Carrier 48TJ016-028 - Manual (Page 26)

Fig. 38 — Outside Air Temperature
Changeover Set Points
Outdoor Enthalpy Changeover — For enthalpy control, ac-
cessoiy enthalpy sensor (part number HH57AC078) is
required Replace the stanckird outdoor diy bulb temperature
sensor with the accessoiy entlialpy sensor in the same mount­
ing location. See Fig. 32. When the outdoor iiir enthalpy rises
above the outdoor enthiilpy changeover set point, the outdoor-
air damper moves to its minimum position, Tlie outdoor
enthalpy changeover set point is set with the outdoor enthalpy
set point potentiometer on the EconoMi$erIV controller. The
set points are A, B, C, and D. See Fig. 40. Tlie factory-installed
620-ohm jumper must be in place across terminals SR and SR-i­
on the EconoMi$er[V controller. See Fig. 32 and 41.
Differential Enthalpy Control — For differential enthalpy
control, the EconoMi$eiTV controller uses two enthalpy sen­
sors (HH57AC078 and CRENTDIF004A00), one in the out­
side air and one in the return airstream or the EconoMiSerlV
tfiune. The EconoMi$eiTV controller compares the outdoor air
enthalpy to the return air enthalpy to determine ExonoMi$eiTV
use, Tire controller selects the lower enthalpy air (return or out­
door) for cooling. For example, when the outdoor air has a low­
er enthalpy than the return air and is below the set point, the
EconoMi$erIV opens to bring in outdoor air for free cooling.
Replace the standard outside aii' diy bulb temperature sen­
sor with the accessoiy enthalpy sensor in the same mounting
location. See Fig. 32, Mount the return air enthalpy sensor in
the return airstream. See Fig. 39. The outdoor enthalpy
changeover set point is set with the outdoor enthalpy set point
potentiometer on the EconoMi$eiTV controller. When using
this mode of changeover control, turn the enthalpy set point
potentiometer fully clockwise to the D setting.
NOTE: Remove 620-ohm resistor if differential entlialpy sen­
sor is installed.
Indoor Air Quality (IAO) Sensor Input — The lAQ input
can be used for demand control ventilation control based on the
level of CO
2 measured in the space or return air duct.
Mount the accessoiy lAQ sensor according to manufacturer
specifications. The lAQ sensor should be wired to the AQ and
AQl terminals of the controller. Adjust the DCV potentiome­
ters to correspond to the DCV voltage output of the indoor air
quality sensor at the user-determined set point. See Fig. 42,
If a separate field-supplied transformer is used to power the
lAQ sensor, the sensor must not be grounded or the
EconoMi$erIV control botii'd will be damaged.
Exhaust Set Point Adjustment — The exhaust set point will
determine when the exhaust fan luns based on dtimper position
(if accessoiy power exhaust is installed). Tlie set point is modi­
fied with the Exhaust Fan Set Point (EXH SET) potentiometer.
See Fig. 37. The set point represents tlie damper position above
which the exhaust fan will be turned on. When there is a
ciill for exhaust, the EconoMi$erfV controller provides a
SENSOR
Fig. 39 — Return Air Temperature or
Enthalpy Sensor Mounting Location
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 unnecessaiy fan overload.
Minimum Position Control — There is a minimum damper
position potentiometer on tlie EconoMiSerlV controller. See
Fig. 37. The minimum diunper position maintains tlie mini­
mum aiiflow into the building during the occupied period.
When using demand ventilation, the minimum damper po­
sition represents the minimum ventilation position for VOC
(volatile organic compound) ventilation requirements. Tlie
maximum demand ventilation position is used for fully occu­
pied ventilation.
When demand ventilation control is not being used, the
minimum position potentiometer should be used to set the oc­
cupied ventilation position. Tlie maximum demand ventilation
position should be turned fully clockwise.
Adjust the minimum position potentiometer to iillow 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
retum-air temperatures.
To determine the minimum position setting, peidbrin the
following procedure:
1. Calculate the appropriate mixed-air temperature using the
following formula:
(Tox
OA
■) -I- (TR X
RA
) = T m
100
" '
100
To = Outdoor-Air Temperature
O A = Percent of Outdoor Air
T r
= Return-Air Teinperature
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 retum-air temperature is 75 F.
(60 X . 10) -r (75 X .90) = 73.5 F
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