Keeping cool, sustainably

A recent study led by the University of Sydney has found that when indoor electric fans are used more often, this allows people to decrease their air conditioner use without changing how hot they feel — demonstrating a simple but effective way to reduce future energy use and greenhouse gas emissions.

The study found that, in terms of reducing greenhouse emissions, the total benefit of using fans to reduce overall air conditioner use surpassed even the switch from incandescent light bulbs to LEDs. According to the study’s modelling, slightly increasing indoor air movement by using indoor fans can reduce electricity consumption — and the associated cost of cooling indoor spaces with air conditioners throughout a typical Australian year — by approximately 70%.

The study was conducted by a team of experts from the University of Sydney alongside colleagues from Monash University, the University of Newcastle and Radboud University Medical Center, based in the Netherlands. Their findings have been published in The Lancet Planetary Health.

The team’s work shows how making the switch to widespread indoor fan use can potentially reduce energy demand and greenhouse gas emissions. The key lies in the fundamental way electric fans operate to cool the human body compared to air conditioners. Electric fans generate higher air speeds across the skin surface to achieve a higher heat loss despite warmer temperatures, while air conditioners by themselves lower temperatures with little air movement.

“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,” said co-senior author Professor Ollie Jay, Director of the Heat and Health Research Incubator in the Faculty of Medicine and Health.

“The latest IPCC Sixth Assessment Report on Mitigation of Climate Change emphasises the need for adoption of low-emission lifestyles, including cooling choices for thermal comfort.”

“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,” said lead author Dr Arunima Malik, Senior Lecturer in Sustainability at the School of Physics and Business School.

The researchers analysed energy use and associated greenhouse gas emissions by modelling five scenarios with different combinations of fan and air conditioner use. After logging data on the impact of the fans on human comfort levels, the number of hours above the thermal comfort limit were calculated to determine air conditioner usage, and associated energy use and greenhouse gas emissions.

“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,” said co-senior author Professor Manfred Lenzen of the School of Physics.

They found that operating fans with air speeds of 1.2 m/s with occasional air conditioner use, compared with air conditioners alone, resulted in a 76% reduction in energy use (from 5592 to 1344 GWh) and associated greenhouse gas emissions (5091 to 1208 kilotonnes).

“We know that curbing greenhouse gas emissions is the only way we will limit future global warming,” Jay said.

“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.”

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