Microprocessor Controller for DOAS
50
Appendix G: Fault Detection and Diagnostics
•
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.
The Fault Detection and Diagnostics (FDD) will send a
feedback signal from the outdoor air (OA) damper to
the controller on the OA damper user interface. This
allows the controller to determine if the economizer
is operating correctly. Various faults and statuses will
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’.
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
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.
OA Actuator Feedback
OA Actuator Output
