Danfoss VLT HVAC Series, Programming Manual, Page: 221 / 338

No Flow Detection is based on the measurement of speed and power. For a certain speed, the adjustable frequency drive calculates the power at no
flow.
This coherence is based on the adjustment of two sets of speed and associated power at no flow. By monitoring the power, it is possible to detect no
flow conditions in systems with fluctuating suction pressure or if the pump has a flat characteristic towards low speed.
The two sets of data must be based on measurement of power at approx. 50% and 85% of maximum speed with the valve(s) closed. The data are
programmed in the par. 22-3*. It is also possible to run a
Low Power Auto Set-up (par.22-20 Low Power Auto Set-up ), automatically stepping through
the commissioning process and also automatically storing the data measured. The adjustable frequency drive must be set for open-loop in par.
1-00
Configuration Mode , when carrying out the Auto Set-up (See No Flow Tuning par. 22-3*).
If to use the integrated PI controller, carry out No Flow tuning before setting the PI controller parameters!
Low speed detection:
Low Speed Detection
gives a signal if the motor is operating with minimum speed as set in par.4-11
Motor Speed Low Limit [RPM]
or par.4-12
Motor
Speed Low Limit [Hz]
. Actions are common with No Flow Detection (individual selection not possible).
The use of Low Speed Detection is not limited to systems with a no flow situation, but can be used in any system where operation at minimum speed
allows for a stop of the motor until the load calls for a speed higher than minimum speed, e.g., systems with fans and compressors.
In pump systems, ensure that the minimum speed in par.4-11 Motor Speed Low Limit [RPM] or par.4-12 Motor Speed Low Limit
[Hz]
has been set high enough for detection as the pump can run with a rather high speed even with valves closed.
Dry pump detection:
No Flow Detection can also be used for detecting if the pump has run dry (low power consumption-high speed). Can be used with both the integrated
PI controller and an external PI controller.
The condition for Dry Pump signal:
- Power consumption below no flow level
and
- Pump running at maximum speed or maximum reference open-loop, whichever is lowest.
The signal must be active for a set time (par.22-27 Dry Pump Delay ) before selected action takes place.
Possible Actions to select (par.22-26 Dry Pump Function ):
- Warning
- Alarm
No Flow Detection must be enabled (par.22-23
No-Flow Function
) and commissioned (par. 22-3*,
No Power Tuning
).
VLT ® HVAC Drive Programming Guide 3 Parameter Description
MG.11.C6.22 - VLT ® is a registered Danfoss trademark
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