Siemens 125-1957 User Manual

Siemens Building Technologies, Inc.  

13 

 

In Application 2283, the Unit Vent Controller

⎯0 to 10V Output controls a unit ventilator 

equipped with a chilled water coil for cooling, and/or a heating coil, which may be hot water, 
steam or electric, for ASHRAE Cycle III. A face-bypass damper can be controlled, replacing 
both the modulating (0-10V) heating and cooling actuators. If a face-bypass damper is used, 
two -position valves on the coils may be controlled. Heating only and cooling only units can 
also be controlled with this application by overriding HEAT.COOL (Point 5). 

Other features available in this application include morning warm-up/cool-down, night mode 
override, free cooling, and auxiliary radiation in heating mode. 

The use of a low temperature detection thermostat (LTDT) is strongly 
recommended for hot water and steam systems. 

This application controls room temperature by directly modulating the coil control devices. 
This application also controls an outdoor air damper according to the schedule as defined by 
ASHRAE Cycle III, to maintain a given mixed air temperature setpoint. The free 
cooling/economizer function is turned on and off by the field panel using FREE CLG (Point 
23). If free cooling is not available, the outdoor air damper will be kept at minimum position; 
otherwise, the outdoor air damper will modulate to maintain the mixed air temperature 
setpoint. The unit ventilator fan is also controlled in this application.