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CNT-SVX05A-EN
Sequence of operation
its current mode to unoccupied (perhaps due to a change based on the system's time
of day schedule), the controller switches
to occupied bypass mode for the remainder of the bypass time or until someone
presses the zone sensor's timed override Cancel button.
Occupancy binary input
You can configure input 9 (IN 9) as an occupancy binary input. The Tracer
™
AH.540 controller uses the occupancy binary input for two occupancy-related
functions. For standalone controllers (any unit not receiving a communicated
occupancy request, typically from a building automation system), the occupancy
binary input determines the occupancy of the unit based on the hardwired signal.
Normally, the signal is hardwired to a binary switch or time clock.
When a hardwired occupancy signal is open, the unit switches to occupied
mode (if the occupancy input is configured as normally open). When a
hardwired occupancy signal is closed, the controller switches to unoccupied
mode.
For controllers that receive a communicated occupancy request from a building
automation system, the hardwired occupancy binary input is used with a
communicated occupancy request to place the controller in either occupied
mode or occupied standby mode.
In occupied mode, the controller operates according to the occupied setpoints.
In occupied standby mode, the unit controller operates according to the
occupied standby setpoints. When the controller receives a communicated
unoccupied request, the controller operates according to the unoccupied
setpoints regardless of the hardwired occupancy input state.
If neither the hardwired binary input nor a communicated request is used to
select the occupancy mode, the controller defaults to occupied mode because
the occupancy binary input (if present) typically is configured as normally open
and no occupancy device is connected.
Constant volume space temperature control
The controller 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's heat/cool mode is determined 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 AH.540 controller must have a valid space temperature and discharge
air temperature input to operate constant volume space temperature control.
When the controller is configured for a constant volume supply fan and space
temperature control, the controller will not operate the unit if the space
temperature or discharge air temperature sensors are missing or have failed.
The controller's space temperature control algorithm uses two control loops:
a space temperature loop and a discharge air temperature loop. The space
temperature control loop compares the active heat/cool space setpoint and
the space temperature and calculates a discharge air temperature setpoint.
The calculated discharge air temperature setpoint range is bound by
configurable heating (maximum) and cooling (minimum) limits.
The discharge air temperature loop compares the discharge air temperature
to the calculated discharge air temperature setpoint (calculated by the space
temperature loop), and calculates a heat or cool capacity to respond to
discharge air temperature setpoint.