JOHNSON CONTROLS
72
FORM 160.79-O3
ISSUE DATE: 11/09/2018
SECTION 2 – OPTIVIEW CONTROL CENTER
Maximum Delta T Setpoint (whereupon “Checking
Maximum Delta T” is displayed), the Maximum Delta
T Time has expired (whereupon “Preparing Chiller for
Lag Run’ is displayed and the lag chiller is brought on
line) or the Chiller Current Limit Setpoint is set to 50%
or less.
“Preparing Chiller for Lag Run”
Displayed while bringing the lag compressor on line.
Displayed during the prelube period and until the Dis-
charge Valve has fully opened (whereupon “Waiting
Minimum Run Time” is displayed). When bringing the
lag compressor on line, a normal prelube is performed.
However, the oil pressure transducer Auto-zeroing is
not performed. The offset calculations done during the
lead compressor prelube are used. The lag compressor
prelube is fixed at 50 seconds.
“Waiting Minimum Run Time”
Displayed for the first 30 minutes after the lag com-
pressor is brought line. Once both compressors are
running, they are run for at least 30 minutes (unless
the Anti-Recycle feature has been disabled, a fault is
detected or a Local or Remote stop is received).
“Checking Minimum Load” and “Waiting
Minimum Load Time”
After the 30 minute Minimum Run Time waiting pe-
riod, the lag compressor will be shutdown if the lead
compressor motor current goes below the Low Load
Setpoint for a period equal to the Low Load Time
Setpoint. After the 30 minute Minimum Run Time has
elapsed, “Checking Minimum Load” is displayed until
the lead compressor motor current decreases below the
Low Load Setpoint (whereupon “Waiting Minimum
Load Time” is displayed). “Waiting Minimum Load
Time” is displayed until the lead motor current is no
longer less than the Low Load Setpoint or the Mini-
mum Load Time has expired (whereupon a soft shut-
down is performed on the lag compressor and “Un-
loading Before Shutdown” is displayed).
“Unloading Before Shutdown”
Displayed while the Pre-rotation vanes are closing dur-
ing a Soft Shutdown of the lag compressor. If the de-
cision is made to shutdown the lag compressor while
continuing to run the lead compressor, a Soft Shut-
down is performed on the lag compressor.
Time Remaining
Displays the time remaining on the following timers:
• “Waiting for Pulldown Delay”
• “Waiting Minimum Run Time”
• “Waiting Minimum Rate Time”
• “Waiting Maximum Delta T Time”
• “Waiting Minimum Load Time”
Minimum Rate and Minimum Rate Time
Access Level Required: VIEW
Allows the user to define the minimum rate of change
of the Leaving Chilled Liquid Temperature that must
be met by the lead compressor during the Chiller Pull-
down Period (this period is in effect until the Leaving
Chilled Liquid Temperature is within 2ºF of setpoint).
If this requirement is not being met, the lag compressor
is started. After the lead compressor has been running
for 3 minutes, the Leaving Chilled Liquid Temperature
is sampled once every minute for 5 minutes to estab-
lish a 5 point rolling average that makes up the dis-
played Delta T Rate value. This 8 minute period is the
Pulldown Delay Period (see
above). When the Pulldown Delay is finished,
and for the remainder of the Chiller Pulldown Period,
if the Delta T Rate is less than the Minimum Rate
Setpoint (0.5ºF/minute to 2.0ºF/minute; default 1.0ºF/
minute) for a period equal to the Minimum Rate Time
Setpoint (1 to 20 minutes; default 5 minutes) and the
Pulldown Demand Limit Setpoint is above 50%, the
lag compressor is brought on line.
Maximum Delta T and Maximum Delta T Time
Access Level Required: VIEW
Allows the user to define the criteria that determines
if the lead compressor is meeting the load require-
ment during the Chiller Steady State Period. If the
requirement is not being met, the lag compressor is
started. After the Chiller Pulldown Period has ended,
the Chiller Steady State Period begins and is in effect
until the chiller is shutdown. During this period, if the
Temperature Differential (Leaving Chilled Liquid tem-
perature minus Setpoint) exceeds the Maximum Delta
T Setpoint (1.0ºF to 5.0ºF; default 1.0ºF) for a period
equal to the Maximum Delta T Time Setpoint (1 to 20
minutes; default 5), the lag compressor is brought on
line.