Siemens 125-1957 - Manual (Page 20)

APOGEE Unit Vent Controller
⎯
0 to 10 V Output Owner’s Manual
10 Siemens Building Technologies. Inc.
Application 2281 – Heating and/or Chilled Water
Cooling, ASHRAE Cycles I and II
In Application 2281, 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 Cycles I and II. A face-bypass damper can be controlled,
replacing both the modulating (0-10V) heating and cooling actuators. If a face-bypass
damper is used, the two-position valves on the coils can 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.
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 resetting the discharge air temperature. It also
controls an outdoor air damper according to the schedules as defined by ASHRAE Cycles I
and II. 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 open in sequence with the
heating and cooling actuators. The unit ventilator fan is also controlled in this application.
Figure 4. Application 2281 Control Drawing.