FORM 160.60-O2 (1004)
7
YORK INTERNATIONAL
1
level is maintained by the subcooler level control valve,
which meters liquid refrigerant into the evaporator to
complete the refrigerant circuit.
The subcooler liquid level is continuously monitored
to provide optimum subcooler, refrigerant condenser
and evaporator performance. The level control valve
automatically adjusts to all “real world” operating
conditions, providing the most effi cient and reliable
operation of refrigerant fl ow control.
CAPACITY CONTROLS
The major components of the chiller are selected to
handle the refrigerant that 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.
During part-load operation at off-design conditions, the
chiller capacity is reduced to maintain a constant leaving
chilled liquid temperature by fi rst decreasing the speed
and closing the compressor pre-rotation vanes ( PRV)
(See Detail A), then opening the hot gas bypass valve.
7619A(D)
DETAIL A –
COMPRESSOR PREROTATION VANES
The hot gas bypass valve admits hot, high-pressure
refrigerant from the compressor discharge back into
the condenser, partially short-circuiting the refrigeration
cycle. This practice prevents compressor surging under
low part-load conditions.
The position of the vanes is automatically controlled
through a lever arm attached to an electric motor
located outside the compressor housing. The automatic
adjustment of the vane position in effect provides the
performance of many different compressors to match
various load conditions from full load with vanes wide
open to minimum load with vanes completely closed.
The combination of PRV position manipulation, speed
reduction and hot gas bypass valve function provides
capacity reduction from 100% to 15% of design capacity.
The speed is controlled by an electro-mechanical throttle
actuator attached to the engine throttle linkage, and is
managed by the capacity control logic.
