Fixed SP Control Mode
The secondary temperature should correspond to the desired setpoint. The default fixed setpoint is 18°C (65°F) and is used
by the control loop to regulate the primary fluid cooling valve position to achieve and maintain the setpoint. The cooling valve
position can be monitored on the Home screen or page 1 of the Status screen (Cooling Demand/Feedback). High and low
temperature alarms are set at a default value of 2°C (4°F) either side of setpoint (floating with the setpoint) when either Fixed
SP or Fixed SP + Dew Point Offset control mode is selected from Configuration—Temperature Control screen, with a default
hysteresis of 1°C (2°F).
• The high and low temperature alarms are ignored for a default period of 20 minutes on startup to allow the
system time to settle without generating nuisance alarms.
• If the secondary temperature deviates by more than 2°C (4°F) below setpoint for 2 minutes or more, an A32—
Secondary Fluid Low Temp alarm is generated. This alarm will remain present until the temperature rises above
the hysteresis value.
• If the secondary temperature deviates by more than the default of 2°C (4°F) above setpoint for 2 minutes or
more, an A33—Secondary Fluid High Temp alarm will be generated. This alarm will remain present until the
temperature falls below the hysteresis value.
4.4 Temperature Control Loop
If necessary to change the PID settings for temperature control, it is recommended that the Ziegler-Nichols manual tuning
method be adopted.
IMPORTANT! The Ziegler-Nichols method requires that the system is operating under typical load conditions. Initially,
it causes the control loop to temporarily become unstable with wide temperature swing oscillations. It is important to
ensure that this does not cause any damage to the equipment being cooled. Logging on at the Engineering level
provides the access to make these changes.
1. Set the Integral Reset Time and Derivative Reset Time (Configuration—Temperature Control screens P309 and
P310) to 0 seconds.
2. Increase the Proportional Band (Configuration—Temperature Control screen P308) to a higher value from the
default. For example, 20°C.
3. Check that the Secondary Supply Temperature (T2) stabilizes.
NOTE: Temperature stabilizes at a higher temperature than the current setpoint. This offset is eradicated once the
Integral reset time is added back in.
4. If temperature control is unstable, raise the Proportional Band to a higher value until the temperature stablizes.
Otherwise gradually decrease the Proportional Band in 1°C steps until the supply temperature (T2) starts to
oscillate at a constant rate.
5. Measure the frequency of the oscillation time (peak to peak) in seconds (t).
4.4.1 PI Control
PI control should be sufficient for systems that have a reasonably steady or slow changing heat loads.
1. Set the Proportional Band to 2.2X the Proportional Band setting at which the system became unstable.
2. Set the Integral Reset Time to 0.83X the oscillation time (t).
3. Leave the Derivative Reset Time at 0.
48 Proprietary and Confidential ©2025 Vertiv Group Corp. 4 Operation
Vertiv™ CoolChip CDU 600 Operation and Maintenance Guide
To Next Page
Loading...
