Air speed needs and local sensitivity of non-frail and pre-frail older adults: A lab study in China

In China's hot summers and cold winters regions, older individuals often use fans or fan-AC combinations for thermal comfort in warm environments. However, there is a lack of research on the preferred air speed settings for varying levels of frailty and the reasons behind their sensitivity to airflow. This study, using the Fried frailty classification method, involved 12 non-frail and 12 pre-frail older participants in experiments conducted at warm temperatures of at 28 °C, 30 °C, and 32 °C. Different air speeds were set to examine subjective air speed needs, physiological changes, and sensitive body areas. Results showed that pre-frail older persons had lower thermal sensation votes in a situation without air speed, and experienced higher air speed sensation votes at the head, calves, and feet. As air speed increased, skin temperatures decreased, with the most significant changes observed in the head, which was also the most sensitive area. Pre-frail individuals also required more time for skin temperatures to stabilize and exhibited lower sweat production in distal limbs, excluding hands. No significant differences were observed in cardiovascular parameters. Comfortable air speed limits for pre-frail individuals were lower across the research temperature range: at 28 °C [0.12, 0.63] m/s, at 30 °C [0.36, 0.76] m/s, and at 32 °C [0.47, 0.78] m/s, compared to non-frail individuals at 28 °C [0.23, 0.89] m/s, at 30 °C [0.54, 1.01] m/s, and at 32 °C [0.65, 1.25] m/s. When creating airflow in warm conditions, it is crucial to consider the frailty level of older individuals to ensure appropriate age-friendly environmental control.