Orion System VCM-X Modular E-BUS - Manual (Page 62)

Zone
Zone
SEQUENCE OF OPERATIONS
VCM-X Modular E-BUS Controller Technical Guide 62
Building Pressure Control
The VCM-X E-BUS can maintain Building Static Pressure any time the
Supply Fan is operating by activating a Constant Volume Exhaust Fan, a
VFD Exhaust Fan, or Modulating Exhaust Damper, or by modulating the
Outdoor Air Damper. A Building Pressure Transducer must be connected
to the VCM-X’s Expansion Module. For Constant Volume Exhaust
Fan applications, only an Exhaust Fan Relay needs to be confi gured
for on/off operation of the Exhaust Fan. VFD or Modulating Building
Pressure control must be confi gured in order for this feature to operate.
An Exhaust Fan Relay can also be confi gured along with Modulating
Building Pressure control for an Enable output. Building Pressure can
be maintained by either Direct or Reverse Acting control.
Direct Acting Modulating Control
If confi gured, a VFD Exhaust Fan or Modulating Exhaust Damper will
be controlled by varying a 0-10 or 2-10 VDC control signal. If an en-
able output is required, an Exhaust Fan Relay can also be confi gured.
The Exhaust Fan Relay and the Modulating Signal will activate when
the Building Static Pressure rises above the Building Static Pressure
Setpoint plus the Deadband. The Exhaust Fan Relay will remain active
until the Building Static Pressure falls below the Building Static Pressure
Setpoint minus the Deadband and the Modulating Signal falls to 0%.
Direct Acting On/Off Control
If you do not require a Modulating Control Signal, you can also confi gure
one of the Relay Outputs as an Exhaust Fan Relay to activate whenever
the Building Static Pressure is above the Building Static Pressure Set-
point plus the Deadband. The Exhaust Fan Relay will deactivate when the
Building Static Pressure falls below the Building Static Pressure Setpoint
minus the Deadband. Only one Relay Output should be confi gured for
this operation. There is no staging of additional Exhaust Fan Relays.
Reverse Acting Modulating Control
If confi gured, on a drop in building static pressure below the building
pressure setpoint minus the deadband, a 2-10 VDC signal will modu-
late to open the outside air damper. When this option is selected, no
economizer-free cooling or IAQ operation will be available.
CAV/MUA Dual Mode ( Hood On/Off
Operation)
The VCM-X E-BUS Controller can be confi gured as a CAV controller
but switch to MUA operation when an exhaust hood is energized. This
MUA force mode occurs when a 24 VOut wet contact closure is received
on the Hood On binary input on a VCM-X E-BUS Controller Expan-
sion Module. Under normal operation (CAV), the unit will operate as
a recirculating space temperature (and space humidity) controlled unit.
When the Hood On contact is made, the unit will open the Outdoor Air
Damper to its full open position. The Heating and Cooling Modes will
then be determined by the Outdoor Air Temperature Sensor using the
same Heating and Cooling Setpoints that were used in the CAV mode.
Dehumidifi cation would then be initiated by an Outdoor Dewpoint Set-
point. When the Hood On Force Mode is removed, the unit will revert
to CAV operation with the Outdoor Damper returning to its minimum
position (unless economizer operation is enabled) and with mode control
initiated by the Space Temperature and Humidity Sensors.
MUA Unoccupied Operation
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 ac-
complished 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 VCM-X E-
BUS Controller will use the Space Humidity Setpoint for unoccupied
Dehumidifi cation calls.
IAQ ( CO
2
) Operation
If you have confi gured the VCM-X E-BUS Controller to monitor and
control CO
2
levels, the Economizer operation will be modifi ed as follows:
1. The Maximum Reset Position the Economizer can open to
is determined by a user-adjustable setpoint called the CO
2
Protection Limit Max Level.
2. The Minimum Position the Economizer can close down
to is reset higher as the level of CO
2
increases above the
CO
2
Protection Limit Max Level programmed. As the CO
2
level increases above the adjustable CO
2
Setpoint,
the Outdoor Air Damper will start opening beyond its
Minimum Position. At the CO
2
Protection Limit Reset
Range above Setpoint, the Economizer will be held to its
Maximum Reset Position and not allowed to open any
further.
If doing both CO
2
and CFM (using an Airfl ow Station) control of the
Economizer, CFM control will not override the CO
2
Max Economizer
Position.
Pre-Heater Operation
In colder climates where freezing temperatures are sometimes experi-
enced, it is desirable to preheat the Outdoor Air being drawn into the
HVAC unit before it reaches the Water Coils to prevent freezing. The
Pre-Heater control option is available by setting a Low Ambient Protec-
tion Setpoint and by confi guring one of the relay outputs as a Pre-Heater.
Only one relay can be confi gured for this option, and therefore, staging
of Pre-heater relays is not available. The Pre-Heater operation will only
operate in the Occupied Mode.
The Pre-Heater sequence operates so that any time during the Occupied
mode, if the Outdoor Air Temperature is below the Low Ambient Protec-
tion Setpoint and the Supply Fan is running, the Pre-heater Relay will
activate. It will remain on until the Outdoor Air Temperature rises 1°F
above the Setpoint or until the Supply Fan shuts down. If the Proof of
Flow option is installed and confi gured, its signal must also be active
for the Pre-Heater Relay to activate.
If using the Preheat-X Controller, an SCR preheater and/or stages of
preheat can be controlled. If the Entering Air Temperature (sensor con-
nected to the Preheat-X) falls below the Pre-Heat Setpoint, then preheat
will be controlled to either a Cooling, Heating or Vent Mode Preheater
Building Pressure Control and CAV/MUA