Bryant DURAPAC PLUS 581A, Installation And Service Instructions Manual

Page: 34 / 56

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Minimum Position Control
There is a minimum damper position potentiometer on the
EconoMi$er IV controller. See Fig. 28. The minimum damper
position maintains the minimum airflow into the building
during the occupied period.
When using demand ventilation, the minimum damper
position represents the minimum ventilation position for
VOC (volatile organic compounds) ventilation requirements.
The maximum demand ventilation position is used for fully
occupied ventilation.
When demand ventilation control is not being used, the min-
imum position potentiometer should be used to set the occu-
pied ventilation position. The maximum demand ventilation
position should be turned fully clockwise.
Adjust the minimum position potentiometer to allow the
minimum amount of outdoor air, as required by local codes,
to enter the building. Make minimum position adjustments
with at least 10° F temperature difference between the out-
door and return-air temperatures. To determine the mini-
mum position setting, perform the following procedure:
1. Calculate the appropriate mixed-air temperature
using the following formula:
T
O
= Outdoor-Air Temperature
OA = Percent of Outdoor Air
T
R
= Return-Air Temperature
RA = Percent of Return Air
T
M
= Mixed-Air Temperature
As an example, if local codes require 10% outdoor air
during occupied conditions, outdoor-air temperature
is 60 F, and return-air temperature is 75 F.
(60 x .10) + (75 x .90) = 73.5 F
2. Disconnect the supply-air sensor from terminals T
and T1.
3. Ensure that the factory-installed jumper is in place
across terminals P and P1. If remote damper posi-
tioning is being used, make sure that the terminals
are wired according to Fig. 26 and that the minimum
position potentiometer is turned fully clockwise.
4. Connect 24 vac across terminals TR and TR1.
5. Carefully adjust the minimum position potentiometer
until the measured mixed-air temperature matches
the calculated value.
6. Reconnect the supply-air sensor to terminals T and
T1.
Remote control of the EconoMi$er IV damper is desirable
when requiring additional temporary ventilation. If a
field-supplied remote potentiometer (Honeywell part num-
ber S963B1128) is wired to the EconoMi$er IV controller, the
minimum position of the damper can be controlled from a
remote location.
To control the minimum damper position remotely, remove
the factory-installed jumper on the P and P1 terminals on
the EconoMi$er IV controller. Wire the field-supplied poten-
tiometer to the P and P1 terminals on the EconoMi$er IV
controller. See Fig. 26.
Damper Movement
Damper movement from full open to full closed (or vice
versa) takes up to 2
1 /
2
minutes.
Thermostats
The EconoMi$er IV control works with conventional thermo-
stats that have a Y1 (cool stage 1), Y2 (cool stage 2), W1
(heat stage 1), W2 (heat stage 2), and G (fan). The
EconoMi$er IV control does not support space temperature
sensors like the T55 or T56. Connections are made at the
thermostat terminal connection board located in the main
control box.
Occupancy Control
The factory default configuration for the EconoMi$er IV con-
trol is occupied mode. Occupied status is provided by the
black jumper from terminal TR to terminal N. When unoccu-
pied mode is desired, install a field-supplied timeclock func-
tion in place of the jumper between TR and N. See Fig. 26.
When the timeclock contacts are closed, the EconoMi$er IV
control will be in occupied mode. When the timeclock con-
tacts are open (removing the 24-v signal from terminal N),
the EconoMi$er IV will be in unoccupied mode.
Demand Control Ventilation
When using the EconoMi$er IV for demand control ventila-
tion, 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.
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
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 mini-
mum damper position potentiometer to the correct position.
(T
O
x
OA
) + (T
R
x
RA
) = T
M
100 100
(T
O
x
OA
) + (T
R
x
RA
) = T
M
100 100