48
BAS-SVX48H-EN
CO
2
-Based Demand Controlled Ventilation
CO
2
-based demand controlled ventilation measures the concentration of carbon dioxide (CO
2
) in
the zone as a means to vary the outdoor airflow delivered as the population of the zone changes.
DCV calculates the required minimum OA damper position based on the current zone CO
2
concentration. However, the OA damper may be opened greater than the design minimum
setpoint if air side economizing is possible.
The UC400 supports CO
2
-based DCV in blower coil, fan coil, and unit ventilator products when
equipped with a modulating outdoor air damper and CO
2
sensor (hard wired or communicated
via the BAS). DCV functions only during occupied modes (Occupied, Occupied Standby,
Occupied Bypass), in either heating or cooling, as long as the fan is operating (HIGH, MEDIUM,
LOW, ON, or AUTO).
NNoottee:: The UC400 continues to maintain space comfort control while DCV is active. DCV can be
enabled/disabled through the controller configuration/setup.
When the fan operates at a constant (single) speed, the controller uses two (2) OA damper
position setpoints and two (2) CO
2
setpoints as shown below:
• When the CO
2
concentration in the zone is equal to, or higher than, the CO
2
Design Setpoint,
the OA damper adjusts to the Design Minimum OA Damper Position setpoint.
• When the CO
2
concentration in the zone is equal to, or lower than, the CO
2
Minimum
Setpoint, the OA damper adjusts to the DCV Minimum OA Damper Position setpoint.
• When the CO
2
concentration in the zone is between the CO
2
Minimum Setpoint and the CO
2
Design Setpoint, the OA damper is determined using a straight proportional calculation
between the two OA damper setpoints.
Figure 21. CO
2
Setpoints
Fan Operating at Multiple Speeds or Single-Zone VAV Control
The UC400 Controller uses four (4) OA damper position setpoints and two (2) CO
2
setpoints as
shown below.
SSeeqquueennccee ooff OOppeerraattiioonn
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