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CNT-SVX05A-EN
Sequence of operation
Certain diagnostic conditions can cause the controller to shut down the unit,
which affects fan operation. See the
Diagnostics
section for details.
If the controller is configured for variable air volume control, variable speed fan
operation is assumed by the controller. The supply fan analog output (AO 1)
and binary output (BO 1) are used to control a variable frequency drive.
Constant volume operation
The Tracer™ AH.540 controller turns on the supply fan continuously during
occupied, occupied standby, and occupied bypass modes of operation.
During unoccupied periods, the supply fan binary output (BO 1) controls the
supply fan off and on depending on heating or cooling requirements.
If the controller is wired to a Trane zone sensor, the user can change the supply
fan operation through the fan mode switch (when present). When the fan mode
switch is in the Off position, the controller shuts down the unit. If the fan mode
switch is moved to the Auto position, the controller operates the fan on and off
according to heat and cool demands and the active occupancy mode.
Variable air volume operation
For variable air volume supply fan operation, the Tracer AH.540 controller must
be configured for variable air volume control and have a duct static pressure and
discharge air temperature sensor available. The controller's supply fan binary
output (BO 1) controls the fan's run/stop input, and the controller's supply fan
analog output (AO 1) controls the supply fan speed.
The supply fan speed is controlled to maintain the air handling unit's duct static
pressure to the desired duct static pressure setpoint.
The Tracer AH.540 controller has a configurable duct static pressure high limit.
Fan operation is controlled to actively avoid exceeding this high pressure limit.
If the duct static pressure exceeds the duct static pressure high limit point, the
controller shuts down the unit and generates
a Duct static press high limit
diagnostic. This latching diagnostic must be cleared from the controller before
unit operation is allowed.
Valve operation
The controller uses analog modulating (0-10VDC or 2-10VDC) valves for heating
or cooling operation. The controller supports one or two modulating valves for
hydronic heating, steam heat, and hydronic cooling operation. The Tracer
AH.540 controller supports both one- and two-valve unit configurations. See the
Configuration
section for further details regarding heating and cooling
configurations.
A one-valve unit can be either cooling only or heating only. A two-valve unit
supports preheat (heating coil before the cooling coil) or reheat coil-valve
configurations (heating coil after the cooling coil).
If the cooling output is configured for cooling and the heating valve is
configured for preheat (or reheat), the controller always assumes hot water
(or steam) is available for the heating valve and cold water is available for the
cooling valve.
The Tracer AH.540 controller operates to either normally open or normally
closed valves. The normal state of the valve is the position of the valve when
power is not applied. When power is applied, the controller has full control of
the valve. For example, if the fan mode switch on the zone sensor is in the Off
position, the controller closes the valve, regardless if it is configured normally
open or normally closed.
