2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
The aim of the present study was twofold: 1) assess whether a bioclimatic index developed
for outdoor environments, can be used reliably for the assessment of the indoor thermal
environment, and 2) determine whether prediction of physiological responses to a thermal
environment is necessary for assessment of thermal comfort, as well as heat stress. The two
issues were addressed by comparing the assessment of the thermal environment according to
ISO standards and the Humidex index.
METHODS
Two software programs were developed for the comparative analysis of the same thermal
environment, carried out by HD and ISO
standardised indices/procedures. The
former, deriving combinations of air
temperature(ta) and relative humidity (RH)
for each HD value, and the latter upgraded
in accordance with the regulations in force
[2], calculates combinations of (ta, RH)
corresponding to:
• a required value of PMV (Predicted
Mean Vote) according to ISO 7730
Standard;
• a required vale of the wet bulb globe
temperature (WBGT) according to ISO
7243 Standard;
• the overall amount of sweat and final
rectal temperature evaluated in accordance
with the PHS (Predicted Heat Stress)
method on which ISO 7933 Standard is
based upon, for eight-hours of continuous
work.
Numerical evaluations were carried out
setting metabolic rate (M) in the range of
light activity (1.4-1.8 met) and static
clothing insulation (Icl) at 0.60 and 1.0 clo
(for summer and winter evaluations) [6].
RESULTS AND DISCUSSION
It is important to emphasise that under typical indoor environment situations, the comparative
analysis is limited to the humidity range 30-70%. The reasons of this are: below 30% RH,
mucous membranes start to dry up, with the consequent reduction of the body defence
mechanisms against germs and bacteria; above 70% allergenic factors, and the superficial
condensate formation responsible for moulds become important. As shown in Fig. 1A, for the
example corresponding to typical summer office conditions (M=1.4 met, Icl = 0.60 clo),
Humidex index appears unable to give a reliable assessment of thermal comfort in every
microclimatic condition. The comparison between comfort curves required for the B-class by
ISO 7730 (PMV= ± 0.50) and those required by Humidex (HD=20 and HD=29) results in a
perfect agreement only in the filled region. In contrast, outside the filled region,
microclimates judged as comfortable by HD, are judged uncomfortable on the basis of the
PMV index. Although the assessment of the same indoor thermal environment shows a
general disagreement between PMV and HD approach, some interesting features need to be
506
Humidity ratio, w a (g/kg)
25
20
15
10
5
0
20
15
10
5
0
15 20 25 30 35
A
HD=20
B
HD=20
PMV= -0,50
HD=29
PMV= -0,50
HD=29
RH=100%
RH=100%
PMV= -0,50
PMV= +0,50
PMV= +0,50
RH=70%
RH=70%
RH=50%
RH=30%
RH=50%
RH=30%
15 20 25 30 35
Air temperature, ta (°C)
Figure 1. Thermal comfort assessment carried out by
means of HD (continuous lines) and PMV (dashed
lines). Metabolic rate M = 1.4 met; Static clothing
insulation Icl = 0.60 clo (A) or Icl = 1.00 clo (B); Air
velocity va=0.1 m/s, ta=tr. Filled area refers to
microclimatic conditions for which there is
agreement between the assessment carried out with
the two indices.