STUDY OF THERMOREGULATORY MECHANISM, SENSATION AND PERFORMANCE OF HUMAN BODY DURING COMMUTE IN A HOT THERMAL ENVIRONMENT

Abstract

To improve the efficiency of work and quality of life of human beings, the study of thermal comfort is essential. Analytical models don't need any experimental setup, making them the most straightforward method for studying physiology. This technique can study all physiological parameters in various environmental conditions. Energy balance can be applied to the human body, which can be viewed as a control volume. The steady state and transient energy balance models are used to solve the physiological energy balance model. The human body is further examined in terms of its exergy analysis. This study extensively examines the steady state analysis of the human body. The human body's steady state heat balance model is used to design a mathematical model. The convective, radiative, respiratory, and evaporative heat transfers are heat transfer mechanisms in this model. The behaviour of mean body, core, and required skin temperatures to attain thermal comfort are investigated by increasing metabolic rate and keeping all other parameters constant.With an increase in metabolic rate, it has been observed that the blood flow rates and evaporative heat transfer increase. The variation of physiological parameters is also studied by increasing ambient temperature and keeping all other parameters constant. The convective, radiative and respiratory heat losses to the environment decrease; however, the evaporative heat loss increases due to the increase in air temperature. Commuting in a hot thermal environment induces thermal stress and exertion in humans, affecting their health and productivity. In this study, we evaluate the impact of such a commute on physiological thermoregulation through experimental and analytical studies. The experiments are administered in a controlled climate simulator with fifteen healthy adults. The variation in skin temperature (Tsk) measured at ten body parts accompanied with subjective responses are obtained for eight different temperatures (30°C – 42°C) and two humidity (40% – 80%) set-points. We find that the variation in Tsk of different body parts is reduced with an increase in air temperature. At higher temperatures, the mean Tsk increases with an increase in relative humidity, while the effect is negligible at lower temperatures. The statistical analysis of subjective responses yields a neutral temperature of 27.27°C and 25.84°C after walking for 40%and 80% RH, respectively. An analytical model is developed to demonstrate the different modes of heat transfer and exergy balance. The effect of evaporative cooling on exergy consumption is demonstrated. This study investigates a commute's physiological and cognitive impacts on students, just prior to a lecture. The commute is simulated in one chamber of the climate simulator, using a bicycle ergometer, at three different temperatures: 30°C, 35°C, and 40°C. Since the university classrooms have central air-conditioning, attending the lecture is simulated in the other chamber with a constant temperature of 26 °C. The participant’s pulse, sweat, blood pressure, skin and tympanic temperatures are recorded during the study. The participants also perform three cognitive tasks targeting working memory, task switching, and inhibition, respectively. The subjective thermal sensation and thermal comfort votes are also gathered from the participants. Linear mixed effect models are used to compare the impact of the outdoor temperature during commute on the cognitive performance of the students. The different commute temperatures did not significantly impact the accuracy obtained in all three cognitive tasks (p > 0.05). However, the reaction time in all three tests was found to have been significantly affected and it took longer time for higher commute temperature (p < 0.05). It is found that stage 1 (i.e. before cycling) and stage 3 (i.e. entry of classroom) illustrate a significant difference in tympanic and skin temperature (p < 0.05), while stage 5 (i.e. end of 1 hour of class) shows no significant difference (p > 0.05). A similar outcome is seen for thermal sensation votes. Overall, the results point to the outdoor air temperature during summer commutes impacting performance, subjective thermal sensation, and objective physiological measures of thermal comfort during the class hour immediately following the commute.