Installation and Maintenance Manual

Startup
UNT-SVX07D-EN 103
speed fan operation. A controller can receive a BAS-
communicated outdoor air damper minimum position.
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 the fan is running at low speed,
regardless of the occupancy state. Refer to Table 34 and
Tab l e 3 5 for more information about how the controller
determines the position of the modulating outdoor air
damper.
Economizing (Free Cooling) (UC400)
Cooling with outdoor air (during the times when the
temperature is low enough to allow) is referred to as
economizing (free cooling). The UC400 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.
Two-position Control Of A Modulating
Outdoor Air Damper (UC400)
The UC400 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.
Electric Heat Operation (UC400)
The UC400 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 UC400
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 UC400 will operate electric heat only
when hot water is not available (for example, in a
changeover unit). In addition, the UC400 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 (UC400)
The UC400 controller supports space dehumidification
when:
• Mechanical (DX or hydronic) cooling is available
Table 34. Modulating outdoor air damper position
setp
oint determination (UC400)
Occupancy
BAS-
communicated
Setpoint
Fan
speed
Active
Minimum
Setpoint
Unoccupied Any value Any value 0% (closed).
• Occupied
• Occupied bypass
• Occupied standby
Valid Any value BAS-
communicated.
• Occupied
• Occupied bypass
• Occupied standby
Invalid Low Occupied low fan
minimum.
• Occupied
• Occupied bypass
Invalid Medium/
high
Occupied
minimum.
Occupied standby Invalid Medium/
high
Occupied
standby
minimum.
Table 35. Relationship between outdoor temperature
sensors and damper position (UC400)
Outdoor Air
Temperature
Modulating outdoor air damper position
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
possible (Refer to
section,
“Economizing
(Free Cooling)
(UC400),”
p. 103
).
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
possible (Refer to
section,
“Economizing
(Free Cooling)
(UC400),”
p. 103
).
Open to occupied
minimum
position.
Open to occupied
standby minimum
position.
Closed.
UNT-SVX07_-EN.book Page 103 Friday, April 27, 2012 9:40 AM