The study and use of thermal storage has increased in recent years due to the need to reduce production cost. The purpose of this paper is the modeling of a thermal storage system using spherical capsules with phase change material (water). The main point of the present work lies in the fact that the this system uses different sizes of balls in a single storage tank (usually, in thermal storage spherical capsules systems spherical capsules with a simple diameter only is employed). To form the ice caps, a fluid, with a temperature below the freezing temperature of water, flows permanently through the capsules, so there is an exchange of heat between the fluid and the capsules with water, which freezer. Ideally, all water inside the capsule should become ice, but the thermal resistance posed by the ice begins to interfere with the formation of the total water within the capsule. Another problem is the temperature of the fluid that exchanges heat with the water capsules. As the fluid temperature increases, downstream, time of ice formation is affected by the smaller temperature difference between fluid and capsule external wall.