Orion System SA Controller - Manual (Page 46)

Zone
Zone
Sequence of Operations
SA Controller Technical Guide 46
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 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 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 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 read-
ing. 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 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 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.
Pre-Heater Operation
In colder climates where freezing temperatures are sometimes experi-
enced, it is desirable to preheat the Entering 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 Entering 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 Entering 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.
Entering Air Lockouts
The Entering Air Cooling and Heating Lockouts Setpoints are designed
to prevent unwanted Mechanical Heating or Cooling operation during
certain Entering Air Temperature conditions.
When the Entering Air Temperature is below the Cooling Lockout
Setpoint, no Mechanical Cooling can operate. However, if the unit is
equipped with a Water Side Economizer (WSE) and the SA Controller is
confi gured to use the WSE, 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 Entering Air Heating Lockout operates so that when the Entering
Air Temperature is above the Entering 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.
Duct Static Pressure Control