Modes of Operation

The modular ICE CHILLER® Thermal Storage Unit can operate in any of five distinct operating modes. These modes of operation provide the flexibility required by building operators to meet their daily HVAC cooling requirements.

Ice Build

In this operating mode, ice is built by circulating a 25% solution (by weight) of inhibited ethylene/ propylene glycol through the coils contained in the ICE CHILLER® Thermal Storage Unit. Figure 1 illustrates typical chiller supply temperatures for 8, 10 and 12 hour build cycles. For a typical 10–hour build time, the supply glycol temperature is never lower than 22°F (-5.6°C). As the graph illustrates, for build times exceeding 10 hours, the minimum glycol temperature is greater than 22°F (-5.6°C). For build times less than 10 hours, the minimum glycol temperature will be lower than 22°F (-5.6°C) at the end of the build cycle. This performance is based on a chiller flow rate associated with a 5°F (2.8°C) range. When a larger temperature range is the basis of the chiller selection, the chiller supply temperatures will be lower than shown in Figure 1.

Figure 1

Ice Build with Cooling

When cooling loads exist during the ice build period, some of the cold glycol used to build ice is diverted to the cooling load to provide the required cooling. The amount of glycol diverted is determined by the building loop set point temperature. BAC recommends that this mode of operation be applied on systems using primary/secondary pumping. This reduces the possibility of damaging the cooling coil or heat exchanger by pumping cold glycol, lower than 32°F (0°C), to this equipment.

Cooling – Ice Only

In this operating mode the chiller is off. The warm return glycol solution is cooled to the desired set point temperature by melting ice stored in the modular ICE CHILLER® Thermal Storage Unit.

Cooling – Chiller Only

In this operating mode the chiller supplies all the building cooling requirements. Glycol flow is diverted around the thermal storage equipment to allow the cold supply glycol to flow directly to the cooling load. Temperature set points are maintained by the chiller.

Cooling – Ice with Chiller

In this operating mode, cooling is provided by the combined operation of the chiller and ice storage equipment. The glycol chiller precools the warm return glycol. The partially cooled glycol solution then passes through the ICE CHILLER® Thermal Storage Unit where it is cooled by the ice to the design temperature.

Modular ICE Thermal Storage Unit