Civil Engineering Reference
In-Depth Information
function of the globe temperature,
T
g
,usingEq.
3.2
.More information about how to
use the black globe thermometer and how to obtain the mean radiant temperature
through the globe temperature can be found in ASHRAE (
2009
), Bedford and
Warmer (
1934
), Vernon (
1932
).With this strategy, only an extra sensor is necessary
to estimate mean radiant temperature. Thus, it is a more efficient methodology, in
economic terms.
1
4
10
8
v
0
.
6
a
in
1
.
10
×
4
T
mr
=
(
T
g
+
273
)
+
(
T
g
−
T
a
in
)
−
273
(3.2)
D
0
.
4
ε
where
T
g
: globe temperature (
◦
C).
•
•
v
a
in
: air velocity (m/s).
T
a
in
: air temperature (
◦
C).
•
•
D
: globe diameter (m).
•
ε
.
: emissivity (0
95 for black globe).
3.3.1.1 Classical Approach
The PMV index is based on human thermal sensation which is strongly related to
the energy balance of the body when the human body is considered in a heat balance
situation, i.e. the heat produced by metabolism equals the net loss of heat, the person
is in ideal conditions of comfort and the PMV index is equal to 0. The classical way
in which the PMV index can be estimated through the six variables that appear in
Table
3.5
was presented in Fanger (
1972
) and it is shown in Eq.
3.3
:
0
028
L
303exp
−
0
.
036
M
PMV
=
.
+
0
.
(3.3)
In the previous equation,
L
is the thermal load in the human body (W/m
2
), defined
as the difference between the internal heat production and the heat loss which occurs
when the person is in a thermal situation. Thermal load can be estimated using Eq.
3.4
(Fanger
1972
).
=
(
−
)
−
.
(
−
T
a
in
)
L
M
W
0
0014
M
34
10
−
3
5733
p
a
in
−
3
.
05
×
−
6
.
99
(
M
−
W
)
−
−
0
.
42
(
M
−
W
−
58
.
15
)
10
−
5
M
−
1
.
72
×
(
5867
−
p
a
in
)
10
−
9
F
cl
4
4
−
39
.
6
×
(
T
cl
+
273
)
−
(
T
mr
+
273
)
−
F
cl
h
c
(
T
cl
−
T
a
in
)
(3.4)
