Pump flow/pressure performance (pump speed) can be controlled through either a flow or
differential pressure control loop depending on Configuration (see Configuration - Pump Control).
Flow Control
Monitors the Secondary flow with a calorimetric flow meter and on start-up, the control loop will
increase the pump speed in stages until the flow matches the demand setpoint.
DP Control
Monitors the Secondary differential pressure with sensors on the supply & return connections of the
CDU and on start-up, the control loop will increase the pump speed in stages until the DP matches the
DP setpoint.
The pump control loop has a default scan time of 10 seconds to avoid control oscillation.
- If Pump 1 fails to reach 90% (default) of the flow/DP demand in a default time period of 100secs,
then it is assumed there is a pump flow/pressure fault. The pump will ramp down to a stop and
Pump 2 will be initialised. At the same time, an ‘A17 – Pump 1 Fault’ alarm will be generated.
- If Pump 2 also fails to reach 90% of the set DP/flow demand within the time limit, an ‘A18 –
Pump 2 Fault’ alarm will be generated.
- The unit will then continue to operate with Pump 2 until faults are investigated and alarms
manually cleared.
- The above assumes Pump 1 is the initial operating pump, the reverse would apply if Pump 2
was the operating pump.
During normal healthy running for run/standby pump operation, the pumps will operate on a duty
sharing cycle, i.e. every 7 days (default) the operational pump will ramp down to a stop and the standby
pump will then start and continue operating for the next 7 days etc. Changeover default time is set at
10:00am on a Monday morning (default) and the complete changeover sequence takes approx. 0.25
seconds (default).
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