7. Economizer
Page 29
PRODIGYT M2 UNIT CONTROLLER
Step 7. Enthalpy Sensor Operation (A7 and A62)
A Connect a DC ammeter as shown in figure 12 to measure current of A7 or A62.
DISCONNECT J/P104
PLACE JUMPER WIRE HERE
READ
CURRENT
HERE
DC AMMETER
−
+
Damper Travel: % of Maximum Open
DISCONNECT J/P105
PLACE JUMPER WIRE HERE
READ
CURRENT
HERE
DC AMMETER
−
+
Measure A62 Current in SeriesMeasure A7 Current in Series
Figure 12. Measure A7 and A62 Current in Series
B The reading will be between 4 and 20 ma. depending on outdoor temperature and humidity. Refer to figure 13 to
approximate reading.
40°F 50°F 60°F 70°F 80°F 90°F 100°F
30
20
10
40
50
60
70
80
90
100
Figure 13. Enthalpy Sensor Output Current Honeywell C7400
C If the meter reads zero, check sensor wiring harness for continuity and/or check polarity of sensor wiring.
7.12. Demand Control Ventilation
7.12.1. General
A field−provided and installed indoor air quality sensor can be used with the modulating economizer to control CO
2
levels in
the conditioned space. The CO
2
level in a space is an indicator of the number of people occupying a room. As the CO
2
level
rises (indicating the occupancy of a room has increased), economizer dampers modulate open − regardless of outdoor air
enthalpy. Likewise, as the CO
2
level falls (indicating the occupancy has decreased), economizer dampers modulate further
closed.
Standard economizer installations have a minimum fresh air ventilation requirement based on maximum room occupancy.
With standard economizer use, the amount of air required for maximum room occupancy is heated or cooled with each
heating or cooling cycle. IAQ economizer installations use the maximum amount of required ventilation air only with maxi-
mum room occupancy; less outdoor air needs to be heated or cooled when fewer people are in the conditioned space.
If the economizer is operating in the free cooling mode and the IAQ control requires the damper to open further, the IAQ
demand will override the free cooling demand. A flashing OAS LED (see figure 8) indicates an IAQ override condition.
The IAQ function is not energized during the unoccupied or night time period.
NOTE − The IAQ sensor may also be used with systems containing a motorized outdoor air damper.
To Next Page
Loading...
Need help?
General
