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RT-SVX063E-EN
Supply Fan Control
All IntelliPak units with the Symbio 800 controller have
two supply fans and two Danfoss VFDs installed. Both
fans are controlled identically. The fans are sent the On/
Off command at the same time and commanded to the
same speed at all times. It is assumed that the VFDs for
each fan are setup identically. Supply fan operation will
be confirmed via a method of proving airflow which is
explained below.
Supply Fan Speed Control
The controller sends a speed command to VFD as a
value from 0-100%. The VFD interprets the commands
as 0% = Minimum frequency and 100% = Maximum
frequency. See Programming Guide, Manual Overrides
for more details.
The supply fan speed requested and commanded value
will remain at 0% any time the Active Supply Fan Run
Command = OFF. Once the Active Supply Fan Run
Command = ON and the unit has transitioned into an
active Heat/Cool state, the supply fan speed will be
controlled as required by unit type.
•
Constant Volume units always run the fans at 100%
after being proved On. The command is 0% while
waiting on proving.
•
Multi Zone VAV units modulate the supply fan
speed to perform Duct Static Pressure Control after
being proved On. During full airflow modes,
Adaptive High Duct Static Limit will control supply
fan speed to 100% or as high as possible subject to
duct static pressure high limit constraints.
•
Zone Temperature units can be configured via
Supply Fan Configuration Command to cycle the
supply fan off when heating or cooling capacity is
inactive. A demand for heat or cooling will
automatically initiate supply fan operation.
•
Single Zone VAV units modulate the supply fan
based on capacity control after being proved On.
Supply Fan Proving Operation and
Method
Supply Fan Proving is active only after the Supply Fan
Run Command is set to ON. Once set to ON, the supply
fan is required to prove greater than 90% of minimum
fan RPM (VFD minimum Hz setting), within 40 seconds.
Fan proving fails anytime the fan is less than 90% of
minimum RPM. A diagnostic is generated and
operation stops.
N
No
otte
e:: Bypass Mode uses an alternate method of fan
proving. See below for more details.
Single Fan Operation
Unit parallel fans permit single fan operation if one fan
fails to prove On. Cooling, external heat and ventilation
continue to operate. Gas heat and electric heat are
disabled. If the second fan fails to prove On, the unit
shuts down.
If the failed fans diagnostic(s) clear, unit operation
resumes.
Supply Fan VFD Bypass Control
All units will have a configurable option to provide
Supply Fan VFD Bypass control. Whenever the bypass
option is installed, the unit will include all of the
necessary components to bypass the VFD assembly
and allow the supply fan to operate at line frequency.
Entering VFD Bypass Control
•
The supply fan must be off and no-discharge air
flow detected for 40 continuous seconds to enter or
leave Supply Fan VFD Bypass Mode.
•
Enabling and disabling Supply Fan VFD Bypass
Mode can only take place from the unit Front Panel.
•
Both supply fan VFDs will be bypassed and the fans
then operate at line frequency.
•
During active Supply Fan VFD Bypass Mode
–
The Modbus communicated command for
supply fan will be set to OFF, and the
communicated speed command will be set to
0%.
–
All supply fan VFD diagnostics will be masked.
–
A warning only, latching “Supply Fan Bypass
Enabled” diagnostic will be generated.
–
A duct static pressure sensor, if installed, will be
used to perform Duct Static Pressure High Limit
protection if enabled for bypass operation.
See Programming Guide (RT-SVP011*-EN) for more
information.
Exiting Supply Fan VFD Bypass Mode
•
The user will not be allowed to remove the unit
from an active
Supply Fan VFD Bypass Mode
at the
front panel until all of the following has occurred:
–
The user has requested
Unit Stop Mode
from
the front panel.
–
All components have been commanded OFF or
CLOSED.
–
The fan proving mechanism indicates a supply
fan no-flow condition has existed for 40
continuous seconds.
•
When the user removes the unit from active Supply
Fan VFD Bypass Mode at the front panel, all of the
following will be enforced:
–
The
Supply Fan Bypass Relay
will remain OFF.
–
The
VAV Box Relay
will be commanded OFF
(de-energized) to indicate normal airflow mode
to the system, and the
VAV Box Stroke Time
will
count down.
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Summary of Contents for IntelliPak RA 20
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