Setting Up The System - Carrier 48AJ Operating And Service Manual

The logic that is used to control the dampers in response to
IAQ conditions is shown in Fig. 10. The ComfortLink control
will begin to open the damper from the IAQ.M position when
the IAQ level begins to exceed the OAQ level by a config-
urable amount, which is referred to as Differential Air Quality
Low Limit (DAQ.L).
If OAQ is not being measured, OAQ can be manually con-
figured. 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. 10. The relationship is a linear
relationship but other non-linear options can be used. The
damper position will never exceed the bounds specified by
IAQ.M and EC.MN during 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 control is configured for air quality
sensors which provide 4 mA at 0 ppm and 20 mA at 2000 ppm.
If a sensor has a different range, these bounds must be
reconfigured. 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.
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. 11.
SETTING UP THE SYSTEM — The IAQ configuration op-
tions are under the Local Display Mode Configuration
See Table 78.
IAQ Analog Sensor Config (Configuration
→
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
no IAQ control.
• IQ.A.C = 1 (IAQ analog input). An indoor air (space or
return air) CO sensor is installed. If an outdoor air CO
2
sensor is also installed, or OAQ is broadcast on the CCN,
or if a default OAQ value is used, then the unit can per-
form IAQ control.
• IQ.A.C = 2 (IAQ analog input with minimum position
override) — If the differential between IAQ and OAQ
is above Configuration
economizer minimum position will be the IAQ override
position (Configuration
• IQ.A.C = 3 (4 to 20 mA minimum position) — With a 4
to 20 mA signal connected to TB5-6 and 7, the econo-
mizer minimum position will be scaled linearly from 0%
(4 mA) to EC.MN (20 mA).
• IQ.A.C = 4 (10K potentiometer minimum position) — With
a 10K linear potentiometer connected to TB5-6 and 7, the
economizer minimum position will be scaled linearly from
0% (0 kilo-ohms) to EC.MN (10 kilo-ohms).
levels are above the
2
→
→
IAQ
→
IAQ EC.MN and there will be
→ → →
IAQ AQ.SP DAQ.H, the
→ → →
IAQ AQ.SP IQ.O.P).
ECONOMIZER
MINIMUM
DAMPER
POSITION
MINIMUM
IAQ
DAMPER
POSITION
AQ
DIFFERENTIAL
LOW (DAQ.L)
IAQ.
→
2
NOTE: Calculating the IAQ.M and EC.MN damper position based
on differential IAQ measurement.
Based on the configuration parameter IAQREACT, the reaction to
damper positioning based on differential air quality ppm can be
adjusted.
IAQREACT = –1 to –5 (less responsive)
Fig. 11 — IAQ Response Curve
64
VENTILATION FOR PEOPLE
VENTILATION FOR SOURCES
100 700 INSIDE/OUTSIDE CO
500 1000
INSIDE CO
AQ
DIFFERENTIAL
HIGH (DAQ.H)
Fig. 10 — IAQ Control
IAQREACT = 1 to 5 (more responsive)
IAQREACT = 0 (linear)
DIFFERENTIAL
2
CONCENTRATION
2
A48-7209
A48-7711