Orion System RNE Modular Controller - Manual (Page 64)

Zone
Zone
SEQUENCE OF OPERATION
RNE Modular Controller Field Technical Guide 64
IAQ, Pre-Heat, Heat Wheel, Single Zone VAV
IAQ ( CO
2
) Operation
If you have confi gured the RNE 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.
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.
Heat Wheel
One of the relay outputs can be confi gured as a Heat Wheel Relay. This
relay will enable the Heat Wheel when the unit goes into the Occupied
Mode. If the unit is confi gured for Economizer Operation, this relay will
disable the Heat Wheel when the unit goes into Economizer Mode. If
the Heat Wheel Relay is active, a Heat Wheel Defrost Cycle will occur
that will disable the Heat Wheel Relay for 2 minutes if the Outdoor Air
Temperature is below the Heat Wheel Defrost Setpoint and 30 minutes
have elapsed since the last Heat Wheel Defrost Cycle.
Single Zone VAV Mode
In this application, the RNE will modulate the Supply Fan VFD to
maintain the Space Cooling or Heating Setpoint while the unit’s cooling
or heating source is modulating to maintain the appropriate Supply Air
Setpoint. This sequence will operate optimally when the HVAC unit has
modulating heating and cooling. Staged heating and cooling should not
be used and will not provide satisfactory performance.
When the Space Temperature rises one deadband above the Space
Cooling Setpoint, the cooling mode is initiated. The Supply Fan will
energize and begin operating at 30% speed. Cooling will modulate to
maintain the Active Supply Air Cooling Setpoint. The Supply Fan will
then proportionally modulate as needed between 30% and 100% as the
Space Temperature rises within the Space Reset Window created by
confi guring a Cooling Reset Source Low Setpoint and a Cooling Reset
Source High Setpoint. The Cooling Mode is disabled when the space
temperature falls one deadband below the Space Cooling Setpoint.
When the Space Temperature falls one deadband below the Space
Heating Setpoint, the Heating Mode is initiated. The Supply Fan will
energize and begin operating at 50% speed. Heating will modulate to
maintain the Active Supply Air Heating Setpoint. The Supply Fan will
then proportionally modulate as needed between 50% and 100% as
the Space Temperature falls within the Space Reset Window created
by confi guring a Heating Reset Source High Setpoint and a Heating
Reset Source Low Setpoint. When Heat Pump heating is operating, the
Supply Fan VFD will operate from 75% to 100%. The heating mode
is disabled when the space temperature rises one deadband above the
Space Heating Setpoint.
When the Space Temperature is satisfi ed and the unit is in the Vent
Mode of operation, the fan will operate at 30%. During Dehumidifi ca-
tion, the fan will operate as described above, depending on if the Space
Temperature is calling for Heating, Cooling, or Vent Mode operation.
Whenever the unit is in CO
2
override operation of the Outdoor Air
Damper, the minimum VFD fan speed is forced to 75% and can modu-
late up from there.
In order for the RNE to operate in Single Zone VAV mode, the unit must
be confi gured as follows:
Mode Enable Sensor = Space Temperature
Reset Source = Single Zone VAV
Duct Static Pressure Control = No
Confi gure the Cooling Reset Source High and Low Setpoints and the
Heating Reset Source High and Low Setpoints to establish the Space
Temperature Cooling and Heating range over which the VFD will
modulate in those modes.