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Sequence Of
Operations
necessary to maintain the current
unoccupied set points. The fan control
point is not utilized on series units. On
electric heating and hot water heating
units, the fan and heat are energized at
the unoccupied heating set point. The
minimum cooling flow set point is reset
to zero unless minimums are being
enforced by a group override. A series
fan will be energized anytime the air
valve's position is greater than 0%.
Heating
If the control action is edited to HEAT ,
the UCM controls the air valve as a
heating source rather than cooling. The
unit fan remains operational. Unit heat
on an electric heat unit is locked out,
but remains active on hot water units.
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 operation is unaffected, but heat
outputs are locked out.
— Drive Air Valve Fully Closed
The air valve is driven fully closed. The
fan and heat outputs are locked out.
— Drive Air Valve to Minimum Flow
The air valve is driven to the minimum
airflow set point. The fan and heat
outputs remain operational.
— Drive Air Valve to Maximum Flow
The air valve is driven to maximum
airflow set point. The fan and heat
outputs remain operational.
Heat Control Override
Heat control can be disabled locking
out heat outputs.
Fan Control Override
Fan control override does not affect fan
operation on series fan-powered units.
Control Offset
Control offset may be enabled which
adjusts the edited cooling and heating
set points.
Recalibrate (Reset)
The recalibrate function can be enabled.
Zone Sensor Functions
The zone sensor utilizes a thermistor
element to measure zone temperature.
26
The zone sensor has the following
options:
Zone Temperature
Each zone sensor module includes a
zone temperature sensor.
Set Point
A UCM will only use the zone sensor
thumbwheel set point (during occupied
time) if "Zone sensor thumbwheel
functions" is edited to ENABLE on the
UCM setup screen.
ON Timed Override (TOV) and CANCEL
Timed Override (TOV)
The ON (TOV) and CANCEL (TOV)
commands can be issued by pressing
the ON or CANCEL buttons on any of
the UCM zone sensor modules.
— When an ON button on a zone sensor
is pressed (shorting the zone
temperature sensor circuit), the UCM
will set a TOV signal, clear the TOV
cancel signal if it is set, and start the
two hour timed override timer. The TOV
signal will be maintained for two
minutes.
— When a CANCEL button on a zone
sensor module is pressed for at least
two seconds, the UCM must set a TOV
cancel signal, clear the TOV signal if it is
set, and set the timed override timer to
zero.
— Pressing any zone sensor module's ON
or CANCEL button will not affect the
zone temperature reported from the
UCM.
Note: TOV pushbuttons should be
pressed for at least 2 seconds and not
more than 15 seconds.
Drive to Max and Go Unoccupied
When a zone sensor thumbwheel is
turned to its high-end limit, indicated by
a "*" on the thumbwheel, and the ON
button is pressed, the UCM will initiate
a "Drive to Max" command. When a
zone sensor thumbwheel is turned to
its low limit, indicated by a "**" on the
thumbwheel, and the ON button is
pressed, the UCM will initiate a "Go
UNOCCUPIED" command. The UCM
will maintain the command until the
zone sensor set point is adjusted to
within the range of 50° to 85°. Any zone
sensor module that has a thumbwheel
and ON (TOV) button can initiate these
commands.
Notes:
•
The UCM will not send these
commands if "Zone sensor
thumbwheel functions" is edited to
DISABLE on the UCM setup screen.
— When an ICS is connected to the UCM,
the UCM will pass the commands to
the ICS without taking any control
action of its own. Since this is true, it
may take a minute or so after the
command is initiated before the UCM
actually goes unoccupied or is driven to
maximum.
— The UCM will not generate a TOV signal
when a Drive Max or Unoccupied
command is initiated.
— Pressing the ON button will not affect
the zone temperature reported from the
UCM.
— The UCM will remain in the Drive Max
or Unoccupied status over power
failures IF "*" or "**" (respectively)
have been initiated prior to the power
failure.
Note: TOV pushbuttons should be
pressed for at least 2 seconds and not
more than 15 seconds.
Flow Sensor
The flow control is pressure indepen-
dent utilizing the VariTrane flow-sensing
ring. The flow ring provides one of the
most accurate differential pressure flow
measurements in the industry by
averaging pressure differentials across
16 sensing points. These sensing
points, arranged in a ring configuration
to compensate for various inlet duct
configurations, provide a signal
accurate to within +/-5% of cataloged
CFM provided there is 1½-inlet diam-
eters of straight ductwork upstream of
the VAV box.
The pressure differential signal from
the flow ring is then converted to an
electrical signal, which is utilized in the
control algorithm of the unit controller.
It is recommended that the recalibrate
sequence be initiated on a weekly basis.
Assuming ½ inlet diameters of straight
duct work and proper system
recalibration, total system flow
VAV-SVX01B-EN
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