where F4 =
holding period at the design temperature T5 of the cold reservoir.
5-3. Iced Reservoirs.
a. As the term implies, iced reservoirs are reservoirs cooled down to the point where ice can coexist
with the water. The heat sink capacity of an iced reservoir is greatly increased by the ice accumulated in
it.
(1) As mentioned previously, the difference in acceptable cooling water temperatures for
refrigeration compressors and diesel engines practically demands two reservoir systems, either or both
of which may be iced.
(2) At the start of use as heat sinks, either or both of the iced reservoirs can furnish chilled water
directly to unit air-conditioner cooling coils until the reservoir temperature rises about 500 F. During
that time the refrigeration equipment does not need to be operated and the heat rejected to the reservoir is
thus reduced accordingly.
(3) The iced reservoir should not be used as a source of chilled water for the air-conditioning
system during normal operating (non-emergency) conditions, because the ice-making equipment
producing ice for a reservoir operates at lower temperature and efficiencies than conventional equipment
for air-conditioning,
b. If the reservoir is filled, or partially filled, with a mixture of water and ice, the water temperature
will remain at or near 320 F during the addition of heat until all the ice is melted. During this period of
time, and neglecting the heat gains from the rock, the mass W1 in lb of ice, having 144 Btu./lb latent heat of
fusion, represents a total heat sink capacity Qi in Btu as follows
The heat gains from the rock may be neglected if the iced reservoir has been maintained at 32 "F for
sufficiently long periods of time so that the heat transfer from the rock (equation 5-9) tends to zero.
c. After the ice has melted, heat will be transferred to the rock, due to the temperature rise of the water.
The remaining heat sink capacity of the reservoir will be determined using equation 5-2, based on the
water cross section when all the ice has melted. A reservoir filled with ice at one end only maintains an
average water temperature of approximately 34 "F in the remaining length of reservoir and serves to
provide an additional heat sink capacity due to sensible cooling of the water and surrounding rock below
the initial temperature of the rock.
d. Ice introduced at one end of a horizontal reservoir floats, packs and jams but does not distribute
itself along the length of the reservoir to a sufficient depth; therefore, some mechanical means must be
made available for this purpose.
(1) The most satisfactory ice distribution method appears to be a helical-screw conveyor. This
horizontal screw conveyor runs the full length of the reservoir above the maximum flotation level of the
ice or a distance above the water level somewhat more than one-tenth of the depth of the water. As a result
the top of the ice accumulating in any section of the reservoir will only reach the screw conveyor when
underlying ice is no longer floating but is resting on the floor of the reservoir.
(2) Ice is dumped from ice making machines at one end of the reservoir. When the ice fed at the
dumping point reaches the level of the screw conveyor, it is conveyed and dumped by the helical-screw
into the next section, filling it to the bottom. Thus, the process repeats and the full ice front progresses in
the direction of the far end.
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