IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration Subtask A Report, November 2009
Fig. 14: Schematic diagram of an external melt ice storage system
Internal melt ice storage systems
Internal melt ice storage systems (IMISS) use the same heat exchanger for charging and
discharging. During discharging the heat transfer medium inside the coils of the heat
exchanger has a higher temperature than the melting temperature of the phase change
material (PCM, e.g. water). The ice adhered to the heat exchanger starts to melt from the
outside of the heat exchanger surface to the outer boundaries of the ice layer (Fig. 14). A
growing layer of liquid water between the heat exchanger surface and the ice is generated.
Hence the discharging rate decreases as the driving temperature difference decreases.
The most important advantage of internal melt systems is the possibility to realize very high
storage capacities since ice block generation does not have to be prevented.
Fig. 14: Charging and discharging process for internal melt system
A disadvantage of internal melting is that simultaneous charging and discharging is not
possible. A simultaneous charging and discharging could be useful in cases where the
absorption chiller generates less cooling capacity than needed to meet the cooling demand.
With external melt systems cooling can be maintained under these conditions. The
absorption chiller then continues to charge the ice store while the cooling demand is met by
discharging the ice store.
Fig. 15 shows the schematic lay-out of an internal melt ice storage system.
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