JOHNSON CONTROLS
6
FORM 155.21-O1 (615)
Description of System and Fundamentals of Operation
Absorber
The concentrated solution coming back from the genera-
tor is partially mixed with solution from the absorber
section then pumped to a solution spray header where
it is sprayed over the tubes in the absorber. Refrigerant
vapor is absorbed into the solution and the solution is
thus diluted. This diluted solution is collected at the
bottom of the absorber where it is again pumped to the
generator.
Generator
The diluted solution is then pumped through the heat
exchanger, where it is preheated by hot concentrated so-
lution from the generator. The heat exchanger improves
the efficiency of the cycle by reducing the amount of
steam or hot water required to heat the dilute solution
in the generator. The dilute solution then continues to
the upper shell containing the Generator and Condenser,
where the absolute pressure is approximately one-tenth
that of the outside atmosphere, or seventy millimeters
of mercury. The dilute solution flows over the generator
tubes and is heated by steam or hot water passing through
the interior of the tubes. The amount of heat input from
the steam or hot water is controlled by a motorized valve
and is in response to the required cooling load. The
hot generator tubes boil the dilute solution, releasing
refrigerant vapor.
Condenser
The refrigerant vapor rises to the condenser and is
condensed by the cooler tower water running through
the condenser tubes. The liquid refrigerant flows back
to the lower shell, and is once again sprayed over the
evaporator. The refrigerant cycle has been completed.
Now the concentrated lithium bromide solution flows
from the generator back to the absorber in the lower
shell, ready to absorb more refrigerant. Its cycle has
also been completed.
Solution Heat Exchanger
A counterflow Solution to Solution Heat Exchanger. A
component that exchanges heat between two streams of
Lithium Bromide solution. The hotter the solution being
supplied to the generators is, the less heat that needs to
be added, thus improving efficiency. Likewise, the cooler
the solution is going to the Absorber, the less heat that
needs to be removed by the cooling tower. Therefore, the
heat exchanger preheats the solution going to the genera-
tor and cools the solution going to the Absorber.
Solution Pump
A hermetically sealed, centrifugal pump located under
the absorber. It receives diluted lithium bromide solu-
tion from the absorber shell and circulates it through a
heat exchanger, then up to the generator. The discharge
of this pump operates in a pressure that is above atmo-
spheric pressure. The pump is cooled by the solution it
is pumping.
Refrigerant Pump
A hermetically sealed, centrifugal pump located down-
stream of the evaporator outlet box. This pump receives
liquid refrigerant from the evaporator and discharges it
back up to the evaporator sprays. It continues to re-cir-
culate the refrigerant while the chiller is operational.
Purge Pump
An external pump connected to the purge system of the
unit. This pump is used to evacuate non-condensables
from the unit.
Eductor
An eductor is a liquid-powered jet pump. Jet pumps
have no moving parts and use a high-pressure stream
of liquid to pass through a nozzle, causing a portion of
a low-pressure stream coming into the side of the pump
to combine with the nozzle stream. This causes a reduc-
tion in pressure at the low-pressure inlet and induces the
rest of the low-pressure inlet substance to flow into the
body of the pump.
On IsoFlow™ units, an eductor is used in place of a
centrifugal pump to induce strong concentrated solu-
tion exiting the generator outlet box to combine with
weak concentrated solution exiting the solution pump
discharge, before going to the absorber spray header.
Level Switches
There are two level switches that sense liquid levels on
the IsoFlow units. Both are located in the refrigerant
circuit. Switch (1F) is at the side of the evaporator re-
frigerant outlet box, and senses the level in the box. At
low levels in this box, the 1F switch will open, causing
the control panel to initiate corrective procedures to keep
the unit from running out of refrigerant. Switch (3F) is
located just before the inlet of the Buffalo refrigerant
pump. It’s main purpose is to keep the Buffalo pump
from cavitation and eventual overheating.
