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Descripción
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| The heating and cooling of buildings represents more than 25% of the global energy consumption. For this reason, interest in low?energy buildings and net?zero energy buildings has grown rapidly in recent years. Low enthalpy geothermal energy is considered as one of the most efficient renewable energy sources to reduce the carbon footprint because, when correctly designed and sized, the resulting geothermal HVAC (heating, ventilation, and air conditioning) systems can provide significant monetary savings and a clean and efficient way of cooling and heating buildings. When using geothermal energy in an HVAC system, the ground can be used in two different ways. First, in extreme climate zones where only heating/cooling is needed, it can be used as a large source/sink into which the heat is exclusively extracted/injected. On the other hand, in moderate climates where heating is needed in winter and cooling is needed in summer, the ground can be used as a large thermal inertia which is recharged with heat in summer and discharged of heat in winter. Depending on which way the ground is employed, the presence of a groundwater stream can be profitable or not from an engineering point of view. On one hand, it is beneficial when using the ground as a heat source/sink because it adds a new convective heat transport mechanism to the already existent conductive one, improving thereby the recharging capacity of the ground. On the other hand, if the ground is used as thermal inertia, the presence of a groundwater stream prevents recovering in wintertime the energy stored during the summer. In the present work the thermal response of a vertical geothermal borehole has been obtained taking into account the groundwater effect. Additionally to the extreme slenderness of the borehole and the slowly varying heat injection rate, the Peclet number based on the radius of the borehole turns out to be small compared to unity. These large disparities in time and length scales have been exploited in the present work by means of matched asymptotic expansion techniques, allowing the derivation of analytical expressions for the sought thermal response of the borehole. The aforementioned heat transfer problem is similar to a classic fluid?mechanical one, the Oseen's problem and the Stokes' paradox, in the sense that in both problems two different regions emerge: the closer to the borehole one in which only diffusive terms are important, and the further away one in which convective and diffusive phenomena are relevant. The results obtained by the asymptotic analysis have successfully been compared against a detailed numerical simulation of the underlying heat transfer problem. | |
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Internacional
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Si |
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Nombre congreso
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First Colloquium of the Spanish Theoretical and Applied Mechanics Society |
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Tipo de participación
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970 |
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Lugar del congreso
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Madrid, España |
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Revisores
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Si |
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ISBN o ISSN
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DOI
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Fecha inicio congreso
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28/03/2019 |
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Fecha fin congreso
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29/03/2019 |
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Desde la página
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55 |
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Hasta la página
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55 |
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Título de las actas
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First Colloquium of the Spanish Theoretical and Applied Mechanics Society: PROGRAMME |