Orion System VCM-X Modular E-BUS - Manual (Page 61)

VCM-X Modular E-BUS Controller Technical Guide
SEQUENCE OF OPERATIONS
61
Air Flow Monitoring/Control
The VCM-X E-BUS Controller with the E-BUS Distribution Module
can monitor airfl ow of the outside air, the supply air, and the return/ex-
haust air streams by utilizing EBTRON
® GTN116 and GTC116 Airfl ow
Monitoring Stations. The VCM-X E-BUS will control the Outdoor Air
Damper to maintain an Outdoor Air CFM Setpoint. No other control
functions are available at this time.
Supply Fan Control
Any time the Supply Fan is requested to start, a timer is checked to make
sure the Supply Fan has been off for at least 1 minute. This 1-minute
delay is a protection against rapid cycling of the Supply Fan. Once the
1-minute delay has been satisfi ed, the Supply Fan relay is activated and
all other outputs are verifi ed to be in the off condition for a period of 1 to 2
minutes. This short period of Supply Fan-Only Operation serves to purge
the stagnant air from the duct before any Heating or Cooling occurs.
Normally, the Supply Fan runs continuously during the Occupied Mode
of operation. If the fan is only required to run in the Occupied Mode
during Heating, Cooling, or Dehumidifi cation Modes, the VCM-X E-
BUS can be confi gured for Fan Cycle Mode.
Duct Static Pressure Control
The VCM-X E-BUS Controller reads and controls Static Pressure in the
duct system if the Supply Fan has been confi gured for Duct Static Pres-
sure Control. Any time the Supply Fan is operating, the VCM-X E-BUS
Controller is controlling Duct Static Pressure. The Duct Static Pressure
Setpoint and Deadband limits are user-adjustable along with a Control
Interval. This Control Interval is the amount of time that elapses between
each adjustment to the Duct Static Pressure Control Output Signal. The
default period is 10 seconds and should not be changed unless close
observation reveals that the Supply Fan is hunting and not maintaining
a stable pressure reading. The Static Pressure Control Output Signal can
be used to control a Supply Fan VFD (Direct Acting Operation) or a
Zoning Bypass Damper Actuator (Reverse Acting Operation).
The Duct Static Pressure Control Output Signal is a non-confi gurable
Direct Acting Signal (0-10 VDC). This Output Signal can be used to
directly connect to a Supply Fan VFD. The Output Signal increases
(increases VFD Speed) if the Duct Static Pressure is below the Duct
Static Pressure Setpoint by the Deadband amount, and the Output Signal
decreases (decreases VFD Speed) if the Static Pressure is above the
Setpoint by the Deadband amount.
Since the Duct Static Pressure Control Output Signal is a non-confi g-
urable Direct Acting Signal (0-10 VDC), when you are using a Zoning
Bypass Damper Actuator to control the Duct Static Pressure, you must
set up the Zoning Bypass Damper Actuator or the Zoning Bypass Damper
so that it is Reverse Acting in operation. The Output Signal increases
(closes Zoning Bypass Damper) if the Duct Static Pressure is below the
Duct Static Pressure Setpoint by the Deadband amount, and the Output
Signal decreases (opens Zoning Bypass Damper) if the Static Pressure
is above the Setpoint by the Deadband amount.
If the Static Pressure ever rises 0.5” above the Duct Static Pressure
Setpoint, the Duct Static Pressure Control Output Signal will be cut
in half every control period until the Static Pressure is brought under
control. This is to prevent damage to the ductwork if all the VAV
boxes are closed or some other blockage occurs in the ductwork.
Warning: The manufacturer does not assume responsibility for
protecting the equipment from over-pressurization! You should
always install mechanical high static protection cutoffs to protect
your system!
Any time the Supply Fan is off, the Duct Static Pressure Control Output
Signal will remain at zero volts. If the Supply Fan control is not con-
fi gured for Duct Static Pressure Control, you can still monitor the Duct
Static Pressure if the Duct Static Pressure Sensor is installed; however,
no control will occur.
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 VCM-X E-BUS can utilize a Duct Static Pres-
sure Sensor (used to monitor the discharge pressure) in conjunction
with a Supply Fan VFD. If the fi lters are getting dirty, the VCM 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.
Air Flow Monitoring, Supply Fan & Duct Static Pressure