FORM 155.21-O1 (615)
5
JOHNSON CONTROLS
SECTION 1
DESCRIPTION OF SYSTEM AND FUNDAMENTALS OF OPERATION
GENERAL INFORMATION
The chiller is controlled by a modern state of the art
Microcomputer Control Center that monitors its op-
eration. The Control Center is programmed by the
operator to suit job specifications. The operating status,
temperatures, pressures, and other information pertinent
to operation of the chiller are automatically displayed
and read on a graphic display. Other display screens
can be observed by pressing the keys as labelled on the
control center.
The principle of refrigeration is the exchange of heat
and, in absorption liquid chilling, there are four basic
heat exchange surfaces: the evaporator, the absorber, the
generator and the condenser.
In absorption chilling, the refrigerant is water but, like
any refrigeration system, absorption chilling uses evapo-
ration and condensation to remove heat. To maintain
effective evaporation and condensation, absorption
chilling employs two shells which operate at different
controlled vacuums.
The lower shell (Evaporator and Absorber) has an
internal absolute pressure of about one one-hundredth
that of the outside atmosphere - or six millimeters of
mercury, a relatively high vacuum. The vacuum allows
water (the refrigerant) to boil at a temperature below that
of the liquid being chilled. Chilled liquid entering the
evaporator can be cooled for air conditioning or process
cooling applications.
Evaporator
The section of a chiller that is responsible for removing
the heat from the chilled water circuit, thus cooling the
chilled water to be used to cool a building, a manufac-
turing process, or whatever application it is intended.
Typically, the chilled water is cooled from 54°F - 44°F
(12.2 - 6.6°C).
In an absorption chiller, the pure refrigerant generated in
the generator is cooled and condensed in the Condenser
and supplied to the Evaporator. Here, it is immediately
exposed to a much lower pressure which causes some
immediate flashing (boiling). Most of the refrigerant
cools to the saturation temperature and remains in liquid
form. It is then pumped and sprayed over the Evapora-
tor tube bundle. As the refrigerant passes over the outer
surface of the tubes, it evaporates (i.e. flashes or boils)
because of the low pressure, approximately 5.5-6.5
mmHg which is equivalent to a saturation temperature
of 36-41°F (2.2-5°C). The refrigerant vapor is then
immediately drawn through the eliminator towards the
Absorber. This vacuum is caused by the hygroscopic
action, the affinity Lithium Bromide has for the refrig
-
erant vapor.
LD14498
FIGURE 1 –
MODEL YIA ABSORPTION CHILLER
