It's midsummer, and you came to work dressed appropriate for the weather outside, but you had to bring a scarf and sweater to survive a day in the meat locker otherwise known as "the office." Meanwhile, the guy next to you is doing fine. He even has his sleeves rolled up. It's like the building was designed to make you uncomfortable.
And in fact, maybe it was. A new study suggests that the insulation that's supposed to make buildings more energy-efficient doesn't keep them warm enough---that the standards are biased toward the metabolic rates of men, who tend to burn hotter than women.
Is the question of which sex gets to control the AC more complicated than that? Guess. Just guess.
Buildings are meant to do more than just keep out the rain. They're supposed to maintain comfort: Cool enough so you can sleep without sweating through your sheets, warm enough so you don't shiver through your work day. At least, that's the ideal. Finding that sweet spot has advantages way beyond a lower complaint-to-person ratio---the right temperature keeps morale up, HVAC costs down, and a building's carbon footprint small.
To make all that happen, engineers follow standards published by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers. ASHRAE standards determine the amount of insulation a building should have by calculating ambient air temperature, heat radiating off surfaces and devices, humidity, and air speed, along with two human factors: metabolic rate and clothing. These numbers all go into an equation called the Predicted Mean Vote---or PMV. In any given building, the solution to this equation will fall between -3 (for cold) to +3 (for hot). 0 is perfect. The ASHRAE standards recommends that a building have a PMV that solves to plus or minus 0.5.
So, easy-peasy, right? The problem, say researchers in a paper published today in the journal Nature Climate Change, is PMV calculation only uses the standard metabolic rate of dudes.
Metabolism is the biochemistry of turning calories into energy. The rate of a person's metabolism has a lot to do with how much energy that person needs to expend to stay at a comfortable temperature. Women typically have lower metabolisms, so as you'd expect they tend to be cold at a temperature men find comfortable.
The new study found that women doing normal office work have a significantly lower metabolic rate than the one office space engineers use. The authors put 16 women one-by-one into a sealed chamber for 45 minutes while they studied, read, and emailed. You know, office stuff. All the while, the chamber measured oxygen and carbon dioxide---inhalations and exhalations---which are good proxies for metabolic rate. "For example, to burn one molecule of glucose, you require six oxygen molecules and produce six carbon dioxide," says Boris Kingma, who studies thermal comfort at Maastricht University Medical Center in the Netherlands and co-wrote the new paper. After collecting their data and running the numbers, Kingma and his co-author estimated that the ASHRAE standard may overestimate female metabolic rate by up to 35 percent.
Come on! Not only do offices have a glass ceiling, but it lets all the warm air out? "In the last 20 years, a lot of effort has been put into insulation," says Kingma, in order to cut down on artificial heating and cooling. But this work is for naught, because half of the people have to crank on the central air to get comfortable. "What's basically happened is there's now a behavioral aspect that's caused this building to consume more energy than expected," he says.