114 OAU-SVX007A-EN
Sequence of Operation v12.0
Description of Program Control
Each Horizon unit has four available control sequences: Space
Control, Discharge Air Control
Occupied Control
Starting Sequence
Occupied operation begins when the unit is placed in occupied
via BAS or when OAUTS-7 and 8 is closed on the field wiring
terminal strip (shipped with factory installed jumper).
Two-Position Outdoor Air Damper
Damper open close command is enabled, energizing the
outdoor air damper actuator. The supply fan starting sequence
begins once the damper end switch is closed.
Two-Position Outdoor and Return Air
Dampers
Damper open close command is enabled, energizing the
outdoor air damper actuator and de-energizing the return air
damper (spring open). The supply fan starting sequence
begins immediately (no end switch installed).
Two-Position Return Air Damper
Damper open close command is enabled, energizing the
outdoor air damper actuator. The supply fan starting sequence
begins once the damper end switch is closed.
Modulating Outdoor and Return Air Dampers
Outdoor air damper position command is adjusted to meet the
outdoor air damper minimum position setpoint. The supply fan
starting sequence begins immediately (no end switch
installed).
Supply Fan Operation
After completing initial startup, the supply fan startup sequence
will begin by enabling the supply fan start stop command and
setting the supply fan speed command to 50% for the initial 30-
seconds of operation.
The following sections describe the standard sequence of
operation based on ordered options. For additional options on
supply fan control, refer to (Additional factory available
features).
Constant Speed Supply Fan
Standard on CV units without airflow monitoring.
The supply fan (VFD) operates at a constant, supply fan speed
setpoint and does not vary supply fan speed to maintain an
airflow setpoint.
Constant Volume Supply Fan
Standard on CV units with airflow monitoring.
The supply fan speed (ECM or VFD) is adjusted to maintain a
constant airflow setpoint based on the reading from the supply
airflow monitoring system. The airflow is factory set but can be
adjusted in the field above the minimum airflow setpoints.
With constant volume operation, the supply fan speed
command is adjusted to maintain the supply fan airflow local to
the supply airflow setpoint active. Supply fan airflow setpoint
active is set to the supply fan airflow setpoint (adj.).
Supply Duct Static Control (Multi-Zone VAV)
Standard (required) with multi-zone VAV control.
Supply fan speed command is adjusted to maintain the duct
static pressure setpoint active. Supply fan speed is limited to
keep the supply airflow above the supply fan airflow minimum
setpoint active, which is a program-determined setpoint based
on factory settings and mode of operation. Factory set
minimum airflow vary between heating and cooling modes,
limited to keep the components within safe operating ranges.
If the heat pump is operating, the "cooling" minimum airflow is
used due to the restriction on the indoor coil. The active
minimum airflow will not fall below the outdoor airflow setpoint.
Space Temperature Control (Single Zone VAV)
Standard (required) with single zone VAV control.
Supply airflow is adjusted to maintain space temperature.
Typically, it operates at minimum airflow until the discharge air
setpoint reaches minimum or maximum, indicating that the
heating/cooling demand is high, at which point the supply
airflow is increased to meet the demand.
With single zone VAV operation, supply fan speed command is
adjusted to maintain the supply fan airflow active to the supply
fan airflow setpoint active. During normal operation, the supply
fan airflow setpoint active is set to the supply fan airflow
minimum setpoint active. If the discharge air temperature
setpoint active (which adjusts based on space conditions)
reaches the discharge air temperature setpoint minimum
(Cooling) or Maximum (Heating), the supply fan airflow
setpoint active will begin to adjust up by comparing the space
temperature active to the space temperature setpoint active.
As the airflow setpoint rises above minimum, the discharge
setpoint is set to the respective minimum/maximum setpoint.
Supply fan airflow minimum setpoint active is a program-
determined point based on factory settings, mode of operation,
outdoor airflow setpoints, or other factors.
Economizer Operation
The following section describe the standard sequence of
operation for economizer. Additional options are available for
enabling economizer mode, such as dry bulb economizer.
Contact the factory for additional information.
Economizer Mode with Supplemental
Mechanical Cooling
Enthalpy (Comparative) Economizer
Units equipped with modulating outdoor/return air dampers
have factory installed outdoor and return air temperature/
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