A dimensionless parameter approach to the thermal behavior of an aquifer thermal energy storage system

TLDR

Predicting the performance of an aquifer thermal energy storage system requires understanding its hydrothermal behavior, which can be approximated by assuming steady radial flow when buoyancy effects are negligible and the well is fully screened in a confined horizontal aquifer. The authors develop a characterization scheme based on four dimensionless parameter groups derived from nondimensionalized energy transport equations for steady radial flow, and use a numerical model to compute heat transfer across injection–storage–production cycles over a range of these groups. Graphical results of production temperatures and energy recovery factors versus the parameter groups agree well with field experiments, validating the dimensionless approach.

Abstract

To predict the performance of an aquifer thermal energy storage system, an understanding of the system's hydrothermal behavior is needed. One possibility is to run a detailed numerical simulation of the system. However, for a single‐well system in which fluid flow is limited to steady radial flow, a characterization scheme based on a set of four dimensionless parameter groups allows production temperatures and energy recovery factors to be read from graphs. The assumption of radial fluid flow is valid when buoyancy flow can be neglected and a well is fully screened in a horizontal aquifer which is confined above and below by impermeable layers. Criteria for little buoyancy flow include a low permeability or vertically stratified aquifer, a small temperature difference between injected and ambient water, and short cycle length. The basic energy transport equations for the aquifer‐confining layer system with steady radial fluid flow in the aquifer are nondimensionalized to derive the key parameter groups. Next a numerical model which calculates the heat transfer in the aquifer and confining layers for an injection‐storage‐production cycle is run for a range of values of these groups. The calculated production temperatures and energy recovery factors are then presented graphically as a function of the parameter groups. Comparisons between results of field experiments and recovery factors read from the graphs show good agreement.