Are women feeling colder than men in air-conditioning buildings?

Bjarne W. Olesen

Intl. Centre for Indoor Environment and Energy

Technical University of Denmark

Denmark

bwo@byg.dtu.dk

Introduction

Recently the international media like in USA, Canada, UK, Denmark, Germany etc. has been discussing the issue of differences between men and women regarding thermal comfort and the preferred room temperature. This presentation will discuss the issue of thermal comfort and the existing knowledge on the influence of gender.

Results

The Dutch study

In their paper, researchers Boris Kingma and Wouter van MarkenLichtenbelt (2015) state, “Indoor climate regulations are based on an empirical thermal comfort model that was developed in the 1960s. Standard values for one of its primary variables—metabolic rate—are based on an average male, and may overestimate female metabolic rate by up to 35 percent”. According to their experiment with 16 females performing sedentary work, they measured a significant lower metabolic rate for women than the metabolic rate for a “standard man”, which they found in literature. This will, according to the authors, result in a higher preferred room temperature for women.

The existing literature

Fanger (1982), Fanger and Langkilde (1975), and Nevins et al. (1966) used equal numbers of male and female subjects, so comfort conditions for the two sexes can be compared. The experiments show that men and women prefer almost the same thermal environments. Women’s skin temperature and evaporative loss are slightly lower than those for men, and this balances the somewhat lower metabolism of women. The reason that women often prefer higher ambient temperatures than men may be partly explained by the lighter clothing normally worn by women.

Subjects were tested under the following standardized conditions: sedentary activity: light clothing 0.6 clo, rel. velocity <0.1 m/s, rel. humidity 50%, mean radiant temperature = air temperature.

Figure 1. Preferred ambient temperatures (air ~operative temperature) in laboratory test with the same sedentary activity level (1-1.1met) and the same clothing (~0.6 clo) for all subjects.

Looking at the existing literature (Karjalainen 2011) clearly more than half of the laboratory and field studies have found that females express more dissatisfaction than males in the same thermal environments. A Meta-analysis shows that females are more likely than males to express thermal dissatisfaction (ratio: 1.74, 95% confidence interval: 1.61–1.89). Females are more sensitive than males to a deviation from an optimal temperature and express more dissatisfaction, especially in cooler conditions.

However, most studies found no significant difference in neutral temperatures between the genders as also shown in the basic studies in the table.

The existing standards

Existing international standards like ISO EN7730, EN 15251 and ASHRAE 55 are based on the same basic studies described above. These standards do not specify different room temperatures for women and men when doing the same work and dressed in similar clothing.

Contrary to what has been suggested, these standards are not devised exclusively for men.  They are based on extensive laboratory studies of both men and women wearing the same clothing, engaged in the same activity, and exposed to a wide variety of thermal conditions (air temperature, surface temperature, humidity and air movement).  Metabolic heat production was simply a proxy for the kind of activity.  And while it is one of many variables used in an empirical formula, it is not an input to a heat balance equation, as one might find in a thermo-physiological model (which exists, but was not the basis for the standards)

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, it was cooler even than the temperature set in the winter to about 23.4°C.

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. So the researchers’ finding of a lower metabolic rate for females will not influence the recommended temperatures in the existing standards. Also their study is not conclusive. They only studied 16 females at a sedentary activity. They should also have studied 16 men at the same activity to be able to compare. 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 suit and tie. So if the thermostat is set to satisfy the men, the women will complain about being too cold. 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

Why are air-conditioned buildings often too cold?

There can be many reasons why buildings are often too cold. Here are some possible explanations:

·  Some buildings overcool air to reduce humidity.

·  Some Air-Conditioning systems do not work well under part load conditions

·  People think the air conditioning isn’t working if it’s not a little cold

·  Being able to make people feel cold in the summer is a sign of power and prestige

·  Men stuffed into heavy suits may control the thermostat

·  Energy is too cheap giving people little incentive to save on the air conditioning

Conclusions

The extensive studies, which form the basis for existing international standards for the thermal environment (ANSI/ASHRAE Standard 55, ISO EN 7730, EN 15251) included equal amount of male and female subjects and no difference in preference was observed. Despite this fact, we may often find women are colder during summer time in air conditioned offices. This can however, in most cases be attributed to the difference in clothing level between men and women. It seems the thermostat settings in summer in air-conditioned buildings are often too low and below the recommended range in existing standards.

References

ASHRAE 2013. Thermal Environmental Conditions for Human Occupancy ASHRAE standard 55-2013.

EN 15251, Indoor environmental input parameters for design and assessment of energy performance of buildings—addressing indoor air quality, thermal environment, lighting and acoustics. CEN, 2007.

EN ISO 7730, Moderate thermal environments—analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort, 2005.

Fanger, P.O., and G. Langkilde. 1975. Inter-individual differences in ambient temperature preferred by seated persons. ASHRAE Transactions 81(2): 140-147.

Fanger, P.O. 1982. Thermal Comfort. Robert E. Krieger, Malabar, FL.

Karjalainen 2011 - Thermal comfort and gender- a literature review. Indoor Air, 2011.

Kingma, B. and van MarkenLichtenbelt, Wouter.2015.  Energy consumption in buildings and female thermal demand. Nature climate change, Letters, August 3, 2015.

Nevins, R.G., F.H. Rohles, Jr., W.E. Springer, and A.M. Feyerherm. 1966. Temperature-humidity chart for thermal comfort of seated persons. ASHRAE Transactions 72(1):28.