Designing an environmentally friendly building means taking into account the temperature that building occupants will want. If this estimate is incorrect, the occupants will spend their lives fiddling with the thermostat and opening the windows, lowering the energy efficiency of the building.
As you can imagine, to work out the right temperature for a building, we need to know what temperature will be comfortable for most people. This might sound easy, but currently we're getting it all wrong because, like so many things, we’re basing the "right" temperature on the assumption that all of humanity is an average-weight, middle-aged man.
A paper in today’s issue of the journal Nature Climate Change argues that the widely used standard for calculating building temperatures is based on outdated assumptions about human metabolic rates. Improving our calculations would not only make the world a little less unfair, but it could also result in more energy-efficient building designs, the authors write.
The widely used standard in setting a comfortable ambient temperature in a building is the predicted mean vote (PMV). It’s an equation that estimates whether a large group of people will vote whether the temperature is neutral, hot, or cold on a scale that runs from -3.0 to 3.0. The gold standard for a building is to have an ambient temperature that falls between -0.5 and 0.5, right about neutral.
To calculate the PMV requires consideration of things like the structural heat loss and efficiency of its air circulation. But one of the variables that needs to be included is the metabolic rate of a building’s occupants. According to Boris Kingma and Wouter van Marken Lichtenbelt, the authors of today's paper, the standard unit of metabolic rate is “set by convention based on the resting metabolic rate of only one 70kg, 40-year-old male.”
This was not such a major problem in the 1960s, when most of the people in an office building would have been closer to this profile. These days, it's more of an issue, because the assumption doesn’t take into account increases in gender diversity, body type diversity, and age diversity. It’s also more of a concern as it becomes ever more essential for buildings to be energy-efficient.
Kingma and van Marken Lichtenbelt wanted to see just how much the current standard could be overestimating the metabolic rate of young adult females performing office work. Based on what can only be called a tiny pilot experiment (see below), they calculated that the currently used measure might overestimate metabolic rate for this group by 20 to 32 percent.
Unfortunately, they used an absolutely tiny sample size for this test: only 16 women. This means that it’s impossible to say whether the current average metabolism is definitely incorrect. Even just comparing the 16 women to 16 men would have been better—if the men had deviated from the established standard, that would have been interesting—but still probably wouldn’t have told us very much. The PMV is based on average votes across very large groups of people, and differences get smoothed out in very large numbers, so this particular test doesn't really tell us that the PMV's assumptions are wrong.
Nevertheless, this isn’t the only research suggesting that temperature affects women differently: past research has shown that women are both uncomfortably hot and uncomfortably cold more than men, writes Joost van Hoof in an accompanying article in Nature Climate Change. This suggests greater sensitivity to temperature swings and a smaller range of comfort.
It’s also not just about women: people with different body types will perceive temperature in different ways, because fat and lean layers create different heat loss profiles. Age adds another complicating factor, too.
It’s probably necessary to re-examine the assumed human metabolism and adjust it to fit modern populations, rather than assuming it’s held firmly in place for the last half-century. That said, it will take a lot more evidence to convince people in the construction industry that the temperature standards need a rethink, writes van Hoof.
Recalibrating standards to take into account the slightly higher temperatures required by women (assuming other members of a more diverse office population don’t swing in the other direction) would mean that buildings could save on cooling costs—costs that will continue rising and have an increasing impact as Earth warms. It’s not clear whether this will outweigh the cost of raised heating requirements in the winter, but it's probably safe to assume that buildings designed with accurate temperatures in mind will ultimately be more energy-efficient.
This post originated on Ars Technica UK