Operating Instructions

Chapter 3—Applications for ATEC—VAV with Reheat
3-28 Siemens Building Technologies, Inc.
Sequence of Operation
Control Temperature Setpoints
Depending on the controller’s current operational mode (day or night), CTL STPT (Point 92)
holds the value of one of the following setpoints:
Day Mode—CTL STPT holds the value of DAY CLG STPT (Point 6) or DAY HTG STPT
(Point 7). If the room temperature sensor has a setpoint dial and STPT DIAL (Point 14) is set
to YES, CTL STPT holds the value of RM STPT DIAL (Point 13).
If the setpoint dial is used and the value of RM STPT DIAL is less than the value of RM STPT
MIN (Point 11), CTL STPT holds the value of RM STPT MIN. If the value of RM STPT DIAL is
greater than the value of RM STPT MAX (Point 12), CTL STPT holds the value of RM STPT
MAX.
Night Mode—CTL STPT holds the value of NGT CLG STPT (Point 8) or NGT HTG STPT
(Point 9).
NOTE: The value of CTL TEMP (Point 78) is the same as ROOM TEMP (Point 4), unless
CTL TEMP is overridden.
Day and Night Modes
The day/night status of the space is determined by the status of DAY.NGT (Point 29). The
control of this point differs depending on whether the controller is monitoring the status of a
wall switch or is connected to a field panel.
When a wall switch is physically connected to the controller at the AI/DI port labeled “AI 4”
(Figure 3-7 on page 3-24, Figure 3-8 on page 3-25, and Figure 3-11 on page 3-35), and
WALL SWITCH (Point 18) is set to YES, the controller monitors the status of DI 4 (Point 24).
When DI 4 is ON (the switch is closed), DAY.NGT is set to DAY indicating that the controller
is in day mode. When DI 4 is OFF (the switch is open), DAY.NGT is set to NIGHT indicating
that the controller is in night mode.
When WALL SWITCH is set to NO, the controller does not monitor the status of the wall
switch, even if one is connected to it. If the controller is operating stand-alone, it stays in day
mode all the time. If the controller is operating with centralized control (that 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 Powers Process Control Language (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.