71
VCCX2 Controller Technical Guide
Internal Week Schedule
An Internal Week Schedule, which supports up to two start/stop
events per day and allows scheduling of up to 14 holiday periods
per year is available for determining Occupied and Unoccupied
schedules. It also allows for daylight saving configuration.
Broadcast Schedule
Eight external broadcast schedules are available with use of the
GPC-XP Controller.
Unoccupied Operation
Uses Unoccupied Setback Offset Setpoints for heating and
cooling calls. If Unoccupied Setback Setpoints are left at the
default 30°F, no Unoccupied Setback operation will occur and
the unit will be off.
The Outdoor Air Damper will be closed except if the unit is in
unoccupied Economizer Free Cooling Mode.
If there is no call for Heating or Cooling, the unit will be off.
HVAC Modes of Operation
There are eight possible HVAC Modes of Operation. They are
as follows:
• Cooling Mode
•
Heating Mode
• Vent Mode
•
Dehumidification Mode
• Purge Mode
•
Heat Pump
•
Warm-Up Mode / Cool-Down Mode
•
Off Mode
Cooling Mode
Occupied Cooling is enabled when the temperature at the Mode
Enable Sensor rises one deadband above the Cooling Setpoint.
Cooling is disabled when the Mode Enable Temperature falls
one deadband below the Cooling Setpoint. The setpoint and
deadband are user-adjustable.
Unoccupied Cooling operation is enabled when the Space
Temperature rises above the Cooling Mode Enable Setpoint plus
the Unoccupied Cooling Offset.
Mechanical cooling is disabled if the Outdoor Air Temperature
(OAT) falls 1°F below the Cooling Lockout Setpoint and will
remain disabled until the OAT rises 1°F above the Cooling
Lockout Setpoint.
If the OAT disables mechanical cooling while it is currently
operating, mechanical cooling will stage off as minimum run
times and stage down delays are satisfied.
If the economizer is enabled, it will function as the first stage of
cooling (
page 73
).
Cooling with the Refrigerant System Modules
(RSMs)
On units with digital or VFD compressors, the VCCX2 Controller
will utilize one or more Refrigerant System Modules (RSMs).
Units with only fixed staged compressors that are doing
dehumidification or that require head pressure control would
also utilize an RSM. Each RSM will control the compressors,
condensers, and EXVs (on Bitzer VFD compressor units) for
one or two refrigeration circuits. Up to four RSMs may be used
in controlling up to eight circuits.
The RSMD is used for digital compressor units, including heat
pumps. The RSMV is used for Bitzer VFD compressor units (non
heat pumps). The RSMV-HP is used for Bitzer VFD compressor
units that are heat pumps. The RSMVC-P is used for Copeland
VFD compressor units.
In Cooling Mode, as the Supply Air Temperature (SAT)
rises above the Active Cooling SAT Setpoint (
page 80
), the
compressors will stage on and modulate to maintain the Active
Supply Air Cooling Setpoint. Each RSM will independently
control its compressors to achieve the most efficient cooling
control. Each stage must meet its Minimum Off Time (adj.)
before it is allowed to energize. Successive stages are subject to
a Cooling Stage Up Delay (adj).
Cooling stages will continue to run until the SAT falls below
the Active Supply Air Temperature Setpoint minus the Cooling
Stage Control Window and the cooling will begin to stage off.
Each stage must meet its Minimum Run Time (adj.) before it is
allowed to stage off. Successive stages are subject to a Cooling
Stage Down Delay (adj.). See the appropriate RSM Technical
Guide for a more detailed sequence of operation.
Staged Cooling without the Refrigerant
System Modules (RSMs)
An RSM will not be used on units with fixed stage compressors
that are not doing dehumidification and that do not require head
pressure control, or on units with On/Off Chilled Water.
In Cooling Mode, as the Supply Air Temperature (SAT) rises
above the Active Supply Air Cooling Setpoint (
page 80
), cooling
will begin to stage on. Each stage must meet its Minimum Off
Time (adj.) before it is allowed to energize, and successive stages
are subject to a Cooling Stage Up Delay (adj).
SEQUENCE OF OPERATIONS
HVAC Modes of Operation