Engineering and Technology
In hot weather, electric fans can potentially provide effective cooling for people, with lower greenhouse
gas emissions and cost than air conditioning. However, international public health organisations regularly discourage
fan use in temperatures higher than 35°C, despite little evidence. We aimed to determine humidity-dependent
temperature thresholds at which electric fans would become detrimental in different age groups.
We used biophysical modelling to determine the upper humidity-dependent temperature thresholds at
which fan use would become detrimental (ie, worsen heat stress) for healthy young adults (aged 18–40 years), healthy
older adults (aged ≥65 years), and older adults taking anticholinergic medication. We also obtained hourly
environmental data for the period Jan 1, 2007, to Dec 31, 2019, for 108 populous cities to determine the number of
days fan use would be effective for cooling, standardised to a 31-day hot weather month. We established simplified
temperature thresholds for future fan use recommendations on the basis of temperatures below which fan use would
never have been detrimental between Jan 1, 2007, and Dec 31, 2019, across all prevailing levels of ambient humidity.
According to our model, fan use would have been beneficial on 30·0 (96·6%) of 31 hot weather days for
healthy young adults and 29·4 (94·9%) of 31 hot weather days for both older adults and older adults taking
anticholinergic medication between Jan 1, 2007, and Dec 31, 2019. Adherence to the current WHO recommendation
of fan use below temperatures of 35°C only, fan use would have been recommended on 27·2 days (87·7%) of 31 hot
weather days. According to our simplified thresholds for fan use (at temperatures
Thermal Ergonomics Laboratoryxs, The University of Sydney, Sydney, NSW, Australia
Copyright: © 2021 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY-NC-ND 4.0 license.