ASHRAE rebuts new thermal comfort research

ASHRAE responded swiftly to research released Monday suggesting that its method of determining thermal comfort standard relies on a model with a gender-discriminating bias, calling the interpretation incorrect.

In the Nature Climate Change article “Energy consumption in buildings and female thermal demand,” Boris Kingma and Wouter van Marken Lichtenbelt claim that indoor climate regulations are based on an outdated model. The predicted mean vote/percentage people dissatisfied (PMV/PPD) index considers clothing insulation and metabolic rate. The problem, they write, is that the 1960s-era model uses a standard metabolic rate based on a resting 40-year-old male who weighs around 150 pounds.

As a consequence, say Kingma and van Marken Lichtenbelt, the model may overestimate the female metabolic rate by as much as 35 per cent, meaning buildings run according to current standards may prompt women to take energy inefficient steps to find comfort.

Ultimately, the authors advocate using actual metabolic rates to capture the real thermal demand of all occupants. The benefits of this approach, they say, is the ability to predict actual energy consumption and reap real energy savings in buildings.

In a news release Tuesday, Bjarne Olesen, a current ASHRAE board member and former chair of the Standard 55 committee, counters that its use of the PMV/PPD method comes from the ISO/EN standard 7730 established in 1982. What’s more, he says, the research on which indoor comfort criteria is based studied 1,000 subjects, half of whom were men and half of whom were 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,” says Olesen. “So the researchers’ finding of a lower metabolic rate for females will not influence the recommended temperatures in the existing standards.”

He concedes that field studies show women prefer a higher room temperature than men, but he pins the discrepancy on differences in level of clothing.

“Women adapt better their clothing to summer conditions while men are still wearing suit and tie,” says Olesen. “So if the thermostat is set to satisfy men, the women will complain about being too cold.”

Since Standard 55 accounts for the switch to summer clothing, he suggests that, logically, it’s more likely that men would complain of discomfort. ASHRAE regularly updates the standard, first published in 1966, to respond to industry shifts and new research. Essentially, it sets out mixes of indoor thermal environmental and personal factors that will keep a majority of occupants (80 per cent) comfortable in a space.

The PMV/PPD method aside, for Alan Hedge, ASHRAE’s 80-per-cent threshold represents “200 unhappy campers” in a building with 1,000 occupants. “If you look at our standards, they’re based on the assumption that, even if you meet them, you will only have satisfied eight out of 10 people,” says Hedge, a Cornell University professor in the Department of Design and Environmental Analysis.

Hedge has examined the effect of the indoor environment, and specifically temperature, on worker productivity. In 2004, he found in a month-long office-based study that at higher temperatures, typing errors decreased and output increased. The opposite, of lower temperatures leading to increased typing errors and decreased output, was also true. The findings suggested to him that by turning up the thermostat a few notches for greater comfort, employers could save roughly $2 per worker per hour.

The Cornell University professor advocates that office temperatures be set to 25 degrees Celsius in the summer on the basis that it’s easier to cool down than to warm up. For those who find it warm, he recommends strategies such as creating different zones, using desk fans and relaxing dress codes.Hedge cites the Japanese government, which in 2005 did the latter, after it mandated a minimum temperature of 28 degrees Celsius in government buildings during the summer. The move came as part of the country’s effort to meet its Kyoto Protocol commitment, but the program has endured and has even spread to the private sector.

The International Facility Management Association (IFMA) noted in a 2009 study a trend toward FM professionals setting the thermostat higher in the summer and lower in the winter as a way to save money.

The study, “Temperature Wars: Savings vs. Comfort,” looked at too cold/too hot calls, which regularly rank number one when the association surveys its facility management members on the top office complaints among employees. It found that “too cold” was the most common HVAC complaint, with too cold complaints most prevalent in office environments.

Respondents identified personal fans, supplemental clothing and personal heaters as being the top three ways occupants adjust to thermal comfort issues. Respondents reported checking airflow, humidity and temperature in the area of complaint against standards, confirming that the HVAC system is running properly and adjusting thermostats as being the top three ways they addressed comfort issues.

But a lot has changed since this study, says Kate Lister, a member of IFMA’s Workplace Evolutionaries group and president of Global Workplace Analytics. This shifting landscape is defined by more open-concept offices and less occupied buildings, more relaxed dress standards and less metabolic activity.

Lister echoes the Nature Climate Change article, saying that while individual solutions such as fans and heaters may help, they may also counteract the steps companies are taking the reduce energy use and its associated costs. But, she adds, the idea of personal control is important.

“There’s one very large employer that I know that put fake thermostats on the walls and people felt warmer,” says Lister, “because they felt like they were able to control it.”

Short of using fake thermostats, she offers other ways of extending a measure of thermal control to employees, such as letting people who find the office cold sit close to the heat source. “I don’t think they’re [facility management professionals] intentionally over-cooling, but there’s an awful lot that goes into it — from the individual person to all of the factors that go into how we perceive temperature,” says Lister.

“It’s not just temperature, but it’s radiant temperature; it’s air speed, fans; how much air’s circulating, how much humidity’s in the air; people’s metabolic rate; what they’re wearing; so it’s really hard to make everybody happy.”

Source: M.Ervin, 2015, CFM&D, 6 August: