2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
Invited presentation
352
HOW LOCAL SKIN TEMPERATURES AND SENSATIONS AFFECT
GLOBAL THERMAL COMFORT?
Victor Candas
CEPA, CNRS, 21, rue Becquerel, Strasbourg, France
Contact person: candas@c-strasbourg.fr
This paper tries to interpret how the human local thermal influences are at the origin of the
thermal sensation and comfort subjective estimates. It is generally admitted that a negative or
a positive heat balance will induce a cold or a warm sensation respectively and the ISO
standard stipulates that these sensations will be associated with thermal discomfort. This
hypothesis will be debated.
In addition to the need of clarifying the way discomfort is defined and assessed, this paper
insists on the fact that comfort or discomfort are not simple notions, it states that some lacks
still exist and it emphasizes the major roles played by the various body areas and their
interactions. If it is clear that the skin temperatures and/or their changes are the inputs to the
subjective ratings. But, thermal discomfort may be found for conditions under which no clear
global thermal sensations are perceived.
In opposition to the ISO standard, the present papers supports also the idea that thermal
discomfort does not vary symmetrically from the neutroneutral zone : obviously, many people
like to be a little warm and the fact that some body parts are generally covered (hands and
head ) or more or less irrigated (feet) while other parts are always covered (trunk, thighs …)
may explain their large impacts on the determinism of thermal comfort.
To elaborate an adequate computer model to determine the discomfort risks, we admitted the
hypothesis that thermal comfort results from the integration of all the thermal inputs
depending on the local thermal deviations from an optimal body cartography. The difficulty to
predict personal comfort probably lies on the fact that each individual may have his own
optimal cartography. Even if a model can reproduce more or less accurately the results
observed in laboratory conditions, where all parameters are well controlled, the results found
in normal life show that the percentages of persons satisfied or not may vary a lot and the
model predictions may show large discrepancies. Some examples derived from human
experimental results illustrate these points. It will show that all local influences should be
carefully.