Aug 29, 2019

How effective are fans in heatwaves?

With global warming one of the most pressing issues of our time, how we keep our bodies cool as temperatures rise is more important than ever before.

The issue is particularly key for older people, who have a reduced ability to adapt to heat, and are particularly vulnerable when it comes to extreme temperatures. Older people are at greater risk of heat cramps, heat exhaustion, and heat stroke, which can be fatal.

Researchers from the University of Sydney have been studying the effectiveness of fans in heatwave conditions, and say fans are not effective in hot, dry climates.

Associate Professor Ollie Jay of the Faculty of Health Sciences at Sydney University, told HelloCare about his team’s findings. 

“If it is VERY hot (47C) and dry (10% relative humidity), such as in peak heatwave conditions in parts of Australia, fan use does make a person hotter and increases the amount of work the heart has to do. Dehydration is accelerated too.”

However, he said under the most common heatwave conditions, fans cool people down.

“We found that under most representative heatwave conditions, which are typically hot and humid (up to 40C with 50%RH), fans are effective cooling devices.” 

“Ditch the fan”

Associate Professor Jay said “ditch the fan” in very hot, dry conditions. “Just spray water on the skin, as you will still get that boost to evaporation.” 

However, he says fans are usually helpful, except in the most extreme circumstances. 

“Under most heatwave conditions, fans should be advocated as effective low-cost cooling devices,” he told HelloCare.

“I would say that under most conditions fans are helpful, but they are probably even more effective if people are given a damp cloth/sponge or spray bottle to keep the skin wet. 

“This moisture will then evaporate and keep the person cool. Evaporation is by far the most effective way of cooling someone down.”

The study

Twelve healthy male volunteers were monitored for thermal strain (rectal temperature), cardiovascular strain (heart rate and blood pressure), dehydration (whole body sweat rate), and thermal comfort (assessed using  a 120mm scale) over a two-hour exposure to two types of simulated heat waves: very hot and dry , and cooler, but more humid with a higher heat index.

The results were published in the Annals of Internal Medicine.

In hot, dry conditions, sweat evaporates from the skin

Associate Professor Jay said fans are less effective in very hot, dry environments “because when it is very dry, all the sweat we secrete onto the skin surface completely evaporates even without a fan, whereas when it is humid sweat accumulates on the skin without evaporating and this process is accelerated with fan use.”

He said fans increase heat stress in dry conditions because you “get extra evaporative heat loss with fan use, extra heat is driven into the body via convection because air temperature is much hotter than skin temperature.”

Recommendations for aged care in Australia

The Department of Health’s guidelines, ‘Caring for Older People in Warmer Weather’, recommend operators should “ensure cooling systems in the facility are adequate and working effectively” during heatwaves.

They say ensure “the temperature in care recipients’ rooms and within the facility is kept comfortable”.

Among other measures, they recommend “tepid showers or sponging” during heatwaves.

Associate Professor Jay’s findings calls into question the recommendations in the Victorian government’s ‘Heatwave ready resource’ never to use a fan to blow air directly onto a person when the indoor air temperature is above 35C.

The research is also in contrast to the statement that “fans are not effective in cooling a person down on very humid days and when the indoor air temperature exceeds 35ºC”.

Associate Professor Jay is now looking at the effectiveness of low-resource cooling systems for heatwave conditions for the elderly and people with medical conditions. They are also examining the impact of various medications on the advice that should be given to the public ahead of extreme heat events.

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