a comparison of control strategies applied to an existing ice-storage system

While ice storage systems are designed according to a defined strategy for warm day loads, it is interesting to consider other conventional control strategies for mid-season day loads. These different control strategies, applied to an existing cooling plant, are compared in terms of operating costs and energy consumption.
A simplified cooling plant model is built. The chillers, cooling towers, and the ice storage system are modeled as different systems connected together. A time stage equal to 15 minutes is considered to simulate the different control strategies. Existing technical constraints and set points are met. The operating costs of the cooling plant are evaluated by taking into account both the energy and the demand cost rate.
In off-design conditions, savings of operating costs are made only if the storage tanks are fully discharged after being fully charged. In this case, ice storage systems reduce the operating costs of the cooling plant by shifting a significant fraction of on-peak energy consumption to off-peak periods and by reducing the on-peak demand. But at the same time, the introduction of an ice storage system in a cooling plant causes the electrical energy consumption to rise because the thermal efficiency of the chillers is reduced when working in ice formation mode.