Commissioning Instructions
Step 8 – Fault detection and diagnostics parameters
17
Unrestricted
A6V12035398
Supply VAV air flow fault determination
IF
AND
THEN
Supply air flow
< Supply air
flow Setpoint
minus flow
tolerance
Supply air flow >
Supply air flow
Setpoint plus
flow tolerance
conditions
exists for
greater than
flow fault
delay
Number of
unstable
positions exceed
change limit
within the
change time
(2)
Supply air flow
FAULT
Supply air
flow
unstable
FAULT
(1)
AHU MODE = ON
NO
-
-
-
Normal
Normal
YES
-
YES
-
Lo Flow
-
-
NO
-
-
Normal
-
-
YES
YES
-
Hi Flow
-
-
-
-
NO
-
Normal
-
-
-
YES
-
Fault
AHU MODE = OFF
-
-
-
-
Normal
Normal
1)
Unstable fault conditions must be manually reset by setting Control reset from ‘Ready’ to ‘Reset’.
2)
Damper position changes must exceed VAV position tolerance for each unstable cycle.
• For FDD Fault determinations to be enabled, the following conditions must be met.
o DXR object ‘AHU MODE’ (set by central commands) present value is ‘On’ (1)
o See note in Step 9 when AHU MODE is overridden for testing.
• Supply VAV air flow fault: Hi Flow
• Supply air flow remains greater than Supply air flow setpoint by Supply VAV airflow fault tolerance for
the duration of Supply VAV air flow fault delay (default 600 seconds)
o When the flow and flow setpoint return to be within the fault tolerance, the fault will be
automatically reset.
• Supply VAV air flow fault: Low Flow
• Supply air flow remains less than Supply air flow setpoint by Supply VAV air flow fault tolerance for the
duration of Supply VAV air flow fault delay (default 600 seconds)
o When the air flow and flow setpoint return to be within the fault tolerance, the fault will be
automatically reset.
• Supply VAV unstable control fault
• Unstable conditions exist if the flow control loop causes the supply damper to repeatably alternate
between open and close directions with transition that exceeds the change position tolerance. The
unstable control fault will be triggered if 5 open/close cycles (Supply change limit count) occur within the
specified Supply change time limit (600 seconds).
o Unstable fault point will remain at Fault until the user/operator commands the Supply VAV
unstable control reset from ‘Ready‘ to ‘Reset‘. This will clear the unstable fault and return the
Unstable control reset back to ‘Ready‘.