Applications Guide Tracer Graphical Programming - Trane

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Chapter 7 Constant-volume AHU example
Figure 131: Constant-volume air handler
Reviewing the sequence of operation
In this scenario a constant-volume air handler provides comfort heating
and cooling to a space. The air handler contains a variable-speed fan, both
cooling and heating coils, and an outdoor air damper. The air handler is a
stand-alone unit (Figure 131).
Modes and setpoints
The following parameters for the sequence of operation are presented
according to the occupancy mode, the heat/cool mode, or the setpoint.
Occupied mode (including occupied bypass)
When the air handler is in occupied mode, operate the supply fan continuously
and modulate the cooling valve, heating valve, and outside air
damper to maintain space comfort conditions. During unoccupied periods,
when the local timed override button (the ON button on the space temperature
sensor) is pressed, transition the air handler to occupied bypass
mode for the configured occupied bypass time period. When the local
CANCEL button is pressed, terminate the timed override request and
revert the air handler to the scheduled mode.
Occupied standby mode
When the air handler is in occupied standby mode, operate the supply fan
continuously and modulate the cooling valve, heating valve, and outside
air damper to maintain space comfort conditions. Use occupied standby
mode to save energy by using lower heating and higher cooling temperature
setpoints and reduced ventilation requirements during intermittent
unoccupied periods.
An occupancy sensor determines the presence of people in the space
served by the air-handling unit. When the space is occupied, operate the
air handler in occupied mode. When the space is unoccupied during a
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