Geothermal applied science harnesses the Earth's heat. Merely a few anxiety below the surface, the Globe maintains a nigh-constant temperature, in contrast to the summer and wintertime extremes of the ambient air to a higher place ground. Further below the surface, the temperature increases at an average rate of approximately ane°F for every seventy feet in depth. In some regions, tectonic and volcanic activity can bring higher temperatures and pockets of superheated water and steam much closer to the surface.
3 primary types of technologies take advantage of World equally a heat source:
Ground source heat pumps
Direct use geothermal
Deep and enhanced geothermal systems
Geothermal free energy is considered a renewable resource. Footing source estrus pumps and direct use geothermal technologies serve heating and cooling applications, while deep and enhanced geothermal technologies generally accept advantage of a much deeper, higher temperature geothermal resource to generate electricity.
For more data on the environmental benefits and effects of geothermal energy, visit EPA's Clean Energy website.
Ground Source Heat Pumps
A ground source heat pump takes reward of the naturally occurring departure between the above-ground air temperature and the subsurface soil temperature to movement oestrus in support of end uses such as space heating, space cooling (air-conditioning), and even h2o heating. A ground source or geoexchange system consists of a heat pump connected to a series of buried pipes. One can install the pipes either in horizontal trenches just below the ground surface or in vertical boreholes that go several hundred feet below basis. The heat pump circulates a heat-conveying fluid, sometimes water, through the pipes to move heat from point to point.
A commercial-scale basis source heat pump system. This example is a demonstration projection at a university. Credit: Craig Miller Productions, NREL 02409
If the footing temperature is warmer than the ambient air temperature, the heat pump can move oestrus from the footing to the building. The rut pump can also operate in reverse, moving estrus from the ambience air in a building into the ground, in effect cooling the building. Ground source heat pumps crave a small amount of electricity to drive the heating/cooling process. For every unit of measurement of electricity used in operating the system, the heat pump can evangelize every bit much as 5 times the energy from the ground, resulting in a cyberspace energy benefit. Geothermal rut pump users should be enlightened that in the absence of using renewable generated electricity to drive the heating/cooling process (east.g., modes) that geothermal estrus pump systems may not be fully fossil-fuel free (e.m., renewable-based).
How It Works
The steps below draw how a heat pump works in "heating mode"—taking estrus from the footing and delivering it to a edifice—and "cooling manner," which removes oestrus from the building and transfers information technology to the ground.
Heating Style
Apportionment: The higher up-ground heat pump moves water or another fluid through a series of buried pipes or basis loops.
Rut absorption: As the fluid passes through the ground loop, it absorbs estrus from the warmer soil, rock, or ground water around it.
Heat exchange and use: The heated fluid returns to the building where it used for useful purposes, such as infinite or water heating. The system uses a rut exchanger to transfer oestrus into the edifice'due south existing air handling, distribution, and ventilation organization, or with the improver of a desuperheater it tin also heat domestic water.
Recirculation: Once the fluid transfers its heat to the building, it returns at a lower temperature to the ground loop to exist heated again. This process is repeated, moving estrus from one point to some other for the user's benefit and comfort.
Cooling Mode
Rut commutation and assimilation: Water or another fluid absorbs estrus from the air inside the edifice through a oestrus exchanger, which is the way a typical air conditioner works.
Circulation: The above-footing heat pump moves the heated fluid through a serial of buried pipes or basis loops.
Heat belch: As the heated fluid passes through the ground loop, it gives off heat to the relatively colder soil, rock, or ground h2o around it.
Recirculation: Once the fluid transfers its rut to the ground, the fluid returns at a lower temperature to the edifice, where information technology absorbs oestrus again. This process is repeated, moving heat from one point to another for the user's benefit and condolement.
The to a higher place-basis estrus pump is relatively inexpensive, with clandestine installation of basis loops (piping) bookkeeping for most of the arrangement'due south cost. Estrus pumps tin support space heating and cooling needs in nearly whatsoever part of the country, and they can too be used for domestic hot water applications. Increasing the capacity of the pipage loops can scale this technology for larger buildings or locations where space heating and cooling, as well equally water heating, may be needed for most of the year.
Learn More Nigh Ground Source Heat Pumps
Directly Use Geothermal
Geothermally heated water reaches the surface at hot springs like this one in Yellowstone National Park. Credit: Patrick Laney, NREL 13104
Direct utilise geothermal systems utilise groundwater that is heated by natural geological processes below the Earth's surface. This water can exist equally hot equally 200°F or more. Bodies of hot groundwater can exist institute in many areas with volcanic or tectonic activity. In locations such as Yellowstone National Park and Iceland, these groundwater reservoirs can reach the surface, creating geysers and hot springs. 1 tin can pump hot water from the surface or from underground for a wide range of useful applications.
How Information technology Works
Pumping: To tap into hot ground water, a well is drilled. A pumping system may exist installed, although in some cases, hot water or steam may ascent upwards through the well without agile pumping.
Delivery: Hot water or steam can be used straight in a diverseness of applications, or it tin be cycled through a heat exchanger.
Refilling: Depending on the use requirements of the system and the weather of the site, the ground h2o aquifer may need to be replenished with water from the surface. In some cases, the movement of ground water might refill the aquifer naturally.
The water from direct geothermal systems is hot enough for many applications, including large-scale puddle heating; space heating, cooling, and on-demand hot water for buildings of most sizes; commune heating (i.e., heat for multiple buildings in a urban center); heating roads and sidewalks to cook snow; and some industrial and agricultural processes. Straight use takes reward of hot water that may exist just a few feet below the surface, and usually less than a mile deep. The shallow depth means that capital costs are relatively small compared with deeper geothermal systems, but this technology is express to regions with natural sources of hot groundwater at or near the surface.
Learn More Virtually Direct Use Geothermal
Deep and Enhanced Geothermal Systems
Deep geothermal systems apply steam from far below the Earth'south surface for applications that require temperatures of several hundred degrees Fahrenheit. These systems typically inject water into the ground through one well and bring water or steam to the surface through another. Other variations can capture steam directly from undercover ("dry out steam"). Unlike basis source heat pumps or straight use geothermal systems, deep geothermal projects tin involve drilling a mile or more below the Globe's surface. At these depths, high pressure keeps the water in a liquid state fifty-fifty at temperatures of several hundred degrees Fahrenheit.
How It Works
Pumping: Hot water or steam is pumped up through a deep well. Every bit the water rises to the surface, the pressure drops and the water vaporizes into superheated steam that can be used for loftier-temperature processes.
Delivery: The rut from the hot water or steam tin can be used to heat a secondary fluid (a "binary" process), or the hot water or steam can be used direct.
Recirculation: One time the heat is transferred to the delivery system, the now-cooler h2o is pumped dorsum undercover.
Dispersal: Different ground source heat pumps, used footing water in this example is simply injected and allowed to disperse back into the ground, rather than being pumped through a closed loop of pipes.
Deep geothermal technologies harness the same kind of energy that produces geysers. Credit: National Park Service; photo by George Marler
Deep geothermal sources provide efficient, clean oestrus for industrial processes and some big-scale commercial and agronomical uses. In improver, steam can be used to spin a turbine and generate electricity. Although geothermal steam requires no fuel and low operational costs, the initial capital costs—specially drilling test wells and production wells—tin can exist financially challenging. Steam resources that are economical to tap into are currently limited to regions with high geothermal action, simply research is underway to develop enhanced geothermal systems with much deeper wells that take advantage of the Globe'due south natural temperature gradient and can potentially be constructed anywhere. Enhanced systems tin use hydraulic fracturing techniques to engineer subsurface reservoirs that let h2o to be pumped into and through otherwise dry or impermeable rock.
Larn More About Deep and Enhanced Geothermal Systems
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