Sequence of operation
CNT-SVX04A-EN
69
Table 40
Relationship between outdoor temperature sensors and damper position
Note 1:
An value of Enable or Disable for nviEconEnable overrides the local decision about damper
position, regardless of the presence of an outdoor air temperature value.
Modulating outdoor air damper calibration
Similar to the modulating valve calibration, the modulating outdoor air damper
calibration is a part of the controller's normal operation, whether at power-up
or during heating and cooling. At power-up, the Tracer ZN.520 zone controller
drives the modulating outdoor air damper to the closed position. The controller
calibrates to the fully closed position by overdriving the actuator (135% of drive
time).
Whenever the Tracer ZN.520 zone
controller generates a damper position
request of zero or 100%, the unit calibrates
the damper actuator by overdriving it.
The controller moves the modulating damper to desired positions based on
calculated capacity. Whenever the controller requests a damper position of
either zero or 100%, the controller overdrives the output by 135% of the stroke
time regardless of the current damper position.
Face and bypass damper operation
The Tracer ZN.520 zone controller actuates face and bypass damper to
modulate a percentage of air to the face of the coil and around the coil (bypass)
to maintain space comfort. Isolation valves (if present) are used to control water
flow through the unit during heating and cooling operation.
In 2-pipe changeover applications, the water temperature needs to suit the
required mode. If the controller requests heating and hot water is available, the
face and bypass damper modulate to the face position. If the controller requests
heating and hot water is not available, the face and bypass damper remains in
the bypass position and water sampling may be invoked. See “Entering water
temperature sampling function” on page 59.
Outdoor air
temperature
Modulating outdoor air damper position (Note 1)
Occupied or
Occupied bypass
Occupied standby
Unoccupied
No or invalid outdoor
air temperature:
Open to occupied
minimum position
Open to occupied
standby minimum
position
Closed
Failed outdoor air
sensor:
Open to occupied
minimum position
Open to occupied
standby minimum
position
Closed
Outdoor air
temperature present
and economizing
feasible:
Economizing,
damper controlled
between occupied
minimum position
and 100%
Economizing,
damper controlled
between occupied
standby minimum
position and 100%
Open and
economizing during
unit operation,
otherwise closed
Outdoor air
temperature present
and economizing not
feasible:
Open to occupied
minimum position
Open to occupied
standby minimum
position
Closed
