Geothermal heat pump
Geothermal heat pumps
Bohrarbeiten für eine Erdwärmeheizung im Gebäudebestand
A geothermal heat pump system is a central heating and/ or air conditioning system that actively pumps heat to or from the shallow ground. It uses the earth as either a source of heat in the winter, or as a coolant in the summer. This design takes advantage of moderate temperatures in the shallow ground to boost efficiency and reduce operational costs. It may be combined with solar heating to form a geosolar system with even greater efficiency.
Geothermal heat pumps are also known by a variety of other names, including geoexchange, earth-coupled, earth energy, ground-source or water-source heat pump. The engineering and scientific community tend to prefer the terms "geoexchange" or "ground-source heat pumps" because very little of the heat originates from true geological sources. Instead, these pumps draw energy from shallow ground heated by the sun in the summer. Genuine geothermal energy from the core of Earth is available only in places where volcanic activity comes close to the surface, and can usually be extracted without the help of a heat pump.
Like a refrigerator or air conditioner, these systems use a heat pump to force the transfer of heat. Heat pumps can capture heat from a cool area and transfer it to a warm area, against the natural direction of flow, or they can enhance the natural flow of heat from a warm area to a cool one. The core of the heat pump is a loop of refrigerant pumped through a vapor-compression refrigeration cycle that moves heat. Heat pumps are always more efficient than pure electric heating, even when extracting heat from air.
But unlike an air-source heat pump, which extracts or exhausts heat to or from the outside air, a ground-source heat pump exchanges heat with the ground. This is much more efficient because underground temperatures are relatively stable through the year. Seasonal variations drop off with depth and disappear below 10 m due to thermal inertia. Like a cave, the shallow ground temperature is warmer than the air above during the winter and cooler than the air in the summer. A ground-source heat pump extracts that ground heat in the winter (heating) and exhausts heat back into the ground in the summer (cooling).
The system cost is much higher than conventional systems, but the difference is usually returned in energy savings in 3–10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop.[3] As of 2004, there are over a million units installed worldwide providing 12 GW of thermal capacity, with an annual growth rate of 10%. If deployed on a large scale, this technology may help alleviate energy costs and global warming.
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Geothermal heating
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 original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.[2] Most 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.
History
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. 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. 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. 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. 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. As of 2004, there are over a million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity. Each year, about 80,000 units are installed in the USA and 27,000 in Sweden.
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.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.
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Subsidence
n 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]
Environmental Impact
Geothermal energy is one of the few renewable energy technologies that—like fossil fuels—can supply continuous, base load power.
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From Wikipedia, the free encyclopedia
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