Sensitivity and preference of local airflows beneath garments with personalised temperatures and velocities

Microclimate ventilation under garment is one of the effective means to relieve heat stress of human body, while the sensitivity and preference of airflow at different body parts are not thoroughly studied. This study investigates the local airflow sensitivity of five body segments by a psychophysical method, whereby twelve subjects were stimulated by three temperatures of ventilation under garment (Tsk - 5 °C, Tsk, or Tsk + 5 °C, Tsk is the initial local skin temperature); at the front chest, upper back, lower back, front thigh, and back thigh areas. Airflow sensitivity was tested to enhance when the airflow became warmer or cooler than the Tsk, showing that human skin can recognise variations in airflow velocity with a difference threshold of 0.23 ± 0.06 m/s. The front chest was the least sensitive of all three airflow temperatures, while the back thigh was the most sensitive to cool airflow. Twelve subjects then underwent controllable local ventilation at 35 °C, RH 40%. The airflow preference, psychological and physiological responses, and energy consumption were analysed. The preferred airflow temperature was approximately 26 °C (25.7 ± 1.8–25.9 ± 1.4 °C), while the preferred airflow velocity had a large individual variation. The lower back should be primarily ventilated, obtaining comfort enhancement with an energy saving of 30–40% compared to others; the front chest or the upper back should be added for higher cooling demand. This study helps us to understand the characteristics of airflow sensitivity on localised skin and optimises the design of individual ventilation.