Thermal energy storage (TES) systems are commonly employed for enhancing the efficiency of commercial and residential heating and cooling systems, by matching thermal energy supply and demand during summer-winter, day-night, and peak-off-peak periods. TES in these systems is usually achieved by changing the temperature of materials (sensible systems) and/or inducing solid-liquid phase change (latent heat systems). Such systems are also categorized as seasonal (long-term) and diurnal (short-term). In this work, the focus is on sensible diurnal TES systems consisting of rock beds, with air as the working fluid. They are relatively simple, easy to construct, inexpensive, and quite effective for many solar energy and building engineering applications. Numerous publications on rock-bed TES systems are available, but there is an urgent need for efficient computational methods for designing and optimizing them. The contributions of this work are the following: proposal of cost-effective mathematical models of fluid flow and heat transfer in rock beds; adaptation of a finite volume method (FVM) for the solution of this model; applications of this FVM to two test problems (with analytical solutions) and one demonstration problem; proposal of suitable thermofluid performance evaluation criteria for the rock-bed TES systems of interest; and presentation and discussions of the results.

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