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The discomfort from air current is defined as an undesired local cooling of the body due to air
motion. The DR indicates the percentage of unsatisfied people due to air current. The DR index is
calculated when the temperature goes from 20 °C to 26 °C and the average wind speed is < 0.5
m/s.
The DR index is calculated using the DeltaLog10 software.
2.1.3 WCI Index
WCI (Wind Chill Index) allows a synthetic evaluation of the effects of cold environments on man.
It shows the cooling index due to the wind. It allows evaluating the discomfort perceived during
exposure to low temperatures and wind. The index does not consider the clothing and the work
intensity. The WCI index is calculated by the instrument in presence of air under 10°C.
The WCI index calculation formula is:
where:
t
: air temperature (in °C);
a
v
: Wind speed (in km/h) calculated at 10 m from the ground.
a
As the instrument measures the wind speed at 1.5 m from the ground, the formula is corrected as
follows:
WCI = 13.12 + 0.6215 t
where v
is the wind speed measured by the instrument at 1.5 m from the ground.
1.5
The following tables report some WCI values and the relevant frostbite risks (source: NOAA –
National Weather Service).
10
10
8.6
2.7
15
7.9
1.7
20
7.4
1.1
25
6.9
0.5
30
6.6
0.1
35
6.3
-0.4
40
6.0
-0.7
45
5.7
-1.0
50
5.5
-1.3
55
5.3
-1.6
60
5.1
-1.8
The values that can cause frostbite within ≤ 30 minutes are reported in bold.
HD32.1
WCI = 13.12 + 0.6215 t
a
5
0
-5
-10
-3.3
-9.3
-15.3
-4.4
-10.6
-16.7
-5.2
-11.6
-17.9
-5.9
-12.3
-18.8
-6.5
-13.0
-19.5
-7.0
-13.6
-20.2
-7.4
-14.1
-20.8
-7.8
-14.5
-21.3
-8.1
-15.0
-21.8
-8.5
-15.3
-22.2
-8.8
-15.7
-22.6
0.16
– 11.37 v
a
a
0.16
– 11.37(1.5 v
)
1.5
Air temperature °C
-15
-20
-21.1
-27.2
-33.2
-22.9
-29.1
-35.2
-24.2
-30.5
-36.8
-25.2
-31.6
-38.0
-26.0
-32.6
-39.1
-26.8
-33.4
-40.0
-27.4
-34.1
-40.8
-28.0
-34.8
-41.5
-28.6
-35.4
-42.2
-29.1
-36.0
-42.8
-29.5
-36.5
-43.4
- 10 -
0.16
+ 0.4275 t
v
a
a
+ 0.4275 t
(1.5 v
)
a
1.5
-25
-30
-35
-39.2
-45.1
-41.4
-47.6
-43.1
-49.4
-44.5
-50.9
-45.6
-52.1
-46.6
-53.2
-47.5
-54.2
-48.3
-55.1
-49.0
-55.8
-49.7
-56.6
-50.3
-57.2
0.16
-40
-45
-50
-51.1
-57.1
-63.0
-51.1
-59.9
-66.1
-55.7
-62.0
-68.3
-57.3
-63.7
-70.2
-58.7
-65.2
-71.7
-59.8
-66.4
-73.1
-60.3
-67.6
-74.2
-61.8
-68.6
-75.3
-62.7
-69.5
-76.3
-63.4
-70.3
-77.2
-64.2
-71.1
-78.0
V2.1
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