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—35—
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 deter-
mine that the range configuration for the CO
2
sensor should
be 1800 ppm. The EconoMi$er IV controller will output the
6.7 volts from the CO
2
sensor to the actuator when the CO
2
concentration in the space is at 1100 ppm. The DCV set point
may be left at 2 volts since the CO
2
sensor voltage will be
ignored by the EconoMi$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 Bryant equipment. See Table 29.
1. Press Clear and Mode buttons. Hold at least 5 sec-
onds until the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appear.
3. Use the Up/Down button to select the preset number.
See Table 29.
4. Press Enter to lock in the selection.
5. Press Mode to exit and resume normal operation.
The custom settings of the CO
2
sensor can be changed any-
time after the sensor is energized. Follow the steps below to
change the non-standard settings:
1. Press Clear and Mode buttons. Hold at least 5 sec-
onds until the sensor enters the Edit mode.
2. Press Mode twice. The STDSET Menu will appear.
3. Use the Up/Down button to toggle to the NONSTD
menu and press Enter.
4. Use the Up/Down button to toggle through each of
the nine variables, starting with Altitude, until the
desired setting is reached.
5. Press Mode to move through the variables.
6. Press Enter to lock in the selection, then press Mode
to continue to the next variable.
Dehumidification of Fresh Air with DCV Control
Information from ASHRAE (American Society of Heating,
Refrigeration, and Air Conditioning Engineers) indicates
that the largest humidity load on any zone is the fresh air
introduced. For some applications, an energy recovery unit
can be added to reduce the moisture content of the fresh air
being brought into the building when the enthalpy is high.
In most cases, the normal heating and cooling processes are
more than adequate to remove the humidity loads for most
commercial applications.
If normal rooftop heating and cooling operation is not
adequate for the outdoor humidity level, an energy recovery
and/or a dehumidification option should be considered.
XII. OPERATING SEQUENCE
A. Cooling, Units Without Economizer
When the thermostat calls for one stage of cooling, Y1 and G
are energized. The indoor-fan contactor (IFC) and compres-
sor contactor(s) (C.A1 and C.B1 on three-compressor units or
C.A1 only on two-compressor units), and outdoor-fan contac-
tors (OFC1 and OFC2 when outdoor temperature is above
FCS [fan cycling switch] setting) are energized and the
indoor-fan motor, compressor(s) (A1 and B1 on three-
compressor units or A1 only on two-compressor units), and
outdoor fans controlled by OFC1 are started. If the outdoor
temperature is above the setting of the low temperature
switch, the outdoor fans controlled by OFC2 are also started.
If more cooling is required, the thermostat will call for a sec-
ond stage of cooling, energizing Y2. This will allow relay CR1
to energize, which in turn energizes the compressor contactor
(C.C1 on three-compressor units or C.B1 on two-compressor
units). The second stage compressor (C1 on three-compressor
units or B1 on two-compressor units) is then started.
Table 29 — CO
2
Sensor Standard Settings
LEGEND
ppm — Parts Per Million
SETTING EQUIPMENT OUTPUT
VENTILATION
RATE
(cfm/Person)
ANALOG
OUTPUT
CO
2
CONTROL RANGE
(ppm)
OPTIONAL
RELAY SETPOINT
(ppm)
RELAY
HYSTERESIS
(ppm)
1
Interface w/Standard
Building Control System
Proportional Any
0-10V
4-20 mA
0-2000 1000 50
2 Proportional Any
2-10V
7-20 mA
0-2000 1000 50
3 Exponential Any
0-10V
4-20 mA
0-2000 1100 50
4
Economizer
Proportional 15
0-10V
4-20 mA
0-1100 1100 50
5 Proportional 20
0-10V
4-20 mA
0- 900 900 50
6 Exponential 15
0-10V
4-20 mA
0-1100 1100 50
7 Exponential 20
0-10V
4-20 mA
0- 900 900 50
8 Health & Safety Proportional —
0-10V
4-20 mA
0-9999 5000 500
9
Parking/Air Intakes/
Loading Docks
Proportional —
0-10V
4-20 mA
0-2000 700 50