BAC-19xxxx FlexStat Application Guide
12 AG200824A
NOTE:
A modulating
OAD
(Outside Air
Damper) is required for DCV. An
OAD is used by both DCV mode and
economizer mode. Economizer mode
brings outside air into a building
for “free” cooling when appropriate
conditions are met. The OAD opens to
the greatest call between the needs of
DCV mode and economizer mode.
NOTE:
Whenever DCV is initiated, the fan is
set to On. If the fan is multi-speed or
modulating, it is set to its maximum
output.
NOTE:
The FlexStat’s CO
2
sensor uses a
self-calibration
technique designed
to be used in applications where
CO
2
concentrations will periodically
drop to outside ambient conditions
(approximately 400 ppm), typically
during unoccupied periods.
(There is
no provision for calibrating with gas.)
NOTE:
Models without CO
2
sensors still
have DCV applications available that
customers can enable in the Control
Basic code for use with external
CO
2
sensors. This requires custom
programming by the customer.
NOTE:
If more than one CO
2
sensor is
attached to the FlexStat (which
requires custom configuration), the
DCV application will use the CO
2
sensor
with the highest CO
2
reading.
NOTE:
Control Ventilation Benefits for Your
Basic DCV Mode
Basic DCV mode is On/Off and aims to optimize
IAQ (Indoor Air Quality). It maximizes the supply
of fresh outside air to the space after a sufficient
level of occupancy is detected (from the CO
2
level
exceeding the CO
2
Setpoint).
During occupied mode, the modulating OAD is
controlled typically by the economizer application.
When the space CO
2
rises above the CO
2
setpoint
(e.g., 1200 ppm), the damper opens to its maxi-
mum position. The OAD remains fully open until
the space CO
2
falls below the CO
2
setpoint minus
the CO
2
deadband (e.g., 200 ppm or a reading of
1000 ppm).
When Basic DCV mode is selected,
adjust the set-
point and deadband for the situation.
Standard DCV Mode
Standard DCV mode is continuously variable and
aims to optimize energy efficiency while also still
supplying adequate levels of fresh outside air to
the space. Setpoints for minimum and maximu-
mum DCV airflows are automatically calculated
based on the lowest weekly measured CO
2
levels.
The setpoint values have no user configuration,
and they do not appear in the menu.
NOTE:
In Standard DCV mode, the damper is
at the minimum position (assuming
there is no other demand on the
economizer) at the DCV start point.
The start point equals the calculated
baseline (e.g., 380 ppm) plus 200
ppm (e.g., 580 ppm). At the maximum
allowed CO
2
level (e.g., 980 ppm), the
damper opens to its maximum position.
