanford.edu/ERE/pdf/IGAstandard/SGW/2000/Brown.pdf |journal=Proceedings of Twenty-Fifth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 24-26, 2000 |pages=233–238}}</ref><ref>{{Cite journal| last1=Atrens |first1=A.D. |last2=Gurgenci |first2=H. |last3=Rudolph |first3=V. |date=2009 |title=CO2 Thermosiphon for Competitive Geothermal Power Generation |url= |journal=Energy Fuels |volume=23 |issue=1 |pages=553–557 |doi=10.1021/ef800601z}}</ref> As of 2004, there are over one million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.<ref name="world">{{Cite journal | last1 =Lund | first1 =J. | last2 =Sanner | first2 =B. | last3 =Rybach | first3 =L. | last4 =Curtis | first4 =R. | last5 =Hellström | first5 =G. | date =September 2004 | title =Geothermal (Ground Source) Heat Pumps, A World Overview | journal =Geo-Heat Centre Quarterly Bulletin | volume =25 | issue =3 | pages =1–10 | url =http://geoheat.oit.edu/bulletin/bull25-3/art1.pdf | issn =0276-1084 | access-date =2009-03-21}}</ref> Each year, about 80,000 units are installed in the US and 27,000 in Sweden.<ref name="world" />

== Economics ==
[[Image:Geothermaldrilling.jpg|thumb|right|Geothermal drill machine]]

Geothermal energy is a type of [[Engineering:Renewable energy|renewable energy]] that encourages conservation of natural resources. According to the US 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.<ref>{{cite web |title=Geothermal Heat Pump Consortium, Inc. |url=http://geoexchange.us/about/how.htm |access-date=2008-04-27}}</ref> 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 as Kansas City Power and Light, offer special, lower winter rates for geothermal customers, offering even more savings.<ref name="heatpumps9-4"/>

==Geothermal drilling  risks==
[[File:Staufen.Cracks.jpg|thumb|Cracks at the historic Town Hall of Staufen im Breisgau presumed 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 of Staufen im Breisgau. After initially sinking a few millimeters, a process called [[Subsidence|subsidence]],<ref>[https://www.telegraph.co.uk/news/worldnews/1583323/Geothermal-probe-sinks-German-city.html The Telegraph: Geothermal probe sinks German city (March 31, 2008)]</ref>  the city center has started to rise gradually<ref>{{cite news |website=Spiegel Wissenschaft |url=https://www.spiegel.de/wissenschaft/natur/nach-erdwaerme-bohrung-eine-stadt-zerreisst-a-589944.html |title=Eine Stadt zerreißt |first=Jens |last=Lubbadeh |date=15 November 2008 |trans-title=A town rips up |language=de}} [http://backreaction.blogspot.com/2008/11/town-rips-up.html Partial translation].</ref> causing considerable damage to buildings in the city center, affecting numerous historic houses including the town hall.  It is hypothesized that the drilling perforated an [[Chemistry:Anhydrite|anhydrite]] layer bringing high-pressure [[Earth:Groundwater|groundwater]] to come into contact with the anhydrite, which then began to expand.  Currently no end to the rising process is in sight.<ref>{{cite journal |last1=Sass |first1=Ingo |title=Damage to the historic town of Staufen (Germany) caused by geothermal drillings through anhydrite-bearing formations |last2=Burbaum |first2=Ulrich |journal=Acta Carsologica |year=2010 |page=233 |volume=39 |issue=2 |doi=10.3986/ac.v39i2.96 |doi-access=free}}</ref><ref>{{cite journal | doi = 10.1007/s00767-010-0154-5 | last1 = Butscher | first1 = Christoph | last2 = Huggenberger | first2 = Peter | last3 = Auckenthaler | first3 = Adrian | last4 = Bänninger | first4 = Dominik | title = Risikoorientierte Bewilligung von Erdwärmesonden  | journal = Grundwasser | year = 2010 | volume = 16 | issue = 1 | pages = 13–24| bibcode = 2011Grund..16...13B | s2cid = 129598890 | url = http://doc.rero.ch/record/321504/files/767_2010_Article_154.pdf}}</ref><ref>{{cite journal | doi =10.1007/s10040-009-0458-7 | last1 =Goldscheider | first1 =Nico | last2 =Bechtel | first2 =Timothy D. | title =Editors' message: The housing crisis from underground—damage to a historic town by geothermal drillings through anhydrite, Staufen, Germany |  journal =Hydrogeology Journal | volume =17 | pages =491–493 | year =2009 | issue =3| bibcode =2009HydJ...17..491G | doi-access =free}}</ref> Data from the [[Engineering:TerraSAR-X|TerraSAR-X]] radar satellite before and after the changes confirmed the localised nature of the situation:

<blockquote>A geochemical process called [[Chemistry:Anhydrite|anhydrite]] swelling has been confirmed as the cause of these [[Earth:Tectonic uplift|uplift]]s. This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into [[Chemistry:Gypsum|gypsum]] (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.<ref>{{Cite web|url=http://www.spacemart.com/reports/TerraSAR_X_Image_Of_The_Month_Ground_Uplift_Under_Staufen_Old_Town_999.html |title=TerraSAR-X Image Of The Month: Ground Uplift Under Staufen's Old Town |website=www.spacemart.com |publisher=SpaceDaily |date=2009-10-22 |access-date=2009-10-23}}</ref>

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).<ref>{{Cite journal|last1=De Giorgio|first1=Giorgio|last2=Chieco|first2=Michele|last3=Limoni|first3=Pier Paolo|last4=Zuffianò|first4=Livia Emanuela|last5=Dragone|first5=Vittoria|last6=Romanazzi|first6=Annarita|last7=Pagliarulo|first7=Rossella|last8=Musicco|first8=Giuseppe|last9=Polemio|first9=Maurizio|date=2020-10-19|title=Improving Regulation and the Role of Natural Risk Knowledge to Promote Sustainable Low Enthalpy Geothermal Energy Utilization|journal=Water|language=en|volume=12|issue=10|pages=2925|doi=10.3390/w12102925|issn=2073-4441|doi-access=free}}</ref> The design defined on the base of site-specific geological, hydrogeological and environmental knowledge prevent all these potential risks.</blockquote>

== See also ==
* Annualized geothermal solar
* [[Physics:Carnot's theorem (thermodynamics)|Carnot's theorem (thermodynamics)]]
* [[Physics:District heating|District heating]]
* [[Geothermal gradient|Geothermal gradient deep in the earth]]
* [[Earth:Geothermal energy|Geothermal energy]]
* [[Earth:Geothermal power|Geothermal power]]
* [[Physics:Geothermal heat pump|Geothermal heat pump]]
* [[Engineering:Thermal battery|Thermal battery]]

== References ==
{{Reflist}}

== External links ==
*[http://www1.eere.energy.gov/geothermal Energy Efficiency and Renewable Energy (EERE) – Geothermal Technologies Program]
*[https://web.archive.org/web/20070930185800/http://geothermal.id.doe.gov/ Idaho National Laboratory – Geothermal Energy]
*[http://geoheat.oit.edu Oregon Institute of Technology – Geo-Heat Center] {{Webarchive|url=https://web.archive.org/web/20090102215401/http://geoheat.oit.edu/ |date=2009-01-02}}
*[http://www.smu.edu/geothermal/ Southern Methodist University – Geothermal Lab]
*[http://www.nrel.gov/geothermal/ Geothermal Technologies Program] at the US National Renewable Energy Lab
*[http://www.geo-exchange.ca/en/ The Canadian GeoExchange Coalition] {{Webarchive|url=https://web.archive.org/web/20140205102150/http://www.geo-exchange.ca/en/ |date=2014-02-05}}


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[[Category:Energy conversion]]
[[Category:Heat pumps]]
[[Category:Geothermal energy|Heating]]
[[Category:Heating]]

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{{Sourceattribution|Geothermal heating}}