Temperature–Humidity-Dependent Wind Effects on Physiological Heat Strain of Moderately Exercising Individuals Reproduced by the Universal Thermal Climate Index (UTCI)

Abstract

Increasing wind speed alleviates physiological heat strain; however, health policies have advised against using ventilators or fans under heat wave conditions with air temperatures above the typical skin temperature of 35 °C. Recent research, mostly with sedentary participants, suggests mitigating the effects of wind at even higher temperatures, depending on the humidity level. Our study aimed at exploring and quantifying whether such results are transferable to moderate exercise levels, and whether the Universal Thermal Climate Index (UTCI) reproduces those effects. We measured heart rates, core and skin temperatures, and sweat rates in 198 laboratory experiments completed by five young, semi-nude, heat-acclimated, moderately exercising males walking the treadmill at 4 km/h on the level for three hours under widely varying temperature–humidity combinations and two wind conditions. We quantified the cooling effect of increasing the wind speed from 0.3 to 2 m/s by fitting generalized additive models predicting the physiological heat stress responses depending on ambient temperature, humidity, and wind speed. We then compared the observed wind effects to the assessment performed by the UTCI. Increasing the wind speed lowered the physiological heat strain for air temperatures below 35 °C, but also for higher temperatures with humidity levels above 2 kPa water vapor pressure concerning heart rate and core temperature, and 3 kPa concerning skin temperature and sweat rate, respectively. The UTCI assessment of wind effects correlated positively with the observed changes in physiological responses, showing the closest agreement (r = 0.9) for skin temperature and sweat rate, where wind is known for elevating the relevant convective and evaporative heat transfer. These results demonstrate the potential of the UTCI for adequately assessing sustainable strategies for heat stress mitigation involving fans or ventilators, depending on temperature and humidity, for moderately exercising individuals.

Thermal stress comfort in a contemporary housing district in a moderate climate zone, Lublin as a case study

“…The study focused on the temperature perception according to the UTCI index for several days [26]. Many articles have highlighted the crucial role of wind in temperature perception [27], [28]. In urbanised areas, the discomfort zones exhibit significant variability over time.…”

Skills of Statistical Learning Algorithms in Thermal Stress Assessment Compared with the Expert Judgement Inherent to the Universal Thermal Climate Index (UTCI)

“…The physiological response to thermal stress was derived at stage 1 from the output of an advanced human model of thermoregulation [27], which had been coupled with an adaptive clothing model with clothing insulation changing depending on air temperature [28]. Extensive simulation 2 runs were performed at stage 2, which also included the validation of predicted physiological responses against experimental laboratory and field data [29][30][31][32]. After the definition of reference conditions in stage 3, stage 4 derived UTCI on an equivalent temperature scale.…”

Application of Statistical Learning Algorithms in Thermal Stress Assessment in Comparison with the Expert Judgment Inherent to the Universal Thermal Climate Index (UTCI)

“…The physiological response to thermal stress was derived at stage 1 from the output of an advanced human model of thermoregulation [27], which had been coupled with an adaptive clothing model with clothing insulation changing depending on air temperature [28]. Extensive simulation runs were performed at stage 2, which also included the validation of predicted physiological responses against experimental laboratory and field data [29][30][31][32]. After the experts reached consensus about the definition of reference conditions in stage 3, stage 4 derived UTCI on an equivalent temperature scale.…”