RT-SVX063E-EN
71
–
Once the above conditions have been satisfied,
the user will be allowed to request
Unit Auto
Mode
at the front panel.
•
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.
N
No
otte
e:: 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 Front Panel
setting.
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
TM
outdoor
air 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 30, p. 72
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 settings to
linearize damper position with the fan curve. See
Table
30, p. 72
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
2
.
Decreasing CO
2
levels will decrease damper position to
DCV minimum damper position setpoint. Increasing
CO
2
level will increase damper position to design
minimum setpoint. DCV requires a valid space CO
2
value.
Demand control ventilation setpoints used in all
methods.
•
Space CO
2
high limit
•
Space CO
2
low limit
DCV when enabled with outdoor airflow control (Traq),
DCV resets the outdoor air minimum flow setpoint
based on space CO
2
. DCV enabled with Outdoor Air
Flow Compensation, DCV resets the outdoor air
damper minimum position based space CO
2
and
supply fan speed. 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.
S
Se
eq
qu
ue
en
ncce
e o
off O
Op
pe
erra
attiio
on
n
