Orion System SA E-BUS Controller - Manual (Page 48)

Zone
Zone
Sequence of Operations
SA E-BUS Controller Technical Guide
48
a range of Supply Air Temperature Setpoints. As the VFD Signal varies
within its range, it will proportionally reset the Supply Air Temperature
Setpoint within its range. For example, in the Cooling Mode, when the
Supply Fan VFD Signal is at its low setpoint, the Supply Air Cooling
Setpoint will be reset to its high setpoint; when the Supply Fan VFD
signal is at its high setpoint, the Supply Air Cooling Setpoint will be
reset to its low setpoint. In the heating mode, the Supply Air Heating
Setpoint reset would react in the opposite fashion with the VFD signal at
its highest setpoint the Supply Air Heating Setpoint is reset to its highest
setpoint, and with the VFD signal at its lowest setpoint the Supply Air
Heating Setpoint is reset to its lowest setpoint. In either mode, if the
VFD signal is halfway (for instance) between the Low Signal Setpoint
and the High Signal Setpoint, the Supply Air Setpoint would be reset
to halfway between its High and Low Setpoint. If Dehumidifi cation
Priority has been confi gured and the unit is in Heating Dehumidifi ca-
tion or Cooling Dehumidifi cation Mode, the Supply Air Temperature
Setpoint is proportionally reset in the same way as in the Heating and
Cooling Modes described above in this paragraph. When the unit is in
the Vent Mode or Vent Dehumidifi cation Mode, the Supply Air Tem-
perature Setpoint will be calculated to be halfway between the HVAC
Mode Enable Setpoints.
If a Remote Reset Signal is confi gured as the Reset Source, a 0-5 or 0-10
VDC signal can be used to reset the Supply Air Temperature Setpoint.
Separately, for the Heating Mode and the Cooling Mode you will need
to enter a Low and a High Supply Air Setpoint.
As an example when using a 0-5 VDC signal, when the Reset Signal
is at 0 VDC, the Supply Air Setpoint will be at its lowest setpoint for
both Heating and Cooling. When the Reset Signal is at 5 VDC, the
Supply Air Setpoint will be at it highest setpoint for both Heating and
Cooling. As the voltage signal changes between 0 VDC and 5 VDC, the
Supply Air Setpoint will be proportionally reset between the Low and
High Supply Air Temperature Setpoint for both Heating and Cooling. If
Dehumidifi cation Priority has been confi gured and the unit is in Heating
Dehumidifi cation or Cooling Dehumidifi cation Mode, the Supply Air
Temperature Setpoint is proportionally reset in the same way as in the
Heating and Cooling Modes described above in this paragraph. When
the unit is in the Vent Mode or Vent Dehumidifi cation Mode, the Supply
Air Temperature Setpoint will be calculated to be halfway between the
HVAC Mode Enable Setpoints.
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 SA E-BUS
Controller can be confi gured for Fan Cycle Mode. This means the Fan
will only run during Heating, Cooling, or Dehumidifi cation and will be
off the rest of the time.
Duct Static Pressure Control
The SA E-BUS Controller reads and controls Static Pressure in the duct
system if the Supply Fan has been confi gured for Duct Static Pressure
Control. Any time the Supply Fan is operating, the SA 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 observa-
tion 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 or a Zoning Bypass Damper Actuator.
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 on 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 SA E-BUS Controller 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 SA E-BUS
Controller 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.
Duct Static Pressure Control