7.2.7 Ice Storage Air Conditioners

Ice Storage Air Conditioner (ISAC) systems contain ice storage tanks distributed throughout the building, with each tank associated with the air-side component of a single HVAC system. In contrast, traditional thermal energy storage systems centralize the storage, which then serves the load of the entire building. The ISAC system will typically rely on cooling fed from the storage tank to an air handler containing either a chilled water or DX coil. The tank will be charged by a condenser during night-time hours, and discharge will occur during the daytime hours. In modeling the ISAC system, the modeler will typically utilize the Split DX system type available in most analysis software. This system type will most closely approximate the performance of the condensing unit that will be used to charge the ice storage tank. In addition, custom cooling curves will need to be input to account for the system performance during the charging mode, since much lower temperatures will need to be produced by the condensing unit.

Operating schedules for the charging and melting model will depend upon the controls configuration of the ISAC system. Some systems are designed and configured to run in a simple charge/melt mode, where the entire daytime load will be handled by the ISAC system, and then the system will be recharged at night. Others are designed to only address peak period loads, and thus will run only during the peak utility period, with the condenser operating in the mornings during the shoulder peak periods. Another variation is an ISAC system that is designed for peak load shaving, with the ice melt supplementing the condenser cooling. These different strategies will require the use of appropriate operating schedules to control the condenser operating strategy as well as the ice tank charge/melt occurrences. 

The baseline building does not have ISAC.