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The secondary fluid temperature is monitored at the reservoir tank. Three temperature sensors are
positioned here to give extended component redundancy (T2a, T2b & T2c). The controller will take an
average between all 3 readings as its input value.
- If the difference between the sensors exceeds a default 1.0°C (2°F), then an 'A40 (A41 or A42) -
Secondary Temp T2a (T2b or T2c) Diff Out of Limits' alarm will be raised (after a default 30
second delay) and the controller will only read & average the two remaining healthy sensors.
- If any of the T2 temp. sensors go open circuit, then an 'A02 (A03 or A04) – T2a (T2b or T2c)
Secondary Temperature Sensor Fault' alarm will be raised (no time delay) and the controller
will only read & average the two remaining healthy sensors.
Temperature sensor (T4) monitors the secondary circuit return temperature and is used in conjunction
with the flow rate to calculate the heat transfer duty.
The secondary temperature should correspond to the desired set point (default 18°C (65°F)) and is
used by the control loop to regulate the primary water control valve to achieve and maintain the set
point. The control 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 set point (floating with set point) for both 'Fixed SP' and 'Fixed SP + Dew Point Offset
control modes, with a default hysteresis of 1°C (2°F).
NOTICE! Fixed SP + Dew Point Offset control will require the installation of an
optional ambient temp/hum sensor.
- If the secondary temperature deviates by more than 2°C (4°F) below set point for 2 minutes or
more, a 'A24 - Secondary Water Low Temp' alarm will be generated. This alarm will remain
present until the temperature rises above the hysteresis value.
- If the secondary temperature deviates by more than 2°C (4°F) (default) above set point for 2
minutes or more, a 'A25 - Secondary Water High Temp' alarm will be generated. This alarm will
remain present until the temperature falls below the hysteresis value.
- The high and low temperature alarms are ignored for a period of 20 minutes (default) on start
up to allow the system time to settle without generating nuisance alarms.
In 'Fixed SP + Dew Point Offset' control mode, the set point can be overridden by a Dew Point condition
when there is a risk of condensation at the IT equipment. The room temperature and relative humidity
are constantly monitored & used to calculate the anticipated dew point adjacent to the CDU (or
wherever the room temp/hum senor has been located).
- Dew Point Offset – When activated, this will be displayed on the Home screen under the Unit
Mode heading.
With this cooling mode, the CDU will operate as per fixed setpoint mode unless the dewpoint
temperature rises to within 3°C (6°F) of this setpoint. When this happens, Dewpoint override
will be activated and the controller will re-adjust the fixed setpoint to keep it at least 3°C (6°F)
above the dewpoint.
Pressure sensors PS1 and PS2 are used to monitor the differential pressure across the Secondary circuit
filter & give pre-warning of potential filter clogging.
- If the filter differential pressure exceeds 0.2Bar (3PSI) for, then an 'A38 – Secondary Filter Dirty'
alarm is generated.
Secondary flow rate is monitored with a calorimetric flow meter at the Secondary outlet from the CDU.
The flow can be read on the Home screen or on page 3 of the Status screen.
NOTICE! Flows below 4L/M (1USgpm) are outside the range of the flow sensor and will
not be displayed.
CDU Operating & Maintenance Guide
Neptune DWC RM100 in-rack Coolant Distribution Unit
26
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