Orion System VCC-X Controller - Manual (Page 63)

VCC-X Controller Technical Guide
SEQUENCE OF OPERATIONS
63
Building Pressure Control and MUA
Duct Static Pressure Control for Filter
Loading
In order to maintain a constant CFM through the supply air ducts on
a mixed air CAV unit, the VCC-X can utilize a Duct Static Pressure
Sensor (used to monitor the discharge pressure) in conjunction with
a Supply Fan VFD. If the fi lters are getting dirty, the VCC-X will
ramp up the VFD to compensate for the decrease in airfl ow. To utilize
this feature, the unit must be confi gured to use VFD Fan Control.
This feature cannot be used if this is a VAV or Zoning application
with typical Duct Static Pressure Control, or if this unit has been
confi gured for Single Zone VAV operation.
Building Pressure Control
The VCC-X can maintain Building Static Pressure anytime the
Supply Fan is operating. A Building Pressure Transducer must be
connected to the VCC-X EM1 Expansion Module. The following
are the available control options.
Direct Acting Building Pressure Control
• On/Off Exhaust Fan —If an On/Off Exhaust Fan is
being used, a relay output must be confi gured for
“Exhaust Fan”. This relay will energize whenever the
Building Pressure rises above the Building Pressure
Setpoint by the Deadband amount. The relay will de-
energize when the Building Pressure falls below the
Building Pressure Setpoint by the Deadband amount.
•
Exhaust Fan VFD or Modulating Exhaust
Damper —If confi gured for Modulating Exhaust, a user-
adjustable voltage output (AOUT4 – Building Pressure
Output on the VCC-X Controller) will be used to control
this fan or damper. An Exhaust Relay can be confi gured
if necessary to enable the fan or damper. Whenever the
Building Pressure rises above the Building Pressure
Setpoint by the Deadband amount, the Exhaust Fan
Relay will energize and the Modulating Signal will
activate to control to the Building Pressure Setpoint.
If the Building Pressure falls below the Building
Pressure Setpoint by the Deadband amount,
the Modulating Signal will modulate towards 0% as it
attempts to maintain the Building Pressure Setpoint.
The Exhaust Fan Relay is energized whenever the
Modulating Signal is above 0%.
Reverse Acting Building Pressure Control
•
Outdoor Air Damper —If this option is confi gured,
the VCC-X will use the user-adjustable Economizer/
Outdoor Air Damper output signal (AOUT2 –
Economizer Control Signal) to maintain the Building
Pressure Setpoint. Whenever the Building Pressure
falls below the Building Pressure Setpoint by the
Deadband amount, the modulating Economizer Output
Signal will modulate the damper open to control to
the Building Pressure Setpoint. If the Building Pressure
rises above the Building Pressure Setpoint by the
Deadband amount, the damper will modulate towards
closed as it attempts to maintain the Building Pressure
Setpoint. When this option is selected, no Economizer
free cooling or CO
2
IAQ operation will be available.
•
Supply Fan VFD —Contact WattMaster regarding this
Reverse Acting Building Pressure Control option. It
should not be used in most applications. If this option
is selected, the user-adjustable Supply Fan VFD Output
(AOUT1 on the VCC-X) will be used to control the
Supply Fan VFD to maintain the Building Pressure
Setpoint in similar fashion to the Outdoor Air Damper
control described above.
MUA Operation
• Occupied Mode— The VCC-X will use the normal
Cooling and Heating Mode Enable Setpoints (not the
Hood On Setpoints) in conjunction with the Outdoor Air
(OA) temperature sensor to determine the mode of
operation. The Outdoor Air Dewpoint Setpoint will
initiate the Dehumidifi cation Mode. See the Cooling,
Heating and Dehumidifi cation Modes of Operation
sections for those details. The Outdoor Air Damper will
be modulated to the Economizer Minimum Damper
Position (normally set at 100% for a MUA unit).
• Unoccupied Mode— Normally, an MUA unit is off
during the Unoccupied Mode. However, if the unit has
Return Air, it can be confi gured to operate as a
recirculating Night Setback Controlled unit during
Unoccupied Hours. This is accomplished by simply
confi guring Night Setback Temperature Setpoints
(anything other than the default 30ºF) on a unit that is
also confi gured for Outdoor Temperature Control
(MUA). With this confi guration, when the unit goes
Unoccupied, it will close the Outdoor Air Damper and
begin to use a Space Temperature Sensor in conjunction
with the existing Heating and Cooling Setpoints, offset
by the Night Setbacks, to make Night Setback calls. If a
Space Humidity Sensor is installed, and the unit is
confi gured for Night Humidity control, the VCC-X
Controller will use the Space Humidity Setpoint for
unoccupied Dehumidifi cation calls.