13. Human Thermal Comfort

Humans are very sensitive to changes in environmental temperature and humidity because our internal body temperature has to be kept at a narrow temperature range of 37 ± 0.5 C. Hypothalamus is the central control organ in the brain that controls our internal body temperature. When our internal body temperature rises above 37.5 C, our blood flow is increased to our skin in order to increase the heat transfer from our skin to the environment. At elevated internal body temperature sweating also starts and cools our skin which increases the heat transfer from the body core to our skin. When our internal body temperature falls below 36.5 C, our blood flow is decreased to our skin in order to decrease the heat transfer from our skin to the environment. Also when our internal body temperature falls below 36.5 C, muscle shivering can start in order to increase the internal metabolic heat generation. Thermal energy balance between a human body and the environment is shown in Equation 13-1.