Effect of vest structure, airflow velocity, and humidity on evaporative cooling capacity using a thermal manikin

Climate change has exacerbated heat stress, particularly for outdoor workers. Evaporative cooling vests (ECVs) mitigate occupational heat stress. Their cooling capacity depends on the structural design, air temperature, air velocity, and humidity. This study investigated the cooling capacity and efficiency of four ECV designs under various environmental conditions. Four ECVs—polymer-based punched (ECVPP), polymer-based (ECVPB), cellulose-based (ECVCB), and TECHNICHE (ECVTECH)—were evaluated via a thermal manikin under controlled conditions (ambient temperatures: 35 °C and 40 °C; relative humidity: 20% and 40%; air velocities: 0.1, 0.4, and 1.0 m/s, respectively). The cooling capacity was measured by monitoring the energy consumption of the manikin over two-hour periods. The efficiency was calculated as the cooling capacity relative to the latent heat of water evaporation. Thermal imaging captured the surface temperature distribution. At 40 °C, ECVCB and 30 °C, the ECVPP consistently outperformed the other vests, achieving cooling capacities of 81.7 W and 78.5 W, respectively. These peak values were observed under higher air velocity conditions (1 m/s). Correlations (R = 0.9, p < 0.001) between the amount of evaporated water and the cooling capacity were observed. Thermal imaging confirmed that the progressive cooling capacity decreased due to evaporation—efficiency varied by vest design, highlighting the superiority of ECV_CB. This study highlights the performance of cellulose-based ECVs in hot, dry conditions, driven by enhanced evaporation rates. Higher air velocities improved the cooling capacity but reduced the efficiency, underscoring the need to balance airflow, humidity, and vest design for optimal performance. These findings provide insights for improving ECV functionality in occupational heat stress scenarios.