Assessing indoor thermal comfort for non-frail older adults in hot and humid regions: An approach to regulating airflow characteristics of fans

Electric fans are commonly used by older adults in hot and humid regions to enhance summer comfort and reduce reliance on air conditioning. However, prolonged exposure to fan-generated airflow can induce discomfort, with existing research lacking quantitative understanding of how specific dynamic airflow parameters—including velocity (V), turbulence intensity (Tu), and power spectral exponent (β)—influence thermal and airflow perception in non-frail older adults. This study quantitatively analyzed the effects of V, Tu, and β on subjective discomfort symptoms and physiological responses within 12 subjects exposed to nine airflow patterns at 30 °C and 70 %RH. Key findings revealed that the neck exhibited significantly higher sensitivity to airflow variations than the head, establishing it as a critical region for airflow perception. The parameter contribution ratios to subjective comfort and skin temperature were approximately V:Tu:β = 0.3:0.1:0.5. Notably, β significantly reduced discomfort symptoms (a 1.0-unit increase reduced discomfort by 0.4 units) by modulating airflow pulsatility, albeit with a mild trade-off of elevating the mean skin temperature (+0.45 °C). Body-region-specific dominance was observed: β contributed about 50 % to head discomfort (e.g., dry eyes and lips), whereas V dominated generalized discomfort by about 50 % (e.g., skin pressure and sweating). Crucially, distinct comfort ranges were identified: head (V = 0.94–1.17 m/s, Tu = 32–40 %, β = 0.78–1.12) and body (V = 0.82–1.17 m/s, Tu = 15–40 %, β = 0.20–1.12). These findings provide targeted guidance for optimizing dynamic airflow settings in age-friendly ventilation systems to mitigate discomfort and enhance thermal acceptability for older adults.