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A peek behind the science curtain

Bethany Brookshire

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Building standards aren’t to blame for chilly offices

woman bundled up in scarf adjusting thermostat

A recent study calculated women’s resting metabolic rate and preferred office temperatures. But to figure out why women tend to be cold in the office, look not to science but to the person who controls the thermostat.

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I remember the summer of 2004 as the “cold summer.” It wasn’t unseasonably cool — or at least, not outdoors. I was working as a temp receptionist in a law firm. The men in suits around me seemed perfectly comfortable with the air conditioning blasting cold air into the office, while I shivered in my skirt and sweater, slurped hot tea and tried not to go torpid. Every day, I spent my carefully allotted 30-minute lunch on a bench in the sun, trying desperately to soak the heat in like a lizard.

My office gig may have been more than a decade ago, but it seems that no one has yet turned up the temperature. Women have been shivering in the office for years, and, as last week’s headlines said, science is on it. The stories stemmed from a new study showing that women have slightly lower resting metabolic rates than men, and thus have a higher temperature at which they are most comfortable. The study’s authors contend that current methods for designing air conditioning systems do not take this metabolic difference into account. The study argues for changes in air conditioning design standards, but differences in resting metabolic rate have little to do with why we women are cold in the office. It has far more to do with who sets the thermostat than with metabolism differences or system design.

Buildings are generally designed to meet standard guidelines for heating and cooling. The building’s ability to keep us cool is based on a series of complex equations that take into account humidity, air temperature, airflow, radiant temperature and the metabolism of the humans theoretically present.

But these complex equations are based on a single metabolic average, says Boris Kingma, a biophysicist at Maastricht University Medical Center in the Netherlands — the average metabolic rate of a 40-year-old man who weighs 70 kilograms, or about 154 pounds. If this man seems a bit on the thin side, it’s because he’s an average, a single number representing the metabolic rates of many people. This hypothetical guy has a resting metabolic rate of 58 watts per square meter. This number goes into the calculations whenconsidering the heating and cooling demands of a building when people are in it.

“If you design a building and you say it’s for 1,000 people, you’re [currently] calculating a thermal load based on 1,000 men,” Kingma says. “You’re computing with an internal load higher than it should be.”

Kingma, who studies how mild temperature changes affect our comfort level and productivity, thought that using this number could result in energy inefficiency in a building, especially if there are a lot of women present who might have lower metabolic rates.

To show this, he measured the thermal states of 16 young women wearing socks, underwear, sweatpants and t-shirts as they sat in a room doing light office work. As they worked, the temperature fluctuated up and down, and sensors measured the women’s skin temperature and heat production and calculated their metabolic rate.

The women had an average resting metabolic rate of 48 watts per square meter, significantly lower than the average used to calculate heating and cooling needs in buildings. Women are also comfortable at higher temperatures — between 23° and 26° Celsius (or 74° and 79° Fahrenheit) — than those previously calculated.  Kingma and coauthor Wouter van Marken Litchenbelt reported their findings August 3 in Nature Climate Change.

“It’s interesting to revisit the basis of these [calculations],” says Brendan Owens, an engineer at the United States Green Building Council. “Exposing the habitation patterns of people in buildings and discussing those is important. Your behavior in a space has a profound impact on energy use.” Kingma argues that these differences should be taken into account when building heating and cooling systems.

So this is why you’re in that office Snuggie, right? The standards are only taking men into account! Well, not quite.

“We are all looking for a reason why women are colder in office buildings than men,” says Gail Brager, a building scientist at the University of California, Berkeley. “But this well-done study does not offer us that answer.” Brager explains that heating and cooling standards are not really based on metabolic rate. Instead, they are based on subjective ratings of men and women, wearing the same clothes and doing the same tasks. In those studies, there is far more variability between any two people than there is between the sexes in terms of what temperature they prefer. The 70-kilogram, 40-year-old man’s metabolic rate is still factored in, but Brager says it’s not a very important factor. Even if more metabolic variation was included, she explains, “I wouldn’t expect the model to be different.”

The standards control how a building’s heating and cooling systems should be built, and they could possibly be built more efficiently if the calculations were made with more than one data point, rather than a single metabolic average. But there are no standards controlling who sets the thermostat. “Yes, it’s probably too cold,” says Bjarne Olesen, a scientist studying the indoor environment at the Technical University of Denmark in Lyngby. “But it’s not because the standards say it should be so cold.”

So who is keeping you so cold? Whoever sets the thermostat, not whoever designed the building. A 2009 study in the journal Indoor Air examined temperatures in 100 office buildings and found the average indoor air temperature in the summer was not only cooler than recommended and cooler than the established comfort zone for office workers (about 22.9° C or 73° F), it was cooler even than the temperature set in the winter (about 23.4° C or 74° F). 

There are several reasons buildings end up too cool, Olesen explains. Some buildings overcool air to reduce humidity. Men stuffed into heavy suits may play a role, but psychology might as well. “People think the air conditioning isn’t working if it’s not a little cold,” he notes. The final factor? “Energy, especially in the United States, is too cheap,” he says, giving people little incentive to save on the air conditioning.

“Setting the thermostats is human behavior,” Kingma says. “People don’t look at any standards or recommendations. They just want to feel cool.” And, he notes, “the American problem is that a lot of female workers are uncomfortable, you don’t need my paper to know that.”

Even though our shivers come down to basic human behavior, Kingma, Brager and Olesen all hope that the media coverage of the latest paper might get people to, well, cool it on the air conditioning. “The good thing is that we’re getting focus on the problem,” says Olesen. “We can improve comfort and save energy.” If a scientific paper can get people to turn up the thermostat, take off the suit jacket and stop shivering, he says, “it’s a net good.” 

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