This paper reports on the development of a computationally efficient numerical simulation model for a shell-and-tube thermal energy storage system, where the heat transfer occurs between a fixed mass of phase-change material (PCM) in contact with a tube through which flows a high-temperature fluid. Simulations of the conjugate heat transfer and melting/solidification of the PCM for a range of heat exchanger designs, including single-tube control/baseline, single tube with longitudinal and circular fins, and multitube configurations, were undertaken and the numerical results were validated using experimental data. The underlying simplifications in the model were tested and verified against two- and three-dimensional simulations. During charging, before complete melting of the PCM, the PCM volume average temperature is predicted to be within 5 degrees C of the experimentally determined value for each heat exchanger design. During discharging there is a good trend-wise agreement between predicted and measured temperatures, with maximum deviations of about 10 degrees C. Comparison of heat transferred during charging and discharging phases between the one-dimensional and refined two-dimensional predictions was in agreement to within 8.5%, indicating the usefulness of the one-dimensional model and the adopted effective conduction approach.