Want to use less air conditioning? Just turn on a fan

Moving air feels cooler than stagnant air and fans use far less energy than AC.

Scientists say we can use about 70% less air conditioning and achieve the same comfort level by increasing air flow with ordinary electric fans. (HT PHOTO)

Earlier this year, the UK attempted to go coal-free. But an increased need for air conditioning forced the usually temperate country to reverse itself and restart an old coal-fired power plant — after only 46 days.

This is a cycle that's likely to get more vicious as hotter weather leads to more air conditioning, which exacerbates both global warming and urban heat islands. But maybe we don't need nearly as much AC as we think.

The answer isn't to suffer in pools of sweat but to use scientific knowledge about human physiology to stay just as cool with a lot less AC. Scientists say we can use about 70% less air conditioning and achieve the same comfort level by increasing air flow with ordinary electric fans.

This makes intuitive sense, as most of us feel uncomfortable in a stuffy room at 80F, but deliciously comfortable at that same temperature in a breezy park or outdoor café.

Researchers in Australia and the US have shown how this works and calculated how it could reduce air conditioning costs.

Ollie Jay, director of the Heat and Health Research Incubator at the University of Sydney, says you can measure comfort scientifically with a seven-point scale. Zero is neutral, -1 is slightly cool and 1 is slightly warm. While comfort levels vary from one person to the next, the percent of people who report being uncomfortable increases as the scale gets further from zero.

Using this scale, Jay and his colleagues showed that fans can make 82 feel just as nice as 72 while using about one-thirtieth the energy. That could have big implications for offices and hotels in the US.

Jay pointed to an article that just ran in The New York Times touting a new kind of white paint that could, in theory, reflect more sunlight off roofs and save 40% in air conditioning costs — once it's available. That's great, and people in hot climates should use it when it comes on the market. But in the meantime, we could cut AC costs by as much as 70% if we just used fans.

In Australia, AC makes up most of people's energy bills in the summer, and that's increasingly becoming the case elsewhere. Reducing summer AC use would also decrease peak demand and avoid the disruption and inconvenience of blackouts or rolling brown-outs.

Sure, electric fans also require electricity, which is still primarily generated from burning fossil fuels. But fans require much less energy than air conditioning. Overall, Jay said, said, using fans to reduce reliance on AC would have an even bigger impact on greenhouse gas emissions than switching from incandescent to LED lighting.

There are two reasons airflow matters so much. One is that the body cools itself by sending blood from the core to the skin, and airflow helps that warmth dissipate into the atmosphere. Second, airflow makes it much easier for sweat to evaporate. (It's not the sweating that cools you, but the evaporation of the sweat.)

Often, it's not the heat but the humidity that makes us uncomfortable — sweat vanishes faster in drier air. Yes, AC takes moisture out of the air, but airflow can have a similar effect. Fans would at least let us turn the AC to a higher temperature.

Clothes, of course, play a role too. Tight, heavy garments can block the benefits of airflow. Western cultures where “professional” dress means trousers, a suit jacket, or nylons year-round should loosen up. In many places around the world, it's common to wear less clothing in warm conditions. Others favor loose-fitting, lightweight, flowing garments that allow air to move around the body.

Scientists are now figuring out how to make air conditioning systems smarter by incorporating the science of comfort and air flow. Jay and his colleagues have a project under review now with the Australian Research Council to develop an algorithm that calculates the optimal airflow at different temperatures. “Then you can have a product where the fan is talking to the air conditioning unit and they're working in concert with each other.”

The Economist Intelligence Unit has predicted vast growth in the market for cooling, while also warning that cooling devices are a major contributor to climate change. Smart ways to use less air conditioning now could ease this vicious cycle.