30
Fig. 20 — Power Exhaust Operation Curves
Indoor Air Quality (IAQ)
Indoor air quality is typically measured using a CO
2
sensor
whose measurements are displayed in parts per million (ppm).
Outdoor air quality may be measured with a CO
2
sensor for in-
door-outdoor differential demand ventilation control. The fac-
tory-installed indoor air quality CO
2
sensor is mounted in the
return section. A field-installed indoor air quality CO
2
sensor
may be mounted in the return or in the occupied space. The in-
door air quality modes of operation can be affected by the IAQ
Analog Input Config (ANALOG IAQ CTRL) and other related
and limit configurations as described below.
IAQ (ANALOG INPUT)
When IAQ assigned channel (IAQ SENSOR CHAN) is set for
an analog input that input channel will be mapped to the Indoor
Air Quality (IAQ LEVEL). The control is configured for in-
door air quality sensors which provide 4 to 20 mA signal for
0 to 2000 ppm CO
2
. If the sensor being used has a different
range, the ppm display range must be reconfigured by entering
new values for the IAQ Sensor Value at 4mA (IAQ PPM @
4MA) and IAQ Sensor Value at 20mA (IAQ PPM @ 20MA).
ANALOG IAQ CTRL = 0 (No IAQ)
This signifies that there is no IAQ sensor installed. The econo-
mizer damper will operate based on the minimum position
curve.
ANALOG IAQ CTRL = 1 (DCV)
During Demand Controlled Ventilation (DCV), the damper
modulates on or between two ventilation curves depending
upon the difference between the Indoor Air Quality (IAQ
LEVEL) and the Outdoor Air Quality (OAQ LEVEL). The
lower of these two curves is referred to as the IAQ Minimum
Position Curve, and the higher curve is the Minimum Position
curve discussed in “Minimum Ventilation” on page 27 under
Economizer Operation. Refer to that section on how the mini-
mum Position curve is created. See Fig 19.
The IAQ Minimum Position curve is created by applying the dif-
ference of the IAQ position at maximum fan speed (IAQ POS @
MAX SPD) and the Economizer minimum at maximum fan
speed (MIN POS @ MAX FAN) in relationship to the minimum
position curve. The IAQ position at maximum fan speed (IAQ
POS @ MAX SPD) should be set to an economizer position that
brings in enough fresh air to remove contaminates and CO
2
gen-
erated by sources other than people. The Economizer minimum
at maximum fan speed (MIN POS @ MAX FAN) should be set
to an economizer position that brings in fresh air to remove con-
taminates and CO
2
generated by all sources including people
when the indoor fan is operating at the IDF Maximum Fan
Speed (MAXIMUM IDF SPEED). The Economizer minimum
at maximum fan speed (MIN POS @ MAX FAN) value is the
design value for maximum occupancy.
The economizer Min Position in Effect (EFFECTIVE MIN
POS) will follow the IAQ Minimum Position curve while the
Indoor Air Quality level (IAQ LEVEL) is less than the Out-
door Air Quality Level (OAQ LEVEL). The control will begin
to open the damper more than the IAQ Minimum Position
curve when the IAQ level begins to exceed the OAQ level by a
configurable amount. This amount is referred to as AQ Differ-
ential Low (LOW AIR.Q DIFF). When the differential be-
tween IAQ and OAQ reaches AQ Differential High (HIGH
AIR.Q DIFF), the economizer Min Position in Effect (EF-
FECTIVE MIN POS) will follow the Minimum Position
Curve. When the IAQ/OAQ differential is between AQ Differ-
ential Low (LOW AIR.Q DIFF) and AQ Differential High
Indoor Fan Speed
Damper Position
Econo Max
Position
(DAMPMAX)
(MP_SPD2,
MP_POS2)
(MP_SPD3,
MP_POS3)
Maximum Speed
(SPEEDMAX)
(MP_SPD1,
MP_POS1)
10%
MINP_MAX
Minimum Position Curve
Key:
(PE1_SPD3,
PE1_POS3)
(PE1_SPD2,
PE1_POS2)
(PE1_SPD1,
PE1_POS1)
PE1PMAX
Power Exhaust 1Curve
(PE2_SPD3,
PE2_POS3)
2(PE2_SPD2,
PE2_POS2)
(PE2_SPD1,
PE2_POS1)
Power Exhaust 2 Curve
PE2PMAX
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