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JOHNSON CONTROLS
19
SECTION 2 – PRODUCT DESCRIPTION
FORM 155.31-ICOM2.EN.UL
ISSUE DATE: 12/21/2018
2
CONDENSER
The refrigerant vapor from the low temperature gener-
ator as well as the condensed refrigerant from the high
temperature generator enter the condenser where they
condense into a liquid state (by the cooling (condenser)
water from the absorber section). The cooled refriger-
ant is sent to the bottom evaporator section through a
U-pipe (liquid seal).
LD19871b4
Condenser
Condensed
Refrigerant
CRYSTALLIZATION
All absorption chillers that use lithium bromide and
water as the solution / refrigerant pair are subject to
crystallization. This is due to the fact that some areas
of the unit operate with solution liquid concentration
levels that are only possible at higher than the normal
ambient temperature surrounding the unit. For exam-
ple, the solution concentration in the generator of a
single stage absorption unit is typically 64.3% lithium
bromide by weight. LiBr solutions begin to crystallize
at 110 °F.
Crystallization happens when the LiBr solution tem-
perature drops too low or the concentration is too high.
The LiBr solution becomes like slush. At this point the
LiBr solution cannot absorb any more water and will
start to solidify (crystallize).
Crystallization occurs in the solution heat exchanger.
In addition, it may happen in the generator. It also hap-
pens in pipes that are not well insulated and are located
in rooms where the temperature can affect the solution
moving through the pipes.
You can prevent crystallization by making sure you
keep the solution temperature high and the concentra-
tion at the optimum percentage (64%).
Since the solution temperature in the generator is nor-
mally high enough, no crystallization will occur as
long as the higher temperature is maintained. Before
the unit is shut down, make sure the solution is suffi-
ciently diluted in all areas of the unit to prevent crystal-
lization during the off cycle. Remember, the solution
temperature will eventually become equal to the ambi-
ent temperature of the room.
To prevent crystallization all units employ a dilution
cycle. As long as the unit is allowed to dilute itself dur-
ing an orderly shutdown sequence, the unit should be
able to sit idle at fairly low plant room ambient temper-
atures without any threat of crystallization. Typically,
after a dilution cycle, the average solution concentra-
tion within the chiller will be below 45% lithium bro-
mide by weight. Although the crystallization line on
Figure 57 on page 153 does not extend that far, you
can see that the solution at 45% concentration will not
have a tendency to crystallize at normal ambient tem-
peratures.
Why Does Crystallization Occur?
The most common reason for crystallization is power
failure. If a chiller is running at full load and power is
interrupted for a sufficient length of time, the concen-
trated solution in the high side of the unit will eventu-
ally cool down. Since no dilution cycle was performed,
the solution concentration in some areas of the unit will
still be high. If the temperature of this concentrated so-
lution is allowed to fall enough, the solution will reach
its crystallization point. Plant room temperature, insu-
lation quality and the solution concentration all play a
part in the determination of how long it will take be-
fore the unit will crystallize. See Water Quality Control
on page 144 for information on water quality control
and crystallization. The Duhring Diagram / PTX Chart
shows the specific temperatures and pressures of the
crystallization area. See Figure 56 on page 148 and
Figure 58 on page 154 .