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The Fault Detection and Diagnostics (FDD) will send
a feedback signal from the outdoor air (OA) damper
to the controller on the user interface. This allows the
controller to determine if the economizer is operating
correctly. Various faults and statuses display on the
controller and through the Building Management
System as per the Title 24 Economizer Fault Detection
and Diagnostic requirements.
Enable Fault Detection and Diagnostics
When ordered, the FDD
will come enabled from
the factory. The FDD
alarms can be disabled
through the service
config menu in the controller. To access the service
config menu, navigate the following way: Ctrl Variables/
Advanced/Unit Config/Service Config. Alarm tolerance
and read frequency will also be able to be adjusted
through this menu.
There will be an 'Actuator Feedback' screen in the
'Service Info' menu that will show the commanded
damper position, the actual feedback position, and
when the damper positions were last read. This screen
is also where the field could force the FDD to read the
damper position via a check box option. The service
info menu can be accessed via the following:
Ctrl Variables/Advanced/Service Info
OA Actuator Output
OA Actuator Feedback
Faults/Alarms -
Additional faults can generate
when the Economizer FDD is enabled, below is a list of
the alarms and a description of each. These alarms can
also be generated through a BACnet® protocol only.
• Not Economizing when it should will generate
when FDD is enabled, the outdoor damper status is
active on economizer, and the feedback signal from
the OA damper is below the damper commanded
Below is the BACnet Point if the Fault Detection and Diagnostic Alarms are to be read through BACnet:
Variable
OAD_Feedback_Error_Not_
Economizing.Active
OAD_Feedback_Error_
Economizing.Active
OAD_Feedback_Error_OAD_Not_
Modulating.Active
OAD_Feedback_Error_Excess_
OA.Active
Appendix G: Fault Detection and Diagnostics
Points List • BACnet®
Description
Feedback indicated OAD is not opening
during economizer
Feedback indicated OAD is open
Feedback indicated the OAD is not
modulating
Feedback indicates the OAD is not closing
position by more than 1VDC. Because of the speed
of the actuator there is a 3-minute alarm delay to
allow the actuator a chance to "catch up" if a sudden
change in damper position happens.
• Economizing when it should not will generate when
FDD is enabled, the outdoor damper status is NOT
active on economizer, and the feedback signal from
the OA damper is above the damper commanded
position by more than 1VDC. Because of the speed
of the actuator there is a 3-minute alarm delay to
allow the actuator a chance to "catch up" if a sudden
change in damper position happens.
• Damper not modulating will show up when FDD
is enabled, Damper
status is NOT Active
on Economizer, and
feedback signal is not
within 1VDC above
or below the damper
commanded position within 180 seconds.
• Excess outdoor air will generate when FDD is
enabled, the outdoor damper status is active on
economizer, and the feedback signal from the OA
damper is above the damper commanded position
by more than 1VDC. Because of the speed of the
actuator there is a 3-minute alarm delay to allow the
actuator a chance to "catch up" if a sudden change
in damper position happens.
BACnet Modbus
Object
Register
BC-25*
10005
BC-26*
10006
BC-27*
10007
BC-28*
10008
Microprocessor Controller for DOAS
Read
Text or Unit of M
or
Active Inactive
Write
R
Alarm Normal
R
Alarm Normal
R
Alarm Normal
R
Alarm Normal
51
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