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SECTION 3 - SYSTEM COMPONENTS DESCRIPTION
Emergency Overspeed
FIGURE 13 - OVERSPEED PROTECTION KNOB
ASSEMBLY
REFRIGERANT FLOW CONTROL
Refrigerant flow to the evaporator is controlled by the
Subcooler Level Control Valve.
A level sensor senses the refrigerant level in the con-
denser and outputs an analog voltage to the Microboard
that represents this level (0% = empty; 100% = full).
Under program control, the Microboard modulates an
electrically actuated valve to control the condenser
refrigerant level to a programmed setpoint. Other set-
points affect the control sensitivity and response. These
setpoints must be entered at chiller commissioning by
a qualified service technician. Only a qualified service
technician may modify these settings.
When the chiller is shut down, the Subcooler Level
Control Valve will be in the fully open position caus-
ing the sensed level to be approximately 0%. When the
chiller is started the valve will remain fully open until
the chiller has been running at or above the minimum
rated speed for 10 minutes. At that time the subcooler
refrigerant liquid level controller setpoint is ramped
up to the desired setpoint at a rate of 0.1% per sec-
ond. This causes the Subcooler Level Control Valve to
slowly close until the refrigerant level in the subcooler
is at the setpoint.
60
LD09901
Trip Knob
OPTIONAL SERVICE ISOLATION VALVES
If the chiller is equipped with optional service isolation
valves on the compressor discharge and main liquid
line to the evaporator, these valves must remain open
during operation. These valves are used for isolating
the refrigerant charge in either the evaporator or con-
denser to allow service access to the system. A separate
refrigerant pump-out unit will be required to isolate the
refrigerant.
Isolation of the refrigerant in this system
must be performed by a qualified service
technician.
HOT GAS BYPASS
The hot gas bypass feature is furnished as a standard
item. The hot gas bypass consists of a control valve in
piping that conveys warm gas from the refrigerant con-
denser to the evaporator. The purpose of the hot gas is
to provide the compressor with sufficient gas to oper-
ate smoothly at times when normal refrigerant gas flow
is too low. The hot gas bypass is 100% open before
startup and during the slow rolling operation to permit
the compressor to operate smoothly as the system is
being brought up to speed. The hot gas is also used
during operation when loads are very light or when
compressor head becomes too high. The OptiView™
control panel will automatically modulate the hot gas
valve open and closed as required. Adjustment of the
setpoints used by the hot gas bypass control logic must
be performed by a qualified technician.
Changes in the minimum and maximum
condenser water inlet temperature after
initial commissioning of the chiller will
require readjustment of the anti-surge
setpoints to ensure proper operation of
the Hot Gas Bypass Valve.
OPTIVIEW™ CONTROL CENTER
The OptiView™ Control Center is factory-mounted,
wired and tested. The electronic panel automatically
controls the operation of the unit in meeting system
cooling requirements while minimizing energy usage.
For detailed information on how the Control Center
controls the start-up and shutdown of the chiller, refer
to Sequence Of Operation on page 26 of this manual
and the OPERATION MANUAL, Form 160.67-O1.
FORM 160.67-O2
ISSUE DATE: 10/9/2020
JOHNSON CONTROLS
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