Danfoss VLT Series Design Manual page 131

VLT ® HVAC Drive Design Guide
After a time delay, the relay for the fixed speed pump cuts in (staged) and this pump becomes
the new lead pump. The new lead pump ramps up to maximum speed, and then down to minimum
speed; when ramping down and reaching the staging frequency, the old lead pump is now cut in
(staged) on the line power as the new fixed speed pump.
If the lead pump has been running at minimum frequency (fmin) for a programmed amount of
time with a fixed speed pump running, the lead pump contributes little to the system. When the
programmed value of the timer expires, the lead pump is removed, avoiding a heat water-circu-
lation problem.
6.1.10. System Status and Operation
If the lead pump goes into sleep mode, the function is displayed on the local control panel. It is
possible to alternate the lead pump on a sleep mode condition.
When the cascade controller is enabled, the operation status for each pump and the cascade
controller is displayed on the local control panel. Information displayed includes:
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•
•
Pumps Status, a read-out of the status for the relays assigned to each pump. The display
shows pumps that are disabled, off, running on the adjustable frequency drive, or run-
ning on the line power/motor starter.
Cascade Status, a read-out of the status for the cascade controller. The display indicates
when: the cascade controller is disabled, all pumps are off, emergency has stopped all
pumps, all pumps are running, fixed speed pumps are being staged/de-staged, and lead
pump alternation is occurring.
De-staging at No-Flow ensures that all fixed speed pumps are stopped individually until
the no-flow status disappears.
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
6. Application Examples
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