Belimo NMV-D2M - Page 43

43
4A1PC-T V2.1 NMV-D2M-EN 11-02-04.doc PM VAV - Subject to technical changes
VAV – Module NMV-D2M
Sequence
- Reference signal hunting
- Volumetric flow following the setpoint
- Damper hunting in the control range
N-P1.9 VAV-Box
............................................................................................................
unstable reference signal
Suggestions for improvements
Match the reference control circuit correctly and adapt
the controller parameters (P-
band, etc.) to suit the
complexity of the plant.
Investigate the positioning of the room tempera
ture
sensor. Mounting (e.g. tension from the con
duit),
draughts, sun, etc. can have a direct effect on the
quality of control.
Suitable Test-Sequences
- Test 2 Max-Auto 6m.txt
- Test 3 Max-Auto-Min 9m.txt
-
Record the symptom with ‘Live Trend’ over an extended period of time,
e.g. overnight. This allows intermittent faults to be lo
cated more easily.
Note:
The Test-Sequence is discontinued because of the lack of system
supply pressure. Fault alarm: ‘Inadequate supply air pressure’ is given.
Cause and consequence
Room temperature control circuits are usually slow-
response control loops: A tendency to hunt is an
indication of either a lack of settings or incorrect set-
tings.
The VAV controller follows the reference signal, which
is its task. Therefore, when a system is hunt
ing it
means that the damper actuator is in con
stant motion.
So an adverse effect on service life is an inevitable
consequence.
Pres
sure control is affected and, as a result, also the
remaining VAV-boxes in the same section.
N-P1.10 VAV-Box
................................................................................
unsuitable reference signal <-> Mode
S
A
D
A
Sequence
a) Step 1 + 3: V’max / V’min
Function correct
b) Step 2: Auto (reference input active)
- DDC output, room controller: 5.0 V
- NMV-D2M regulates to 245 instead of 275 m
3
/h
c) Step 2: Auto (reference input active)
- DDC output, room controller: 0.0 V
- Damper closes completely instead of to V’min
Suggestions for improvements
a) Change over the NMV-
D2M to the 0...10 V mode,
or
b) Change over the DDC output, room controller to
working range 2...10 V (if this is possible).
Suitable Test-Sequences
- Test 2 Max-Auto 6m.txt
- Test 3 Max-Auto-Min 9m.txt
Note:
If the system does not attain the required supply pressure – during the
test start – the Test-Sequence is discontinued and the fault alarm ‘In-
adequate supply air pressure’ is given.
Natura lly , the op posi te situ ation c an also ar ise: ‘DDC 2...10 V, NMV-
D2M 0...10 V’.
In this case the result is a worse deviation in the V’min range.
Cause
- The external reference signal (DDC, room tempera-
ture controller) has a working range of 0...10 V
- The NMV-D2M is is set to 2...10 V mode
Function: 0 V = Close
2...10 V = V’min...V’max
The NMV-D2M is closed completely by the 0 V sig-
nal instead of to the required V’min (see c).
a
b
c
S
A
D
A
a
NMV-D2M – Diagnosis
Legend
Legend