CNT-SVX05A-EN
31
Sequence of operation
If a space temperature input is provided to the controller when configured as
constant volume discharge air control or variable air volume control, the
controller uses the space temperature to perform morning warm-up and
daytime warm-up functions. Morning or daytime warm-up functions allow the
controller to automatically change to heating if space temperature is less than
the heating setpoint. Morning or daytime warm-up functions can also be
initiated through a communicated request.
Other temperature inputs, such as mixed air temperature or outdoor air
temperature, aid the controller's ability to maintain comfort and protect the
air handling unit.
Economizer cooling requires a mixed air temperature sensor and outdoor air
temperature value to be present. If an outdoor temperature is not available, a
communicated request from Tracer Summit
™
can enable economizer cooling.
Economizer cooling is possible when the air handling unit is equipped with a
mixing box. The mixed air sensor is used as a low temperature limit, to keep
mixed air temperatures above freezing.
Active heating and cooling setpoints are affected by the controller's occupancy
mode. Valid occupancy modes for the three different control modes are shown
in the following table.
Table 20 — Tracer
™
AH.540 occupancy modes of operation
The controller's occupancy mode is determined by either a binary input to the
controller (IN 9) or via a communicated request (from a system-level controller
or another peer controller).
Power up sequence
When 24VAC power is initially applied to the controller, the following sequence
occurs:
• Green Status LED turns on
• All binary outputs are controlled to their de-energized state, and analog
outputs are set to the normally closed output voltage
• The controller reads the inputs to determine initial values
•
Power-up control wait
feature is applied.The controller waits 300 seconds to
allow ample time for the communicated control data to arrive. If after
300 seconds, the controller has not received any communicated control data,
the unit assumes standalone operation
• Normal operation begins
Manual output test can be initiated at any time in the power up sequence or
during normal operation. Refer to the
Manual output test
section.
Constant volume space temperature control
Occupied (default)
Unoccupied
Occupied standby
Occupied bypass
Constant volume discharge air temperature
control
Occupied (default)
Unoccupied
Occupied bypass
Variable air volume control
Occupied (default)
Unoccupied
Occupied bypass
