CNT-SVX05A-EN
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Sequence of operation
Variable air volume control
The Tracer
™
AH.540 controller that is operating with variable air volume control
uses both a discharge air temperature control routine and a duct static pressure
control routine. The unit’s discharge air temperature is controlled using the
discharge air temperature control sequence. The air handling unit's duct static
pressure is maintained by a duct static pressure control sequence.
Duct static pressure control
The supply fan variable frequency drive, in a variable air volume system, is
controlled to maintain the duct static pressure setpoint. When the fan is On, the
controller reads and compares the duct static pressure input to the duct static
pressure setpoint and adjusts the supply fan speed analog output signal (AO 1)
to the variable frequency drive.
The duct static pressure signal can be from a wired sensor or communicated via
a network variable. If the controller does not have a valid duct static pressure
from a wired sensor or communicated, the controller generates a
Duct static
press failure
diagnostic and shuts down the unit. The controller does not
operate duct static pressure control without a valid duct static pressure input.
If the controller has both a hardwired and communicated duct static pressure
input, the communicated value is used for duct static pressure control. The
greater of the two values, hardwired or communicated, is used for duct static
pressure high limit shutdown.
The Tracer AH.540 controller has a configurable duct static pressure high limit
setpoint. If the duct static pressure exceeds the duct static pressure high limit
setpoint, the controller shuts down the unit and generates a
Duct static
pressure high limit
diagnostic. This latching diagnostic must be cleared from
the controller before unit is allowed to operate.
Supply fan operation
The Tracer AH.540 controller determines fan operation based on the selected
control mode. If the Tracer AH.540 controller is configured for constant volume
space temperature control or constant volume discharge air control, the
controller turns the supply fan binary output (BO 1) on continuously during
occupied, occupied standby, and occupied bypass modes.
When a supply fan status binary input sensor is wired to the controller (IN 10) it
is used to verify fan operation before heating and cooling start. Upon
energizing the supply fan output (BO 1) the Tracer AH.540 controller 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 detected when the controller is
commanding the fan On and the fan status switch is not in the closed position,
or if the fan status switch does not close the binary input within the configured
time limit after the controller commanding the fan On. This is a latching
diagnostic and discontinues unit operation until the diagnostic is cleared from
the controller.
