This story has been updated from its original publication to include comments from ASHRAE.
Energy benchmarking is challenging enough for a building owner or facility manager. A new study, published yesterday in the journal Nature Climate Change, adds another layer to their dilemma—one that may not be a surprise to anyone who's ever stored a sweater, scarf, or space heater at their desks. Maintaining the right temperature in an office isn’t just about keeping workers content, productive, and present. It’s also a factor in fulfilling a building’s energy-performance expectations, which often fall to the wayside with lax post-occupancy reporting and human interventions such as cracking a window or adding a floor of servers. And for some, it has a battle-of-the-sexes edge, with women complaining that a space is too cold while the men don't seem to notice. (We'll let you be the judge of your own office.)
In their report titled "Energy Consumption in Buildings and Female Thermal Demand," the authors, who hail from Maastricht University in the Netherlands, propose an alternative method for determining whether an occupant will sweat or shiver through the workday. Typically, building engineers in the U.S. and elsewhere use ASHRAE’s Standard 55 to establish thermal comfort, which uses an equation that gauges the outdoor air temperature, thermal radiation, humidity, and air speed, as well as the PMV/PPD index from the 1982 ISO/EN standard 7730 that considers occupants' clothing insulation and metabolic rate.
That last variable is where the researchers think the current practice gets it wrong. They reference a go-to value for metabolic rate that was determined in the 1960s and that assumes a 40-year-old, 155-pound male—a member of the population who the authors say tends to expend more energy in a resting state than most women and seniors, for example. The guidelines also assume that, for business environments, men largely wear the same amount of clothing year-round while women are more apt to adapt their wardrobe to the season.
To inform their observation that members of a mixed-sex group could experience environmental conditions differently in the same space, the researchers measured the metabolic rate of 16 women performing light office work in a climate-controlled hub. They found their rates to be lower than the original, male-centric model, confirming their gendered hypothesis. However, the report doesn't address the participants' body composition.
In a press release Tuesday, ASHRAE officials called the authors' interpretation of Standard 55 incorrect, noting that research for establishing indoor comfort criteria included more than 1,000 people, with and equal number of men and women.
"In the main studies, where they did the same sedentary work and wore the same type of clothing, there were no differences between the preferred temperature for men and women," said Bjarne Olesen, an ASHRAE board member and former chair of the Standard 55 committee. "So the researchers' finding of a lower metabolic rate for females will not influence the recommended temperatures in the existing standard."
The researchers' methods and results raise the question of whether thermal comfort can be so cut-and-dry, or if it is indeed a nuanced equation of body types and personal preferences.
In an interview with Wired, the researchers acknowledged that their report wasn’t comprehensive and didn't intend to be. For one thing, they didn’t observe a group of men under the same conditions. And the women in the study, numbering just 16, were clad in T-shirts and sweatpants, which have neither the insulating effect of a polyester pantsuit nor the breeziness of a cotton sundress and sandals.
Clothing insulation, Olesen says, is continually the key factor in the thermal comfort debate. "The reason why we, in some field studies, find that women prefer higher room temperature than men is attributed to the level of clothing. Women adapt better their clothing to summer conditions while men are still wearing [a] suit and tie. ... In the standard, this adaption of clothing to summer is taken into account so if the standard is followed the women would be satisfied, but maybe not the men."
Understanding the varied thermal demands of individuals among members of the broader AEC industry has led to the development of products and systems that offer occupants more control over their internal environment regardless of what they're wearing—with user-adjustable lighting, occupancy sensors, and motion-activated HVAC systems among them. Still, developing a more representative thermal comfort metric can in turn lower the prediction bias in building energy use and make for smarter structures that perform as intended.