Application

Sequence of Operation
Control Temperature Setpoints
6
Siemens Industry, Inc. Application Note, App 2520 140-1217
2015-05-06
Sequence of Operation
The following paragraphs present the sequence of operation for Application 2520,
Base VAV - Cooling Only.
Control Temperature Setpoints
This application has a number of different room temperature setpoints (NGT CLG
STPT, RM STPT DIAL, and so on.). The application actually controls to CTL STPT.
CTL STPT is set to different values depending on its override status, the time of day,
and the type of RTS used.
CTL STPT is Overridden
If CTL STPT is overridden, that value is used regardless of any other settings.
CTL STPT in Night Mode
The controller is in Night mode if DAY.NGT = NGT and NGT OVRD = NGT.
When the controller is in Night mode, CTL STPT holds the value of NGT CLG STPT.
When the controller is in Night mode the value of RM STPT DIAL is ignored.
CTL STPT in Day Mode
The controller is in Day mode if DAY.NGT = DAY or NGT OVRD = DAY.
Without setpoint dial:
When the controller is in Day mode and STPT DIAL = NO, CTL STPT holds the value
of DAY CLG STPT.
With setpoint dial:
When the controller is in Day mode and STPT DIAL = YES, CTL STPT holds a value
based on RM STPT DIAL depending on your room unit model/revision.
Day and Night Modes
The day/night status of the space is determined by the status of DAY.NGT.
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
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, 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 changes to DAY. After the override time elapses, the
controller returns to night mode and the status of NGT OVRD changes back to NIGHT.
The override switch on the room sensor only affects the controller when it is in Night
mode.