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9. Demand Control Ventilation (DCV)
9.1.
General
A field-provided and installed indoor air quality (IAQ) sensor can be used with the modulating economizer or motorized
outdoor air damper (OADM) to control carbon dioxide levels in the conditioned space. The carbon dioxide level in a space
is an indicator of the number of people occupying a room. As the carbon dioxide level rises (indicating the occupancy of a
room has increased), dampers modulate open - regardless of outdoor air suitability. Likewise, as the carbon dioxide level
falls (indicating the occupancy has decreased), dampers modulate further closed.
Standard economizer installations have a minimum fresh air ventilation requirement based on maximum room
occupancy. With standard economizer use, the amount of air required for maximum room occupancy is heated or cooled
with each heating or cooling cycle. IAQ installations use the maximum amount of required ventilation air only with
maximum room occupancy; less outdoor air needs to be heated or cooled when fewer people are in the conditioned
space.
If the economizer is operating in the free cooling mode and the indoor air quality control requires the damper to open
further, the indoor air quality demand will override the free cooling demand.
The IAQ function is not energized during the unoccupied or night time period.
NOTE: The IAQ sensor may also be used with systems containing a motorized outdoor air damper.
9.2.
Default Operation
The M3 unit controller has a 0-10VDC indoor air quality input for a standard 0 - 2000ppm carbon dioxide sensor. The
economizer starts opening at a carbon dioxide level of 700 ppm (default) (start open set point) and reaches full open at a
carbon dioxide level of 1200ppm (default) (full open set point).
The damper opens to a default position of 50% (see parameter 117). Determine damper travel position using the following
formula.
% Damper Travel = carbon dioxide ppm - Start Open ppm
Example: At a carbon dioxide level of 750ppm, the damper will be approximately 50% open:
% Damper Travel =
Use the applicable menu interface to read carbon dioxide ppm.
DATA > IN/OUTPUTS > SENSORS > C02
DATA > IN/OUTPUTS > SENSORS > NETWORK > C02
Figure 10 shows default or proportional operation.
9.3.
Maximum and Minimum Demand Control Ventilation Damper Settings
Maximum position is set using the following menu path:
Go to SETTTINGS > RTU OPTIONS >DAMPER > DAMPER CONTROL VENTILATION OPTIONS and select DEMAND CONTROL VENTILATION.
Options are:
•
DEMAND CONTROL VENT > DAMPER START OPEN = XXXX PPM
•
DEMAND CONTROL VENT > DAMPER FULL OPEN = XXXX PPM
•
DEMAND CONTROL VENT > DAMPER MAX OA CFM = X CFM (only visible if configuration id 1, position 2 is set correctly).
•
DEMAND CONTROL VENT > DAMPER MAX OPENING = XXX.X %.
5
750-500
=
5
49
50%
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