MIL-HDBK-1011/2
4.5.4.10
Insect Screening. Insect screening decreases the ventilative
effectiveness of openings. The amount of decrease in velocity varies with
screen type and the incident wind direction and velocity. Decreases in
velocity are greater with lower windspeeds and oblique winds, and can be as
high as 60 percent (refer to Table 4).
Because insect screening lowers the effectiveness of the openings
for ventilation, its presence must be factored in when sizing windows. In the
window sizing procedure in Appendix C, Section 1, a porosity factor is used to
lower the opening's ventilative effectiveness when screens are used.
If possible, place insect screening across the larger area at the
front of the balcony rather than at each opening (see Figure 34). This
creates less resistance to airflow and results in greater interior velocities.
Table 3
Reduction in Wind Velocity Due to Insect Screens
As a Function of Incidence Angle
+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),
*
*
Normal Incidence
67.5 degree incidence
* Outside Velocity
*
*
Inside Velocity Reduction *
Inside Velocity Reduction
* m/s
*
fpm
m/s
fpm
%
m/s
fpm
%
* 0.75
47 *
150
0.49
98
35
04.0
80
* 1.23
39 *
250
0.87
178
29
0.75
153
* 2.50
60 *
500
1.33
267
47
1.00
200
* 3.30
60 *
650
1.79
353
47
1.33
262
* 3.80
42 *
750
2.64
520
31
2.23
438
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44
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