Commissioning Instructions

Step 8 – Fault detection and diagnostics parameters
27
Unrestricted
A6V12035398
Dual Duct VAV fault determination
Duct 1 and Duct 2 have separate faults and configurations. Dual duct
configurations can be set to specify which duct is for cooling or heating
temperature control.
IF
AND
THEN
Duct1(2) air
flow < Duct1(2)
air flow Setpoint
minus flow
tolerance 1(2)
Duct1(2) air flow
> Duct1(2) air
flow Setpoint
plus flow
tolerance 1(2)
conditions
exists for
greater than
flow fault
delay1(2)
Number of
unstable
positions exceed
change limit1(2)
within the
change time
1(2)
(2)
Duct1(2) air
flow
FAULT
Duct1(2) 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 reset1(2) from ‘Ready’ to ‘Reset’.
2)
Damper position changes must exceed VAV position tolerance1(2) for each unstable cycle.
Note: for Dual Duct faults, each duct has individual configuration limits/delays.
• For each duct, FDD Fault determinations to be enabled, the following conditions must be met.
o Common DXR object ‘AHU MODE’ (set by central commands) present value is ‘On’
o See note in Step 9 when AHU MODE is overridden for testing.
• Supply air flow fault 1 (2): Hi Flow
▪ Supply air flow 1 (2) remains greater than Supply air flow setpoint 1 (2) by Supply airflow fault
tolerance 1 (2) for the duration of Supply air flow fault delay 1 (2) (default 600 seconds each)
o When the flow and flow setpoint return to be within the fault tolerance, the fault will be
automatically reset.
• Supply air flow fault 1 (2): Low Flow
▪ Supply air flow 1 (2) remains less than Supply air flow setpoint 1 (2) by Supply air flow fault
tolerance 1 (2) for the duration of Supply air flow fault delay (default 600 seconds each)
o When the air flow and flow setpoint return to be within the fault tolerance, the fault will be
automatically reset.
• Supply unstable control fault 1 (2)
▪ Unstable conditions exist if the flow control loop causes the Supply air VAV position 1 (2) to
repeatably alternate between open and close directions with transition that exceeds the Supply
position tolerance 1 (2). The unstable control fault will be triggered if the open/close cycles is equal
to or greater than the Supply position change limit 1 (2) and occur within the specified Supply
position change time limit 1 (2) (600 seconds).