Abstract

This paper introduces an analytical model analyzing the effect of groundwater flow on heat transfer in an infinite conductive-convective porous domain representing shallow geothermal systems with arbitrarily configured cylindrical heat sources. The model is formulated based on the moving source concept and solved based on the spectral analysis method and the superposition principle. Compared to models based on the Green’s function and the Laplace transform, the proposed spectral model has a simpler formulation, computationally efficient and easy to implement in computer codes. It can handle random time-dependent thermal loads and any arbitrarily configured grid distribution. The verification and numerical examples demonstrate the computational capabilities of the model, and show how the groundwater flow can play an important role in the thermal interaction between heat sources. They also feature how to make use of the direction of groundwater flow to avoid undesirable thermal interaction between neighboring installations, rapid depletion of energy sources and unfair mining of geothermal energy.

Highlights

  • Groundwater flow in subsurface formations can have a notable effect on the amount of energy gained from shallow geothermal systems, and on the extent of thermal interactions between heat sources

  • The signif­ icance of the heat gain due to groundwater flow and the thermal in­ teractions between heat sources is highly manifested in the ground source heat pump (GSHP) technology, which normally involves neigh­ boring heat sources and installations consisting of arbitrarily configured borehole heat exchangers (BHE)

  • Heat convection due to groundwater flow can have a significant ef­ fect on the amount of energy gained from the ground source heat pump (GSHP) system; a booming technology for yielding thermal energy from shallow depths of the earth to be utilized for heating and cooling of buildings

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Summary

Introduction

Groundwater flow in subsurface formations can have a notable effect on the amount of energy gained from shallow geothermal systems, and on the extent of thermal interactions between heat sources. The analytical methods, are more intricate in solving the governing heat equations They are not by-definition equipped to tackle these two aspects, and the solution has to be tailored to the physics of the problem (1D, 2D or 3D), the geometry of the heat source (line or cy­ lindrical), the kind of boundary conditions (Dirichlet or Neumann) and whether the domain encompasses a single or multiple heat sources. Each of these modeling features needs a special treatment. The novelty of the resulting spectral model, compared to existing analytical models, can be summarized as follows:

Single cylindrical heat source
Multiple heat sources with Neumann boundary condition
Multiple heat sources with Dirichlet boundary condition
Multiple cylindrical heat sources
Model verification
Conclusions

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