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.
NB!
Only valid if par. 25-50
Lead Pump Alternation
is different from
Off
[0].
25-56 Staging Mode at Alternation
Option: Function:
This parameter is only active if the option selected in par. 25-50
Lead Pump Alternation
is different
from
Off
[0].
Two types of staging and destaging of pumps are possible. Slow transfer makes staging and de-
staging smooth. Quick Transfer makes staging and destaging as fast as possible; the variable speed
pump is just cut out (coasted).
[0] * Slow At alternation, the variable speed pump is ramped up to maximum speed and then ramped down
to a stand still.
[1] Quick At alternation, the variable speed pump is ramped up to maximum speed and then coasted to stand
still.
The below figure is an example of the Slow transfer staging. The variable speed pump (top graph) and one fixed speed pump (bottom graph) are running
before the staging command. When the
Slow
[0] transfer command is activated, an alternation is carried out by ramping the variable speed pump to
par. 4-13
Motor Speed High Limit [RPM]
or par. 4-14
Motor Speed High Limit [Hz]
, and then decelerated to zero speed. After a “Delay Before Starting
Next Pump” (par. 25-58
Run Next Pump Delay
) the next lead pump (middle graph) is accelerated and another original lead pump (top graph) is added
after the “Delay Before Running On Mains” (par. 25-59
Run on Mains Delay
) as a fixed speed pump. The next lead pump (middle graph) is decelerated
to Motor Speed Low Limit and then allowed to vary speed to maintain system pressure.
3 Parameter Description VLT
®
HVAC Drive Programming Guide
250
MG.11.C9.02 - VLT
®
is a registered Danfoss trademark
3
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