Belimo NMV-D2M - N-D Miscellaneous and Formulae; N-D1 Function checks of the NMV-D2 M; N-D1.1 Level 2 function check

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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
N-S1.2.1 Control range
The control of volumetric flow of a CAV/VAV box is based upon the differ-
ential pressure measuring picked up at its baffle device. This requires a
minimal differential of approx. 2…5 Pa independently of the VAV box type
or its manufacturer. This due to the fact that that the minimal limitation is a
physical limitation given by the entire control equipment (design and me-
chanical construction, pick-up device and the differential pressure meas-
urement). The proper control of a VAV control loop can not be achieved
below that border.
The Belimo VAV controller NMV-D2M has an incorporated feature called
‘creep flow suppression’ which suppresses the differential-pressure sig-
nals around zero. The limiting is able to prevent undefined movements of
the actuator within the pressure range below 2 Pa until the setpoint re-
quires an volumetric flow above that area.
The smallest useable volumetric flow setting within the control range of a
VAV box get influenced by the V’nom – V’max ratio. The smaller the
V’max setting the bigger gets the influence of the physical control limita-
tion to the usable control range width.
Below you’ll find a chart showing the dependencies and influences.
The example shows a Belimo VAV compact controller NMV-D2M (with 2
Pa creep flow suppression) with different V’Max settings:
Adjustment
Case 1 Case 2 Case 3 Case 4
V’nom
660 m3/h
V’max s etting 660 m
3
/h 500 m
3
/h 300 m
3
/h 200 m
3
/h
smallest controllable volu-
metric flow (equals ~2 Pa)
~60 m
3
/h
usable Control range
(box depending)
x...100% V’nom
9...100%
usable Control range 60...660 m
3
/h 60...500 m
3
/h 60...300 m
3
/h 60...200 m
3
/h
resulting smallest V’min
setting (equals ~2 Pa)
(in % of V’max)
9% 12% 20% 30%
conclusion .
good good over sized over sized
Note: the values of the chart are VAV box specific values, they might differ for other boxes!
As a rule, an oversized VAV-Box has a smaller control range than a cor-
rect sized one.
- V’min setting below the usable control range
A V’min settings below the usable control range can be adjusted for cer-
tain applications e.g. box requires shut-off position. To inform the user
that he is using a difficult setting, the value in the ‘% of V’max’ field
changes its colour to red.
Display in tab ‚Service’
Display in ‚Trend View’