Orion System SA E-BUS Controller - Manual (Page 49)

SA E-BUS Controller Technical Guide
Sequence of Operations
49
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 E-BUS
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.
Supply Air Cutoffs
The Supply Air Temperature Cutoffs are designed to prevent extremely
High and Low Temperature Supply Air from entering the building.
High Supply Air Temperature Cutoff
High Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature rises above the HI SAT Cutoff Setpoint. When this occurs,
Heating stages will be deactivated until the Supply Air Temperature falls
5°F below the HI SAT Cutoff Setpoint.
Low Supply Air Temperature Cutoff
Low Supply Air Temperature Cutoff is initiated when the Supply Air
Temperature falls below the LO SAT Cutoff Setpoint. If the SA E-BUS
Controller is in WSE Operation, Vent Mode, or Heating Mode and the
Supply Air Temperature falls below the LO SAT Cutoff Setpoint for 10
minutes, it is assumed a Mechanical Failure has occurred and all Heat-
ing will be deactivated and the Supply Air Fan will shut off. If the SA
E-BUS Controller is in the Cooling or Dehumidifi cation Mode and the
Supply Air Temperature falls below the LO SAT Cutoff Setpoint, the
Cooling Signal or Cooling Stages will immediately begin deactivating.
To restore normal operation, one of the following three things must occur:
1. The Supply Air Temperature rises above the LO SAT
Cutoff Setpoint by 5°F.
2. The SA E-BUS Controller goes from Occupied to
Unoccupied or from Unoccupied to Occupied Mode.
3. The SA E-BUS Controller’s power is cycled.
Pre-Heater Operation, Entering Air Lockouts & Supply Air Cutoffs