This paper describes simulation-based results of an investigation of a commercial cooling plant with an ice storage system. Various ice storage systems, chiller compressors, and building types were analyzed under four different control strategies. Optimal control as the strategy that minimizes the total operating cost (demand and energy charges) served as a benchmark to assess the relative performance of three conventional controls (chiller-priority, constant-proportion, and storage-priority control) and to determine aspects in need of improvement in order to apply these conventional controls better and to enhance the cost saving potential of ice storage systems.
Independent of the non-cooling electrical load profile, it was found that good efficiency of the cooling plant in the icemaking mode and rate structures with strong load-shifting incentives are prerequisites for making cool storage successful. Chillers with poor performance at subfreezing evaporator temperatures require significant on- to off-peak differentials in the energy and demand rates to yield substantial savings. The relative performance benefit of optimal control over conventional controls increases when rate-based load-shifting incentives are weak. With cooling-related electrical loads being large compared to non-cooling loads, all conventional controls improve their performance when slowly recharging during off-peak periods to contain off-peak demand. On-peak demand reduction of storage-priority is near-optimal for many cases. Guidelines are presented to improve the load-shifting performance of chiller-priority and constant-proportion control. # 2002 Elsevier Science B.V. All rights reserved.
Keywords: Commercial buildings; Equipment; Thermal energy storage systems; Optimization; Guidelines