2007, Piran, Slovenia

Universal Thermal Climate Index
COMPARISON OF FIALA MODEL PREDICTIONS WITH
EXPERIMENTAL DATA FOR EXTREME COLD CONDITIONS.
Wojciech Szarek 1,2 , KalevKuklane 1 , Ingvar Holmér 1
1 EAT , Dept. Of Design Sciences, Lund University, Lund, Sweden
2 Dept. of Geography, Faculty of Sciences, Masaryk University, Brno, Czech Republic
Contact person: szarek@mail.geogr.muni.cz
INTRODUCTION
The commonly used evaluation models of human exposure to thermal environment deal with
specific temperature ranges, e.g. IREQ (Holmér, 1984), PHS (Malchaire et al., 2000), PMV
(Fanger, 1970). For the purpose of developing a universal thermal climate index (UTCI) a
general human heat balance model should be used. This paper presents the validation of the
Fiala model (Fiala et al., 1999) with experimental data from subjects exposed to extreme cold.
The Fiala model simulations were modified by changing some clothing parameters. The bases
for the comparison were the data from the Subzero project (Meinander et al., 2003).
METHODS
The background to the Subzero subjects’ tests and the results were described in more detail by
Holmér et al. (2003) and Kuklane et al. (2003). This paper validates the Fiala model by
comparing the observed responses of mean skin temperature (Tsk), rectal temperature (Trec),
and skin evaporation (me) with those predicted by the model. In one test condition the air
temperature was set to -40 ºC and the wind speed to 3 m/s (D3), and in the second to –23 ºC
and 10 m/s respectively (D10). The task consisted of 90 minutes walking on a treadmill with a
speed of 5 km/h on 0,5° inclination. Metabolic rate and heat balance components were
calculated based on oxygen consumption, measured temperatures, weight loss and sweat
accumulation in the garment pieces. As the next step the experimental data were compared
with Fiala model simulations. The basic input data passed adjustments. The metabolic rates of
299 W/m² for D3 and 383 W/m² for D10 (corrected for walk on inclination) were further
reduced for work against wind by 10 W per each 1 m/s. The simulations were as follows:
1) Un - uniform thermal insulation without wind correction (equation 2 of Annex C of EN
342, 2004); 2) Uw - uniform thermal insulation with wind correction; 3) Dn - different
thermal insulation distribution over body without wind correction; 4) Dw - different thermal
insulation distribution over body with wind correction. The uniform clothing insulation
utilizes the same total clothing insulation value (Itot,D=0,629 m 2 °C/W) measured on a thermal
manikin for all UTCI body zones. Differently distributed clothing insulation utilizes the
specific insulation values of a body zone measured on the manikin corresponding to an UTCI
zone. The simulation values were acquired each 5 minutes and compared to corresponding
subjects’ data.
RESULTS
Rectal temperature: The rectal temperature of the subjects increased in both conditions within
the first 40-50 minutes and then remained relatively stable. Because of the higher metabolic
rate in wind 10 m/s condition (D10) the increase in body core temperature was greater than in
the 3 m/s wind (D3) trial. Comparison of the observed (subject data) and predicted values are
presented in Figures 1 and 2. It can be observed that all the simulation curves for rectal
temperature were very close, i.e. independent of clothing insulation, but differed from the
observed data, particularly in the latter part of trial D10.
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