Section 1 - Ventilation
13 Honeywell Economizers 63-8594-02
Example 1: Using the Outside Air Percentage Chart
1. Measure the return air temperature.
2. Measure the outside air temperature.
3. Draw a line from the return air
temperature to the outside air
temperature.
4. Measure the mixed air temperature in
multiple locations and determine the
average.
5. Draw a line down from the mixed air
temperature to the point where it
intersects the first line.
6. Draw a line from the point of intersection
to the outside air percentage on the left
side of the chart.
According to the results from this chart this air
handler is supplied with 26% outside air. If the
total supply volume is 20,000 cubic feet per
minute (cfm) (566 m
3
/min) then:
0.26 X 20,000 cfm of total supply air equals
5,200 cfm of outside air (147 m
3
/min).
This indicates that when the measurements
were done on this air handler the total volume
of outside air in the mixed air was 5,200 cfm of
outside air (147 m
3
/min).
OUTSIDE AIR TEMPERATURE
MIXED and RETURN AIR TEMPERATURES
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
%
O
U
T
S
I
D
E
A
I
R
%
O
U
T
S
I
D
E
A
I
R
49 C
120 F
43
110
38
100
32
90
27
80
21
70
16
60
10
50
4
40
-1
30
-7
20
-12
10
-18
0
-23
-10
-29 C
-20 F
120 F
49 C
110
43
100
38
90
32
80
27
70
21
60
16
50
10
40
4
30
-1
20
-7
10
-12
0
-18
-10
-23
-20 F
-29 C
Draw a line straight
down from the mixed air
temperature till it
intersects the line that
was just drawn.
Draw a line from the return
air on top to the outside air on
the bottom.
Measure the outside air temperature.
At the point of
intersection draw a
line to the left till the
percentage of outside
air is indicated.
Measure the mixed air
temperature. This should be
done in 4 or more locations and
averaged.
6
4
3
70 F (21 C)
1
Measure the
return air
temperature.
2
5
RETURN AIR TEMP
MIXED AIR TEMP
OUTSIDE AIR TEMP
OUTSIDE
AIR
CHART
59 F
(15 C)
25 F (-4 C)
M25275A
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