JOHNSON CONTROLS
20
FORM 160.84-OM1
ISSUE DATE: 9/21/2017
SECTION 2 - SYSTEM OPERATING PROCEDURES
CHILLER OPERATION
Upon start request, the following occur in sequence:
1. Chiller's system pump run contacts close
2. VSD pre-charges (~12 seconds)
3. VSD pre-regulates (~3 seconds)
4. Motor runs
The chiller will vary capacity to maintain the leaving
chilled liquid temperature setpoint by a specific se-
quencing of optional hot gas bypass, variable geometry
diffuser, and compressor speed.
Throughout capacity control, the compressor speed is
maintained above the minimum required for the prevail-
ing head condition, to avoid surge. Otherwise, the device
maintaining capacity is controlled by a proportional-in-
tegral-derivative control based on leaving chiller liquid
temperature. Pressure and motor current overrides also
apply as necessary to maintain operating limits.
The Input Current limit threshold value is determined
from several settings, depending on the chiller control
source selected according to the Table 1.
TABLE 1 - INPUT CURRENT LIMIT THRESHOLD
CONTROL
SOURCE
ACTIVE INPUT CURRENT
LIMIT THRESHOLD
Local
Lowest of:
Local Input Current Limit Setpoint (% Input Job FLA)
Pulldown Input Current Limit (when active)
ISN Remote Input Current Limit Setpoint (comms)
Analog
Remote
Lowest of:
Local Input Current Limit Setpoint (% Input Job FLA)
Analog Remote Input Current Limit Setpoint
Pulldown Input Current Limit (when active)
Digital
Remote
Lowest of:
Local Input Current Limit Setpoint (% Input Job FLA)
Digital Remote Input Current Limit Setpoint
Pulldown Input Current Limit (when active)
CHILLED LIQUID CONTROL SETTINGS
Temperature Control Setpoint
The temperature to which the chiller will control the
chilled fluid leaving the evaporator must be set by the
Operator. The way it is selected depends whether the
Operator wants this value set locally or modulated by
a remote input.
TABLE 2 - TEMPERATURE SETPOINT
CONTROL
SOURCE
LEAVING CHILLED LIQUID TEMPERATURE SETPOINT
Local Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel. It is programmable over the
range of 38.0°F to 70.0°F (water) or 10.0°F to 70.0°F (brine). If Smart Freeze (see previous) is enabled,
the range is 36.0°F to 70.0°F (water). The default is 45 °F.
ISN (BAS) Remote Leaving Chilled Liquid Temperature Setpoint value sent over communications. The setpoint
entered from the panel is ignored. If nothing is written to the address, the default is 45 °F.
Analog Remote Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel plus the temperature offset
dened by the remote analog input signal. A remote device can provide an analog signal (0-20mA,
4-20mA, 0-10VDC or 2-10VDC) that creates the temperature offset in Analog Remote mode. The span
of the offset may be dened as 10, 20, 30, or 40ºF using the Local Leaving Chilled Liquid Temperature
Range setting from the panel. For example, if this Range Setpoint is programmed for 10°F and the
Local Leaving Chilled Liquid Temperature Setpoint is 45°F, then the remote device can set the Leav-
ing Chilled Liquid Temperature setpoint over the range 45.0 to 55.0°F as its voltage or current changes
from minimum to maximum.
Digital Remote Local Leaving Chilled Liquid Temperature Setpoint, entered from the panel plus the temperature offset
dened by the remote pulse width signal. A remote device can provide a Pulse Width Modulation
(PWM) signal in Digital Remote mode that creates the temperature offset in Digital Remote mode. The
span of the offset may be dened as 10, 20, 30, or 40ºF using the Local Leaving Chilled Liquid Tem-
perature Range setting from the panel. For example, if this Range Setpoint is programmed for 10°F
and the Local Leaving Chilled Liquid Temperature Setpoint is 45°F, then the remote device can set the
Leaving Chilled Liquid Temperature setpoint over the range 45.0 to 55.0°F as its pulse duration chang-
es from minimum to maximum. The PWM input is in the form of a 1 to 11 second relay contact closure
that applies 115VAC to the I/O Board TB4-19 for 1 to 11 seconds. A contact closure time (pulse width)
of 1 second produces a 0°F offset. An 11 second closure produces the maximum offset. The relay
contacts should close for 1 to 11 seconds at least once every 30 minutes to maintain the setpoint to the
desired value. If a 1 to 11 second closure is not received within 30 minutes of the last closure, the offset
is defaulted to zero. A closure is only accepted at rates not to exceed once every 70 seconds. Offset
(°F) = (pulse width in seconds – 1)( Local Leaving Chilled Liquid Temperature Range) divided by 10.
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