This paper develops an optimization methodology for the Thermal Energy Storage (TES) tank embedded with Phase Change Materials (PCMs) for domestic water heating applications with respect to the design parameter constraints and tank size. It presents the optimum design conditions for two different TES configurations considering different control strategies for the conventional cascaded system and the multiple entry independent PCM modules. The optimum configurations are determined using adaptive simulated annealing algorithm aimed to enhance the energy content and compare the systems outputs, namely the available energy and the heat transfer fluid outlet temperature at the optimum conditions for the two systems. The present study is conducted during a complete melting and solidification processes. It simultaneously validates the effectiveness of the multiple entry independent PCM modules in satisfying the low and high user requirements of domestic hot water and highlights the reduction in the electric power consumption throughout the year compared to the conventional TES system.