Supply Fan Operation; Constant-Volume Supply Fan Operation - Trane Tracer AH540 Setup And Operation

Chapter 4 Sequence of operation
50

Supply fan operation

The controller determines fan operation based on the selected control
mode. If the controller is configured for space temperature control, the
supply fan operates in constant-volume. If configured for discharge air
temperature control, the supply fan can be configured to operate either
with constant-volume or variable-air-volume.
With both constant-volume and variable-air volume supply fan operation,
the controller turns the supply fan binary output (BO1) On continuously
during occupied, occupied standby, and occupied bypass modes.
During the unoccupied heating and cooling modes of operation, the sup-
ply fan will cycle Off when the space temperature is between the heating
and cooling setpoints. If electric heat is energized during unoccupied
heating periods of operation, the supply fan will run for an additional
120 seconds after electric heat capacity is de-energized.
The supply fan is normally Off during air-handler operation with the fol-
lowing exceptions:
During unoccupied mode when there is no requirement for heating
•
and cooling
When entering water temperature sampling is initiated
•
As a result of certain diagnostic conditions
•
• During manual or system overrides
If a supply fan status binary input sensor is wired to the controller (at
IN10) it is used to verify fan operation before heating and cooling start.
Upon energizing the supply fan output BO1, the Tracer AH540/541 con-
troller waits a configurable time period (fan status delay) to allow the fan
time to reach a desired air flow. Then the controller verifies fan operation
(fan status).
A Low Supply Fan Air Flow diagnostic is generated if the controller pow-
ers the fan On and the fan status switch is not in the fan running posi-
tion, or if the fan status switch is not set to make the fan run within the
configured time limit after the controller commands the fan On. This
latching diagnostic discontinues unit operation until the diagnostic is
cleared from the controller. Fan operation can also be affected by other
diagnostic conditions that cause the controller to shut down the unit. See
Table 63 on page 91 for details.

Constant-volume supply fan operation

For constant-volume supply fan operation, the controller must be config-
ured either for space temperature control or for discharge air tempera-
ture control with constant-volume.
In constant-volume operation, the fan runs continuously during occupied,
occupied standby, and occupied bypass modes of operation, except when
the controller is in occupied mode and turns the fan Off during entering
water sampling periods. During unoccupied periods, the supply fan
binary output BO1 controls the supply fan Off and On depending on heat-
CNT-SVX05B-EN