Siemens 125-1957 - Manual (Page 26)

APOGEE Unit Vent Controller
⎯
0 to 10 V Output Owner’s Manual
16 Siemens Building Technologies. Inc.
Application 2284 – Heating and DX Cooling, ASHRAE
Cycles I and II
In Application 2284, the Unit Vent Controller
⎯0 to 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 Cycles I and II. 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.
While in heating, this application controls room temperature by resetting the discharge air
temperature. While in cooling, this application controls room temperature by cycling the DX
unit. This application also controls an outdoor air damper according to the schedules as
defined by ASHRAE Cycles l 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 actuator or the DX. The unit ventilator fan is also
controlled in this application.
Figure 14. Application 2284 Control Drawing.