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Assessing the impact of thermal feedback and recycling in open-loop groundwater heat pump (GWHP) systems: a complementary design tool

Content Provider	Springer Nature Link
Author	Milnes, Ellen Perrochet, Pierre
Copyright Year	2012
Abstract	Thermal feedback and thermal recycling in open-loop groundwater heat pump (GWHP) systems occurs when a fraction of the injected water in a well doublet returns to the production well. They reflect two different mathematical representations of the same physical process. Thermal feedback assumes a constant injection temperature, while thermal recycling couples the injection and production temperatures by a constant temperature difference. It is shown that thermal feedback, commonly used in GWHP design, and recycling reflect two thermal end-members. This work addresses the coupled problem of thermal recycling, which is, so far, the missing link for complete GWHP assessment. An analytical solution is presented to determine the return-flow fraction in a well doublet and is combined with a heat-balance calculation to determine the steady-state well temperatures in response to thermal feedback and recycling. This is then extended to advective-dispersive systems using transfer functions, revealing that the well temperatures in response to thermal feedback and recycling are functions of the capture probability. Conjunctive interpretation of thermal feedback and recycling yields a novel design approach with which major difficulties in the assessment of the sustainability of GWHP systems can be addressed.Le percement thermique et le recyclage thermique se produisent dans un doublet géothermique ouvert lorsqu’une fraction de l’eau injectée retourne au puits productif. Ils reflètent deux représentations mathématiques du même processus. Le percement thermique suppose une température d’injection constante, alors que le recyclage thermique relie la température d’injection et de production par une différence de température constante. On montre que le percement thermique, communément utilisé pour le dimensionnement de doublets géothermiques, et le recyclage définissent deux cas de sollicitation thermique extrêmes. Cet article traite du problème couplé du recyclage thermique, en général négligé lors de l’évaluation d’un doublet géothermique ouvert. Une solution analytique est établie pour déterminer la fraction du débit de retour, puis combinée avec un bilan thermique donnant les températures d'équilibre aux puits en réponse au percement thermique et au recyclage thermique. Cette nouvelle approche est ensuite étendue aux systèmes advectif-dispersifs au moyen des fonctions de transfert, révélant que ces températures d'équilibre sont entièrement déterminées par la probabilité de capture du puits productif. L'interprétation combinée des effets liés au percement thermique et au recyclage thermique fournit des critères plus réalistes pour le dimensionnement et l'évaluation des performances d'un doublet géothermique ouvert.La retroalimentación térmica y el reciclado térmico en sistemas de bomba de calor de agua subterránea en circuito abierto (GWHP) ocurren cuando una fracción del agua inyectada en pozos dobles retorna al pozo de producción. Ello configura dos representaciones matemáticas diferentes de un mismo proceso físico. La retroalimentación térmica supone una inyección a temperatura constante, mientras que el reciclado térmico la inyección se acopla a la temperatura de producción a través de una diferencia de temperatura constante. Se muestra que la retroalimentación térmica, comúnmente usada en el diseño GWHP, y el reciclado reflejan dos miembros térmicos extremos. Este trabajo aborda el problema del acoplamiento del reciclado térmico, que es, hasta aquí, el eslabón perdido para completar la evaluación de GWHP. Se presenta una solución analítica para determinar la fracción del flujo de retorno en un pozo doble y se combina con un cálculo de balance de calor para determinar el estado estacionario de temperaturas del pozo en respuesta a la retroalimentación y al reciclado térmico. Esto es luego extendido a sistemas dispersivos – advectivos usando funciones de transferencia, lo que revela que las temperaturas del pozo en respuesta a la retroalimentación y reciclado térmico son funciones de la probabilidad de captura. La interpretación conjunta de retroalimentación y reciclado térmico brinda un enfoque de nuevo diseño con el cual pueden ser abordadas las mayores dificultades en la evaluación de la sustentabilidad de los sistemas GWHP. Retorno térmico e reciclagem térmica em sistemas de bombas de calor baseados em água subterrânea em circuito aberto (open-loop groundwater heat pump – GWHP) ocorrem quando uma fração da água injetada no furo emparelhado retorna ao furo de produção. Estes termos correspondem a duas representações matemáticas do mesmo processo físico. O retorno térmico assume uma temperatura constante de injeção, enquanto a reciclagem térmica agrega as temperaturas de injeção e de produção através de uma diferença de temperatura constante. É mostrado que o retorno térmico, comummente usado nos projetos GWHP, e a reciclagem refletem dois membros térmicos finais. Este trabalho analisa o problema acoplado da reciclagem termal, o qual é, até agora, o elo perdido para avaliação completa do GWHP. É apresentada uma solução analítica para determinar a fração de retorno de fluxo num furo emparelhado e é combinada com um cálculo de balanço de calor para determinar o estado estável da temperatura nos furos em resposta ao retorno e reciclagem térmicas. Isto é então estendido a sistemas advetivo-dispersivos, recorrendo ao uso de funções de transferência, mostrando que as temperaturas no furo em resposta ao retorno e reciclagem térmicas são funções da probabilidade de captura. A interpretação conjuntiva do retorno e reciclagem térmicas leva a uma nova forma de aproximação que pode resolver situações que apresentavam maiores dificuldades de avaliação da sustentabilidade dos GWHP.
Starting Page	505
Ending Page	514
Page Count	10
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	21
Issue Number	2
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2012-09-28
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Groundwater heat pump Thermal feedback Thermal recycling Analytical solutions Numerical modeling Hydrogeology Geology Waste Water Technology Water Pollution Control Water Management Aquatic Pollution
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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