Variability in thermal comfort and behavior of elderly individuals with different levels of frailty in residential buildings during winter

Research on the indoor thermal comfort of elderly individuals has become increasingly detailed, yet studies focusing on the impact of health levels on elderly thermal comfort are still relatively scarce. Due to aging and various chronic diseases, elderly individuals exhibit different physical states, affecting their physiological regulatory functions in response to thermal environmental changes. This study aimed to validate the impact of health levels on elderly thermal comfort and behavior during winter, by employing the Fried frailty assessment method. A survey was conducted in the HSCW regions of China, gathering 1437 valid questionnaires. The analysis revealed that frailty significantly impacts the winter thermal comfort and behavior of the elderly. Specific findings include: 1) Frailer elderly individuals express greater complaints about indoor environments; 2) Frailer elderly are more dependent on heating devices; 3) Frailer elderly have higher rates of closing windows with higher T_out prompting window closure. The T_out prompting non-frailty elderly to completely close windows is 8.1 °C, while for pre-frail and frail elderly, it is 16.7 °C and 16.0 °C, respectively; 4) Frailer elderly individuals exhibit higher I_cl, with median values of 1.56 clo for non-frail, 1.68 clo for pre-frail, and 1.71 clo for frail elderly; 5) Frailer elderly individuals have lower MR daily, with median metabolic rates of 1.71 met for non-frail, 1.42 met for pre-frail, and 1.17 met for frail. This study found that the level of frailty significantly impacts the winter thermal comfort and behavior of the elderly and should be considered in future elderly-friendly architectural designs.