Operating Instructions

Chapter 3—Applications for ATEC—VAV with Reheat
3-6 Siemens Building Technologies, Inc.
If the controller is operating stand-alone, it stays in day mode all the time. If the controller is
connected to a field panel, the field panel can send an operator or PPCL command to
override the status of DAY.NGT. See the APOGEE
® PPCL User’s Manual (125-1896) and
Field Panel User’s Manual (125-1895) for more information.
Night Mode Override Switch
If an override switch is present on the room temperature sensor and a value (in hours) other
than zero has been entered into OVRD TIME (Point 20), pressing the override switch resets
the controller to day operational mode for the time period that is set in OVRD TIME. The
status of NGT OVRD (Point 21) changes to DAY. After the override time elapses, the
controller returns to night mode and NGT OVRD changes back to NIGHT.
It is only when the controller is in night mode that the override switch on the room sensor has
any effect on the controller.
Control Loops
The terminal box is controlled by two Proportional, Integral, and Derivative (PID) control
loops: a temperature loop and a flow loop.
Temperature Loop—The temperature loop uses the values of CTL STPT (Point 92) and
CTL TEMP (Point 78) to generate the cooling loopout, which is then used to generate the
value of FLOW STPT (Point 93). See Control Temperature Setpoints (page 3-5). FLOW
STPT is calculated between the values of CLG FLOW MIN (Point 31) and CLG FLOW MAX
(Point 32).
Flow Loop—The flow loop maintains the airflow between the values of CTL FLOW MIN
(Point 76) and CTL FLOW MAX (Point 77) by modulating DMPR COMD (Point 48).
Calibration of Air Velocity Sensor
Calibration of the controller’s internal air velocity sensor is periodically required to maintain
accurate air velocity readings. CAL SETUP (Point 95) is set with the desired calibration
option during controller startup. Depending on the value of CAL SETUP, calibration may be
set to take place automatically or manually. When CAL AIR (Point 94) has a setting of YES,
calibration is in progress.
• For a controller used without an Autozero Module (CAL MODULE, Point 87, is set to
NO), the damper is commanded closed to get a zero airflow reading during
calibration.
• For a controller used with an Autozero Module (CAL MODULE is set to YES),
calibration occurs without closing the damper.
At the end of a calibration sequence, CAL AIR automatically returns to NO. A setting of NO
indicates that the controller is not in a calibration sequence.