Thermal storage systems utilising the latent heat of fusion of a phase change material (PCM) are simulated for symmetric-balanced/unbalanced conditions in terms of the conventional thermal effectiveness and newly proposed performance characteristic factors. A unified two-phase model is formulated to accommodate the performance prediction of cyclic thermal regenerators with encapsulated PCM or conventional packing. The effects of flow channelling and transverse thermal condition on the performance of such systems are also discussed.