Control Gains; Heating/Cooling Mode Control - Trane Tracer AH540 Setup And Operation

Chapter 4 Sequence of operation
32
(supply air temperature) that the unit must deliver to maintain space
temperature at the space heating or cooling setpoint.
The space temperature can be hard-wired to analog input IN1 on the ter-
mination board (10 kΩ thermistor only) or can be communicated to the
controller via Comm5. Similarly, a setpoint can be provided with either a
hard-wired setpoint thumbwheel to analog input IN2 on the controller,
with a communicated value, or by using the stored default setpoints in
the controller. The discharge air temperature must be a hard-wired ana-
log input IN4 to the termination board (10 kΩ thermistor only).
The controller heat/cool mode is determined by either a communicated
request or by the controller itself, when the heat/cool mode is Auto. When
the heat/cool mode is Auto, the controller compares the active space set-
point and the active space temperature and decides if the space needs
heating or cooling.
The Tracer AH540/541 controller must have a valid space temperature
and discharge air temperature input to operate space temperature con-
trol.
When the controller is configured for a supply fan and space temperature
control, the controller will not operate the unit if the space temperature
or discharge air temperature sensors are missing or have failed.
The space temperature control algorithm uses two control loops: a space
temperature loop and a discharge air temperature loop. The space tem-
perature control loop compares the active heat/cool space setpoint and the
space temperature and calculates a discharge air temperature setpoint.
The calculated discharge air temperature setpoint range is bound by con-
figurable heating (maximum) and cooling (minimum) limits.
The discharge air temperature loop compares the discharge air tempera-
ture to the calculated discharge air temperature setpoint (calculated by
the space temperature loop), and calculates a heat or cool capacity to
respond to the discharge air temperature setpoint.
The capacity calculation, as a result of the discharge air temperature con-
trol loop, is used to drive the air-handling unit actuators to maintain
space temperature at the space temperature setpoint.

Control gains

Figure 9 on page 33 illustrates the separate control for the space-temper-
ature control loop and discharge air temperature control loop. The gain
parameter values that control the different loops have been determined
through extensive testing of different types of heating or cooling capaci-
ties and at operating conditions of the air-handling unit.

Heating/cooling mode control

The heating or cooling mode of the controller can be determined two
ways:
Communicated request
•
Automatically by the controller
•
CNT-SVX05B-EN