## 4 Open Issues: Vulnerable People and Special Environments  
Describing adaptive approach in ASHRAE Standard 55, [PERSON] and [PERSON] [167] state that \"adaptive principles assume the persons are able-bodied without physiological and physical challenges [...] or mental health and/or cognitive disabilities preventing the ability to adapt\", and that \"Standard 55-2017 does not directly cover vulnerable populations\". Figure 19: Readiness level of the analyzed papers. Figure 20: Costs estimated for office/commercial and residential building applications as a function of conditioned area (bi-logarithmic scale). Indeed, studies on the thermal comfort perception of some categories of vulnerable people exist in the literature, but practical implementations are almost entirely missing. Therefore, they cannot be found among the publications that the analysis in Section 3 is built upon. This subsection has the purpose to touch on this subject by providing references to recent studies that focus on the peculiarities of vulnerable groups in terms of thermal comfort needs. The aim is to outline some situations in which a tailored thermal comfort-based system may be useful, but few or no application-oriented work has been carried out yet. Differences in thermal comfort perception due to age have been widely explored by researchers, with elderly people being a particularly interesting group due to their frailty and to the aging of the world's population. [PERSON] et al. [15] noted that the presence of secondary factors is indeed the reason behind such differences, rather than age, per se. [PERSON] and co-authors investigated summer [168] and winter [169] thermal conditions of elderly people in the UK by means of extensive surveys, revealing that modeling frameworks according to reference standards often fail to provide reliable predictions. The specific effect of dementia on the applicability of different thermal comfort approaches was analyzed in the recent survey by [PERSON] et al. [170]. Conversely, few studies can be found on thermal-comfort-related needs of people with physical disabilities. These people may have different thermal requirements due not only to the disability itself, but also to postural and mobility impairment, and possibly to pharmacological treatments ([PERSON], 2002 [171]). Recently, the work by [PERSON] et al. [172] proposed an IoT-based modeling approach to make comfort evaluation possible even in case of difficulties in expressing a feedback; the study confirmed that differences exist between people with and without disabilities, and between people with different disabilities as well. Similar attention to the survey planning stage can be found in [PERSON] et al. [173], whose study reaffirmed that PMV tends to predict excessive comfort temperatures, and proposed a tailored adaptive model. Cognitive impairment has not been frequently associated with indoor comfort requirements, although authors have demonstrated that these vulnerable people can benefit from a comfortable environment because it reduces triggers of negative behavior [174]. [PERSON] et al. [175] stressed the importance of adapting the environment to the needs of people with neurodevelopmental disorders to give them the opportunity of \"independent living projects\". [PERSON] et al. [176; 177] reported that experimental observations from questionnaires (filled in by \"proxy respondents\", such as parents or caregivers, in case of people with severe disorders) do not indicate thermo-hygrometric conditions as a cause of stress in people with autistic spectrum disorder. However, they noted how very few investigations can be found in the literature on the individuals' sensitivity to the different comfort domains, and they anticipated the need for more studies to develop quality thresholds and design guidelines for indoor environments. Healthcare facilities are especially challenging spaces to deal with. Both patients and healthcare workers should feel thermally comfortable in places where they have to spend long time periods. [PERSON] et al.