Page 6
Determine Outdoor Air Percentage
Outdoor air percentage can be estimated in the same
manner for both manual and motorized dampers.
Measure outdoor air temperatures according to the
following steps and calculate the outdoor air percentage.
For motorized dampers, refer to unit specific damper
adjustment details following these steps.
1- Measure outdoor air temperature. Mark the point on
the bottom line of chart 1 and label the point “A” (40°F,
4°C shown).
2- Measure return air temperature. Mark that point on
the top line of chart 1 and label the point “B” (74°F,
23°C shown).
3- Measure mixed air (outdoor and return air)
temperature. Mark that point on the top line of chart
1 and label point “C” (70°F, 21°C shown).
4- Draw a straight line between points A and B.
5- Draw a vertical line through point C.
6- Draw a horizontal line where the two lines meet. Read
the percent of outdoor air intake on the side.
7- If outdoor air percentage is less or more than desired,
increase or decrease minimum damper position.
Then, repeat steps 2 through 7 until calculation reads
desired outdoor air percentage.
-20
-29
-10
-23
0
-18
10
-12
20
-7
30
-1
40
4
50
10
60
16
70
21
80
27
90
32
100
38
0
10
30
40
50
60
70
80
90
100
20
OUTDOOR AIR TEMPERATURE
0
10
30
40
50
60
70
80
90
100
20
MIXED AND RETURN AIR TEMPERATURE
CHART 1
CALCULATE MINIMUM OUTDOOR AIR PERCENTAGE
A
B
C
_
F
_
C
_
F
_
C
-20
-29
-10
-23
0
-18
10
-12
20
-7
30
-1
40
4
50
10
60
16
70
21
80
27
90
32
100
38
_
F
_
C
_
F
_
C
