JOHNSON CONTROLS
19
SECTION 2 – PRODUCT DESCRIPTION
FORM 155.32-ICOM1.EN.GB
ISSUE DATE: 10/13/2017
2
CONDENSER
The cooling water from the absorber section enters into
the condenser section. This helps condense the refrig-
erant vapors produced in the LTG as well as the con-
densed refrigerant from the drain heat exchanger. The
liquid refrigerant is then sent back to the evaporator
section through a U-pipe (liquid seal).
This completes the cooling cycle.
Condenser
LD19980_a5
Condensed
Refrigerant
Cooling Water
Outlet
CRYSTALLIZATION
All absorption chiller-heaters 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 lev-
els that are only possible at higher than the normal am-
bient temperature surrounding the unit. For example,
the solution concentration in the generator of a single
effect absorption unit is typically 64.3% lithium bro-
mide by weight. LiBr begins to crystallize at 43.3°C.
Crystallization is the result of the LiBr solution tem-
perature going too low or the concentration 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 will occur in the solution heat exchang-
er and sometimes even in the generator. It will also
happen in pipes not well insulated where room temper-
ature 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 in
most load conditions, no crystal-
lization will occur as long as the higher solution tem-
peratures are maintained. Special measures do have to
be taken before the unit is shut down so that the solu-
tion is sufficiently diluted in all areas of the unit to pre-
vent crystallization during the off cycle, since the solu-
tion temperature will eventually equal the surrounding
ambient temperature.
All units employ some sort of dilution cycle, which
fulfills this requirement. As long as the unit is allowed
to dilute itself during an orderly shutdown sequence,
the unit should be able to sit idle at fairly low plant
room ambient temperatures for extended periods of
time without any threat of crystallization. Typically, af-
ter a dilution cycle, the average solution concentration
within the chiller-heater will be below 45% lithium
bromide by weight and will have no tendency to crys-
tallize at normal ambient temperatures.
WHY DOES CRYSTALLIZATION OCCUR?
The most common reason for crystallization is due to
power failures. If a chiller-heater is running at full load
and power is interrupted for a sufficient length of time,
the concentrated solution in the high side of the unit
(Condenser/Generator Section) will eventually cool
down. Since no dilution cycle was performed, the solu-
tion concentration in some areas of the unit may still be
relatively high. If the temperature of this concentrated
solution is allowed to fall low enough, the solution will
reach its crystallization point. Plant room temperature,
insulation quality, and the solution concentration all
play a part in determining how long it will take before
the unit will crystallize. See
for information on water quality control and
crystallization. The Duhring Diagram / PTX Chart
shows the specific temperatures and pressures of the
crystallization area. See
and
