JOHNSON CONTROLS
8
FORM 160.54-O1
The refrigerant vapor, which is produced by the boiling
action in the cooler, ows to the compressor where the
rotating impeller increases its pressure and temperature
and discharges it into the condenser. Water owing
through the condenser tubes absorbs heat from the refrig-
erant vapor, causing it to condense. The condenser water
is supplied to the chiller from an external source, usu-
ally a cooling tower. The condensed refrigerant drains
from the condenser into the liquid return line, where the
variable orice meters the ow of liquid refrigerant to the
cooler to complete the refrigerant circuit.
The major components of a chiller are selected to handle
the refrigerant, which would be evaporated at full load
design conditions. However, most systems will be called
upon to deliver full load capacity for only a relatively
small part of the time the unit is in operation.
7619A(D)
DETAIL A – COMPRESSOR PREROTATION VANES
CAPACITY CONTROL
The major components of a chiller are selected for full
load capacities, therefore capacity must be controlled
to maintain a constant chilled liquid temperature leav-
ing the cooler. Prerotation vanes (PRV), located at the
entrance to the compressor impeller, compensate for
variation in load (See Detail A).
The position of these vanes is automatically controlled
through a lever arm attached to an electric motor located
outside the compressor housing. The automatic adjust-
ment of the vane position in effect provides the perfor-
mance of many different compressors to match various
load conditions from full load with vanes wide open to
minimum load with vanes completely closed.
Description of System and Fundamentals of Operation
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