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Unit Startup
3. External fan control in bypass mode is supported. An
external Supply Fan Speed Setpoint value = 0% will
turn the fan Off, and any value > 0 will turn the fan On.
The Supply Fan Speed Status always reports 100%
speed during active supply fan bypass operation.
Minimum Ventilation Control
Symbio 800 provides outdoor air minimum ventilation
control via options described below. Traq
flow control is the highest priority when installed and
enabled. If Traq becomes disabled or inactive, Outdoor Air
Flow Compensation will calculate a damper minimum
position setpoint (this option should be disabled on
constant volume units). If Outdoor Air Flow Compensation
is disabled, Outdoor Air Minimum Position Setpoint will
calculate damper minimum position setpoint.
Outdoor Air Flow Control (Traq)
The outdoor air damper is modulated to provide outdoor air
flow (cfm) required by Outdoor Air Minimum Flow Setpoint.
The outdoor air damper will modulate closed and open to
maintain the required outdoor air minimum flow rate. See
Table 34, p. 68
for additional information and settings.
The provided air flow measurement capabilities include
periodic, automatic calibration; however, air flow gain and
offset settings are provided for field adjustment.
Outdoor Air Flow Compensation
The outdoor air damper minimum position is modulated to
provide outdoor air based on a variable supply fan speed.
When supply fan increases speed the outdoor air damper
minimum position is reduced, to prevent over ventilation.
When supply fan decreases speed the outdoor air damper
minimum position is increased to maintain design outdoor
air flow requirements. There are three user editable
Table 34.
Outdoor air damper minimum ventilation control methods
Traq
Enabled/Active
Enabled/Active
68
TM
outdoor air
Outdoor Air Flow
Demand Control
Compensation
Ventilation
Disabled
Disabled
Disabled
Enabled/Active
settings to linearize damper position with the fan curve.
See
Table 34, p. 68
for additional information.
Outdoor Air Minimum Position Control
This function provides a fixed damper position for minimum
outdoor airflow requirements. The damper is controlled to a
position determined by Economizer Minimum Position
Setpoint Active. This feature is available on all unit types
with an outdoor air damper, but commonly used on
constant volume units.
Demand Control Ventilation (DCV)
Demand control ventilation reduces energy consumption
by reducing the outdoor air damper below minimum
ventilation based on space CO
will decrease damper position to DCV minimum damper
position setpoint. Increasing CO
damper position to design minimum setpoint. DCV requires
a valid space CO
value.
2
Demand control ventilation setpoints used in all methods.
•
Space CO
high limit
2
•
Space CO
low limit
2
DCV when enabled with outdoor airflow control (Traq),
DCV resets the outdoor air minimum flow setpoint based
on space CO
. DCV enabled with Outdoor Air Flow
2
Compensation, DCV resets the outdoor air damper
minimum position based space CO
DCV enabled with Outdoor Air Minimum Position Control
resets the outdoor air damper minimum position based on
space CO
.
2
Table below summarizes the settings used for each
Minimum Damper Position Control and Demand Control
Ventilation.
Description
Damper controls to outdoor
air minimum flow setpoint
Outdoor Air Flow setpoint is
reset based on space CO
. Decreasing CO
levels
2
2
level will increase
2
and supply fan speed.
2
Outdoor Air Damper
Controlling Setpoints
Setpoint:
Outdoor Air Minimum Flow
Setpoint Active
Outdoor Air Minimum Flow
Setpoint Status
Setpoint:
.
Outdoor Air Minimum Flow
2
Setpoint Status
Settings:
Design Min Outdoor Air Flow
Setpoint
DCV Min Outdoor Air Flow
Setpoint
RT-SVX073A-EN
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