Carrier WeatherMaker 50TCQ 17-24 Series, Service And Maintenance Instructions

Page: 41 / 76

41
Fig. 65 — CO
2
Sensor Maximum Range Settings
EXHAUST SETPOINT ADJUSTMENT
The exhaust setpoint will determine when the exhaust fan runs
based on damper position (if accessory power exhaust is in -
stalled). The setpoint is modified with the Exhaust Fan Setpoint
(EXH SET) potentiometer. See Fig. 60. The setpoint represents
the damper position above which the exhaust fans will be turned
on. When there is a call for exhaust, the EconoMi$er IV controller
provides a 45 ± 15 second delay before exhaust fan activation to
allow the dampers to open. This delay allows the damper to reach
the appropriate position to avoid unnecessary fan overload.
MINIMUM POSITION CONTROL
There is a minimum damper position potentiometer on the
EconoMi$er IV controller. See Fig. 60. The minimum damper po -
sition maintains the minimum airflow into the building during the
occupied period.
When using demand controlled ventilation, the minimum damper
position represents the minimum ventilation position for Volatile
Organic Compound (VOC) ventilation requirements. The maxi -
mum demand ventilation position is used for fully occupied venti -
lation.
When demand control ventilation is not being used, the minimum
position potentiometer should be used to set the occupied ventila -
tion position. The maximum demand ventilation position should
be turned fully clockwise.
Adjust the minimum position potentiometer to allow the mini -
mum 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
= 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 oc -
cupied conditions, outdoor-air temperature is 60°F, and return-air
temperature is 75°F.
(60 x 0.10) + (75 x 0.90) = 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 positioning is being
used, make sure that the terminals are wired according to
Fig. 60 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 calcu -
lated value.
6. Reconnect the supply air sensor to terminals T and T1.
Remote control of the EconoMi$er IV damper is desirable when
requiring additional temporary ventilation. If a field-supplied re -
mote potentiometer (Honeywell part number S963B1128) is
wired to the EconoMi$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$er IV controller. Wire the field-supplied potentiometer
to the P and P1 terminals on the EconoMi$er IV controller. (See
Fig. 64.)
DAMPER MOVEMENT
Damper movement from full open to full closed (or vice versa)
takes 2
1
/
2
minutes.
THERMOSTATS
The EconoMi$er IV control works with conventional thermostats
that have a Y1 (cool stage 1), Y2 (cool stage 2), W1 (heat stage 1),
W2 (heat stage 2), and G (fan). The EconoMi$er IV controller
does not support space temperature sensors. Connections are
made at the thermostat terminal connection board located in the
main control box.
OCCUPANCY CONTROL
The factory default configuration for the EconoMi$er IV controls
is occupied mode. Occupied status is provided by the black jump -
er from terminal TR to terminal N. When unoccupied mode is de -
sired, install a field-supplied timeclock function in place of the
jumper between TR and N. When the timeclock contacts are
closed, the EconoMi$er IV controls will be in occupied mode.
When the timeclock contacts are open (removing the 24-v signal
from terminal N), the EconoMi$er IV system will be in unoccu -
pied mode.
DEMAND CONTROLLED VENTILATION (DCV)
When using the EconoMi$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 out -
side air design criteria.
A proportional anticipatory strategy should be taken with the fol -
lowing conditions: a zone with a large area, varied occupancy, and
equipment that cannot exceed the required ventilation rate at de -
sign 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 sup -
plied to increase as the room CO
2
level increases even though the
CO
2
setpoint has not been reached. By the time the CO
2
level
reaches the setpoint, the damper will be at maximum ventilation
and should maintain the setpoint.
In order to have the CO
2
sensor control the EconoMi$er damper in
this manner, first determine the damper voltage output for mini -
mum or base ventilation. Base ventilation is the ventilation re -
quired to remove contaminants during unoccupied periods. The
(T
O
x
OA
) + (T
R
x
RA
) = T
M
100 100
0
1000
2000
3000
4000
5000
6000
2 3 4 5 6 7 8
RANGE
C
ONFIGURA
TION
(ppm)
DAMPER VOLTAGE FOR MAX VENTILATION RATE
CO SENSOR MAX RANGE SETTING
2
800 ppm
900 ppm
1000 ppm
1100 ppm