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VCCX2 Controller Technical Guide
Supply Fan Operation
Any time the Supply Fan is requested to start, a one-minute
minimum off timer must be satisfied. If the timer is satisfied, the
Supply Fan relay is activated while all other outputs are held off
until their minimum off timers have been met.
Upon going into the Occupied Mode or upon power-up, the
controller will initiate a user-adjustable Fan Starting Delay to
provide a staggered start for systems with several HVAC units.
In Fan Cycle Mode or when going unoccupied, the Supply Fan
is held on for 10 seconds after Cooling has staged off or after
Leaving Vent Mode and 90 seconds after the Heating has staged
off.
Purge Mode
When going into Occupied Mode, an optional “Purge Mode”
is initiated. The fan runs with the Economizer closed, and all
Cooling and Heating is de-energized. The length of the Purge
Mode is user-adjustable.
Occupied Mode
The Supply Fan can be configured to run continuously (default)
or to cycle with Heating, Cooling, or Dehumidification.
Unoccupied Mode
Upon going Unoccupied, the Cooling or Heating will turn off
immediately. The Fan will then turn off in 30 to 60 seconds.
Typically, thereafter, the Supply Fan will cycle on a call for
Heating, Cooling, or Dehumidification. The Supply Fan can also
be configured for continuous operation during Unoccupied Mode.
HVAC Source Configuration Options
The VCCX2 Controller can be configured to have various
HVAC Source options that will determine the mode of operation
(Heating, Cooling, or Vent Mode) of the unit. The following are
descriptions of those options.
Space Temperature
—Typical selection for CAV recirculating
units.
Return Air Temperature
—Optional selection for CAV
recirculating units.
Single Zone VAV
—Selected for a Space Temperature
controlled Single Zone VAV application.
Outdoor Air Temperature
—Typical selection for 100%
Outdoor Air (MUA) or High Percentage Outdoor Air units.
Supply Air Temperature
—Selected for Cooling Only. VAV
units with optional Morning Warm-Up/Cool-Down.
Supply Air Tempering
—Selected for VAV units maintaining
a Cooling Setpoint with Cooling or Heating as required that may
need heat to temper the Supply Air Temperature during very
cold conditions.
Space Temperature with High Outdoor Air %
— Provides
Space Temperature (instead of Outdoor Air Temperature) control
of 100% or high percentage Outdoor Air units by tempering the
air during the Space Vent Mode of operation to prevent dumping
of hot or cold air into the space.
HVAC Mode Set by Remote Contact
— Provides for wet
contact closures to force the unit into Heating, Cooling, and
Dehumidification modes. If this option is selected, it applies to
all three modes, and all three modes will only be initiated by
these contact closures. If both the Heating and Cooling contacts
are made, the unit will be in the Vent mode.
Occupied/Unoccupied Mode of
Operation
The VCCX2 Controller can utilize several methods for
determining the Occupied Mode of Operation. These are as
follows:
• Forced Schedule
•
Remote Forced Occupied Signal
•
Internal Week Schedule
•
Push-Button Override Signal
•
Broadcast Week Schedule from GPC-XP
The VCCX2 Controller can be forced into the Occupied Mode
by inputting a Forced Schedule from any operator interface.
Remote Forced Occupied Signal
This Forced Occupied Input can be used in place of, or in
conjunction with, the internal VCCX2 schedule. When this wet
contact input closes, it will force the VCCX2 Controller into the
Occupied Mode. When the Remote Forced Occupied Signal is
removed, the controller will revert to the Unoccupied Mode of
operation, or if an internal VCCX2 schedule is also being used,
it will revert back to the current scheduled mode.
Setting the Internal Week Schedule to ‘0’ will cause the
controller to only look for the Remote Forced Occupied Signal
for Occupied/Unoccupied commands.
SEQUENCE OF OPERATIONS
Supply Fan and Occupied/Unoccupied Operation
