Belimo NMV-D2M - Diagnosis ________________________________________________________________ N-P; Index of Recorded Test-Sequences

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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-P Diagnosis
The ‘Test’ function in the ‘Service’ register allows VAV-/CAV-boxes to be
diagnosed in easy and efficient fashion.
An active check of system supply pressure provides an indication of the
function and efficiency of the pressurising device and its control system.
Test reports produced with this function serve as test logs, as plant
documentation and, the event of a fault, as an aid for the control and ven-
tilation technicians involved.
By means of 10 examples the results of the diagnosis function are ex-
plained and the most suitable Test-Sequences for similar situations sug-
gested. Due to the great variety of
Plant concepts, appropriate for particular types of buildings
Plant sizing and rating
Control strategies
Design-related differences between different makes of air box
the examples shown here may differ from the records obtained from your
plant.
Below are descriptions and explanations of 10 examples of VAV- / CAV -
boxes that are functioning either correctly or incorrectly.
N-P1 Index of recorded Test-Sequences
# Air unit type..................................................................................................Function / Fault
1. VAV..............................................................................correct function
2. CAV..............................................................................correct function
3. VAV / CAV................................................no system supply pressure
4. VAV / CAV..................................insufficient system supply pressure
5. VAV / CAV....................................excessive system supply pressure
6. VAV / CAV................................................................ oversized air box
7. VAV / CAV................................................. wrong direction of rotation
8. VAV / CAV............................. leakage air with VAV controller closed
9. VAV..............................................................unstable reference signal
10. VAV..........................................unsuitable reference signal <-> Mode
System test
The following points should be checked before any faults
in the installation or faults in operation of the VAV/CAV-
boxes are recorded and analysed:
- Installation: anti-rotation device / spindle attachment /
sensor connection
- Connection: power / wiring / polarity
- Control: conventional or bus system
See 4. NMV-D2M Product Information
for more information on function testing and NMV-
D2M
analysis options.
Planning and installation faults
and malfunctions resulting from them can only be cor-
rected to a limited extent and sometimes not at all.
Therefore, it is essential to adhere to the sizing and
installation instructions provided by the manu
facturer of
the air box.
System supply pressure
A functioning VAV-/CAV-installation needs a cor
rectly
designed and adjusted pressurizing device.
The air volume controller adjusts the control dam
per of
the VAV-/CAV-box according to the
value of supply
pressure available. If there is no supply pressure, or
insufficient pressure, the control damper will remain in
the open position. This does not mean that the air vol-
ume controller is malfunc
tioning but simply the result of
the lack of air. The pressure con
ditions in the ducting
system must be correct in order for control to be effec-
tive.