JOHNSON CONTROLS
43
SECTION 2 - PRE-STARTUP AND SYSTEM OPERATING PROCEDURES
FORM 160.67-O2
ISSUE DATE: 10/9/2020
2
To provide protection for retrofitted chillers that do not
have the ability to monitor turbine first stage pressure,
the logic monitors the governor valve actuator output
from the chiller panel as done on previous chillers.
The Governor Position Controller is inactive when the
chiller is stopped with its’ outputs set to 100%. When
the chiller is running at or above the minimum rated
speed, if the integrated speed control PID attempts to
open the governor valve more than a preset value (de-
termined by field testing at start up), the output of the
Governor Position Controller will decrease.
LSR2 and LSR1 will select the lower signal to over
-
ride the Leaving Chilled Liquid Temperature Control-
ler output and unload the chiller as described above
using the Capacity Ratchet Mode Selector to direct the
controllers output to the appropriate controlled device
depending on system load and system pressure differ-
ential. With the load reduced, the turbine will begin to
speed up and the speed control PID will begin to close
the governor valve, thus limiting the torque output of
the turbine.
While the Governor Position Controller is active, the
primary Leaving Chilled Liquid Temperature Control-
ler is inactivated and its output is set to equal the ap-
propriate tieback, thus providing a bumpless transfer to
normal leaving chilled liquid temperature control. Af-
ter the load is reduced sufficiently to return the gover-
nor valve to a safe position for 5 seconds, the Leaving
Chilled Liquid Temperature Controller is reactivated
and its’ PID algorithm begins controlling the output at
the tieback value.
Turbine Horsepower Limiting
All new YST chillers are provided with a transmitter to
monitor the turbine first stage pressure. This pressure
is used along with the steam inlet pressure and tem-
perature and the turbine exhaust pressure to calculate
the turbines power output.
A separate PID controller is provided to unload the
chiller when the turbine power approaches the maxi-
mum that the compressor bearings are rated for or
115% of the turbine design horsepower, whichever is
lower. The logic will calculate the actual horsepower
based on the steam inlet temperature and pressure so
that the override controller automatically adapts to
fluctuations in the quality of the steam supplied to the
turbine inlet.
If the calculated horsepower increases above the set
point, the output of the Turbine Horsepower Limit
Controller will decrease. LSR2 and LSR1 will select
the lower signal to override the Leaving Chilled Liquid
Temperature Controller output and unload the chiller
as described above.
With the load reduced, the turbine will begin to speed
up and the speed control PID will begin to close the
governor valve, thus reducing the horsepower output
of the turbine. While the Turbine Horsepower Limit
Controller is active, the primary Leaving Chilled Liq-
uid Temperature Controller is inactivated and its output
is set to equal the appropriate tieback, thus providing a
bumpless transfer to normal leaving chilled liquid tem-
perature control.
After the turbine horsepower has not exceeded the set
point for 5 seconds, the Leaving Chilled Liquid Tem
-
perature Controller is reactivated and its’ PID algo-
rithm begins controlling the output at the tieback value.
OPERATING LOG SHEET
A permanent daily record of system operating condi-
tions (temperatures and pressures) recorded at regular
intervals throughout each 24 hour operating period
should be kept.
An optional status printer is available for this purpose
or
shows a log sheet used by
Johnson Controls personnel for recording test data on
chiller systems. It is available from the factory in pads
of 50 sheets each under Form 160.44-F7 and may be
obtained through the nearest YORK office. Automatic
data logging is possible by connecting the optional
printer and programming the DATA LOGGER func
-
tion.
See Form 160.67-O1, Section 3 - Printers for ad-
ditional information.
An accurate record of readings serves as a valuable ref-
erence for operating the system. Readings taken when
a system is newly installed will establish normal condi-
tions with which to compare later readings.
For example, an increase in condenser approach tem-
perature (condenser temperature minus leaving con-
denser water temperature) may be an indication of
dirty condenser tubes.
