FORM 160.73-O2 (605)
7
YORK INTERNATIONAL
1
source, usually a cool ing tower. The condensed re frig -
er ant drains from the con dens er into the liquid return
line, where the variable orifi ce meters the fl ow of liquid
re frig er ant to the evaporator to com plete the refrigerant
cir cuit.
7619A(D)
DETAIL A –
COMPRESSOR PREROTATION VANES
Description of System and Fun da men tals of Operation
The major components of a chiller are selected to han dle
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 leav ing
the evaporator. Prerotation vanes (PRV), located at the
en trance to the compressor impeller, compensate for
vari a tion in load (See Detail A).
The position of these vanes is automatically controlled
through a lever arm attached to an electric motor lo cat ed
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.