Siemens 125-1957 - Manual (Page 17)

Basic Operation
Siemens Building Technologies, Inc. 7
Day Cooling Operation
The controller maintains the room temperature by resetting the unit ventilator's discharge
temperature setpoint (2281), running the face-bypass damper at full all the time, modulating
or cycling the available coil control device (DX coil – 2284) or positioning the outdoor air
damper.
Night Heating Operation
The controller maintains the room temperature turning the fan and heating on and off as
required.
Night Cooling Operation
The controller maintains the room temperature by turning the fan and cooling on and off as
required.
Night Mode Override Switch
If the RTS has an override switch, it can be used to command the controller into day mode
for an adjustable amount of time. This only affects a controller in night mode.
Valve Configuration
2-Pipe Heating/Cooling – units with one valve, controlling a coil that may have hot water or
chilled water (depending on the season).
4-Pipe Heating or Cooling – units that are heating or cooling only, units with a heating and a
cooling coil, units with electric heating, etc.
Heating and Cooling Switchover
NOTE: For 2-pipe heating/cooling (Application 2281 and 2283), a field panel must
control the switchover between heating and cooling.
The heating/cooling switchover determines whether the controller is in heating or cooling
mode by monitoring the room temperature and the demand for heating and cooling (as
determined by the temperature control loops).
Control Loops
Room Loop – uses the control setpoint and room temperature to set the discharge setpoint
between the minimum and maximum discharge temperature (2281, 2284).
Heating Loop – maintains room temperature setpoint by turning valves and/or electric heat
stages on and off.