Closed Loop Control; Staging / De-Staging Of Variable Speed Pumps Based On Drive Speed - Danfoss VLT Series Operating Instructions Manual

1 Extended and Advanced Cascade Controller
Option

1.5.3 Closed Loop Control

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The master drive is the primary controller for the system. It monitors the output pressure, adjusts the speed of the frequency converters and decides
when to add or remove stages. To perform this function the master drive must be setup in closed loop mode with a feedback sensor connected to an
analog input of the Drive.
The PID controller of the master drive must be setup to match the needs of the installation. Setting up the PID parameters is described in the
Drive Programming Guide

1.5.4 Staging / De-staging of variable speed pumps based on Drive Speed

In Master-Follower configurations and Mixed Pump configurations the variable speed pumps are staged and de-staged based on the speed of the Drives.
Staging occurs when the speed of the Drives has reached the value in parameter 27-31 (27-32) Stage on Speed. At this speed the system pressure is
still maintained but the pumps are beginning to operate outside of their peak efficiency points. Staging on an additional pump will lower the speed of all
of the running pumps and provide a more energy efficient operation.
De-staging occurs when the speed of the Drives drops below the value in parameter 27-33 (27-34) Stage Off Speed. At this speed the system pressure
is still maintained but the pumps are beginning to operate below their peak efficiency points. De-staging a pump will cause the speed of the Drives to
increase into a more energy efficient range.
Parameters 27-31 (27-32) Stage on Speed and 27-33 (27-34) Stage Off Speed are installation dependent. These parameters are indexed parameters
with one set of entries for each pump stage.
The stage on and de-stage off speed can be auto tuned during automation or set manually. If Auto-tune is enabled the system will start operation using
default settings or the pre settings done by the user in P27-31 (27-32) and 27-33 (27-34) before enabling the auto-tune.
The goal is to find the stage on and off speeds where the system is most energy efficient. See drawing below.
Illustration 1.14: Staging:
A: Wrong adjusted stage on speed
B: Correct adjusted stage on speed
C: Stage on speed pump 2
When the system is set in operation it will monitor the actual energy consumption and fine adjust every time a stage or de-stage takes place.
This feature will over time ensure the most energy efficient way of operation taking into account wear and tear of the pump system.
Danfoss has available the Multiple Unit Staging Efficiency Calculator (MUSEC), a free software program available on the Danfoss web site. By entering
pump and system data, MUSEC provides the optimal settings for the Stage on Speed and Stage off Speed parameters.
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and will not be covered in this manual. Please see also application note Master/Follower Operation, included in this manual.
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