US HVAC technical association responds to media excitement over thermal comfort, refutes the critcism of its Standard 55 and weighs in on the Dutch researchers who started the argument
ASHRAE, the revered HVAC technical association has responded to the media hubbub over men’s and women’s thermal comfort - and the Dutch researchers who challenged it - with a statement of its position. The Dutch research published yesterday that suggested current air conditioning protocols are based on outdated assumptions implicitly criticised the ASHRAE Standard 55 Thermal Environmental Conditions for Human Occupancy, so ASHRAE has sought to set the record straight - and it has come out fighting.
ASHRAE said in a statement: “Keeping building occupants comfortable while minimising energy use is a balancing act for engineers who design HVAC&R systems and buildings. One way they can achieve this balance is through requirements in a standard from an international technical association. ASHRAE’s Standard 55, specifies the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space. Earlier this week, research that looks at the method used to determine thermal comfort in Standard 55 was published via an article, “Energy Consumption in Buildings and Female Thermal Demand,” in Nature Climate Change.”
The research concluded that the series of factors that make up the determination of Standard 55 included one assumption - male and female metabolic rates, and thus their bodies’ response to temperature changes - that was out of date.
Perhaps not surprisingly, ASHRAE has robustly refuted the charge.
ASHRAE President David Underwood notes that the standard has been continually refined and updated since it was first published in 1966, reflecting changes in the industry and new research as it becomes available. Standard 55 is based on an earlier document developed in 1938 by two predecessor societies of ASHRAE, titled Code for Minimum Requirements for Comfort Air Conditioning.
Mr Underwood said: “The standard continues to focus on defining the range of indoor thermal environmental conditions acceptable to a majority of occupants, while also accommodating an ever increasing variety of design solutions intended to provide comfort and to respect today’s imperative for sustainable buildings”.
ASHRAE has also brought in its heavyweight scientists to defend its workings: Bjarne Olesen, PhD a member of the ASHRAE Board of Directors, former chair of the Standard 55 committee and described by the body as ‘internationally renowned thermal comfort researcher’ said: “The interpretation of the authors regarding the basis for Standard 55 is not correct, the part of the standard they are referring to is the use of the PMV/PPD index. This method is taken from an ISO standard 7730, which has existed since 1982. The basic research for establishing comfort criteria for the indoor environment was made with more than 1,000 subjects with equal amount of women and men.”
Dr Olesen pointed out that this study would not be affected by differences in metabolic rates, as the Dutch researchers claim: “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.”
But more seriously, Dr Olesen contends, the Dutch study is not comparative and thereofore cannot be 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.”
Perhaps most interesting though is Dr Olesen’s conclusion, that it is all down to clothing choice: “The reason why we, in some field studies, find that women prefer higher room temperatures 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.”
Dr Olesen also noted that the Dutch researchers should have consulted other studies and technical guidance: “They should also have looked at the ASHRAE Handbook, Fundamentals, which explains the background for the standard and addresses differences between men and women, young and elderly, etc. with literature references,” he said.
In their paper, researchers Boris Kingma and Wouter van Marken Lichtenbelt conclude that the current standards may overestimate female metabolic rate by up to 35 per cent, saying: “This may cause buildings to be intrinsically non energy-efficient in providing comfort to females. Therefore, we make a case to use actual metabolic rates.”
But in all the brouhaha about standards, it is important not to overlook the crux of their argument, which is that their new biophysical analysis builds up predictions from actual ‘physical and physiological constraints, rather than statistical association to thermal comfort.’ This, they say, will add flexibility to predicting the thermal demand of subpopulations and individuals. Ultimately, an accurate representation of thermal demand of all occupants leads to actual energy consumption predictions and real energy savings of buildings that are designed and operated by the buildings services community.”
If the new analysis can enable HVAC controls specialists to develop protocols that are even more accurately matched to occupant comfort, then the result will be better energy efficiency, and happier occupants - both male and female.