We cannot wish away air-conditioning in today’s world, but we can be reasonable in choosing where, when and how to resort to the energy guzzlers
Thermal comfort standard needs to be embedded in the cultural and meteorological context. credit: author In a battle to estimate what is comfortable room temperature, I and my New York roommate reluctantly settled on 23.5°C (read about the difference in my first blog). This temperature seems close to the power ministry’s recent advisory to set the default temperature setting in air-conditioners at 24°C but the reasoning is different.
Why did we choose 23.5°C?
Our varying perception of what is comfortable was manipulated by the Heat Ventilating Air Conditioning (HVAC) industry. Standards set by an international body since late 1970s acclimatised US millennials like my roommate to 21.5 ± 1.5°C temperature band.
Meanwhile, millennials in India like me who grew up in the absence of air-conditioning had a wider and warmer perception of what was comfortable temperature. According to the National Building Code of India, the comfort range for people used to naturally ventilated buildings is 19-34°C.
We settled for 23.5°C because as it would have been insane of me to expect 27-28°C indoor temperature in New York City where the daily mean temperature in their hottest month is just 24.7°C. Further, I was getting used to an overall colder climate and eventually got comfortable with lower temperatures both indoors and outdoors.
Migration and adaptability to new environments
Humans’ ability to get used to new environments made migration possible and successful. This exchange has been going on even before invention of air-conditioning. Many Swedes live and work in India even when Sweden’s official definition of heat wave is 25°C. On the other hand, according to Indian standard, comfortable indoors can get as high as 36°C depending upon outdoor conditioners and the type of building.
A 1993 study published by Abdulshukor of University of London found that Malaysians living in Malaysia and England had considerable difference in comfort temperature preference. Those in Malaysia and London had neutral temperatures (value corresponding to zero on PMV scale implying optimum comfort) of 28.7°C and 25.7°C respectively. This indicated that comfort expectations can change between two groups that are ethnically same but have been living in climatically different regions.
The science is clear.
If one chooses to live in an indoor environment controlled at 21.5 ± 1.5°C, after an initial phase of discomfort they will be acclimatised to this temperature eventually. But the reverse of this is also true. One can have adapted to 27.5 ± 2.5°C if they were to live in this temperature band long enough.
Today technology enables both but at a hugely varying cost to the environment. The question is how to find an optimum balance between comfort and environment.
Building for climate
Buildings are being constructed to reach a thermal equilibrium with their surroundings. Every degree increase in the difference between the buildings’ internal temperature and the outdoor climate has a heavy energy/environmental penalty attached. As a society we have to be mindful of it.
Institutions across the globe are taking measure to fix the refrigerator syndrome inflicted on us by the HVAC industry. As part of its Standard Operating Efficiency Procedures, California mandates that “the temperature set point should be no higher than 68°F (20°C) in winter and no lower than 78°F (25.6°C) in summer, unless such a temperature in a particular job or occupation may expose employees to a health and safety risk.”
Similarly in even colder regions, Harvard University introduced a temperature policy mandating set points range from 74-78°F (23.3-25.6°C) during the summer. London School of Economics has mandated 24 ± 1°C at all its facilities for summer and their website sternly says, “This provides for an optimum comfort vs. environmental benefit. This is in accordance with the LSE school policy, health and safety requirements and environmental recommendations. Therefore, we cannot accommodate personal preferences that fall outside the above parameters.”
Japan’s environment ministry has been running a successful cool business campaign since 2005, seeking commercial establishments to voluntarily set their indoor temperature at 28°C during summer and asking people to ditch formal dressing for more comfortable and season appropriate clothing.
Following the global examples, India issued an advisory setting default temperature of air conditions at 24°C. Although a positive move, 24°C is an arbitrarily chosen benchmark that does not evaluate optimum comfort vs. environmental benefit. It is likely that resistance from the HVAC industry lowered the temperature from the original 27°C. Further, India is too climatically diverse a nation to have a uniform national comfort temperature.
For instance, Delhi and Shimla have the daily mean temperature of 33.4°C and 19.5°C respectively for their hottest month, imposing same indoor condition on both lacks nuance.
A new approach to comfort
There are four environmental variables for thermal comfort—temperature, humidity, heat radiation and air movement—and two human variables—clothing and an individual’s metabolism rate. There is a need to stop looking at these variables as whim of an individual. Instead treat thermal comfort as endemic to the meteorology (environmental variables) and culture (human variables) of a given geography.
Introducing adaptive thermal comfort model has found partial acceptance in the standards as well but is limited by class bias.
According to ISO 7730, “Ethnic, national or geographical differences need also to be taken into account when considering non-conditioned spaces.” There is no need to include “ethnic” and “non-conditioned” in the standard. People adapt to the local climate even if they aren’t native to it due to natural process of acclimatisation. Thermal comfort standard needs to be embedded in the cultural and meteorological context where it needs to be applied. It needs to be balanced in a way that provides optimum comfort and environmental benefit while being agnostic to building typologies and class of its occupant. Individual buildings can be given reasonable freedom to locate themselves on this thermal comfort bandwidth and to choose means to deliver it.
People should also be educated to dress according to climate. For instance, in my process to adjust to 23.5°C, I had to forgo my Indian habit of being barefoot at home, while my roommate had to stop wearing a jacket indoors.
We cannot wish away air-conditioning or any other means of delivering thermal comfort in today’s world. Cities have grown in a fashion that most buildings won’t be able to employ just passive architectural systems even if they want to achieve thermally livable conditions. But we can be reasonable in choosing where, when and how to resort to these energy guzzlers. We can try to avoid getting addicted to unnaturally narrow prescription promoted by the HVAC industry.
(This is the last blog in a series on the science of comfort. See below for previous blogs).
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