What is the best temperature to keep air conditioning at?

Hello, and welcome to New Scientist’s Business Insights newsletter. I’m Chris Stokel-Walker, and before we talk about this edition’s topic – keeping cool – I wanted to let you know that we are running an AI business event in September – click here for more details.

Summer means one thing for large parts of the world: stiflingly hot workplaces. As this season ramps up in the northern hemisphere, it is an issue that is getting worse as our climate changes, with the first week in July being Earth’s hottest on record. And as we struggle to keep on top of emissions, the temperature is rising even further.

For many people, air conditioning is the only thing that makes working in these conditions tolerable – but unfortunately, it may only be contributing to the problem.

Air conditioning and electric fans account for 20 per cent of all electricity used inside buildings worldwide, according to the International Energy Agency (IEA) – and 10 per cent of all global electricity consumption. Much of that is, of course, generated by burning fossil fuels, which in turn leads to more emissions and further warming. The IEA says there will be 3.7 billion air conditioners operating by 2050, with potentially extraordinary power demands.

Cool it

So, should you be cutting out the air con to save the planet? Not necessarily. If we use smarter, more efficient models, the energy demand from cooling could drop 45 per cent by 2030. Other approaches can help, too. For example, using propane as a refrigerant in air con units could also significantly reduce the extent of global warming, according to Austrian researchers. That is chiefly because when it leaks into the atmosphere, for example when an air con unit is scrapped, propane causes far less warming than current refrigerants.

If you do want to cut your energy use, there are some alternatives. The obvious solution is to close blinds and open windows, letting air through and keeping light out of your workplace. So-called “passive cooling” works wonders, as we have previously explored, but unfortunately many modern offices are designed with windows sealed shut. Fans will simply recirculate air, meaning they are less effective than air conditioning, but may still make you feel cooler, while keeping hydrated will help stave off some of the more damaging impacts of heat. Swap the coffee for cold drinks – not only are cooler beverages better, but the UK’s National Health Service suggests avoiding caffeine in hot weather.

Needs must

But let’s say that things get really unbearable, and opening windows, judiciously using shade and wearing lighter clothes just isn’t cutting it. You need to turn on the air con. There is a whole other debate about what level you should set it at.?

A 2015 study by Boris Kingma at the Netherlands Organisation for Applied Scientific Research and his colleagues suggests that there is a wide gap in the temperatures that men and women feel comfortable with. Women generally find around 24 or 25°C is right for them – 2.5 °C warmer than men.

The reason is down to biology. Gulfs in the average metabolic rate of males and females could contribute to how they feel the cold. A person’s resting metabolic rate is the minimum rate of energy expended while resting. And on average, women have a lower resting metabolic rate than men. Heat is a form of energy, meaning that a lower resting metabolic rate produces less body heat.

One of the main determinants of a person’s metabolic rate is their fat-free body mass: things like bone, muscle and skin, but not fat. And on average, men have that at higher levels than women. This suggests there is no temperature that will keep everyone happy. “The biological variation is so big, it’s easy to conclude there’s no one-size-fits-all solution,” says Kingma.

Even if you find the temperature likely to satisfy most people, there will still be 5 per cent of people who are uncomfortably warm or cold, he says. Thankfully, there is a solution – those people can adjust their clothing, says Kingma.

Here, loosening restrictions on what employees are allowed to wear during the summer may play a part. It is an approach that seems to work in Japan, which, since 2005, has encouraged a “Cool Biz” policy to run from 1 May to 30 September. It suggests businesses don’t turn on their air conditioning until the temperature indoors gets above a sweltering 28°C, but at the same time allows people to ditch the traditional business suit and instead wear short-sleeved shirts when too hot or slip on another layer if too cold. It is a fairly simple approach that could help cut your energy use and keep workers more comfortable.

More information

• Our guide to keeping your house cool during a heatwave can be adapted to businesses – and could prevent getting hot under the collar.
• Feel the mercury rising? Learn about why it is occurring with our explainer on how heatwaves happen.
• Want to learn more about air conditioning? Our review of a book on the subject is worth a look.

Thanks for reading, and do share this newsletter with any colleagues who might find it useful by hitting the repost button.

Chris Stokel-Walker