FORM 160.75-O1 (211)
JOHNSON CONTROLS
22
SECTION 3 - SYSTEM COMPONENTS DESCRIPTION
REFRIGERANT FLOW CONTROL
Refrigerant flow to the evaporator is controlled by a
variable orifice.
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 a
variable orifice 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 qualified
service technician. Only a qualified service technician
may modify these settings.
While the chiller is shut down, the orifice will be in the
fully open position causing the sensed level to be ap-
proximately 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 lev-
el setpoint. This ramp causes the setpoint to go from the
initial refrigerant level (approximately 0%) to the pro-
grammed setpoint over a programmable period of time.
If the actual level is greater than the setpoint when the
VMS opens, there is no pulldown period, it immedi-
ately begins to control to the programmed setpoint.
While the chiller is running, the refrigerant level is nor-
mally controlled to the level setpoint. However, any-
time the vanes fully close (VMS closes), normal level
control is terminated, any refrigerant level setpoint in
effect is cancelled and the outputs to the level control
will be constant open.
OPTIONAL SERVICE ISOLATION VALVES
If your chiller is equipped with optional service isola-
tion 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 qualified service
technician.
OPTIONAL HOT GAS BYPASS
Hot gas bypass is optional and is used to eliminate
compressor surge during light load or high head op-
eration. The OptiView control panel will automatically
modulate the hot gas valve open and closed as required.
Adjustment of the hot gas control valve must be per-
formed by a qualified service technician following the
Hot Gas Set-up procedure.
Changes in chilled water flow will require
re-adjustment of the hot gas control to
insure proper operation.
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 the Control Center, refer to
SECTION 2 - SYSTEM OPERATING PROCEDURES
of this manual.
SOLID STATE STARTER (OPTIONAL)
The Solid State Starter is a reduced voltage starter that
controls and maintains a constant current flow to the
motor during start-up. It is mounted on the chiller. Pow-
er and control wiring between the starter and chiller
are factory installed. The starter enclosure is NEMA-1
with a hinged access door with lock and key. Electrical
lugs for incoming power wiring are provided.
VARIABLE SPEED DRIVE (OPTIONAL)
A Variable Speed Drive can be factory packaged with
the chiller. It is designed to vary the compressor mo-
tor speed and prerotation vane position by controlling
the frequency and voltage of the electrical power to
the motor. Operational information is contained in the
Variable Speed Drive – Operation (Form 160.00-O1)
.
The control logic automatically adjusts motor speed
and compressor prerotation vane position for maxi-
mum part load efficiency by analyzing information fed
to it by sensors located throughout the chiller.