Global warming has increased the risk of heat stress of outdoor workers and one measure against heat stress is wearing passive personal cooling clothing. Passive body cooling systems, including phase change material (PCM) cooling vests, are considered as an effective solution to improve the working endurance of outdoor active workers.
The objective of this study is to assess the effective placement of PCM packets in the cooling vest by examining the local and overall sensation and comfort when: (i) only the frontal segment of the human torso is covered (ii) only the back segment of the human torso is covered and (iii) both segments are covered. The PCM cooling vest is worn by human subjects performing cycling at about 3 Mets and for 30 minutes in a climatic chamber maintained at 28 °C and 60 % relative humidity. The used PCM melting temperature is 28 °C with a coverage area of 642 cm2 and total weight of the vest of 1.19 kg including 8 PCM packets (87.5 grams each). The physiological/thermal responses such as body core and mean skin temperatures, heart rate, and skin wittedness are monitored during the experiments while exercising and wearing the vest. In particular, the frontal and back torso skin temperatures are examined after being subjected to local cooling compared to the case when no PCM packets cover the torso segment. Moreover, subjective votes of thermal comfort, whole body and torso thermal sensations, skin and clothing wetness sensation and perceived exertion are recorded throughout the experiment. The experiment was repeated on five male subjects to ensure robustness of the obtained results. It was found that the core temperature changed slightly when wearing the vest, however the local skin temperature of the back and front torso segments decreased by about 5 °C and 3 °C at the end of the exercise, respectively. Gradual improvement in comfort that reaches a stable level when the PCM starts melting till the end of the exercise was also noticed.