Operating instructions

3.23.4 25-5* Alternation Settings
Parameters for defining the conditions for alternation of the
variable speed pump (lead), if selected as part of the control
strategy.
25-50 Lead Pump Alternation
Option: Function:
Lead pump alternation equalizes the use of
pumps by periodically changing the pump that
is speed controlled. This ensures that pumps
are equally used over time. Alternation
equalizes the usage of pumps by always
choosing the pump with the lowest number of
used hours to stage on next.
[0]
* Off No alternation of lead pump function will take
place. It is not possible to set this parameter to
options other that Off [0] if par. 25-02 Motor
Start is set other than Direct on Line [0].
[1] At staging Alternation of the lead pump function will take
place when staging another pump.
[2] At
command
Alternation of the lead pump function will take
place at an external command signal or a pre-
programmed event. See par. 25-51 Alternation
Event for available options.
[3] At staging
or
command
Alternation of the variable speed (lead) pump
will take place at staging or the “At Command”
signal. (See above.)
NOTE
It is not possible to select other than Off [0] if
par. 25-05 Fixed Lead Pump is set to Yes [1].
25-51 Alternation Event
Option: Function:
This parameter is only active if the options At
Command [2] or At Staging or Command [3]
have been selected in par. 25-50 Lead Pump
Alternation. If an Alternation Event is selected,
the alternation of lead pump takes place every
time the event occurs.
[0]
* External Alternation takes place when a signal is
applied to one of the digital inputs on the
terminal strip and this input has been assigned
to Lead Pump Alternation [121] in parameter
group 5-1*, Digital Inputs.
[1] Alternation
Time Interval
Alternation takes place every time
par. 25-52 Alternation Time Interval, expires.
[2] Sleep Mode Alternation takes place each time the lead
pump goes into sleep mode.
Par. 20-23 Setpoint 3 must be set to Sleep Mode
[1] or an external signal applied for this
function.
25-51 Alternation Event
Option: Function:
[3] Predefined
Time
Alternation takes place at a defined time of the
day. If par. 25-54 Alternation Predefined Time, is
set, the alternation is carried out every day at
the specified time. Default time is midnight
(00:00 or 12:00AM depending on the time
format).
25-52 Alternation Time Interval
Range: Function:
24 h * [1 - 999
h]
If Alternation Time Interval [1] option in
par. 25-51 Alternation Event, is selected, the
alternation of the variable speed pump takes
place every time the Alternation Time Interval
expires (can be checked out in
par. 25-53 Alternation Timer Value).
25-53 Alternation Timer Value
Range: Function:
0 * [0 - 0 ] Readout parameter for the Alternation Time Interval
value set in par. 25-52 Alternation Time Interval.
25-54 Alternation Predefined Time
Range: Function:
Application
dependent
*
[Applica-
tion
dependant]
If optionPredefined Time [3] in
par. 25-51 Alternation Event, is selected,
the variable speed pump alternation is
carried out every day at the specified
time set in Alternation Predefined
Time. Default time is midnight (00:00
or 12:00AM depending on the time
format).
25-55 Alternate if Load < 50%
Option: Function:
If Alternation If Capacity <50% is enabled, the pump
alternation can only occurs if the capacity is equal
to or below 50%. The capacity calculation is the
ratio of running pumps (including the variable
speed pump) to the total number of available
pumps (including variable speed pump, but not
those interlocked).
Capacity =
N
RUNNING
N
TOTAL
× 100 %
For the Basic Cascade Controller all pumps are equal
size.
[0] Disabled The lead pump alternation will take place at any
pump capacity.
[1]
*
Enabled The lead pump function will be alternated only if
the numbers of pumps running are providing less
than 50% of total pump capacity.
Parameter Description
VLT
®
HVAC Drive Programming Guide
174 MG.11.CA.02 - VLT
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