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Aquifer thermal energy storage (ATES) is the storage and recovery of thermal energy in the subsurface. ATES is applied to provide heating and cooling to buildings. Storage and recovery of thermal energy is achieved by extraction and injection of groundwater from aquifers using groundwater wells. Systems commonly operate in a seasonal mode. The groundwater that is extracted in summer, is used for cooling by transferring heat from the building to the groundwater by means of a heat exchanger. Subsequently, the heated groundwater is injected back into the aquifer, which creates a storage of heated groundwater. In wintertime, the flow direction is reversed such that the heated groundwater is extracted and can be used for heating (often in combination with a heat pump). Therefore, operating an ATES system uses the subsurface as a temporal storage to buffer seasonal variations in heating and cooling demand. When replacing traditional fossil fuel dependent heating and cooling systems, ATES can serve as a cost-effective technology to reduce the primary energy consumption of a building and the associated CO2 emissions. In 2009 United Nations Climate Change Conference in Copenhagen, Denmark, many countries and regions have made targets for global climate protections. European Union also set target to reduce greenhouse gas emissions, increase use of sustainable energy and improve energy efficiency. For this target, ATES can actually contribute significantly, as about 40% global energy consumption is buildings and is mainly for heating and cooling.〔De Rosa, M., Bianco, V., Scarpa, F. and Tagliafico, L.A., 2014. Heating and cooling building energy demand evaluation; a simplified model and a modified degree days approach. Applied Energy, 128: 217-229.〕 Therefore, the development of ATES has been paid a lot of attention and the number of ATES has increased dramatically, especially in Europe. For example, in the Netherlands, a number of about 20,000 ATES systems could be achieved in 2020 was estimated.〔Godschalk, M. and Bakema, G., 2009. 20,000 ATES Systems in the Netherlands in 2020-Major step towards a sustainable energy supply. Proceedings Effstock.〕 This can possibly contribute the CO2 emission reduction of about 11%, for the target of the Netherlands. Besides the Netherlands, Belgium, Germany, Turkey, and Sweden are also increasing the application of ATES. == System types == In its basic form, an ATES system consists of two wells (called a doublet). One well is used for heat storage, and the other for cold storage. During winter, (warm) groundwater is extracted from the heat storage well and injected in the cold storage well. During summer, the flow direction is reversed such that (cold) groundwater is extracted from the cold storage well and injected in the heat storage well. Because each well serves both as an extraction and injection well, these systems are called bi-directional.〔Dickinson, J., Buik, N., Matthews, M. and Snijders, A., 2009. Aquifer thermal energy storage: theoretical and operational analysis. Geotechnique, 59(3): 249-260.〕 There are also mono-directional systems. These systems do not switch pumping direction, such that groundwater is always extracted at the natural aquifer temperature. Although thermal energy is stored in the subsurface, there is usually no intention to retrieve the stored energy. Thermal energy storage can also be achieved by circulating a fluid through a buried heat exchanger, that usually consists of a horizontal or vertical pipeline. As these systems do not extract or inject groundwater, they are called closed systems and are known as borehole thermal energy storage or ground source heat pumps. Another thermal application that uses the subsurface to provide thermal energy is geothermal energy production, which commonly uses the deeper subsurface where temperature is higher. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Aquifer thermal energy storage」の詳細全文を読む スポンサード リンク
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