Bryant 548J - Manual (Page 52)

52
TR1
24 Vac
COM
TR
24
Vac
HOT
1 2
3 4
5
EF EF1
+
_
P1
T1
P
T
N
EXH
2V 10V
EXH
Set
Set
2V 10V
2V 10V
DCV
DCV
Free
Cool
B C
A D
SO+
SR+
SR
SO
AQ1
AQ
DCV
Min
Pos
Open
Max
N1
C06038
Fig. 77 -- EconoMi$er IV Control
Differential Enthalpy Control
For differential enthalpy control, the EconoMi$er IV
controller uses two enthalpy sensors (HH57AC078 and
CRENTDIF004A00), one in the outside air and one in the
return air duct. The EconoMi$er IV controller compares
the outdoor air enthalpy to the return air enthalpy to
determine EconoMi$er IV use. The controller selects the
lower enthalpy air (return or outdoor) for cooling. For
example, when the outdoor air has a lower enthalpy than
the return air, the EconoMi$er IV opens to bring in
outdoor air for free cooling.
Replace the standard outside air dry bulb temperature
sensor with the accessory enthalpy sensor in the same
mounting location. (See Fig. 66.) Mount the return air
enthalpy sensor in the return air duct. (See Fig. 75.)
Wiring is provided in the EconoMi$er IV wiring harness.
(See Fig. 66.) The outdoor enthalpy changeover setpoint is
set with the outdoor enthalpy setpoint potentiometer on
the EconoMi$er IV controller. When using this mode of
changeover control, turn the enthalpy setpoint
potentiometer fully clockwise to the D setting.
Indoor Air Quality (IAQ) Sensor Input
The IAQ input can be used for demand control ventilation
control based on the level of CO
2
measured in the space
or return air duct.
Mount the accessory IAQ sensor according to
manufacturer specifications. The IAQ sensor should be
wired to the AQ and AQ1 terminals of the controller.
Adjust the DCV potentiometers to correspond to the DCV
voltage output of the indoor air quality sensor at the
user-determined setpoint. (See Fig. 78.)
0
1000
2000
3000
4000
5000
6000
2 3 4 5 6 7 8
800 ppm
900 ppm
1000 ppm
1100 ppm
RANGE
CONFIGURA
TION
(ppm)
DAMPER VOLTAGE FOR MAX VENTILATION RATE
CO SENSOR MAX RANGE SETTING 2
C06039
Fig. 78 -- CO
2
Sensor Maximum Range Settings
If a separate field-supplied transformer is used to power
the IAQ sensor, the sensor must not be grounded or the
EconoMi$er IV control board will be damaged.
When using demand ventilation, the minimum damper
position represents the minimum ventilation position for
VOC (volatile organic compounds) ventilation
requirements. The maximum demand ventilation position
is used for fully occupied ventilation.
When demand ventilation control is not being used, the
minimum position potentiometer should be used to set the
occupied ventilation position. The maximum demand
ventilation position should be turned fully clockwise.
Exhaust Setpoint Adjustment
The exhaust setpoint will determine when the exhaust fan
runs based on damper position (if accessory power
exhaust is installed). The setpoint is modified with the
Exhaust Fan Setpoint (EXH SET) potentiometer. (See
Fig. 72.) The setpoint 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. 72.) The minimum
damper position maintains the minimum airflow into the
building during the occupied period.
When using demand ventilation, the minimum damper
position represents the minimum ventilation position for
VOC (volatile organic compound) ventilation
requirements. The maximum demand ventilation position
is used for fully occupied ventilation.
When demand ventilation control is not being used, the
minimum position potentiometer should be used to set the
occupied 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 outdoor and return-air temperatures.
548J