Start Up
64
UNT-SVX041D-EN
Sequence of Operation
Power-Up Sequence
When 24 Vac power is initially applied to the controller, the
following sequence occurs:
1. The Power Marquee LED turns on as red, then flashes
green, and then turns a solid green.
2. All outputs are controlled
OFF
and all modulating
valves and dampers close.
3. The controller reads all input local values to determine
initial values.
4. The random start timer begins (refer to the following
section, Random Start).
5. The random start timer expires.
6. Normal operation begins, assuming there are no
generated diagnostics. If any points are in fault or
alarm mode, the Power Marquee LED flashes red.
Important:
Flashing red does not indicate that the
controller will fail to operate. Instead, the
point(s) that are in fault or alarm mode
should be checked to determine if the status
of the point(s) is acceptable to allow
equipment operation.
Random Start
Random start is intended to prevent all units in a building
from energizing at the same time. The random start timer
delays the fan and any heating or cooling start-up from 5
to 30 seconds.
Occupancy Modes
Occupancy modes can be controlled in the following ways:
•
The state of the local (hard wired) occupancy binary
input BI1.
•
A timed override request from a Trane zone sensor (see
“Timed Override Control,” p. 64
).
•
A communicated signal from either a Tracer® SC or
BAS.
A communicated request, from either a Tracer® SC or
BAS, takes precedence over local requests. If a
communicated occupancy request has been established,
and is no longer present, the controller reverts to the
default (occupied) occupancy mode after 15 minutes (if no
hard wired occupancy request exists). The controller has
the following occupancy modes:
•
Occupied
•
Unoccupied
•
Occupied standby
•
Occupied bypass
Occupied Mode
In Occupied Mode, the controller maintains the space
temperature based on the occupied space temperature
setpoint ± occupied offset. The controller uses the
occupied mode as a default mode when other forms of
occupancy request are not present and the fan runs
continuously. The outdoor air damper, if present, will close
when the fan is OFF. The temperature setpoints can be
local (hard wired), communicated, or stored default values
(configurable using the Tracer® TU service tool).
Unoccupied Mode
In unoccupied mode, the controller attempts to maintain
the space temperature based on the unoccupied heating
or cooling setpoint. The fan will cycle between high speed
and
OFF
. In addition, the outdoor air damper remains
closed, unless economizing. The controller always uses
the stored default setpoint values (configurable using the
Tracer® TU service tool), regardless of the presence of a
hard wired or communicated setpoint value.
Occupied Standby Mode
The controller is placed in occupied standby mode
only
when a communicated occupied request is combined with
an unoccupied request from occupancy binary input BI1. In
occupied standby mode, the controller maintains the
space temperature based on the occupied standby heating
or cooling setpoints. Because the occupied standby
setpoints have a typical temperature spread of 2°F (1.1°C)
in either direction, and the outdoor air damper is closed,
occupied standby mode reduces the demand for heating
and cooling the space. The fan will run as configured
(continuously) for occupied mode. The controller always
uses the stored default setpoint values (configurable using
the Tracer®
TU service tool), regardless of hard wired or
communicated setpoint values. In addition, the outdoor
air damper uses the economizer occupied standby
minimum position setpoint to reduce the ventilation rate.
Occupied Bypass Mode
The controller is placed in occupied bypass mode when
the controller is operating in the unoccupied mode and
when either the timed override
ON
button on the Trane
zone sensor is pressed or the controller receives a
communicated occupied bypass signal from a BAS. In
occupied bypass mode, the controller maintains the space
temperature based on the occupied heating or cooling
setpoints. The fan will run as configured (continuous or
cycling). The outdoor air damper closes when the fan is
OFF
. The controller remains in occupied bypass mode
until either the
CANCEL
button is pressed on the Trane
zone sensor or the occupied bypass time (configurable
using the Tracer® TU service tool) expires. The
temperature setpoints can configured as local (hard
wired), communicated, or stored default values using the
Tracer® TU service tool.
Timed Override Control
If the controller has a timed override option (
ON
/
CANCEL
buttons), pushing the
ON
button initiates a timed override
on request. A timed override on request changes the
occupancy mode from unoccupied mode to occupied
