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3 pumps
One lead pump, see
par. 25-05, Fixed Lead Pump
. Two fixed speed pumps controlled by built-in relays.
3.23.3. 25-2* Bandwidth Manager
Parameters for setting the bandwidth within which the pressure will be allowed to operate before staging/destaging fixed speed pumps. Also includes
various timers to stabilize the control.
25-20 Staging Bandwidth [%]
Range:
Function:
10%
*
[1 - 100 %]
Set the staging bandwidth (SBW) percentage to accommodate normal system pressure fluctuation. In cascade
control systems, to avoid frequent switching of fixed speed pumps, the desired system pressure is typically kept
within a bandwidth rather than at a constant level.
The SBW is programmed as a percentage of par. 3-02 Minimum Reference and par. 3-03 Maximum Reference.
For example, if the set-point is 5 bar and the SBW is set to 10%, a system pressure between 4.5 and 5.5 bar is
tolerated. No staging or de-staging will occur within this bandwidth.
25-21 Override Bandwidth [%]
Range:
Function:
100% = Disabled
*
[1 – 100%]
When a large and quick change in the system demand occurs (such as a sudden water demand), the system
pressure rapidly changes and an immediate staging or destaging of a fixed speed pump becomes necessary to
match the requirement. The override bandwidth (OBW) is programmed to override the staging/destaging timer
(par. 25-23/25-24) for immediate response.
The OBW must always be programmed to a higher value than the value set in
Staging Bandwidth
(SBW), par.
25-20. The OBW is a percentage of par.3-02 Minimum Reference and par. 3-03 Maximum Reference..
Setting the OBW too close to the SBW could defeat the purpose with frequent staging at momentary pressure
changes. Setting the OBW too high might lead to unacceptably high or low pressure in the system while the SBW
timers are running. The value can be optimized with increased familiarity with the system. See
Override Band-
width Timer
, par. 25-25.
VLT
®
HVAC Drive Programming Guide
3. Parameter Description
MG.11.C5.02 - VLT
®
is a registered Danfoss trademark
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