Unit installation

CDU Installation Guide Page 33
Cooling Distribution Unit
OPERATION (continued)
6.3 Automatic operation
After commissioning, the unit will be ready to run in automatic mode – press the Start/Stop button on
the control panel to start the unit.
Secondary Circuit Operation
On receiving a start signal, the green Start/Stop push button will illuminate and providing the
reservoir level switch is made, Pump 1 will start to increase in speed – the pump speed as a
percentage of maximum can be read from the second welcome screen (see Section 6.1). The
inverter display will also show the actual ‘frequency’ output to the pump motor.
- If the level switch is not made, signifying insufficient water, then neither main pump
will be allowed to run.
- In this event, the fill pumps will automatically initialise in an attempt to refill the system
and the green ‘Fill Pump Enable’ lamp will illuminate. If after a period of 3 minutes the
level switch has still not made, then the fill pumps will stop and an ‘Insufficient Water
Level’ alarm will be generated. It will not be possible to restart the unit until the alarm
has been manually cleared.
The system pressure at the pump suction (PS1) is continuously monitored (see controller
screen 3-4) to ensure that the system is always pressurized.
- A low system pressure of 0.3Bar (5PSI) or less at PS1 will not stop the main pumps
from running, but will again initialise the fill pumps (after a 10 second delay) to raise
the PS1 pressure to 0.5Bar (8PSI), at which point the fill pumps will stop. At the same
time a ‘Check Water Make-up Level’ warning will be generated. As previously, if the fill
pumps run for more than 3 minutes and the PS1 pressure has still not reached 0.5Bar
(8PSI), then the fill pumps will stop and a ‘Water Make-up Empty’ warning will be
generated. This is a latched warning and will need to be manually cleared, but will not
stop the unit operating.
The differential pressure across the operational pump is monitored with sensors PS1 & PS2
(see controller screen 3-4) and on start up, the pump speed is increased in stages via a
control loop until the differential pressure matches a predefined setting in the software, based
on the number of RDHx’s set during the commissioning stage. The pump pressure control
loop has a scan default time of 10 seconds to avoid control oscillation.
- If Pump 1 fails to reach within 0.5Bar (8PSI) of this differential pressure in a set time
period (default 80secs), then it is assumed that there is a pump flow fault – Pump 1
will ramp down to a stop and Pump 2 will be initialised after a 5 second interval. At the
same time, a ‘Pump 1 Inverter Low Flow’ alarm will be generated.
- If Pump 2 also fails to reach the differential pressure within the time limit, then this
pump will also ramp down to a stop and Pump 1 will be started direct on line (DOL). At
the same time, a ‘Pump 2 Inverter Low Flow’ alarm will be generated.
- If Pump 1 DOL fails to reach an alternative differential pressure set for DOL operation
(default 2Bar (30PSI)), then it too will stop and Pump 2 will be started DOL. At the
same time, a ‘Pump 1 DOL Low Flow’ alarm will be generated.
- In the event that Pump 2 DOL also fails to reach pressure, a ‘Pump 2 DOL Low Flow’
alarm will be generated. The unit will then continue to operate with Pump 2 DOL until
alarms are manually cleared and faults investigated.
During normal healthy running, 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 after a 5 second delay to continue operating for the next 7 days etc. Changeover default
time is set at 03:00 in the morning.
The secondary water temperature is monitored at the reservoir outlet. Two temperature
sensors are positioned here to give component redundancy. The controller will take an
average between the two readings as its input value. If the difference between the two
sensors exceeds 1.0°C (2°F), then a ‘Secondary Temp Diff Error’ alarm will be raised (after a 2
minute delay).