Orion System VCM-X Modular E-BUS - Manual (Page 63)

VCM-X Modular E-BUS Controller Technical Guide
SEQUENCE OF OPERATIONS
63
Leaving Air Setpoint - depending on if the VCM-X is currently in the
Cooling, Heating, or Vent mode of operation. These setpoints are all set
in the VCM-X Controller. See the PREHEAT-X Controller Technical
Guide for more details.
Heat Wheel
One of the relay outputs can be confi gured as a Heat Wheel Relay. This
relay will enable the Heat Wheel when the unit goes into the Occupied
Mode. If the unit is confi gured for Economizer Operation, this relay will
disable the Heat Wheel when the unit goes into Economizer Mode. If
the Heat Wheel Relay is active, a Heat Wheel Defrost Cycle will occur
that will disable the Heat Wheel Relay for 2 minutes if the Outdoor Air
Temperature is below the Heat Wheel Defrost Setpoint and 30 minutes
have elapsed since the last Heat Wheel Defrost Cycle.
Single Zone VAV Mode
In this application, the VCM-X E-BUS will modulate the Supply Fan
VFD to maintain the Space Cooling or Heating Setpoint while the unit’s
cooling or heating source is modulating to maintain the appropriate
Supply Air Setpoint. This sequence will operate optimally only when
the HVAC unit has modulating heating and cooling. Staged heating and
cooling should not be used and will not provide satisfactory performance.
When the Space Temperature rises one deadband above the Space
Cooling Setpoint, the cooling mode is initiated. The Supply Fan will
energize and begin operating at 30% speed. Cooling will modulate to
maintain the Active Supply Air Cooling Setpoint. The Supply Fan will
then proportionally modulate as needed between 30% and 100% as the
Space Temperature rises within the Space Reset Window created by
confi guring a Cooling Reset Source Low Setpoint and a Cooling Reset
Source High Setpoint. The Cooling Mode is disabled when the space
temperature falls one deadband below the Space Cooling Setpoint.
When the Space Temperature falls one deadband below the Space
Heating Setpoint, the Heating Mode is initiated. The Supply Fan will
energize and begin operating at 50% speed. Heating will modulate to
maintain the Active Supply Air Heating Setpoint. The Supply Fan will
then proportionally modulate as needed between 50% and 100% as
the Space Temperature falls within the Space Reset Window created
by confi guring a Heating Reset Source High Setpoint and a Heating
Reset Source Low Setpoint. When Heat Pump heating is operating, the
Supply Fan VFD will operate from 75% to 100%. The heating mode
is disabled when the space temperature rises one deadband above the
Space Heating Setpoint.
When the Space Temperature is satisfi ed and the unit is in the Vent
Mode of operation, the fan will operate at 30%. During Dehumidifi ca-
tion, the fan will operate as described above, depending on if the Space
Temperature is calling for Heating, Cooling, or Vent Mode operation.
Whenever the unit is in CO
2
override operation of the Outdoor Air
Damper, the minimum VFD fan speed is forced to 75% and can modu-
late up from there.
In order for the VCM-X E-BUS to operate in Single Zone VAV (SZ
VAV) mode, the unit must be confi gured as follows:
Mode Enable Sensor = Space Temperature
Reset Source = SZ VAV or SZ VAV with CAV Heating
Duct Static Pressure Control = No
Heat Wheel, and Single Zone VAV Mode
Confi gure the Cooling Reset Source High and Low Setpoints and the
Heating Reset Source High and Low Setpoints to establish the Space
Temperature Cooling and Heating range over which the VFD will
modulate in those modes.
Outdoor Air Lockouts
The Outdoor Air Cooling and Heating Lockouts Setpoints are designed
to prevent unwanted Mechanical Heating or Cooling operation during
certain Outdoor Ambient Temperature conditions.
When the Outdoor Air Temperature is below the Cooling Lockout
Setpoint, no Mechanical Cooling can operate. However, if the unit is
equipped with an Economizer and the VCM-X E-BUS is confi gured to
use the Economizer, it can be used to provide free Cooling when the
Mechanical Cooling is locked out. For Heat Pumps, the Cooling Lockout
also applies to Compressor Heating, which means it usually will be a
lower setting than on Cooling units that are not Heat Pumps.
The Outdoor Air Heating Lockout operates so that when the Outdoor
Air Temperature is above the Outdoor Air Heating Lockout Setpoints,
no Mechanical Heating can operate. This applies to any type of Heating
except Compressor Heating as used on Heat Pumps. The lockout for
Compressor Heating is explained in the previous paragraph regarding
Cooling Lockout Setpoints.
Supply Air Cutoffs
The Supply Air Temperature Cutoffs are designed to prevent extremely
High and Low Temperature Supply Air from entering the building.
High Supply Air Temperature Cutoff
High Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature rises above the HI SAT Cutoff Setpoint. When this occurs,
Heating stages will be deactivated until the Supply Air Temperature falls
5°F below the HI SAT Cutoff Setpoint. Also, the Outside Air Damper
will move to its Minimum Economizer Position.
Low Supply Air Temperature Cutoff
Low Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature falls below the LO SAT Cutoff Setpoint. If the VCM-X
E-BUS is in Economizer Operation, Vent Mode, or Heating Mode and
the Supply Air Temperature falls below the LO SAT Cutoff Setpoint
for 10 minutes, it is assumed a Mechanical Failure has occurred and all
Heating will be deactivated, the Supply Air Fan will shut off, and the
Outdoor Air Dampers will close. If the VCM-X E-BUS is in the Cooling
or Dehumidifi cation Mode and the Supply Air Temperature falls below
the LO SAT Cutoff Setpoint, the Cooling Signal or Cooling Stages will
immediately begin deactivating.
To restore normal operation, one of the following three things must occur:
1. The Supply Air Temperature rises above the LO SAT
Cutoff Setpoint by 5°F.
2. The VCM-X E-BUS goes from Occupied to Unoccupied or
from Unoccupied to Occupied Mode.
3. The VCM-X’s power is cycled.