Application

Sequence of Operation
Control Temperature Setpoints
6
Siemens Industry, Inc. Application Note, App 2521 140-1218
2015-05-06
Sequence of Operation
The following paragraphs present the sequence of operation for Application 2521,
Base VAV - Cooling and Heating.
Control Temperature Setpoints
CTL STPT is Overridden
If CTL STPT is overridden, that value is used regardless of any other settings. This
disables the setpoint deadband feature.
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 or
NGT HTG STPT depending on the value of HEAT.COOL. 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 or DAY HTG STPT depending on the value of HEAT.COOL.
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.
Heating/Cooling Switchover
In order for the controller to function properly, use one of the following two options for
the heating/cooling switchover for this application.
1. If the controller is connected to a field panel, the field panel can command SUPPLY
TEMP.
When SUPPLY TEMP is commanded below the value of COOL TEMP, the
controller sets HEAT.COOL to COOL, switching the controller to cooling mode.
When SUPPLY TEMP is commanded above the value of HEAT TEMP, the
controller sets HEAT.COOL to HEAT, switching the controller to heating mode.
2. If the controller is connected to a field panel, the field panel can switch the
controller between heating and cooling modes by commanding HEAT.COOL to
HEAT or COOL.
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.