In 2050, those over 65 will represent 66% of the world’s population. To improve their quality of life in cities, thermal comfort is one of the most influential factors, both indoors and outdoors. Taking this data as a starting point, María Teresa Baquero Larriva and Ester Higueras García addressed a deep systematic review of the literature that identified differences in thermal comfort temperature between older adults and other age groups, as well as determining the factors that influence them, focusing on studies published between 2000-2018. The results, recently shared by the Spanish Journal of Geriatrics and Gerontology demonstrate that, for physiological, psychological and physical reasons, there are differences between 0.2 and 4 ° C. However, published studies are heterogeneous in terms of methodologies and sample size. Likewise, few determine the comfort temperature range for older people in a given climate, evidencing the opportunity for future lines of research.
According to the predictions, in southern Europe, the temperature will increase intensely. Climate-related diseases produce more than 150,000 deaths each year, where children and the elderly are the most vulnerable groups. The climatic extremes increase the risk of the elderly to have pneumonia, cardiac arrest, dehydration, hypothermia and hyperthermia, since with the age the muscular strength, the sweating, the capacity to transport heat to the skin, the levels of hydration are reduced, vascular reactivity and cardiovascular stability. During the heatwave of 2003, in England, the mortality of those over 75 years exceeded 33%, while in those under 13.5%.
Effect of physiological changes
The physiological changes that occur in the human body with age and that affect the thermal sensitivity of the elderly have been evidenced, decrease their ability to detect and respond to temperature changes, making them vulnerable to thermal extremes. To this must be added the effects of the medication that can further alter its thermal regulation, since most of the elderly suffer from chronic diseases such as hypertension, diabetes and cardiovascular diseases.
Although in 1966, ASHRAE26 suggested that the optimum indoor temperature for people over 40 should be 0.5 °C major, for the first studies on this subject there were no significant differences between older adults and other people. However, 43 of the researches analyzed in this study have found them, although without reaching a consensus. On the one hand, 10 authors conclude that older people are more sensitive to high temperatures and prefer lower temperatures than young adults, as in the case of Bills et al.42 in Adelaide, Australia, where older people expressed the desire to ” be colder “when the thermal conditions were within the comfort zone established by ASHRAE Standard 55. In another case, in an analysis of outer space use in Athens by Nikolopoulou and on the other hand, 18 of the selected studies,
Effect of psychological and physical thermal adaptation
Factors such as origin, expectation, experience, exposure time and attitude influence this and the subjective comfort of each person. Psychological factors help to understand why people perceive the same environment differently.
Personal attitude is another influential psychological factor, according to Knez and Thorsson, there are two types of people, those of “open-air” who find pleasure in nature and the “urban” that prefer the city, indicating the influence of emotions on the psychological perception of the place, in one of his studies Knez et al. they found that thermal comfort increases with age for those in the first group, while decreasing for those in the second.
Physical adaptation, on the other hand, occurs through behavior. Either by manipulating elements such as windows and air conditioners in indoor environments or by adjusting the level of clothing (clo). Some studies carried out indoors show that older people tend to manipulate air conditioning devices less and that their adaptive behavior is preferably the adjustment of the level of clothing that is generally higher in the elderly. Hwang and Chen found that older adults required an additional 0.1 clo for every 1.4 ° C, which lowered the temperature while younger ones required the same level of additional clothing for every 2 ° C less temperature.
Differences in thermal comfort temperature for older adults
Although older adults have different characteristics, a thermal comfort assessment index that considers them has not been established, since everyone tries to establish comfort conditions by applying them to the general user, such as those used in the selected articles: Predicted Mean Vote (PMV ) 25 used in 14 studies, the Universal Thermal Climate Index (UTCI) used by 5 studies and the Physiologically Equivalent Temperature (PET) used in 3 studies.
For their part Novieto and Zhang have made an approximation, applying in their study the IESD-Fiala model to represent the aged human body taking into account the metabolic rate, heart rate, and weight, which differ between 10 and 19.2% of the characteristics of the type person. For this, they use sensitivity tests and simulations to establish the impact of these factors on the thermal comfort of the elderly. They obtained that the basal metabolic rate was the most influential factor.
Only 9 of the studies reviewed have determined quantitative differences between the comfort temperature range or the preferred temperature for the elderly and the rest of the age groups. However, a statistical comparison of these values between studies is not possible, due to the heterogeneity of the samples and methodologies. Within these, only two refer to outdoor environments, while others evaluate indoor thermal comfort, whether in homes, senior centers or air-conditioned rooms; some obtain differentiated ranges for summer, others for winter, others do not specify and in no climatic zone is it identified for both cases.
As a result of this literature review, 43 articles were found that identify differences in the perception and thermal comfort of older adults and other people. The greatest consensus is given in 22 articles that recognize that with age the overall thermal sensitivity decreases, both cold and heat. From 9 studies of different contexts, methodologies and sample size, it is identified that this difference is 0.2-4 ° C and that the external comfort ranges are wider, indicating that the elderly are more tolerant of the outside temperature.
In addition, it is determined that the factors that influence thermal comfort differences are:
- The physiological changes of aging that affect thermal sensitivity and decrease its ability to detect and respond to temperature changes;
- Thermal adaptation to the environment, both psychological, given by origin, expectation, experience, exposure time and attitude; such as physical adaptation, because there are differences in the way in which the elderly adjust their clothing level (clo) and control the air conditioning mechanisms in indoor environments.
The need to adapt to the phenomenon of population aging, in order to achieve more inclusive, comfortable and healthy environments, is a challenge of a multidisciplinary approach to the cities of the 21st century. This article confirms the diversity of perspectives that produce sectorized conclusions and it is evident that future research needs to be addressed according to the different climatic zones and urban microclimates, taking into account in addition to climate change, the island of urban heat and the appearance of population over 80 It would increase the problems detected in this investigation.