Page 46
LGH/LCH420, 480, 540, 600
1.10. Demand Control Ventilation
1.10.1. General
A field-provided and installed indoor air quality (IAQ) sensor
can be used with the modulating economizer or 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.
1.10.2. 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
500 ppm (default) (start open set point) and reaches full
open at a carbon dioxide level of 1000ppm (default) (full
open set point).
The damper opens to a default position of 100% (see
Parameter 117). Determine damper travel position using
the following formula.
% Damper Travel = carbon dioxide ppm - Start Open ppm
5
Example: At a carbon dioxide level of 750ppm, the damper
will be approximately 50% open:
% Damper Travel = 750-500 = 50%
5
Use the menu interface to read carbon dioxide ppm. DATA
> IN/OUTPUTS > SENSORS > C02. Figure 40 shows
default or proportional operation.
1.10.3. Maximum and Minimum Demand Control
Ventilation Damper Settings
Maximum position is set using the following menu path:
Go to SETUP > TEST & BALANCE > DAMPER >
DAMPER MAX OPENING = .%
Use the following menu path to modified the minimum
damper positions for both high and low blower operations.
Go to SETUP > TEST & BALANCE > DAMPER > MIN
DAMPER POSITION BLOWER ON HIGH = .%
Go to SETUP > TEST & BALANCE > DAMPER > MIN
DAMPER POSITION BLOWER ON LOW = .%
1.10.4. Parameter Adjustments
Default indoor air quality economizer operation is based
on common or average applications. Adjustments may be
made to the indoor air quality parameters to alter operation
or meet required specifications. Use the user interface to
change Parameter 117 through 119. Go to SETTINGS >
RTU OPTIONS > EDIT PARAMETER
Select a demand control ventilation mode with Parameter
134. Modes 3 and 4 will bring on the unit blower when
demand control ventilation calls for maximum damper
open, and returns to auto-blower when demand control
ventilation damper returns to 0. The other modes only
operate when the unit blower is on, but will not bring it on
themselves.
Some applications require a different carbon dioxide set
point range than default settings. Damper “start open"
(Parameter 118 and “full open" (Parameter 119) carbon
dioxide set points may be adjusted from 0 to 2000 ppm.
Use the following formula to determine damper travel.
NOTE - When changing carbon dioxide set point range,
“start open" set point should be less than “full‐open" set
point.
% Damper Travel = carbon dioxide ppm - Start Open ppm X
Full Open Start Open
Max Open (Parameter 117) Full Open - Start Open
Example: An application requires the dampers open
at 800 CO
2
ppm and reach full open at 1200. If the
carbon dioxide level in the space reads 1000 ppm,
calculate the damper percent open as follows.
% Damper Travel = 1000 - 800 or 200 or .5 =0.5 x 100 = 50%
1200 - 800 400
To Next Page
Loading...
Need help?
General
