Keeping cool in high temperatures is often not easy, even more so when trying to do so sustainably. Scientists have now looked at both human comfort and the cost-benefit analysis of using fans and air conditioning (AC) and discovered ways to stay cool and still massively reduce greenhouse gas emissions.

The US currently uses as much electricity for air conditioning each year as the UK does as a whole. According to the International Energy Agency, air conditioning and electric fans account for a fifth of the total electricity in buildings around the world, or 10 percent of all global electricity consumption, and as the world warms, this is set to rise.

In a paper published in The Lancet Planetary Health, researchers led by a team from the University of Sydney (US) found that by combining indoor fans and AC, it is possible to still maintain human comfort indoors in hot weather while reducing reliance on AC. In particular, the use of fans can expand the indoor thermal threshold – the level before it becomes uncomfortable for humans – by up to 4°C (7.2°F) while using the AC less reduces electricity consumption. If this approach was used in Australia, the yearly emissions and cost associated with cooling indoor spaces could be cut by 70 percent.

"The latest 'IPCC Sixth Assessment Report on Mitigation of Climate Change' emphasizes the need for adoption of low-emission lifestyles, including cooling choices for thermal comfort," said lead author Dr Arunima Malik, Senior Lecturer in Sustainability at the School of Physics and Business School at US said in a statement.

"Our study confirms that low-cost solutions such as fans have the potential to contribute emission reductions for meeting the goals of the Paris Agreement."

The model they created to compare energy use and associated emissions employed five different scenarios. One used just air conditioning, and the other four had fans at different speeds and the use of AC only when the temperature got too high for comfort.

By modeling temperature data for the whole of Australia, they found the scenario with the fastest fan creating airspeed flows of 1.2 meters per second had a reduction of 76 percent in energy usage.

"To carry out this calculation we needed to process hourly temperature data for an entire year, for the entire continent on a 150,000-cell raster grid. We were able to do this using supercomputers," explained co-senior author Professor Manfred Lenzen of the School of Physics.

If the electricity produced is from just fossil fuel plants, the switch to fan + AC could save 3,883 kilotonnes of carbon dioxide per year, dropping Australia's annual associated greenhouse gas emissions from 5,091 kilotonnes to 1,208 kilotonnes. However, it's still a small fraction of what will have to be addressed on the road to net zero.

"We know that curbing greenhouse gas emissions is the only way we will limit future global warming," explained co-senior author Professor Ollie Jay, Director of the Heat and Health Research Incubator in the Faculty of Medicine and Health at US.

"By increasing indoor air movement with fans, you can feel the same at a higher temperature as you will do at a lower temperature using an air conditioning unit. This is a really easy thing that most people can do now to help reduce the prodigious emissions associated with cooling homes and indoor spaces in Australia."