2007, Piran, Slovenia

Universal Thermal Climate Index
ASSESSING THE EFFECTS OF ENVIRONMENTAL RADIATION ON
WIND CHILL EQUIVALENT TEMPERATURES
Avraham Shitzer
Department of Mechanical Engineering, Technion, Israel Institute of Technology, Haifa,
Israel
Contact person: mersasa@tx.technion.ac.il
Heat losses from exposed body areas in cold weather, due to combinations of wind-driven
convection and environmental radiation, make the environment "feel" colder. These heat
exchange mechanisms form the basis for estimating wind chill equivalent temperatures
(WCETs). Radiation effects on humans may be differentiated between direct solar and
environmental. Solar radiation on bright sunny winter days has beneficial effects, as it
counters and offsets, to a certain extent, the effects due to wind and low air temperatures. This
mechanism is excluded from the present analysis. Environmental radiation effects, which are
included, enhance heat loss from the human body, thus affecting the overall thermal sensation
due to the environment. This study compares the relative contributions of wind-driven
convection and environmental radiation to calculated WCETs. It is shown that, over a wide
range of low air temperatures and wind speeds, convection dominates over environmental
radiation. At low wind speeds the latter contributes up to about 20% of the overall heat loss
from exposed skin areas. Its relative contribution reduces even further as the time of the
exposure prolongs and skin temperatures continue to drop. At still higher wind speeds,
environmental radiation effects become much smaller decreasing to about 5% of the total heat
loss to the environment. These values fall well within the uncertainties associated with the
parameter values assumed in the estimation of WCETs. It is also shown that environmental
radiation effects may conveniently be accommodated by adjusting wind speeds slightly above
their measured values.
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