Civil Engineering Reference
In-Depth Information
5.4 Ice Slurry Storage System
Thermal energy is stored in this system by making use of both the sensible and
latent heat characteristics of heat transfer fluid and water contained in the storage
tank, respectively. Ice slurry storage usually comprises of a cooling system and a
secondary heat exchanger coupled to the building space conditioning unit.
In practice, the storage tank is filled with a designed proportion of a heat
transfer fluid and water. The refrigerating loop of the cooling plant enables the heat
transfer fluid to be maintained at very low temperature.
Through the direct-contact heat exchange mechanism exhibited between the
cooled heat transfer fluid and the water, small ice-like structures are formed and
float over the top of the tank in the form of ice slurries. The ice slurries are then
pumped to the secondary heat exchanger that is in contact with the space condi-
tioning unit in building.
The net heat transfer rate taking place in the heat exchanger decides the cooling
effect in indoor environment. The volumetric capacity ratio of water to the heat
transfer fluid determines the rate of formation of ice slurries in the storage tank.
The modified form of ice slurry storage system consists of a vertical shell and
tube heat exchanger, wherein the shell acts as the evaporator and the tubes serve as
the heat transfer surface. Typically, the heat energy from the fluid flowing through
the tubes are retrieved by the refrigerant present in the shell, thereby facilitating
the formation of thin flakes of ice on the surface of the tubes. The ice flakes or
crystals thus formed are then transported to the collector and ice slurry tanks at
regular intervals based on the thermal load demand in buildings.
The instantaneous phase change characteristics of the heat transfer fluid plays a
vital role in the formation of ice slurries required for providing cooling in build-
ings with TES. Interestingly, for the designed cooling load, mass flow rate and
temperature of the chilled water returning from the building, the outlet temperature
of the ice slurry storage almost remains consistent.
5.5 Ice Storage with Low Temperature Air Cooling
The air supplied to indoor spaces in buildings is conditioned to meet out the
conditions related to thermal comfort to occupants in addition to achieving energy
efficiency in cooling systems. In contrast to the conventional chilled water cooling,
the supply air is conditioned to attain temperature between 3 and 9 C using the ice
storage facility. The low temperature acquired by the air paves way for main-
taining the relative humidity in indoor environment in the range of 40-55 %.
Having the low-temperature air supply in the conditioned zones, the size of air
distribution systems and its associated operational and maintenance costs being
involved can be collectively reduced by 10-20 %. Furthermore, for the designed
