Civil Engineering Reference
In-Depth Information
Fig. 3.9
PPD as a function of the PMV
3.3.3.2 Operative Temperature
Operative temperature can be defined as the average between the mean radiant and
indoor air temperatures weighted by their respective heat transfer coefficients, see
Eq.
3.16
. Furthermore, for a given value of metabolic rate, clothing insulation, air
velocity and humidity, a thermal comfort zone can be defined. More specifically,
this comfort zone is defined as a function of the operative temperature ranges which
provide acceptable thermal conditions (ASHRAE55
1992
).
h
r
T
mr
+
h
c
T
a
in
T
o
=
(3.16)
h
r
+
h
c
In the previous equation
T
o
is the operative temperature (K),
T
mr
and
T
a
in
are the
mean radiant and indoor air temperatures in (K) respectively,
h
c
is the convective
heat transfer coefficient (W/m
2
K), and finally,
h
r
is the heat transfer coefficient by
radiation (W/m
2
K).
As an example, in Fig.
3.10
it can be observed that the range of operative temper-
ature associated with winter and summer comfort zones for a rate of people satisfied
with the thermal environment equal to 80%, and under these conditions: people
inside the environment have activity levels which result in metabolic rates between
1
.
0 and 1
.
3met, that is typical office activity levels, the indoor air velocity is lower
than 0
.
2m/s, and clothing insulation is between 0
.
5 clo (typical summer value) and
1
0 clo (winter value). More information about how to use this index under other
conditions can be found in ASHRAE55 (
1992
).
.
