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Neptune DWC RM100 in-rack Coolant Distribution Unit
2.3.2 Primary Circuit Operation
The primary water temperature (T1) is monitored at the inlet to the RM100 cabinet. The nominal
cooling performance of the CDU has been calculated on a chilled water temperature between 4 and
10°C (40 and 50°F).
- If the primary temperature falls below default 4°C (40°F), an 'A22 - Primary Water Low Temp'
alarm will be generated. This alarm will remain present until the temperature rises above the
default 1°C (2°F) reset hysteresis.
- If the primary temperature rises above default 11°C (52°F), an 'A23 - Primary Water High Temp'
alarm will be generated. This alarm will remain present until the temperature falls below the
default 1°C (2°F) reset hysteresis.
- The high and low temperature alarms are ignored for a default 20-minute period on start up to
allow the system time to settle without generating nuisance alarms.
The temperature PID control loop will be operational from when the Start/Stop button is pressed and
the pump has ramped up to speed. If the secondary circuit temperature rises above the set point, then
Control Valve will start to open to allow more primary cooling water through the heat exchanger. The
control valve will modulate from 0% (full by-pass) to 100% (full flow through heat exchanger) if a 3-
way valve is fitted, or from 0% (no flow) to 100% (full flow through heat exchanger) if a 2-way valve is
fitted. The valve position can be monitored on the Home screen or page 1 of the Status screen. The
demand signal to the valve is compared to a position feedback signal every 15 minutes (default) to
check the healthy operation of the valve.
- If the feedback signal is more than 10% (default) different from the demand signal (allowing
for the drive time of the actuator to respond to load changes), then a 'A20 - Valve Fault' event
will be generated. The valve will continue to operate until fault is rectified.
The Control Valve is a drive open/spring return device and in the event of the positioning signal being
lost, it will return to a full by-pass position (3-way valve), or closed position (2-way valve), i.e. no cooling.
Primary flow rate is monitored with a calorimetric flow meter at the Primary inlet to the CDU. The flow
can be read on the Home screen or on page 2 of the Status screen.
NOTICE! The flow meter will only read the 'total' primary flow through the RM100 unit,
it does not monitor the flow rate through the heat exchanger, unless a 2-way control
valve is used
- An 'A21 – Primary Water Low Flow' alarm is generated if: - The 'A25 – Secondary Water High
Temperature' alarm is active, demand to the control valve is at 100%, but Primary water
temperature is within normal limits.
An 'A33 - Primary No Flow' alarm can also be generated if: - The 'A25 - Secondary Water High
-
Temperature' event is active, demand to the control valve is at 100% and there is a 'A23 -
Primary Water High Temperature' alarm present.
NOTICE! Flows below 2L/M (0.5USgpm) are outside the range of the flow sensor and
will not be displayed.
CDU Operating & Maintenance Guide
27
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