Sequence of Operation
82
OAU-SVX006E-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
.
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
.
Figure 51.
Heat cool mode arbitration graph.
