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