2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
Insulation (m 2 °C/W)
436
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Wet excl evap Dry
IMP PERM
Condition
Figure 3. Insulation reduction due to moist clothes measured on a manikin at 10 °C (ambient
water vapour pressure 1 kPa). Wet excl evap correction was based on mass loss.
In dry conditions at 10°C, the insulation from the subjects was relatively close to the manikin
values (Figure 2). The sweating and body heat storage change were minimal. The observed
differences could be related to motion patterns that the correction equations for manikins did
not explain. In IMP10W, the insulation from the subjects was considerably lower than the
manikin values, while in permeable coverall insulation values were close after correcting heat
losses for evaporation based on mass loss. In both coveralls, there should have been present
an effect of lower material heat resistance that could stand for 3-5% of higher heat losses. In
IMP10W, the dry heat loss was overestimated due to calculating evaporation from mass loss,
and the effect of condensation (Havenith et al., 2007) was not accounted for. This effect
should be negligible in permeable clothes (Figure 3), although it would probably occur at
lower ambient temperatures (outer surface temperature below dew point). Evaporation was
assumed to take place at skin surface, however, that would not be true, especially for wet
tests. For wet and dry tests at 25°C, both coveralls behaved similarly. This could have been
due to the fact that by the end of the test, even in the dry conditions, clothing became quite
wet. In PERM25D and especially in PERM25W, the high evaporative heat losses most
probably masked dry heat losses in the heat balance calculation, and did increase the error in
the insulation calculation. In PERM25W the calculated dry heat losses were so small, that the
calculated insulation was out of reasonable range. On average, 35 g of accumulated moisture
in IMP10D (20 g on outer layer at the end of 60 minutes test) did affect the results only a
little, compared to PERM10D (~3 g accumulation) and manikin values. The biggest effect of
condensation was observed in IMP10W with ~950 g moisture in the system (~80 g on outer
layer). In homogenous conditions (Tsk=Ta), the condensation effect would not be present.
IMP25D with ~200 g (~50 g on outer layer) and IMP25W with ~1000 g moisture in the
system (~80 g on outer layer) did not differ much. In both cases the humidity during last 30
min was 100%.
DISCUSSION
When using subjects for insulation measurements, then the test conditions should be chosen
with care, to ensure reaching a stable state, keep sweating and changes in body heat storage
low, but temperature gradients reasonably high. Unknown moisture quantities involved in
condensation, eventual re-evaporation, wicking etc. and their effect on heat transfer,
especially in impermeable clothes, increases the uncertainty of the results. Moist clothes (not
dripping wet) seem to reduce clothing insulation up to 5%. The biggest cooling effect was
related to evaporation (permeable) from, and the condensation effect (impermeable) in, the