Discharge Air Temperature Control - Trane Tracer AH540 Setup And Operation

Chapter 4 Sequence of operation
38

Discharge air temperature control

The controller requires a discharge air temperature sensor (10 kΩ ther-
mistor only) to operate in the discharge air temperature control mode.
Discharge air temperature control modulates the heating or cooling out-
puts to maintain discharge air temperature at the discharge air tempera-
ture setpoint regardless of the entering air conditions of the air-handling
unit.
Figure 11 shows the steps the Tracer AH540/541 controller takes to con-
trol discharge air. First the controller determines if a communicated dis-
charge-air heating setpoint and discharge-air cooling setpoint are
present. The communicated setpoint has precedence over the configured
(default) setpoint. If no communicated value is present, the controller
uses the configured discharge air temperature setpoint.
Figure 11. Discharge air temperature control flow diagram
Configured value:
discharge-air heating setpoint
discharge-air cooling setpoint
↓
Communicated value:
discharge-air heating setpoint
discharge-air cooling setpoint
Effective heat/cool mode
Discharge air temperature (wired
sensor)
Discharge air temperature control
gains
Discharge air temperature setpoint minimum and maximum limits are
placed on the discharge air setpoint depending on the effective heat or
cool mode. If the effective heat/cool mode is cool, the maximum discharge-
air cooling setpoint limit and minimum discharge-air cooling setpoint
limit the discharge-air cooling setpoint. See Chapter 5, "Configuration"
for more information about discharge-air heating and cooling setpoint
limits.
The effective discharge air temperature setpoint is determined from:
• Communicated or configured discharge air temperature setpoint
value
• Minimum and maximum heat/cool setpoint limits
• Effective heat/cool mode
→
The communicated heat/cool setpoint value has
precedence over the configured discharge air tempera-
ture heat/cool setpoint
↓
→
Discharge-air heating
setpoint
↓
Discharge-air
heating setpoint limits
↓
→
Effective discharge air temperature setpoint
↓
→
Discharge air temperature control loop
→
Calculate heat/cool capacity
Use capacity to drive actuators
↓
Discharge-air cooling
setpoint
↓
Discharge-air
cooling setpoint limits
↓
↓
↓
CNT-SVX05B-EN