Thermal energy storage in an unconfined aquifer: 2. Model development, validation, and application

Abstract

A fully three‐dimensional numerical model for simulating coupled density‐dependent groundwater flow and thermal energy transport is developed and validated. The transport solution is based on a finite element time integration algorithm which generates a symmetric coefficient matrix while retaining second‐order accuracy in time. The use of a symmetric conjugate gradient solver for both the flow and transport matrices results in a high degree of computational efficiency. Three‐dimensional deformable block elements are used to allow the model to conform to domains with irregular geometry. The thermal transport model is validated against the results of the Borden thermal injection field experiment presented in the companion paper. The model simulations provide an excellent match with the observed temperature distribution over time, with the effects of thermal buoyancy and losses across the ground surface accurately reproduced by the model. The model is shown to be a practical tool for simulating the type of low‐temperature thermal transport problems that arise in connection with seasonal aquifer thermal energy storage and ground source heat extraction systems.