GHM Delta OHM HD32.3TCA, Operating Manual

Page: 18 / 46

HD32.3TC
- 18 -
V1.1
3.4 T
URBULENCE INTENSITY
TU
AND DRAFT RATE
DR
The local turbulence intensity, in percentage, is defined as the ratio between the local air speed
standard deviation and the local average air speed (ISO 7726):
100
× =
a
V
SD
TU
where:
V
a
= average local wind speed
SD = local wind speed standard deviation
( )

=
− ⋅
−
=
n
i
a a
V V
n
SD
i
1
2
1
1
From the turbulence calculation, knowing the average values of the local wind speed and ambient
temperature, the Draft Rate
DR is obtained, according to ISO 7730:
( ) ( ) ( )
14 . 3 37 . 0 05 . 0 34
62 , 0
+ ⋅ ⋅ ⋅ − ⋅ − =
TU V V T DR
a a a
The air current discomfort is defined as an undesired local cooling of the body due to air motion.
The Draft Rate DR indicates the percentage of people who are dissatisfied due to the air current.
The DR index is calculated when the temperature is between 20 and 26 °C and the
average air speed is less than 0.5 m/s.
To calculate the turbulence intensity, the AP3203.2 or AP3203 hot wire air speed probe must
be connected.
To calculate the turbulence intensity TU and the Draft Rate DR, reference is made to the stand-
ards:
•
ISO 7726
•
ISO 7730