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Fan-Powered Units
Fan Actuation Schedule
FAN TYPE
Series
Parallel based on
Cool mode: ON if zone temp
Temperature
<heating set point + fan
offset fan offset + 0.5°F
Heat mode: fan off unless
reheat is on
Parallel based
Cool mode: ON if flow < fan
on Flow
set point OR if flow < active
minimum flow set point
Heat mode: fan off unless
reheat is on
Parallel Fan-Powered Units
Occupied Units
Air valve control for parallel fan-
powered units is the same as for single
duct units.
The first heat output is utilized to
control the fan. The remaining outputs
are utilized to control heat. Fan
energization is a function of the
"Parallel Fan Control Offset" . The
parallel fan control can be specified as
an offset temperature in degrees above
the heating set point or as a flow offset
in CFM. The fan will be energized above
the fan control offset if reheat is
required.
Note: The fan control offset is entered in
CFM when used on a VariTrane unit.
If the fan control is based on flow, the
unit fan will be energized whenever
primary airflow is below this set point.
For this parallel fan configuration, the
fan control point, if specified in a
percentage of unit airflow, must be set
between 15% and 30% of the units
cataloged airflow to assure proper
operation. A differential of 5% exists to
avoid excessive fan cycling.
When the fan control offset is in terms
of a temperature above the heating set
point, the fan shall be energized
whenever the zone temperature is
below the heating set point plus the fan
control offset. A differential of 0.5°F
shall apply to this switch over to avoid
fan cycling.
VAV-SVX01B-EN
Sequence Of
Operations
OCCUPIED
ON
Cool mode: OFF if zone
temp > heating set point +
Heat mode: fan off unless
reheat is on
Cool mode: OFF if flow >
fan set point + 5% AND
flow > active minimum
flow set point
Heat mode: fan off unless
reheat is on
Heat stages are energized on the
following schedule:
Stage
ON Switch point
point
1
At the heating
set point
2
1°F below the
heat set point
Whenever the fan is energized, the
primary airflow is controlled at the
"Heating Minimum Flow" set point.
Override Conditions
(Parallel Fans)
The UCM occupied controls can be
overridden by the following override
commands:
Unoccupied
If the control mode is unoccupied, the
unoccupied cooling and heating
temperature set points are used for
temperature control. Fan and heat
outputs are activated at the unoccupied
heating set point.
Heating
If the control action is HEAT , the UCM
controls the air valve as a heating
source rather than cooling. Fan and
heat outputs are disabled for parallel
units with electric heat. If the heat type
is hot water heat, then the fan will
remain on if the heat is on during the
heating control action.
Flow Control Override
Flow control may be overridden by any
of the following commands:
— Drive Air Valve Fully Open
The air valve will be driven fully open.
Fan and heat outputs are disabled.
— Drive Air Valve Fully Closed
The air valve is driven fully closed. Fan
and heat outputs are disabled.
UNOCCUPIED
— Drive Air Valve to Minimum Flow
OFF if valve closed
The air valve is driven to the minimum
AND reheat off
airflow set point. The fan and heat
OFF unless local
outputs remain operational.
reheat is on
— Drive Air Valve to Maximum Flow
The air valve is driven to the maximum
airflow set point. The fan and electric
OFF unless local
reheat is on
heat outputs are disabled (hot water
heat remains enabled).
Heat Control Override
Heat control can be disabled, locking
out heat outputs.
Fan Control Override
Fan control can be disabled, locking out
OFF Switch
both fan and heat outputs. This affects
only parallel fan-powered units.
0.5°F above the
heat set point
Control Offset
0.5°F below the
Control Offset may be enabled, which
heat set point
adjusts the edited cooling and heating
set points.
Recalibrate (Reset)
The recalibrate function can be enabled.
Series Fan-Powered Units
Occupied Units
Air valve control for series fan-powered
units is the same as both single duct
and parallel fan-powered units.
During the occupied mode of
operation, the series fan is continuously
energized. Heat stages are energized on
the following schedule:
Stage ON Switch point
1
2
Override Conditions
(Series Fan)
The UCM occupied controls can be
overridden by the following override
commands:
Unoccupied
If the control mode is edited to unoccu-
pied, the unoccupied cooling and
heating temperature set points are used
for temperature control. The series fan
and heat outputs will be activated as
OFF Switch point
At the heating
0.5°F above the
set point
heating set point
1°F below the
0.5°F below the heat
heat set point
set point
25
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