Civil Engineering Reference
In-Depth Information
Fig. 3.8
Acceptable operative temperature ranges for naturally conditioned spaces.
Source
:
(ASHRAE55
1992
)
3.3.3 Other Indices
In this section another couple of indices which allow the reader to estimate the
building's users thermal comfort sensation are presented.
3.3.3.1 Predicted Percent Dissatisfied (PPD)
There is another index very related to the PMV, the Predicted Percentage Dissatisfied
(PPD) index. This index reflects the percentage of people that are dissatisfied with the
thermal environment (ISO7730
1994
), and it can be estimated according to Eq.
3.15
.
95 exp
0
2179PMV
2
03353PMV
4
PPD
=
100
−
−
.
+
0
.
(3.15)
The relationship between PPD and PMV indices can be observed in Fig.
3.9
.From
this figure, it can be easily deduced that, although an optimal comfort situation will be
reached, it is a PMV index equal to zero, it is impossible that 100% of the people will
be satisfied with the thermal environment since comfort is a psychological condition,
and thus, each person has his own thermal comfort concept. Moreover, for a PMV
index equal to zero, approximately 5% of the people are dissatisfied with the thermal
environment. The PMV-PPD model is widely accepted in the framework of comfort
conditions and it is recognised by international standards as ISO 7730 (ISO7730
1994
).
