When the control is changed to local from any other source, it remains in run mode if already
running or it remains in stop mode if already stopped. A hardware safety stop button is also located
on the side of the panel.
The chiller starts if the following conditions are met:
• Leaving chilled liquid temperature is above the restart temperature
• Chilled liquid flow is established
• No uncleared faults or start inhibits exist
Chiller operation
When a start request is received, the following sequence occurs:
1. The chiller's system pump run contacts close.
2. The magnetic bearing levitates.
3. The variable speed compressor drive pre-charges for approximately 12 s.
4. The variable speed compressor drive pre-regulates for approximately 3 s.
5. The motor runs.
The chiller varies capacity to maintain the leaving chilled liquid temperature setpoint by a specific
sequencing of the variable geometry diffuser and compressor speed.
Throughout capacity control, the compressor speed is maintained above the minimum required
for the prevailing head condition, to avoid surge. Otherwise, the device maintaining capacity is
controlled by a proportional-integral-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 following table.
Table 9: 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)
BAS Remote Input Current Limit setpoint (comms)
0 to 10 or 4 mA to 20 mA
Lowest of:
• Local Input Current Limit setpoint (% Input Job FLA)
• Analog Remote Input Current Limit setpoint
• Pulldown Input Current Limit (when active)
PWM
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
The following section contains information on the temperature control setpoint, automatic
temperature shutdown, and automatic temperature restart.
Temperature control setpoint
The temperature at which the chiller controls the chilled fluid leaving the evaporator must be set by
the operator. The operator can select whether the temperature value is set locally or modulated by
a remote input.
YVAM with OptiView Control Center32
To Next Page
Loading...
