The fundamental concept of an ice storage cooling system is to operate a chiller during periods of low utility rates (typically at night) to transform a volume of liquid water, held in one or more large, unpressurized, insulated containers, into ice. This ice is then melted to supply cooling during the subsequent peak loading period.
One possibility is a configuration called a “full storage” system. In this approach, the amount of ice created during a given “off-peak” period will be sufficient to meet the building’s entire cooling load during the subsequent “on-peak” period. In theory, this eliminates the need to operate the chiller during the “on-peak” period, and significantly lowers both the cost of operation and the peak power demand of the system. Most commercial buildings are billed for both the amount of electrical energy used over a billing period (e.g., kilowatt•hours), as well as the peak power demand (e.g., kilowatts) over any 15-minute period during that billing period.
Another scenario, referred to as a “partial storage” system is to displace the majority (but not all) of the on-peak cooling load using ice storage, and supply the balance of the load by operating the chiller. This approach typically has a higher operating cost relative to a full storage system, but also has a significantly lower installation cost since the chiller and ice bank storage can be smaller.
Figure 9-5 shows an array of large unpressurized insulated thermal storage tanks that serve as the “ice bank®.”