Trane VUV Installation, Operation And Maintenance Manual page 87

A BAS-communicated minimum position setpoint has priority
over all locally configured setpoints. When a communicated
minimum position setpoint is not present, the controller uses
the configured minimum position for low fan speed whenever
Table 33. Modulating outdoor air damper position setpoint determination
Occupancy
Unoccupied
Occupied
Occupied bypass
Occupied standby
Occupied
Occupied bypass
Occupied standby
Occupied
Occupied bypass
Occupied standby
Table 34. Relationship between outdoor temperature sensors and damper position
Outdoor Air Temperature
No or invalid outdoor air temperature
Failed outdoor air sensor
Outdoor air temperature present and
economizing possible (Refer to section,
"Economizing (Free Cooling)"
Outdoor air temperature present and
economizing not possible (Refer to section,
"Economizing (Free Cooling)"
Economizing (Free Cooling)
Cooling with outdoor air (during the times when the
temperature is low enough to allow) is referred to as
economizing (free cooling). The controller and applications
with modulating outside air damper, support economizing. The
modulating outdoor air damper provides the first source of
cooling for the controller.
The controller initiates economizing if the outdoor air
temperature is below the economizer enable point
(configurable using the Tracer® TU service tool). If
economizing is initiated, the controller modulates the outdoor
air damper (between the active minimum damper position and
100 percent) to control the amount of outdoor air cooling
capacity. When the outdoor air temperature rises 5°F (2.8°C)
above the economizer enable point, the controller disables
economizing and moves the outdoor air damper back to its
predetermined minimum position, based on the current
occupancy mode or communicated minimum outdoor air
damper position. If an outdoor air temperature value is not
present, economizing is disabled.
Modulating Outdoor Air Damper
The controller supports two-position outdoor air damper
actuators. However, a modulating outdoor/return air damper
actuator can be used for two-position control. Two-position
control can be achieved by not providing an outdoor air
temperature (neither hard wired nor communicated) to the
controller, and by setting the damper minimum position (using
the Tracer® TU service tool) to the desired value, typically
100 percent.
UV-SVX005G-EN
BAS-communicated Setpoint
Any value
Valid
Invalid
Invalid
Invalid
Occupied or Occupied Bypass
Open to occupied minimum position
Open to occupied minimum position
Economizing; damper controlled between
occupied minimum position and 100
)
percent
Open to occupied minimum position
)
the fan is running at low speed, regardless of the occupancy
state. Refer to Table 33, p. 87
information about how the controller determines the position of
the modulating outdoor air damper.
Fan speed
Any value
Any value
Low
Medium/high
Medium/high
Modulating outdoor air damper position
Occupied Standby
Open to occupied standby minimum
position
Open to occupied standby minimum
position
Economizing; damper controlled
between occupied standby minimum
position and 100 percent
Open to occupied standby minimum
position
Electric Heat Operation
The controller supports both SCR (modulating) and staged
electric heat (1- or 2-stages). SCR heat is only a field-installed
option. In a unit configured with staged electric heat, the
electric heating circuit(s) are cycled ON and OFF appropriately
to maintain the desired space temperature at the active
heating setpoint. In a unit configured with SCR (modulating)
electric heat, the controller will send a 0 to 10 Volt DC signal
to adjust SCR capacity in order to maintain the desired space
temperature.
In both staged and modulating electric heat applications, the
simultaneous use of electric and hydronic heat is not
supported and the controller will operate electric heat only
when hot water is not available (for example, in a changeover
unit). In addition, the controller will run the supply fan for 30
seconds after electric heat is turned OFF in order to dissipate
heat from the unit
Note: This delay does not apply to steam or hydronic heating.
Factory-configured electric heat units have built-in mechanical
protections to prevent dangerously high discharge air
temperatures.
Dehumidification Operation
The controller supports space dehumidification when:
• Mechanical (DX or hydronic) cooling is available
• The heating capacity is located in the reheat position
• The space relative humidity is valid
Start-Up
and Table 34, p. 87 for more
Active Minimum Setpoint
0 percent (closed)
BAS-communicated
Occupied low fan minimum
Occupied minimum
Occupied standby minimum
Unoccupied
Closed
Closed
Open and economizing during unit
operation; otherwise closed
Closed
87