Trane LPC, Install And Operation Instructions

Page: 63 / 110

LPC-SVX01C-EN 63
Operation
sequence of
operation
Sequence of Operation
The Tracer AH540/541 is a configurable
controller. All of the controller sequences
of operation are predefined with no need
for programming the controller.
Configurable parameters are provided to
allow the user to adjust the controller
operation. For example, the minimum
occupied outdoor air damper position can
be changed.
All configuration parameters are set to
defaults predetermined through exten-
sive air-handling unit testing in several
different operating conditions. The factory
default settings are also based on the air-
handling unit configuration and order
information.
Control modes
The Tracer AH540/541 controller is
configurable to operate in one of two
air-handling temperature control modes:
1. Space temperature control
2. Discharge air temperature control
When the AH540/541 is configured for
space temperature control, it conforms to
the LonMark® Space Comfort Controller
(SCC) profile. When theAH540/541 is
configured for discharge air temperature
control, it conforms to the LonMark®
Discharge Air Controller (DAC) profile.
Note: Some sequences in this chapter are
specific to the space temperature control
mode and some are specific to the
discharge air temperature control mode.
Some sequences are common to both
modes, but operate differently. Where
mode-dependent differences exist, they
are explained in this chapter.
Space temperature control
The Tracer AH540/541 controller requires
both a space temperature and discharge
air temperature sensor to be present for
space temperature control operation
(also called cascade control). In this
control mode, the Tracer AH5405/541
uses the space temperature and the
measured discharge air temperature to
maintain the space temperature at the
active space cooling setpoint or the active
space heating setpoint. The controller
modulates its heating or cooling outputs
to control the discharge air temperature
to the discharge air temperature setpoint.
This calculated discharge air temperature
setpoint is the desired discharge air
temperature (supply air temperature)
that the unit must deliver to maintain
space temperature at the space heating
or cooling setpoint.
The space temperature can be hard-
wired to analog input IN1 on the termina-
tion board (10k
Ω
thermistor only) or can
be communicated to the controller via
Comm5. Similarly, a setpoint can be
provided with either a hard-wired
setpoint thumbwheel to analog input IN2
on the controller, with a communicated
value, or by using the stored default
setpoints in the controller. The discharge
air temperature must be a hard-wired
analog input IN4 to the termination board
(10k
Ω
thermistor only).
The controller heat/cool mode is deter-
mined by either a communicated request
or by the controller itself, when the heat/
cool mode is Auto. When the heat/cool
mode is Auto, the controller compares
the active space setpoint and the active
space temperature and decides if the
space needs heating or cooling.
The Tracer AH540/541 controller must
have a valid space temperature and
discharge air temperature input to
operate space temperature control.