Peak-hour tariff typically troubles commercial office buildings in hot and humid climates where cooling demands are high during summer. Because the local power company rate structure strongly favors the practice of load shift and conversely penalizes peak load demand during peak hours, a multi-functional office building in Taipei seeks to reduce its cooling cost by ways of an ice thermal energy storage system in which harvested ice is stored during cheaper off-peak hours and thawing the storage medium during peak hours. The system uses partial storage approach to satisfy off-peak cooling demand while peak-hour cooling burden is relieved by chilled water built the previous night. Two screw chillers would be integrated with each other for the implementation to allow feeding chill water to the air-handler coils while producing ice for storage at the same time. The refrigeration cycle of water chilling operates under two modes, the ice mode for thermal storage, and the chill water mode for instantaneous air cooling. Super-cooled air from melted icewater makes humidity levels to be lower than conditioned with conventional systems, as well as load shift incentives. Cool air is introduced to variable air volume terminal boxes and is mixed with induced plenum air to bypass any reheat, yielding additional saving. V C 2015 AIP Publishing LLC.