Sequence of Operation
90
OAU-SVX01K-EN
Space Control or Single Zone VAV Control
with No Energy Recovery Wheel and 100%
Outdoor Air
Heating Mode is enabled whenever the Outdoor Air
Temperature Active falls below the Outdoor Air Heating
Enable Setpoint. When this occurs, cooling and
dehumidification is not allowed, regardless of space
conditions.
When the Outdoor Air Temperature Active is above the
Outdoor Air Heating Enable, but below the Outdoor Air
Cooling Enable Setpoint, Heating Mode is enabled
according to the graph shown in
. Using
the graph, setpoint is Space Temperature Setpoint Active,
offset is Occupied Offset, and temperature is Space
Temperature Active.
During Heating Mode, Heat Capacity is adjusted to
maintain the Discharge Air Temperature Local to
Discharge Air Temperature Setpoint Active.
Figure 55.
Heat cool mode arbitration graph.
Gas Heat Ignition Failure
The unit monitors the status of the heater using Heat On
Off Status Local. In the event of ignition failure, the unit will
make three ignition attempts before displaying
Diagnostic: Heat Failure. The unit is shut down when a
heat failure occurs and resets four hours later to re-
attempt ignition.
Heat Pump Heating Mode
Heat pump heating is enabled using the same criteria as
Primary Heating Mode, except that heat pump is
attempted first before using the primary heater. The same
setpoints are used to adjust Compressor Heating Capacity.
During heat pump operation the hot gas reheat is at 100%.
When the unit switches from heat pump to primary
heating, Auxiliary Heating Mode changes to Allowed.
Auxiliary Heating Mode is locked as Allowed for a
minimum of fifteen minutes.
If the Compressor Heating Capacity is at 100%, and
Discharge Air Temperature Local falls 3°F below the
Discharge Air Temperature Setpoint Active for ten
minutes, the unit toggles Auxiliary Heating Mode to
Allowed, Outdoor Air Temperature Active is recorded as
Heat Pump Fail Switch Point. Heat pump operation is re-
attempted when the temperature rises by 5°F.
The unit switches Auxiliary Heating Mode to Allowed
when the Outdoor Air Temperature Active falls below the
Heat Pump Disable Temperature Setpoint (adj. 0-60°F,
default 25°F).
Water Source Heat Pump
Outdoor Coil Water Flow Status uses a differential
pressure switch(es) across the supply and return to prove
water flow. Outdoor Coil Water Low Temperature Switch
uses temperature switch(es) on the return (35°F, water;
20°F, glycol). Heat pump operation is disabled if Outdoor
Coil Water Flow Status goes Off for ten seconds, and
immediately if the Outdoor Coil Water Low Temperature
Switch is open.
Air Source Heat Pump – Demand Defrost
Control
Defrosting of the outdoor coil may occur when the
Outdoor Air Temperature Active is below 52°F and the
Outdoor Coil Refrigerant Temperature Local (Circuit 1 or 2)
is below 35°F. The unit monitors the condenser conditions,
and Defrost Mode is enabled once there is frost
accumulation. During Defrost Mode the reversing valve(s)
are switched into the cooling position and the condenser
fans are shut off. The primary heat will be enabled on units
with gas or hot water heat. Units with electric or no heat
will close the outdoor damper (if installed).
Cooling Mode
Discharge Air Control
Cooling Mode is enabled whenever the Outdoor Air
Temperature Active rises above the Outdoor Air Cooling
Enable Setpoint. The Outdoor Air Temperature Active
must be above the Outdoor Air Heating Enable Setpoint.
During Cooling Mode, Cooling Capacity is adjusted to
maintain Discharge Air Temperature Setpoint Active.
Multi-Zone VAV Control
Cooling Mode is enabled according to the graph shown in
. Using the graph, setpoint is Discharge Air
Temperature Setpoint Active, offset is 2°F, and
temperature is Discharge Air Temperature Local.
Dehumidification Mode takes priority over Cooling Mode.
During Cooling Mode, Cooling Capacity is adjusted to
maintain Discharge Air Temperature Setpoint Active.
