Carrier SINGLE PACKAGE ROOFTOP UNITS 48PG20-28 - Manual (Page 43)

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Minimum Position Control — There is a minimum damper
position potentiometer on the EconoMi$er IV controller. See
Fig. 28. The minimum damper position maintains the mini-
mum airflow into the building during the occupied period.
When using demand ventilation, the minimum damper
position represents the minimum ventilation position for VOC
(volatile organic compounds) ventilation requirements. The
maximum demand ventilation position is used for fully occu-
pied ventilation.
When demand ventilation control is not being used, the
minimum position potentimeter should be used to set the occu-
pied ventilation position. The maximum demand ventilation
position should be turned fully clockwise.
Adjust the minimum position potentiometer to allow the
minimum amount of outdoor air, as required by local codes, to
enter the building. Make minimum position adjustments with
at least 10° F temperature difference between the outdoor and
return-air temperatures. To determine the minimum position
setting, perform the following procedure:
1. Calculate the appropriate mixed air temperature using the
following formula:
(T
O
x OA) + (T
R
x RA) = T
M
T
O
= Outdoor-Air Temperature
OA = Percent of Outdoor Air
T
R
= Return-Air Temperature
RA = Percent of Return Air
T
M
= Mixed-Air Temperature
As an example, if local codes require 10% outdoor air
during occupied conditions, outdoor-air temperature is
60 F, and return-air temperature is 75 F.
(60 x .10) + (75 x .90) = 73.5 F
2. Disconnect the mixed air sensor from terminals T and T1.
3. Ensure that the factory-installed jumper is in place across
terminals P and P1. If remote damper positioning is being
used, make sure that the terminals are wired according to
Fig. 26 and that the minimum position potentiometer is
turned fully clockwise.
4. Connect 24 vac across terminals TR and TR1.
5. Carefully adjust the minimum position potentiometer
until the measured mixed air temperature matches the
calculated value.
6. Reconnect the mixed air sensor to terminals T and T1.
Remote control of the EconoMi$er IV damper is desirable
when requiring additional temporary ventilation. If a
field-supplied remote potentiometer (Honeywell part number
S963B1128) is wired to the EconoMi$er IV controller, the
minimum position of the damper can be controlled from a re-
mote location.
To control the minimum damper position remotely, remove
the factory-installed jumper on the P and P1 terminals on the
EconoMi$er IV controller. Wire the field-supplied potentiome-
ter to the P and P1 terminals on the EconoMi$er IV controller.
See Fig. 26.
Damper Movement — When the EconoMi$er IV board re-
ceives initial power, it can take the damper up to 2
1 /
2
minutes
before it begins to position itself. After the initial positioning,
subsequent changes to damper position will take up to 30 sec-
onds to initiate. Damper movement from full open to full
closed (or vice versa) takes 2
1 /
2
minutes.
Thermostats — The EconoMi$er IV control works with con-
ventional thermostats that have a Y1 (cool stage 1), Y2 (cool
stage 2), W1 (heat stage 1), W2 (heat stage 2), and G (fan). The
EconoMi$er IV control does not support space temperature
sensors like the T55 or T56. Connections are made at the ther-
mostat terminal connection board located in the main control
box.
Demand Control Ventilation — When using the Econo-
Mi$er IV for demand control ventilation, there are some equip-
ment selection criteria which should be considered. When
selecting the heat capacity and cool capacity of the equipment,
the maximum ventilation rate must be evaluated for design
conditions. The maximum damper position must be calculated
to provide the desired fresh air.
Typically the maximum ventilation rate will be about 5 to
10% more than the typical cfm required per person, using nor-
mal outside air design criteria.
A proportional anticipatory strategy should be taken with
the following conditions: a zone with a large area, varied
occupancy, and equipment that cannot exceed the required
ventilation rate at design conditions. Exceeding the required
ventilation rate means the equipment can condition air at a
maximum ventilation rate that is greater than the required
ventilation rate for maximum occupancy. A proportional-
anticipatory strategy will cause the fresh air supplied to
increase as the room CO
2
level increases even though the CO
2
set point has not been reached. By the time the CO
2
level
reaches the set point, the damper will be at maximum ventila-
tion and should maintain the set point.
In order to have the CO
2
sensor control the economizer
damper in this manner, first determine the damper voltage
output for minimum or base ventilation. Base ventilation is the
ventilation required to remove contaminants during unoccu-
pied periods. The following equation may be used to determine
the percent of outside-air entering the building for a given
damper position. For best results there should be at least a
10 degree difference in outside and return-air temperatures.
(T
O
x OA) + (T
R
x RA) = T
M
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
Once base ventilation has been determined, set the mini-
mum damper position potentiometer to the correct position.
The same equation can be used to determine the occupied or
maximum ventilation rate to the building. For example, an
output of 3.6 volts to the actuator provides a base ventilation
rate of 5% and an output of 6.7 volts provides the maximum
ventilation rate of 20% (or base plus 15 cfm per person). Use
Fig. 29 to determine the maximum setting of the CO
2
sensor.
For example, a 1100 ppm set point relates to a 15 cfm per
person design. Use the 1100 ppm curve on Fig. 29 to find the
point when the CO
2
sensor output will be 6.7 volts. Line up the
point on the graph with the left side of the chart to determine
that the range configuration for the CO
2
sensor should be 1800
ppm. The EconoMi$er IV controller will output the 6.7 volts
from the CO
2
sensor to the actuator when the CO
2
concentra-
tion in the space is at 1100 ppm. The DCV set point may be left
at 2 volts since the CO
2
sensor voltage will be ignored by the
EconoMi$er IV controller until it rises above the 3.6 volt
setting of the minimum position potentiometer.
Once the fully occupied damper position has been deter-
mined, set the maximum damper demand control ventilation
potentiometer to this position. Do not set to the maximum
position as this can result in over-ventilation to the space and
potential high-humidity levels.
CO
2
Sensor Configuration — The CO
2
sensor has preset
standard voltage settings that can be selected anytime after the
sensor is powered up. See Table 29.
Use setting 1 or 2 for Carrier equipment. See Table 29.
1. Press Clear and Mode buttons. Hold at least 5 seconds
until the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appear.