CH-85-01-4 -- Control of Brine-Type Ice Storage Systems PDF

Cooling storage for load management began to mushroom in 1984 as electric utility demand charges rose sharply in much of the world and some off-peak commercial energy charge differentials became meaningful.

Brine-type ice storage systems are attractive to many engineers and companies since they are compact, may be used with standard package chillers including centrifugals, and are uniquely adaptable to lower cost partial storage or demand-limiting systems.

System designers are faced with a number of control choices:

1. Operating strategy, such as partial or full storage, demand limited storage, economizer cycle vs. ice, and schematic arrangements for locating chiller either before, after, or beside the storage. Chiller priority vs. ice priority will be dealt within a companion paper.
2. Use of presently available controls needed to implement the strategy, such as the type of time-of-day controls, temperature controlled blending valves, and four-way rotary valves.
3. New controls, such as the ability to limit building demand by controlling chiller operation, an ice inventory sensor to level out night chiller operation, and a new comfort control that biases indoor temperature to balance lower relative humidity caused by colder coils.

Methods of arriving at these answers, including their relation to particular design jobs, are given. A full description of the need for each control and its importance to the system is covered.

For thermal storage to achieve the load management potential needed by electric utili­ties, thousands of air-conditioning megawatts must be controlled in new ways. The author foresees an immediate program being undertaken to provide such control and control strategies prompted by market demand caused by new electric rate structures.