Improving thermal comfort and cognitive ability of manual workers by cooling garment of different temperatures based on EEG analysis

Nowadays, hot waves happen frequently in summer, and lead to hot indoor environment where air-conditioning system is absent, which can be more intolerable for manual workers taking higher activity levels. This study investigates the effects of phase change cooling garments (PCCG) on thermal comfort, cognitive performance, and electroencephalography (EEG) signals of subjects under a hot condition of 33 degrees C. Twenty participants were asked to conduct an activity with metabolic rate of 2.7 met in three conditions (with normal garments, with PCCG of 21 degrees C and 17 degrees C). Skin temperature, core temperature, EEG signals, heart rate were measured. Subjective votes (thermal sensation, thermal comfort, cold stimuli sensation) were collected. Four cognitive tests were performed including letter search test, picture recognition test, Stroop test, and number remember test. Results indicated that the PCCG significantly improved thermal perception votes. The PCCGs led to decrease in mean skin temperature and core temperature, with a more pronounced effect in the 17 degrees C condition. The 17 degrees C PCCG significantly reduced heart rate, and the heart rate variable index of RMSSD was increased, while the LF/HF was decreased. Subjects' cognitive performance was also effectively improved, and the lower the cooling temperature the better the cognitive performance. The total EEG power decreased significantly in the 17 degrees C condition. The use of PCCGs led to significant decrease in power of the 0-band, and increase in alpha and n-band. The alertness level and the concentration index were also increase, while the fatigue index was decreased. The effect of PCCG became more significant in the 17 degrees C cooling temperature. No significant difference was found between the two cooling temperature conditions. The power of alpha-band was negatively correlated with thermal sensation vote. Correlations between the EEG indicators and cognitive performance were found, and the attention ability was positively related to the power of alpha and n-band, respectively. The results indicate that the EEG can be used to evaluate thermal comfort and cognitive ability of manual workers during the use of cooling garments.