Abstract
Heatwaves are one of the most dangerous natural hazards causing more than 166,000 deaths from 1998–2017. Their frequency is increasing, and they are becoming more intense.Electric fans are an efficient, and sustainable solution to cool people. They are, for most applications, the cheapest cooling technology available. However, many national and international health guidelines actively advise people not to use them when indoor air temperatures exceed the skin temperature, approximately 35 °C.We used a human energy balance model, to verify the validity of those recommendations and to determine under which environmental (air temperature, relative humidity, air speed and mean radiant temperature) and personal (metabolic rate, clothing) conditions the use of fans would be beneficial.We found that current guidelines are too restrictive. Electric fans can be used safely even if the indoor dry-bulb temperature exceeds 35 °C since they significantly increase the amount of sweat that evaporates from the skin. The use of elevated air speeds (0.8 m/s) increases the critical operative temperature at which heat strain is expected to occur by an average of 14 °C for relative humidity values above 22 %. We also analyzed the most extreme weather events from 1990 to 2014 recorded in the 115 most populous cities worldwide, and we determined that in 93 of them the use of fans would have been beneficial.We developed a free, open-source, and easy-to-use online tool to help researchers, building practitioners, and policymakers better understand under which conditions electric fans can be safely used to cool people.
Highlights
The World Meteorological Organization (WMO) and World Health Organization (WHO) describe heatwaves as: ‘‘periods of unusually hot and dry or hot and humid weather that have a subtle onset and cessation, a duration of at least two or three days, usually with a discernible impact on human and natural systems" [1]
We compared our results with those obtained from the PHS model that can be used to determine the thermal stress experienced by a subject in a hot environment
We assumed that elevated air speed is detrimental when the maximum allowable exposure time for heat storage estimated with a V =0.8 m/s is higher than the value estimated with a V =0.2 m/s
Summary
The World Meteorological Organization (WMO) and World Health Organization (WHO) describe heatwaves as: ‘‘periods of unusually hot and dry or hot and humid weather that have a subtle onset and cessation, a duration of at least two or three days, usually with a discernible impact on human and natural systems" [1]. The International Energy Agency (IEA) estimated that in 2016 the energy required for cooling during heatwaves accounted for more than 70 % of residential consumption in regions such as the Middle East and some parts of the U.S [4]. Such increased demand can cause power shortages and blackouts, which can cripple the water supply system as it happened in Pakistan in 2015. This heatwave claimed more than 700 lives and hospitals had to cope with an increased number of people suffering from heatstroke and dehydration [5]
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