The periodic melting of encapsulated ice for cold thermal energy storage has been investigated numerically. A horizontal rectangular container is used as a storage capsule, since warm coolant fluid (glycol) flows over the upper and lower walls of the capsule, melting the ice. The enthalpy method is employed to model the phase change at the two moving interfaces. The effect of cyclic time variant coolant fluid temperature on the heat transfer efficiency and the corresponding energy stored has been investigated. Also, the influence of the convection heat transfer coefficient and coolant fluid temperature on the melting behavior has been studied and reported. The results show that the coolant fluid temperature markedly affects the melting behavior rather than the convection heat transfer coefficient. (c) 2006 Elsevier Ltd. All rights reserved.