JOHNSON CONTROLS
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SECTION 2 - SYSTEM OPERATING PROCEDURES
FORM 160.84-OM1
ISSUE DATE: 9/21/2017
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Regardless of which method is used to select the de-
sired Leaving Chilled Liquid Temperature (LCHLT),
the chiller controls to its own Active LCHLT Setpoint.
The Active Setpoint is a target to the programmed
setpoint. When the chiller is not running, the Active
Setpoint is set to Entering Chilled Liquid Temperature
minus a programmable offset (default 5°F), but not ad-
justed to less than the programmed LCHLT setpoint.
When the compressor motor starts, the Active LCHLT
Setpoint is ramped from this value to the programmed
LCHLT Setpoint at the programmable LCHLT Setpoint
Ramp Rate (default 0.1°F/second). This keeps the
chiller from undershooting setpoint excessively dur-
ing pulldown. Any time the programmed setpoint is
changed during operation, the active setpoint is ramped
to the new value at this rate.
Automatic Temperature Shutdown
The temperature below the LCHLT setpoint at which
the chiller is desired to automatically cycle off when
load is less than the chiller minimum capability is
programmed from the panel as Leaving Chilled Liq-
uid Temperature Cycling Offset; Shutdown. This set-
ting defines the temperature offset below the LCHLT
setpoint where shutdown is expected. It is program-
mable over a range of 1°F to 64°F. However the actual
shutdown temperature will never be calculated to low-
er than 36°F (water), 34°F (water with Smart Freeze
enabled) or 6°F (brine). Anytime the LCHLT setpoint
is decreased, the shutdown threshold decreases to the
new LCHLT active setpoint minus offset at a rate equal
to the programmed LCHLT Setpoint Ramp Rate. Any-
time the Leaving Chilled Liquid Temperature setpoint
is increased, the shutdown threshold increases to the
new LCHLT active setpoint minus offset at a rate = 1/2
the programmed LCHLT Setpoint Ramp Rate. This al-
lows time for the chiller to change temperature without
shutting down first.
Automatic Temperature Restart:
The temperature above the LCHLT setpoint at which
the chiller is desired to automatically restart after a low
LCHLT shutdown per above is programmed from the
panel as Leaving Chilled Liquid Temperature Cycling
Offset; Restart. This setting defines the temperature
offset above the LCHLT setpoint where automatic re-
start is expected. It is programmable over a range of
0°F to 70°F. However, the restart temperature will nev-
er be calculated above 80°F. This setpoint can be used
to reduce chiller cycling by delaying the chiller restart
until the cooling load has increased sufficiently.
OPERATOR SETPOINTS QUICK REFERENCE
The most common Operator level setpoints can be
found on the Setpoints screen or the following screens:
Leaving Chilled
Liquid Temperature: Evaporator Screen
Shutdown Temperature Offset: Evaporator Screen
Restart Temperature Offset: Evaporator Screen
Local Input Current Limit: VSD Screen
Pulldown Demand Limit: VSD Screen
Pulldown Demand Time: VSD Screen
Control Source: Setpoints - Setup -
Operations Screen
Head Pressure Setpoint Condenser - Head
(When The Feature Is Enabled) Pressure
Control Screen
STOPPING THE SYSTEM
To stop the chiller, proceed as follows:
1. Push the Soft Stop key on the home screen of the
OptiView
TM
panel if in LOCAL control or send a
stop command through the remote system if in RE-
MOTE or BAS control. If the chiller is in a remote
control source and the local Soft Stop key is used
to stop the chiller, the Start key must be pressed be-
fore the chiller will again permit starts through the
remote source. In the event of an unusual circum-
stance requiring immediate stoppage, a safety stop
switch is located on the side of the control panel.
Normal stop eases the driveline to stop and should
always be used instead of the safety stop during
regular operation.
2. Stop the chilled water and/or condenser water
pumps if not wired into the Microcomputer Con-
trol Center, (in which case it will shut off auto-
matically. The actual water pump contact timing
operation is dependent upon the selection on the
SETUP screen.)
3. Open the switch to the cooling tower fan motors,
if used.
The OptiView™ Control Center can be programmed
to start and stop automatically (maximum - once each
day) whenever desired.
Refer to Schedule Screen on page 65 in the SEC-
TION 3 - OPTIVIEW™ CONTROL CENTER FUNC-
TIONS AND NAVIGATION of this manual.
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