Johnson Controls York MaxE YK Series, Manual

Page: 106 / 139

FORM 160.75-O1 (309)
7
JOHNSON CONTROLS
1
source, usually a cooling tower. The condensed refrig-
erant drains from the condenser into the liquid return
line, where the variable orifice meters the flow of liquid
refrigerant to the evaporator to complete the refrigerant
circuit.
7619A(D)
detail a – COMPRESSOR PREROTATION VANES
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.
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 leaving
the evaporator. 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.