Electric fan effectiveness and thresholds for healthy young adults during prolonged heatwaves : updated thermoregulation modeling

Abstract

Heat extremes significantly impact human health, with vulnerability such as poverty further exacerbating these effects. As global climate change intensifies, the world faces even hotter weather, necessitating efficient and sustainable cooling strategies, especially in resource-limited regions. Electric fans offer an affordable cooling option; however, their effectiveness under varying extreme environmental conditions and activity levels remains debated. This study introduces an advanced thermoregulation model to investigate the thresholds and limitations of electric fan use during prolonged heatwave conditions. Key model modifications include the computation of hydration-dependent sensor signals and set-point temperatures, refined sweating and vasodilation responses, and segment-specific convective heat transfer coefficients. Using this improved model, we evaluated core temperature responses and hyperthermia onset times under different fan speeds, ambient temperatures, relative humidity levels, and physical activity intensities. According to the results, fans effectively delay hyperthermia onset at moderate conditions (up to 42 °C and 10–20 % RH, activity level 1.2 PAR) but become detrimental under extreme conditions (above 43 °C and 30 % RH). Higher fan speeds (3.0 m/s) accelerate heat gain in severe conditions due to enhanced sensible heat transfer, counteracting evaporative cooling benefits. Additionally, increased physical activity notably reduces safe exposure durations by compounding metabolic and environmental heat stress. Fans provide optimal thermal relief at lower activity intensities and moderate environmental conditions. This study provides essential evidence to refine public health guidelines, highlighting the conditions under which electric fans are beneficial and cautioning their limitations in extreme scenarios.