Siemens 125-1957 Benutzerhandbuch

Siemens Building Technologies, Inc. 

7 

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. 

The controller maintains the room temperature turning the fan and heating on and off as 
required.  

The controller maintains the room temperature by turning the fan and cooling on and off as 
required. 

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. 

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. 

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). 

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.