20
Fig. 44 — EconoMi$er IV Controller Potentiometer and LED Locations
OCCUPANCY CONTROL
The factory default configuration for the economizer control is
occupied mode. Occupied status is provided by the black wire
from Pin 3. When unoccupied mode is desired, install a
field-supplied time clock function in place of the jumper between
TR and N. (See Fig. 15.) When the time clock contacts are closed,
the EconoMi$er IV control will be in occupied mode. When the
time clock contacts are open (removing the 24-v signal from
terminal N), the economizer will be in unoccupied mode.
DEMAND CONTROLLED VENTILATION
When using the EconoMi$er IV system for demand controlled
ventilation, there are some equipment 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 normal
outside air design criteria.
An exponential 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
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. An exponential-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
ventilation 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 unoccupied 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
= 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 minimum
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. 43 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. 43 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
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 determined, set
the maximum damper demand control ventilation potentiometer
to this 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 setting that can be
selected anytime after the sensor is powered up. (See Table 5.)
Use setting 1 or 2 for this equipment. (See Table 5.)
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.
Exhaust Fan
Setpoint
LED lights when
exhaust contact
is made
Minumum Damper
Postion Setting
Maximum Damper
Demand Control
Ventilation Setpoint
LED lights when
demand control
ventilation input is
above setpoint
Demand Control
Ventilation Setpoint
LED lights when
outdoor air is
suitable for
free cooling
Free Cooling /Enthalpy
Changeover Setpoint
T
O
x OA + (T
R
x RA ) = T
M
100
100
