Orion System VCM Controller - Manual (Page 37)

VCM Controller
Technical Guide
37
Sequence Of Operations
Occupied/Unoccupied
Mode of Operation
The VCM controller can utilize several methods for determining the
Occupied Mode of Operation. These are:
Forced Schedule
Remote Forced Occupied Signal
Internal Schedule
Push Button Override Signal
Forced Schedule
The VCM controller can be forced into the Occupied Mode by input-
ting a Forced Schedule from any operator interface.
Remote Forced Occupied Signal
When this wet contact input closes, it will force the VCM controller
into the Occupied Mode. When the Remote Forced Occupied Signal is
removed, the controller will revert to the Unoccupied Mode of opera-
tion if no Internal or External Schedule has been configured or is in
effect when this occurs.
Note: If the Remote Forced Occupied Mode is to be used, it
is necessary to set all the Internal Week Schedules to
‘0’ so that the Internal Schedule always commands the
Unoccupied Mode.
Internal Week Schedule
An Internal Week Schedule, which supports up to two start/stop events
per day, is available for determining Occupied and Unoccupied Sched-
ules. If you are using the Internal Schedule, an Optimal Start calcula-
tion is also available. See the Scheduling Section of this manual for
more information on the Optimal Start Feature.
Push Button Override Signal
During Unoccupied hours, the user can force the VCM controller back
to Occupied operation by pressing the Override Button on the Space
Temperature Sensors for a period of less than 3 seconds. This initiates
the Override or resets the Override Timer back to zero during Unoccu-
pied hours of operation.
During Override operations, the user can cancel the Override by press-
ing the Override Button for a period of time between 3 seconds and 10
seconds. This restores the VCM controller to Normal Unoccupied Op-
eration.
If the Override Button is held for more than 10 seconds, it causes a
Space Sensor Failure Alarm. This is due to the fact that the Override
Button actually shorts the Space Temperature Sensor input to ground. If
this input is shorted to ground or left floating with no Space Tempera-
ture Sensor detected for more than 10 seconds, it is considered a Space
Temperature Sensor failure.
You can still use the Space Temperature Sensor input for an Override
Command even when a Space Temperature Sensor is not connected.
Simply provide a Momentary Push-Button connected between AIN1
and the Ground Terminal on the same terminal block. Follow the above
procedure for initiating Overrides, even on Supply Air Temperature Con-
trolled Cooling only HVAC units.
HVAC Modes of Operation
There are 6 possible HVAC Modes of Operation. They are:
Vent Mode
Cooling Mode
Dehumidification
Heating Mode
Warm-Up Mode
Off Mode
Vent Mode Operation
This Mode only applies to the Occupied Mode of Operation. The Vent
Mode is defined as the Supply Fan running with no Heating, Cooling or
Dehumidification demand.
Vent Mode can occur during the Occupied Mode if the Space, Return or
Outdoor Air Temperature Sensors are selected as the HVAC Mode En-
able Sensor. Vent Mode can also occur if the Supply Air Temperature
Sensor is the HVAC Mode Enable Sensor and the VCM has been con-
figured for Remote Forced Heating and Cooling. See the Remote Con-
trol of HVAC Mode section in this manual for complete details.
Note: During Vent Mode, all Cooling and Heating Stages are
deactivated and the Economizer Damper is maintained
at a Minimum Position to provide fresh air into the
building. The Static Pressure is still maintained by the
Supply Fan VFD or Zoning Bypass Damper Signal
since the Supply Fan is still operating in this Mode.
Cooling Mode Operation
Occupied Cooling Mode occurs whenever the HVAC Mode Enable Tem-
perature is above the HVAC Mode Enable Cooling Setpoint. Unoccu-
pied Cooling Mode only occurs if a Space Temperature Sensor is con-
nected to the VCM, or a broadcast of Space Temperature is being re-
ceived from an Averaging Broadcast Controller and only then if the
Space Temperature is above the Cooling Setpoint.
The Mechanical Cooling will be disabled if the Outdoor Air Tempera-
ture is below the Cooling Lockout Setpoint by 1°F. This gives a 2°F
hysteresis around the Cooling Lockout Setpoint to prevent unwanted
cycling in and out of Mechanical Cooling Mode. If the Outdoor Air
Temperature disables the Mechanical Cooling while it is currently op-
erating, the Mechanical Cooling will stage off if all staging and run
times are satisfied.
If the Economizer has been enabled for operation, it is used as the first
stage of Cooling and the Mechanical Cooling will be activated if neces-
sary. See the Economizer Operation section for a more detailed operat-
ing sequence.