Bryant 549B - Manual (Page 16)

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Indoor Air Quality (IAQ) Sensor Input
The IAQ input can be used for demand control ventilation
control based on the level of CO
2
measured in the space or
return air duct.
Mount the accessory IAQ sensor according to manufacturer
specifications. The IAQ sensor should be wired to the
AQ and AQ1 terminals of the controller. Adjust the DCV
potentiometers to correspond to the DCV voltage output of
the indoor air quality sensor at the user-determined set
point. See Fig. 30.
If a separate field-supplied transformer is used to power the
IAQ sensor, the sensor must not be grounded or the
EconoMi$er IV control board will be damaged.
Exhaust Set Point Adjustment
The exhaust set point will determine when the exhaust fan
runs based on damper position (if accessory power exhaust is
installed). The set point is modified with the Exhaust Fan
Set Point (EXH SET) potentiometer. See Fig. 25. The set
point represents the damper position above which the
exhaust fans will be turned on. When there is a call for
exhaust, the EconoMi$er IV controller provides a 45 ±
15 second delay before exhaust fan activation to allow the
dampers to open. This delay allows the damper to reach the
appropriate position to avoid unnecessary fan overload.
Minimum Position Control
There is a minimum damper position potentiometer on the
EconoMi$er IV controller. See Fig. 25. The minimum damper
position maintains the minimum airflow into the building
during the occupied period.
When using demand ventilation, the minimum damper posi-
tion represents the minimum ventilation position for VOC
(volatile organic compound) ventilation requirements. The
maximum demand ventilation position is used for fully occu-
pied ventilation.
When demand ventilation control is not being used, the min-
imum position potentiometer should be used to set the occu-
pied ventilation position. The maximum demand ventilation
position should be turned fully clockwise.
Adjust the minimum position potentiometer to allow the
minimum amount of outdoor air, as required by local codes,
to enter the building. Make minimum position adjustments
with at least 10 F temperature difference between the out-
door and return-air temperatures.
To determine the minimum position setting, perform the
following procedure:
1. Calculate the appropriate mixed air temperature
using the following formula:
T
O
= Outdoor-Air Temperature
OA = Percent of Outdoor Air
T
R
= Return-Air Temperature
RA = Percent of Return Air
T
M
= Mixed-Air Temperature
As an example, if local codes require 10% outdoor air
during occupied conditions, outdoor-air temperature
is 60 F, and return-air temperature is 75 F.
(60 x .10) + (75 x .90) = 73.5 F
2. Disconnect the supply air sensor from terminals T
and T1.
3. Ensure that the factory-installed jumper is in place
across terminals P and P1. If remote damper posi-
tioning is being used, make sure that the terminals
are wired according to Fig. 20 and that the minimum
position potentiometer is turned fully clockwise.
4. Connect 24 vac across terminals TR and TR1.
5. Carefully adjust the minimum position potentiometer
until the measured mixed-air temperature matches
the calculated value.
6. Reconnect the supply-air sensor to terminals T and T1.
(T
O
x
OA
) + (T
R
x
RA
) = T
M 100 100
Fig. 25 — EconoMi$er IV Controller Potentiometer
and LED Locations
LED ON
LED ON
LED ON
LED ON
LED OFF
19
18
LED OFF
LED OFF
LED OFF
17
16
15
14
13
12
11
10
9
40 45 50 55 60 65 70 75 80 85 90 95 100
DEGREES FAHRENHEIT
mA
D
C
B
A
Fig. 26 — Outside Air Temperature Changeover Set Points
ECONOMI$ER IV
ECONOMI$ER IV
CONTROLLER
GROMMET
RETURN AIR
SENSOR
RETURN DUCT
(FIELD-PROVIDED)
Fig. 27 — Return Air Temperature or Enthalpy
Sensor Mounting Location