Danfoss VLT Programming Manual page 175

Parameter Description
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.
3 3
25-50 Lead Pump Alternation
Option:
[0] Off
*
[1] At staging
[2] At
command
[3] At staging or
command
NOTE
It is not possible to select other than Off [0] if 25-05 Fixed
Lead Pump is set to Yes [1].
25-51 Alternation Event
Option:
[0] External
*
[1] Alternation
Time Interval
[2] Sleep Mode
174
®
VLT
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.
No alternation of lead pump function will take
place. It is not possible to set this parameter to
options other that Off [0] if 25-02 Motor Start is
set other than Direct on Line [0].
Alternation of the lead pump function will take
place when staging another pump.
Alternation of the lead pump function will take
place at an external command signal or a pre-
programmed event. See 25-51 Alternation Event
for available options.
Alternation of the variable speed (lead) pump
will take place at staging or the "At Command"
signal. (See above.)
Function:
This parameter is only active if the options At
Command [2] or At Staging or Command [3]
have been selected in 25-50 Lead Pump
Alternation. If an Alternation Event is selected,
the alternation of lead pump takes place every
time the event occurs.
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.
Alternation takes place every time
25-52 Alternation Time Interval, expires.
Alternation takes place each time the lead
pump goes into sleep mode. 20-23 Setpoint 3
must be set to Sleep Mode [1] or an external
signal applied for this function.
MG.11.CB.02 - VLT
HVAC Drive Programming Guide
25-51 Alternation Event
Option:
[3] Predefined
Time
25-52 Alternation Time Interval
Range:
24 h [1 - 999
*
h]
25-53 Alternation Timer Value
Range:
0 [0 - 0 ] Readout parameter for the Alternation Time Interval
*
25-54 Alternation Predefined Time
Range:
Size related
*
25-55 Alternate if Load < 50%
Option:
[0] Disabled The lead pump alternation will take place at any
[1] Enabled The lead pump function will be alternated only if
*
NOTE
Only valid if 25-50 Lead Pump Alternation is different from Off
[0].
®
is a registered Danfoss trademark
Function:
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).
Function:
If Alternation Time Interval [1] option in
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 25-53 Alternation
Timer Value).
Function:
value set in 25-52 Alternation Time Interval.
Function:
[0 - 0 ]
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).
N RUNNING
Capacity =
× 100 %
N TOTAL
For the Basic Cascade Controller all pumps are
equal size.
pump capacity.
the numbers of pumps running are providing less
than 50% of total pump capacity.