Belimo NMV-D2M - Page 41

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4A1PC-T V2.1 NMV-D2M-EN 11-02-04.doc PM VAV - Subject to technical changes
VAV – Module NMV-D2M
Legend
Sequence
a) Step 1: V’max
- Volumetric flow at setpoint
- Damper control range ~42%
b) Step 3: V’min
- Volumetric flow at setpoint
- Damper control range ~28%
N-P1.5 VAV- / CAV-Box
.........................................................................
excessive system supply pressure
Suggestion for optimising
Set the fan and pressure control so that the damper
position of the VA-V/ CAV-boxes in V’max opera
tion is
approximately 80%
Suitable Test-Sequences
- BasicTest Max-Min 5m.txt
Cause
Fan or pressure control rated too high or set up too
high.
a
b
S
A
D
A
Suggestion for a remedy
- Increase the operating flow rate setting so that the
V’min volumetric flow setting corresponds to an ac-
tive differential pressure setting of more than 2 Pa.
- Investigate changing the air box (smaller nominal
diameter).
N-P1.6 VAV- / CAV-Box
.............................................................................................................
oversized air unit
Sequence
a) The setpoint is reduced in 1% steps
b) - Setpoint less than active differential pressure
2 Pa
- NMV-D2M function
Leakage-flow suppression activated
c) - Setpoint less than active differential pressure
2 Pa
- Actual volumetric flow rate = 0
Suitable Test-Sequences
- Test 5 Max-Min-Max [1%] 37m.txt
- Test 4 Max-Mid-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.
See:
- Air box manufacturer’s documentation on minimum air flow for the VAV-/CAV-
box
- section ‘N-S1.2.1 Control range’
Causes and consequences
- VAV-/CAV-box oversized for the required value of
volumetric flow
- Oversized air boxes are being operated in a difficult-
to-control, sometimes uncontrollable, range
- The function range of the VAV-/CAV-box must not
exceed 2 Pa. Otherwise the air box will be operated
near leakage-flow suppression, i.e. in the uncontrol-
lable range.
a
b
c
S
A
D
A
NMV-D2M – Diagnosis
Legend