Danfoss VLT HVAC Series Programming Manual page 262

3 Parameter Description
3.23.3 25-2* Bandwidth Settings
Parameters for setting the bandwidth within which the pressure will be allowed to operate before staging/de-staging fixed speed pumps. Also includes
various timers to stabilize the control.
25-20 Staging Bandwidth
Range:
10 %* [1 - par. 25-21 %]
3
25-21 Override Bandwidth
Range:
100 %* [par. 25-20 - 100 %]
3-238
Function:
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.20-13
Maximum Reference/Feedb.
20-14 . For example, if the setpoint 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.
Function:
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 de-staging of a fixed speed pump
becomes necessary to match the requirement. The override bandwidth (OBW) is programmed to
override the staging/de-staging timer (par.25-23
Delay
) for immediate response.
The OBW must always be programmed to a higher value than the value set in
Staging Bandwidth
(SBW), par.25-20
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
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VLT ® HVAC Drive Programming Guide
Minimum Reference/Feedb.
SBW Staging Delay
and par.25-24
. The OBW is a percentage of par. and par. .
and par.
SBW De-staging
Staging Bandwidth