Start Up
UNT-SVX041D-EN
67
Note:
Exhaust fan configuration cannot be selected with
3-speed fan operation.
Important:
If exhaust control is added to an existing
configuration, all other configuration
options should be verified to match the
correct equipment options.Temperature
and flow setpoints will revert to default
values.
The exhaust function is coordinated with the supply fan
and outdoor/return air dampers as follows:
•
The exhaust fan energizes when the fan is running and
when the outdoor air damper position is greater than
or equal to the exhaust fan enable position (or the
outside air damper position at which the exhaust fan
turns
ON
).
•
The exhaust fan turns
OFF
when the fan either turns
OFF
or the outdoor air damper closes to 10 percent
below the exhaust fan enable position.
•
If the exhaust fan/damper enable setpoint is less than
10 percent, the exhaust output is energized if the
outdoor air damper position is at the setpoint and de-
energized at 0.
Valve Operation
The controller supports one or two modulating or two-
position valves, depending on the application. The
controller opens and closes the appropriate valve(s) to
maintain the active zone temperature setpoint at the
heating setpoint in heating mode or the cooling setpoint in
cooling mode (refer to “Cascade Zone Control,”
).
Three-Wire Modulating Valve Operation
The controller supports tri-state 3-wire modulating valve
control. Two binary outputs control each valve: one to
drive the valve open and one to drive the valve closed. The
stroke time for each valve is configurable using the
Tracer® TU service tool. The controller supports the
following:
•
Heating
•
Cooling
•
Heat/cool changeover with a single valve and coil for 2-
pipe applications
•
Cooling or heat, cool changeover with the main valve,
and coil
•
Only heating with the auxiliary valve and coil for 4-pipe
applications
The controller moves the modulating valve to the desired
positions based on heating or cooling requirements.
Three-Wire Modulating Valve Calibration
Modulating valve calibration is automatic. During normal
controller operation, the controller overdrives the actuator
(135 percent of the stroke time) whenever there is a
request for a position of 0 percent or 100 percent. At either
power-up, after a power outage, or when the occupancy
status changes to unoccupied, the controller first drives all
modulating valves (and dampers) to the closed position.
The controller calibrates to the fully
CLOSED
position by
over driving the actuator (135 percent of the stroke time).
Thereafter, the controller resumes normal operation.
Two-position Valve Operation
The controller supports two-position valves with a single
binary output for each valve. Controllers used for 2-pipe
applications support heating, cooling, or heat/cool
changeover with a single valve/coil. A controller used for
4-pipe applications supports cooling or heat/cool
changeover with a main valve/coil and heating
only
with
an auxiliary valve/coil.
Electric Heat Operation
The controller supports staged electric heat (1- or 2-
stages). 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 staged 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 (hydronic) cooling is available
•
The heating capacity is located in the reheat position
•
The space relative humidity is valid
The space relative humidity can be a BAS-communicated
value or come directly from a wired relative humidity
sensor. The controller begins to dehumidify the space
when the space humidity exceeds the humidity setpoint.
The controller continues to dehumidify until the sensed
humidity falls below the setpoint minus the relative
humidity offset.
