Siemens 125-1957 - Manual (Page 28)

APOGEE Unit Vent Controller
⎯
0 to 10 V Output Owner’s Manual
18 Siemens Building Technologies. Inc.
Application 2286 - Heating and DX Cooling, ASHRAE
Cycle III
In Application 2286, the Unit Vent Controller—0 - 10V Output controls a unit ventilator
equipped with a DX coil for cooling, and/or a heating coil, which may be hot water, steam, or
electric, for ASHRAE Cycle Ill. A face-bypass damper can be controlled, replacing the
modulating (0-10V) heating actuator, but will modulate only in heating mode. If a face-bypass
damper is used, two -position valves on the coils may be controlled. Cooling only units can
also be controlled with this application by overriding HEAT.COOL (Point 5) to COOL.
Other features available in this application include morning warm-up/cool-down, night mode
override, free-cooling, and auxiliary radiation in heating mode.
NOTE: 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.
Figure 17. Application 2286 Control Drawing.