31
IAQ (Analog Input)
The ComfortLink control is configured for indoor air quality
sensors which provide 4 to 20 mA for 0 to 2000 ppm. If a sensor
has a different range, the ppm display range must be reconfigured
by entering new values for Configuration→AIR.Q→I.4M and
Configuration→AIR.Q→I.20M.
IA.CF = 0 (No IAQ)
IA.CF = 0 signifies that there is no IAQ sensor installed. The
damper will operate at the Configuration→AIR.Q→EC.MN
position when the space is occupied and the indoor fan is on.
IA.CF = 1 (DCV)
When IA.CF = 1, the IAQ algorithm is set for Demand Control
Ventilation (DCV). During DCV, the damper modulates between
two user configurations depending upon the relationship between
the IAQ and the Outdoor Air Quality (OAQ). The lower of these
two positions is referred to as the Minimum IAQ Damper Position
(Configuration→AIR.Q→AQ.MN) while the higher is referred to
as Economizer Minimum Position (EC.MN). The AQ.MN should
be set to an economizer position that brings in enough fresh air to
remove contaminants and CO
2
generated by sources other than
people. The EC.MN should be set to an economizer position that
brings in enough fresh air to remove contaminants and CO
2
generated by all sources including people. The EC.MN value is the
design value for maximum occupancy.
The ComfortLink control will begin to open the damper from the
AQ.MN position when the IAQ level begins to exceed the Outdoor
Air Quality (OAQ) level by a configurable amount. This amount is
referred to as AQ Differential Low
(Configuration→AIR.Q→AQD.L). When the differential
between IAQ and OAQ reaches AQ Differential High
(Configuration→AIR.Q→AQD.H), the economizer position will
be EC.MN. When the IAQ/OAQ differential is between AQD.L
and AQD.H, the control will modulate the damper between
AQ.MN and EC.MN in a linear manner as shown in Fig. 22. The
damper position will never exceed the bounds specified by
AQ.MN and EC.MN during IAQ control.
IA.CF = 2 (Override IAQ)
When IA.CF =2, the IAQ algorithm maintains the damper at
Configuration →AIR.Q→EC.MN until the override condition
triggers. The override triggers when the IAQ/OAQ differential is
greater than Configuration→AIR.Q→AQD.H. The override
position is Configuration→AIR.Q→OVR.P (Economizer
Override Position). The economizer position will return to EC.MN
when the IAQ/OAQ d ifferential is less than Configuration
→AIR.Q→AQD.L.
The Override algorithm will operate whenever the building is
occupied and the indoor fan is operating or whenever the IAQ
algorithm has caused the indoor fan to operate. The configuration
IA.FN determines whether or not the IAQ algorithm can turn on
the indoor fan.
If the indoor fan is not operating, the economizer position will be
zero. If the override is not active and the building is
unoccupied, the economizer position will be zero. The damper
position may exceed Configuration→AIR.→EC.MN or
Configuration→
AIR.Q→OVR.
P to pr
ovide economizer cooling.
48/50PG and PM
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