Startup
74 RT-SVX34F-EN
Economizer Damper Adjustment
Economizer (O/A) Dampers
Arbitrarily adjusting the outside air dampers to open fully
when the return air dampers are fully closed can overload
the supply fan motor or deliver higher CFM to the space
than designed. This causes higher operating duct static
pressures and over pressurization of the space when the
unit is operating in the “economizer” mode.
The O/A and R/A damper linkage is attached to a plate with
a series of holes that allows the installer or operator to
modify the O/A damper travel to compensate for various
R/A duct losses. The purpose of adjusting the amount of O/
A damper travel is to maintain a balance or equal pressure
between the O/A dampers and the pressure drop of the
return air system. Figure 55, p. 75 illustrates the damper
assembly and Table 53, p. 74 through Table 56, p. 75 list
the various damper positions based on the air flow (CFM)
and the return duct losses (static pressure) for Downflow
and Horizontal units.
To adjust the O/A damper for the correct pressure drop:
1. Measure the return duct static pressure.
2. Enter the calculated CFM from the previous section
“Verifying Proper Airflow”
Tab le 43, p. 68 to obtain the
return air damper pressure drop.
3. Add the measured return duct static pressure and the
return air damper pressure drop together to obtain the
Total Return Static Pressure. Apply this calculation and
the calculated CFM to the appropriate
Tab le 53, p. 74
through Ta bl e 56, p. 75.
4. Set the drive rod swivel to the appropriate hole
according to Tabl e 53, p. 74 through Ta b l e 56, p. 75.
The units are shipped using hole “A” with no reference
to any specific operating condition.
Figure 53. (Upflow) Standard exhaust maximum
damper position
Figure 54. (Horizontal) Standard exhaust maximum
damper position
Table 53. 27.5 - 35 Ton downflow economizer (O/A)
damper static pressure setup
System
Design
Return Air Duct Static +
Return Air Damper Static
(Inches of Water)
CFM 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Drive Rod Position
8000 B EEEEEE
8500 B D EEEEE
9500 A C EEEEE
10000 A C D EEEE
10500 A C D EEEE
11000 A B D D E E E
11500 A B C D E E E
12000 A A C D E E E
12500 A A C D D E E
13000 A A B B C D E
Table 54. 27.5 - 35 Ton horizontal economizer (O/A)
damper static pressure setup
System
Design
Return Air Duct Static +
Return Air Damper Static
(Inches of Water)
CFM 0.20 0.40 0.60 0.80 1.00 1.20 1.40
Drive Rod Position
8000 A F GGGGG
8500 A F GGGGG
9000 A E GGGGG
9500 A E F GGGG
10000 A D E GGGG
11000 A D E F G G G
11500 A B E F G G G
12000 A A D F G G G
12500 A A D E F G G
13000 A A D E F G G
13500 A A C E F F G
14000 A A C D E F G
14500 A A B D E F F
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