Carrier WeatherExpert 48N2 Controls, Start-Up, Operation, Service, And Troubleshooting page 85

OPERATION
The unit's indoor air quality algorithm modulates the position
of the economizer dampers between 2 user configurations de-
pending upon the relationship between the IAQ and the out-
door air quality (OAQ). Both of these values can be read at the
Inputs  AIR.Q submenu. The lower of these 2 configurable
positions is referred to as the IAQ Demand Vent Min Position
(IAQ.M), while the higher is referred to as Economizer Mini-
mum Position (EC.MN). The IAQ.M should be set to an econ-
omizer position that brings in enough fresh air to remove con-
taminants and CO generated by sources other than people.
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The EC.MN value should be set to an economizer position that
brings in enough fresh air to remove contaminants and CO
generated by all sources including people. The EC.MN value is
the design value for maximum occupancy.
The logic that is used to control the dampers in response to
IAQ conditions is shown in Fig. 12. The ComfortLink controls
will begin to open the damper from the IAQ.M position when
the IAQ level begins to exceed the OAQ level by a configu-
rable amount, which is referred to as Differential Air Quality
Low Limit (DAQ.L).
If OAQ is not being measured, OAQ can be manually config-
ured. It should be set at around 400 to 450 ppm or measured
with a handheld sensor during the commissioning of the unit.
The OAQ reference level can be set using the OAQ Reference
Set Point (OAQ.U). When the differential between IAQ and
OAQ reaches the configurable Diff. Air Quality Hi Limit
(DAQ.H), then the economizer position will be EC.MN.
When the IAQ–OAQ differential is between DAQ.L and
DAQ.H, the control will modulate the damper between IAQ.M
and EC.MN as shown in Fig. 12. The relationship is a linear re-
lationship but other non-linear options can be used. The damp-
er position will never exceed the bounds specified by IAQ.M
and EC.MN during IAQ control.
ECONOMIZER
MINIMUM
DAMPER
POSITION
VENTILATION FOR PEOPLE
MINIMUM
IAQ
DAMPER
POSITION
VENTILATION FOR SOURCES
100
500
AQ
DIFFERENTIAL
LOW (DAQ.L)
Fig. 12 — IAQ Control
If the building is occupied and the indoor fan is running and the
differential between IAQ and OAQ is less than DAQ.L, the
economizer will remain at IAQ.M. The economizer will not
close completely. The damper position will be 0 when the fan
is not running or the building is unoccupied. The damper posi-
tion may exceed EC.MN in order to provide free cooling.
The ComfortLink controls are configured for air quality sen-
sors which provide 4 mA at 0 ppm and 20 mA at 2000 ppm. If
a sensor has a different range, these bounds must be reconfig-
ured. These pertinent configurations for ranging the air quality
sensors are IQ.R.L, IQ.R.H, OQ.R.L and OQ.R.H. The bounds
represent the PPM corresponding to 4 mA (low) and 20 mA
(high) for IAQ and OAQ, respectively.
700 INSIDE/OUTSIDE CO DIFFERENTIAL
2
1000
INSIDE CO CONCENTRATION
2
AQ
DIFFERENTIAL
HIGH (DAQ.H)
If OAQ exceeds the OAQ Lockout Value (OAQ.L), then the
economizer will remain at IAQ.M. This is used to limit the use
of outside air which outdoor air CO
OAQ.L limit. Normally a linear control of the damper vs. the
IAQ control signal can be used, but the control also supports
non-linear control. Different curves can be used based on the
Diff.IAQ Responsiveness Variable (IAQ.R). See Fig. 13.
SETTING UP THE SYSTEM
The IAQ configuration options are under the Local Display
Mode Configuration  IAQ. See Table 57.
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NOTE: Calculating the IAQ.M and EC.MN damper position based
on differential IAQ measurement.
Based on configuration parameter IAQREACT, the reaction to damper
positioning based on differential air quality ppm can be adjusted.
IAQREACT = 1 to 5 (more responsive)
IAQREACT = 0 (linear)
IAQREACT = –1 to –5 (less responsive)
Fig. 13 — IAQ Response Curve
IAQ Analog Sensor Config (Configuration  IAQ 
AQ.CF  IQ.A.C)
This is used to configure the type of IAQ position control. It
has the following options:
• IQ.A.C = 0 (No analog input). If there is no other mini-
mum position control, the economizer minimum position
will be Configuration  IAQ  DCV.C  EC.MN and there
will be no IAQ control.
• IQ.A.C = 1 (IAQ analog input). An indoor air (space or re-
turn air) CO sensor is installed. If an outdoor air CO
2
sor is also installed, or OAQ is broadcast on the CCN, or if
a default OAQ value is used, then the unit can perform
IAQ control.
• IQ.A.C = 2 (IAQ analog input with minimum position
override) — If the differential between IAQ and OAQ is
above Configuration  IAQ  AQ.SP  DAQ.H, the econ-
omizer minimum position will be the IAQ override posi-
tion (Configuration  IAQ  AQ.SP  IQ.O.P).
85
levels are above the
2
sen-
2