Lennox PRODIGY M2

7. Economizer
Page 30
506457−01 05/10
7.12.2. Default Operation
The M2 has a 0−10VDC IAQ input for a standard 0−2000ppm CO
2
sensor. The economizer starts opening at a CO
2
level of
500 ppm (start open" setpoint) and reaches full open at a CO
2
level of 1000ppm (full open" setpoint). The damper opens to
100%. Determine damper travel position using the following formula.
% Damper Travel = CO
2
ppm − Start Open ppm
5
Example: At a CO
2
level of 750ppm, the damper will be approximately 50% open:
% Damper Travel = 750−500 = 50%
5
Use Displaying Sensor Inputs" section to read CO
2
ppm. Figure 14 shows default or proportional operation.
33
66
100
500
ECTO 5.17
1000
ECTO 5.18
Low Temp. Operation High Temp. Operation
CO
2
(ppm)
10°F ECTO 5.19
20°F
30°F
40°F ECTO 5.20
105°F ECTO 5.22
95°F
85°F
75°F ECTO 5.21
0
Min. Position
Damper Travel: % of Maximum Open
(ECTO 5.16)
Figure 14. Default DCV Operation
7.12.3. ECTO Adjustments
Default IAQ economizer operation is based on common or average applications. Adjustments may be made to the IAQ
ECTO parameters to alter operation or meet required specifications. Use the ECTO Control Parameters" section to change
ECTO parameters 5.16 through 5.22.
Select a DCV or OAC mode with ECTO 5.26. Modes 4 and 5 will bring on the unit blower when DCV calls for maximum
damper open, and returns to auto−blower when DCV damper returns to 0. The other modes only operate when the unit
blower is on, but will not bring it on themselves.
Some applications require a different CO
2
setpoint range than default settings. Damper start open" (ECTO 5.17) and full
open" (ECTO 5.18) CO
2
setpoints may be adjusted from 0 to 1992ppm. Use the following formula to determine damper
travel.
NOTE − When changing CO
2
setpoint range, start open" setpoint should be less than full-open" setpoint.
% Damper Travel = CO
2
ppm − Start Open ppm X MaxOpen (ECTO 5.16)
Full Open − Start Open
Example: An application requires the dampers open at 800 CO
2
ppm and reach full open at 1200.
If the CO
2
level in the space reads 1000 ppm, calculate the damper percent open as follows.
% Damper Travel = 1000 − 800 or 200 or .5 = 0.5 x 100 = 50%
1200 − 800 400
7.12.3.1. Setpoint Control Option
Setpoint Control mode is commonly used in areas with high occupancy and frequent change out such as classrooms or
conference rooms.
In applications requiring this on/off damper response to CO
2
levels, set the start open" (ECTO 5.17) setpoint higher than the
full open" (ECTO 5.18) setpoint. The dampers will drive to fully−open position immediately. Figure 15 shows the setpoint
control option.
Change ECTO 5.19 and 5.20 to set the minimum outdoor temperature limits. Change ECTO 5.21 and 5.22 to set the maxi-
mum temperature value.
IMPORTANT − Mixed air temperatures less than 45°F (7°C) on units with an aluminized heat exchanger or less than 30°F
(−1°C) on stainless steel heat exchangers will void the manufacturer’s warranty.