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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
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
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
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
. 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
25-52 Alternation Time Interval
, expires.
[2]
Sleep Mode
Alternation takes place each time the lead
pump goes into sleep mode.
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
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
, is selected, the
alternation of the variable speed pump takes
place every time the Alternation Time Interval
expires (can be checked out in
25-53 Alternation Timer Value
Range:
Function:
0
*
[0 - 0 ] Readout parameter for the Alternation Time Interval
value set in
25-52 Alternation Time Interval
25-54 Alternation Predefined Time
Range:
Function:
Size related
*
[0 - 0 ]
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 =
NRUNNING
NTOTAL
× 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.
NOTE
Only valid if
is different from
Off
[0].
Parameter Description
VLT
®
HVAC Drive Programming Guide
174
MG.11.CB.02 - VLT
®
is a registered Danfoss trademark
3
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