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•
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.
Note: Bypass Mode uses an alternate method of fan
proving. See below for more details.
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
(duct static pressure) 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 user interface.
•
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.
RT-SVX073A-EN
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 user
interface until all of the following has occurred:
–
The user has requested Unit Stop Mode from the
user interface.
–
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 user interface, 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.
–
Once the above conditions have been satisfied, the
user will be allowed to request Unit Auto Mode at
the user interface.
•
At all times when the unit is not in an active Supply Fan
VFD Bypass Mode, the Supply Fan Bypass Relay will
be commanded OFF (de-energized).
Supply Fan Proving with VFD Bypass
Units configured with Supply Fan VFD Bypass option
require two modes of supply fan proving. During non-
Bypass unit operation supply fan proving will use the fan's
VFD RPM as is used normally. The enabling and disabling
of Supply Fan Bypass Mode, as well as unit operation
during an active bypass event, requires Duct Static
Pressure to be used for supply fan proving.
Note: The enabling and disabling of VFD Bypass will be
dis-allowed until the Duct Static Pressure indicates
no flow per the below option.
Proving criteria for proof of flow: When Duct Static
Pressure rises above the Bypass Duct Static Diff Pressure
setting, the supply fan will indicate a Flow condition.
Proving criteria for proof of no flow: If this pressure remains
below 30% of the Bypass Duct Static Diff Pressure setting
for 40 continuous seconds, the supply fan will indicate a
No-Flow condition.
Operation during Manual Override and VOM
(Emergency Override) Modes
Manual Override, VOM, and Emergency Override modes
will operate as defined except for the following
modifications:
1. If the fan is ON it will run at line frequency.
2. The VAV Box Relay will follow the defined operation
specified in each VOM Mode user interface setting.
Unit Startup
67
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