Handbook of air conditioning and refrigeration / Shan K

31.16 CHAPTER THIRTY-ONE
FIGURE 31.6 Schematic diagram of a typical ice-harvesting ice storage system.
Ice Making or Charging
hollow inner part of the plate heat exchanger, in which liquid refrigerant is vaporized, and produces
a refrigeration effect.
The central plant (cooling) and brine incorporated ice storage system in an ice-harvesting ice
storage system consists of the following equipment and main components: chillers, an ice harvester,
storage tank, air system controls, piping, and accessories, as shown in Fig. 31.6.
During ice-making or -charging mode, a chilled aqueous ethylene glycol solution with a concentration
of 25 to 30 percent is pumped from the storage tank and distributed over the outer surface of
the evaporator plates at a temperature equal to or slightly above 32°F (0°C). It then flows downward
along the outer surface of the plate in a thin film. Water is cooled and then frozen into ice sheets approximately
0.2 to 0.3 in. (5 to 7.5 mm) thick. Periodically, hot gas is introduced into one-fourth of
the evaporator plates by reversing the refrigerant flow. Ice is harvested, or released from the outer
surface of the plates, in the form of flakes or chunks and falls into the storage tank below. Ice is
formed in 20 to 30 min and is harvested within 20 to 40 s. During harvesting, this section of plate
evaporator acts as a condenser.
Ice accumulates in the storage tank to occupy slightly less than 60 percent of the volume of the
tank. Because the ice flakes are usually smaller than 6 in. by 6 in. by 0.25 in. (1500 mm by 1500
mm by 63 mm), there is a large contact area between the return brine from the cooling coils and the
ice. The time required to melt the ice in the storage tank is less than one-tenth of the time needed in
ice making or charging.
For a reciprocating compressor using an evaporative condenser, the power consumption of the
chiller during ice making is about 0.95 to 1.1 kW/ton (COP 3.7 to 3.22). Because the evaporator