RT-SVX063E-EN
87
External Control
Symbio 800 provides the ability for an external
controller or program to control supply fan, exhaust
fan, and outdoor air damper. This capability allows for
custom programming suited for specific application
needs.
External Supply Fan Control
External supply fan control applies to variable volume
supply fan equipment. Supply fan operation must
prove running and any unit startup timing must expire
before external control is allowed. Supply Fan Speed
Control Enabled provides an enabled status when
Supply Fan Speed Setpoint is in control. The controller
will annunciate External Supply Fan Control on the
user interface, operating modes screen when active.
Supply Fan Speed Setpoint will only override the
controller’s fan control in occupied Cool, Heat, and Fan
Only modes of operation. All other modes (such as
Morning Warm Up, Pre Cool, Daytime Warm Up) the
supply fan is operated under Symbio 800 control.
Supply fan speed will increase under Symbio 800
control according to heating and cooling capacity
requirements; space temperature control unit
configurations. Supply fan speed will decreases under
Symbio 800 control when high duct static pressure
limits are approached; discharge air control unit
configurations.
Table 35.
External supply fan control points
Object
Name
Description
Supply Fan
Speed
Setpoint
Enable
Enables supply fan speed setpoint control
Supply Fan
Speed
Control
Enabled
Supply fan speed is control via Supply Fan Speed
Setpoint. If disabled/inactive, speed control is
under Symbio 800 control
Supply Fan
Speed
Limited
Supply fan speed is being increased or decreased
due to a limit control action.
Supply Fan
Speed
Setpoint
External supplied supply fan speed setpoint value
Supply Fan
Speed
Setpoint
Active
Active setpoint input to supply fan speed control
Supply Fan
Speed
Status
Indicates the requested speed to the supply fan,
0% when fan is off.
Table 36.
Supply fan speed setpoint summary
Supply Fan
Speed Setpoint
Enable
Supply Fan
Speed Setpoint
Supply fan
operation
Disable
NA
Fan under Symbio
800 control
Enable
0%
Commands the fan
off
Enable
1% to 37%
(a)
Fan operates at
drive minimum Hz
setting
Enable
38% to 100%
Fan ramps between
drive min-Hz and
max-Hz setting.
(a)
For example, if drive setting is 22 min-Hz and 60 max-Hz, it will
correlate to 37% reported fan speed.
External Relief Fan Control
External Relief fan control is allowed anytime a relief
fan is configured. Supply fan and relief fan operation is
proven before external fan control is allowed. Relief fan
operation is effectively interlocked with supply fan
operation. No other control limits are applied; building
static pressure high limit is not enforced.
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an
ntt:: A valid space static pressure sensor is not
required for external relief fan control;
therefore, proper building static pressure
control must be considered.
The controller will annunciate External Relief Fan
Control on the user interface, operating modes screen,
when active. All modes of operation are supported,
except when supply fan is off. If the supply fan cycles
off with capacity, the relief fan will also turn off.
External relief fan speed is also interlocked with relief
damper position and relief damper diagnostics. The
relief damper movement will limit relief fan speed
changes accordingly. The controller will impose speed
limitations as required.
Table 37.
External relief fan control points
Object Name
(a)
Description
Object States or
values
Exhaust Fan Speed
Setpoint Enable
Enables Relief fan
speed setpoint
control
0 = Disable
1 = Enable
Exhaust Fan Speed
Control Enabled
Relief fan speed is
control via Exhaust
Fan Speed
Setpoint. If
disabled/inactive,
speed control is
under local control.
0 = Disabled
1 = Enabled
Exhaust Fan Speed
Setpoint
External supplied
exhaust fan speed
setpoint value
0 to 100%
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