Experimental Study on the Investigation of Thermal Comfort in Night Sleep Conditions

This study investigates the interplay between thermal comfort, sleep quality, and physiological responses during nocturnal rest. Despite the critical role of temperature in sleep regulation, existing thermal comfort standards fail to define specific thresholds for sleeping conditions. A three-phase experimental protocol was conducted in Tehran during the summer of 2023, involving 12 healthy adults (six men and six women, aged 28–39). Using temperature–humidity data loggers, wearable health sensors, sleep tracking software, and postsleep surveys, the study evaluated both objective and subjective indicators of sleep-related thermal comfort. Descriptive statistics, Pearson’s correlation, two-way repeated measures ANOVA, and Bonferroni’s post hoc tests were used to analyze associations between temperature, physiological responses, and perceived sleep quality. Results revealed strong correlations between bed surface temperatures, body temperature, and heart rate. Specifically, the optimal lower bed temperatures ranged from 21.70°C to 26.85°C for men and 24.76°C to 28.11°C for women, while upper bed temperatures ranged from 22.29°C to 26.24°C for men and 23.70°C to 28.41°C for women. Compared to ASHRAE and ISO 7730 daytime standards, the male temperature ranges fell within acceptable limits, while female comfort ranges exceeded these standards by approximately 1.5°C–2.5°C. These findings highlight the need for gender-specific thermal comfort guidelines in sleep environments and underscore the limitations of current standards in addressing nocturnal physiological needs.