Murky science of comfort part 2
Do people in warm climate zones prefer warmer indoor temperatures than people living in cold climate zones?
Tropical nations have consistently used higher temperature threshold to define heat wave compared to their temperate friends. But P O Fanger, a Danish professor who is regarded as the father of comfort science didn’t believe that there was any dissimilarity in how different people were affected by temperatures; a view largely accepted globally.
But all of the research done by Fanger was done in the US and Denmark. [the author] wondered if the same results could be observed in tropical environments.
In the mid 1980s, M R Sharma and Sharafat Ali, scientists at Roorkee-based Central Building Research Institute (CBRI), conducted thermal comfort studies in India in indoor environments typical to India. Sharma and Ali employed Fanger’s seven-point cold-hot scale to gauge people’s comfort perception.
They believed that there was heterogeneity in human response to the same temperature. “The purpose of a thermal comfort index is to estimate the influence of environmental factors…the fact that thermally equivalent conditions produce different subjective sensations due to the level of adaptation, living patterns, eating habits, etc... (is) the reason to look for an index of thermal comfort for Indian subjects,” Sharma and Ali wrote.
Published in 1986, the study found that Indians preferred warmer indoors than what Fanger considered comfortable. It proposed a Tropical Summer Index (TSI) to calculate thermal comfort conditions for Indians. They said that Indians were comfortable between TSI values of 25oC and 30oC with an optimum condition at 27.5oC. The National Building Code of India accepted these albeit with some caveats (more on that in the upcoming blogs).
Two years later, the World Health Organization (WHO)’s European office was to recommend 18-22°C as room temperature in its Healthy Housing guidelines for member states.
Finding of these studies showed people were comfortable beyond comfort limits prescribed in standards but still it wasn’t enough for me to disprove the universality of Fanger’s formula.
But evaluation of the PMV index is not easy as many of the parameters have to be estimated or require sensing modalities that may not be available. For this reason, international standards (ASHRAE Standard 55 and ISO 7730) introduced simplified prescription methodologies to define acceptable limits for thermal comfort.
Since Fanger’s PMV model has no relation with the outdoor climatic conditions, the seasonal variation in the standards’ simplified prescription is merely a function of the assumed change in people’s clothing between summer and winter, and associated relative humidity requirement for different clothing type ...