JOHNSON CONTROLS
17
SECTION 2 – PRODUCT DESCRIPTION
FORM 155.30-ICOM2.EN.UL
ISSUE DATE: 12/21/2018
2
TWO STEP EVAPORATOR-ABSORBER
The evaporator and the absorber are split into two sec-
tions. This design allows the cycle concentration to be
lower than a conventional absorber / evaporator. The
lower concentrations mean the unit is more reliable,
operates with increased efficiency, has a lower corro-
sion potential, and uses lower temperature hot water in
the generator.
Chilled water flows through both evaporator sections.
It enters the lower evaporator tubes first. It then moves
to and through the upper evaporator tubes before it
leaves the chiller.
Each evaporator operates at a slightly different tem-
perature and pressure. The refrigerant in the lower
evaporator boils at a slightly higher temperature than
in the upper evaporator. The chilled water is cooled in
two steps.
The absorber is split into two sections as well. A strong
solution enters the top of the upper absorber. It flows
down through the upper absorber bundle.
The upper bundle operates at a lower vapor pressure.
As a result, the upper evaporator can operate at a lower
pressure and temperature.
The solution flows into the top of the lower absorber
section. When the LiBr solution enters the lower Ab-
sorber section it is already diluted by the refrigerant
vapor that boiled off in the upper evaporator. Since the
lower evaporator is the first step of the chilled water
cooling, the dilute solution vapor pressure is adequate
to maintain the lower evaporator at the required tem-
perature and pressure.
The cooling tower water enters the lower absorber sec-
tion first, keeping the vapor pressure of the weaker so-
lution as low as possible.
LD19939a1
LD19839a1
Evaporator
(Upper)
Evaporator
(Lower)
Absorber
(Lower)
Absorber
(Upper)
LiBr
Refrigerant
Chilled
Water
Out
Chilled
Water
In
Cooling
Water In
Refrigerant
LiBr
Chilled
Water
Out
Cooling
Water In
Chilled
Water
In
SOLUTION HEAT EXCHANGER
The dilute (weak) LiBr solution leaving the lower
absorber section is pumped to the generator section
through a solution to solution heat exchanger. It is pre-
heated prior to entering the generator section. Such
pre-heating of the dilute solution reduces the driving
heat source requirement in the generator and also helps
to cool down the concentrated (strong) solution before
entering the upper absorber section.
LD19939a2
LD19839a2
(P2)
Solution Heat
Exchanger
Concentrated
Solution
Dilute
Solution
Concentrated
Solution
Dilute
Solution
