In this work, we address the modeling and control challenges posed by optimizing the operation of phase change material (PCM) thermal energy storage (TES) devices for commercial buildings. Based on daily demand patterns and total storage capacity, we identify complex load characteristics which require advanced control (rather than simple heuristics) for operating the TES system. We develop a mathematical model for the storage system based on industrial equipment, and formulate the optimal operation problem as a mixed-integer dynamic optimization. We introduce a numerical solution approach that results in low solution times and is amenable to real-time implementation. We present simulation results based on realistic demand data collected from a commercial building, comparing the operating patterns devised using different electricity price structures encountered in the United States and the European Union.