Your Fans and AC Can Tag Team to Keep You Cool and Save Energy

The question of keeping cool in a warming world is one of the many catch-22s presented by the climate crisis. More frequent and severe heat waves are likely to prompt people to turn up the air conditioning, which will, in turn, increase greenhouse gas emissions and lead to even hotter temperatures. 

Luckily, researchers led by a team from the University of Sydney in Australia have come up with a relatively cheap and simple solution that could save energy: using electric fans to postpone the moment when you need to resort to air conditioning. 

“[L]ow-cost solutions such as fans could be very effective in tackling the climate challenge,” study lead author Arunima Malik, senior lecturer in sustainability at the University of Sydney’s School of Physics and Business School, tells Treehugger in an email. 

Deadliest Disasters 

Heat waves are one of the deadliest kinds of extreme weather events. During an average year in the U.S., they kill more people than any other weather hazard, including flooding or hurricanes, according to figures from the National Oceanic and Atmospheric Administration (NOAA). 

During a heat wave, air conditioning can be a lifesaver. For example, when a heat wave baked the U.S. in 1995, more than 1,000 people died, according to an NOAA report. The report found those most likely to be affected were elderly adults living in urban areas who, among other factors, either could not afford to have air conditioning or did not know how to operate it. The Centers for Disease Control and Prevention (CDC) is also adamant that air conditioning is an essential tool for people especially vulnerable to heat waves, including adults over 65, children under two, and those with chronic health problems. 

“Air-conditioning is the number one way to protect yourself against heat-related illness and death,” the CDC writes. “If your home is not air-conditioned, reduce your risk for heat-related illness by spending time in public facilities that are air-conditioned and using air conditioning in vehicles.”

The agency also advises against using fans as your primary line of defense against abnormally high temperatures. However, the fact that fossil fuels are still responsible for about 80% of the global power supply means air conditioner use does contribute to the climate crisis. This will only increase as temperatures rise throughout the 21st century, the authors of the new study note. 

“Through their sole purpose of lowering air temperatures, air conditioners feed a cycle of high electricity consumption—often delivered by fossil fuel power stations that in turn contribute to further increases in emissions,” co-senior author Professor Ollie Jay, director of the heat and health research incubator in the University of Sydney’s faculty of medicine and health, said in a press release. 

This leads to a conundrum: How can we keep everyone safe from hotter than average temperatures while taking action so that these temperatures don’t rise any higher? 

Thermal Comfort

The new study, published in the Lancet Planetary Health this month, stakes out a sort of compromise position. Instead of replacing air conditioning, people can simply delay the moment at which they switch it on. 

The study revolves around the idea of “thermal comfort.” The Green Education Foundation defines thermal comfort as a state in which someone does not feel either too hot or too cold. 

“As you may guess, thermal comfort has to do with more than the temperature. It can be achieved only when the air temperature, humidity, and the movement of the air are in proper balance with each other,” the site explains. 

This balance is why fans can play a role in keeping a building cool. 

“Fans circulate air, which increases the upper limit of comfort threshold, delaying the turning on of air conditioners in hot weather,” Malik explains to Treehugger. 

In fact, using fans can raise the point at which humans require air conditioning for thermal comfort by 5.4 degrees Fahrenheit (3 degrees Celsius) to 7.2 degrees Fahrenheit (4 degrees Celsius). Because using fans requires around 30 times less energy than cooling 3,178 cubic feet of space with central air conditioning, this strategy has the potential to help reduce greenhouse gas emissions during hot weather. The study authors, therefore, set out to determine exactly how effective this strategy could be.

Fans for Paris

To this end, the study authors modeled energy use and greenhouse gas emissions for five different scenarios: one air-conditioning-only scenario and four scenarios combining fans with air conditioning at different fan airspeeds ranging from 0.3 to 3.9 feet per second (0.1 to 1.2 meters per second). They looked specifically at the potential consequences of fan and air-conditioning use in Australia because it has a long and hot summer, its biggest cities tend to have longer summers than winters, air-conditioning use is on the rise, and the majority of its energy still comes from fossil fuels.  

“We enumerated the effect of residential fans on the thermal comfort threshold, and in turn on air conditioning use and greenhouse gas emissions, through an hourly simulation on a spatially gridded map of Australia,” the study authors explain. 

For each day in 2010, the researchers looked at the maximum temperature for thermal comfort and whether it would be surpassed, requiring air conditioning. They then determined the total number of hours of air conditioning use throughout the year in each scenario and the resulting greenhouse gas emissions. 

They found using fans at a speed of 3.9 feet per second (1.2 meters per second) could reduce air conditioning use in Australia by as much as 76%. Further, they estimated that if every household in Australia used one or two pedestal fans per air-conditioning unit at a speed of 2.6 feet per second (0.8 meters per second), the country could reduce its greenhouse gas emissions from electricity by 0.7%, or its total emissions by 0.4%. Ultimately, using fans to delay air-conditioning use would enable the country to meet 1.2% of its 2030 emissions reduction target under the Paris Agreement. 

However, the study has implications beyond Australia. 

“If our methodology were to be applied across more densely populated and tropical regions (e.g., India, China, or Indonesia), in which the non-fan upper-temperature limit for thermal comfort will be exceeded daily throughout the year, the reductions in energy requirements and associated greenhouse gas emissions from air conditioner with parallel fan use would presumably be much greater,” the study authors write. 

For now, Malik advises anyone who wants to save energy once the temperature rises to first turn on fans at speeds of 2.6 to 3.9 feet per second (0.8 to 1.2 meters per second), and then switch on the air conditioning if it gets uncomfortable. 

Malik has a suggestion for policymakers as well. 

“Consider shifting to renewable sources of electricity, and making people aware of the benefits of using fans,” she says. 

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