035-19569-101 (0109)
2-6
GB
Stub-out water nozzle connections with Victaulic grooves
are welded to the water boxes. These nozzle connections
are suitable for Victaulic couplings, welding or fl anges,
and are capped for shipment. Plugged ¾" drain and vent
connections are provided in each water box.
2.8 Refrigerant Flow Control
Refrigerant fl ow to the evaporator is controlled by a
variable orifi ce.
A level sensor senses the refrigerant level in the condenser
and outputs an analog voltage to the microprocessor
that represents this level (0% = empty; 100% = full).
Under program control, the microprocessor modulates
a variable orifi ce to control the condenser refrigerant
level to a programmed setpoint. Other setpoints affect
the control sensitivity and response. These setpoints
must be entered at chiller commissioning by a qualifi ed
service technician. Only a qualifi ed service technician
may modify these settings.
While the chiller is shut down, the orifi ce will be in
the fully open position causing the sensed level to be
approximately 0%. When the chiller is started, after the
vane motor end switch (VMS) opens when entering
SYSTEM RUN, if actual level is less than the level
setpoint, a linearly increasing ramp is applied to the
level setpoint. This ramp causes the setpoint to go from
the initial refrigerant level (approximately 0%) to the
programmed setpoint over a period of 15 minutes.
If the actual level is greater than the setpoint when the
VMS opens, there is no pulldown period, it immediately
begins to control to the programmed setpoint.
While the chiller is running, the refrigerant level is
normally controlled to the level setpoint. However,
anytime the vanes fully close (VMS closes), normal
level control is terminated, any refrigerant level setpoint
pulldown in effect is cancelled and the outputs to the level
control will be opposite that which is supplied to the vane
motor (i.e., when a close pulse is applied to the vane
motor, an open pulse is applied to the level control, etc.).
When the VMS opens, if the refrigerant level is less than
the level setpoint, a refrigerant level setpoint pulldown
is initiated as described above. Otherwise, the level is
controlled to the programmed setpoint.
2.9 Options and Accessories
2.9.1 Service Isolation Valves
If the chiller is equipped with optional service isolation
valves on the discharge and liquid line, these valves
must remain open during operation. These valves are
used for isolating the refrigerant charge in either the
evaporator or condenser to allow service access to the
system. A refrigerant pump-out unit will be required to
isolate the refrigerant.
Isolation of the refrigerant in this system must be
performed by a qualifi ed service technician.
2.9.2 Hot Gas Bypass
Hot gas bypass is optional and is used to eliminate
compressor surge during light load or high head
operation. The control panel will automatically modulate
the hot gas valve open and closed as required.
Adjustment of the hot gas control valve must be
performed by a qualifi ed service technician following
the Hot Gas Set-up procedure.
Changes in chilled water fl ow will require re-adjustment
of the hot gas control to insure proper operation.
2.9.3 Solid State Starter
The optional Solid State Starter is a reduced voltage
starter that controls and maintains a constant current
fl ow to the motor during start-up. It is mounted on the
chiller. Power and control wiring between the starter and
chiller are factory installed. Available for 380-600 volts,
the starter enclosure is IP54 with a hinged access door
with lock and key. Electrical lugs for incoming power
wiring are provided.
2.9.4 Variable Speed Drive
An optional 400V – 3-Ph – 60/50Hz Variable Speed Drive
can be factory packaged with the chiller. It is designed to
vary the compressor motor speed and pre-rotation vane
position by controlling the frequency and voltage of the
electrical power to the motor. Operational information
is contained in Form 160.00-O1 (VSD 658 HP and 900
HP) or 160.00-O4 (VSD OptiSpeed 292 HP and 419
HP). The control logic automatically adjusts motor speed
and compressor pre-rotation vane position for maximum
part load effi ciency by analysing information fed to it by
sensors located throughout the chiller.
The VSD eliminates the need for a starter and has a
soft starting characteristic that never exceeds 100%
full load amps. It also provides automatic power factor
correction.
An optional harmonic fi lter limits electrical power supply
distortion from the variable speed drive and further
improves power factor correction.
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