Experimental Study On A Phase Change Cooling Garment To Improve Thermal Comfort Of Factory Workers

Due to the high investment and operation cost of air conditioning system,the combination of natural ventilation and local fan is usually used to cool down workshops in summer,but the cooling effect is limited.If workers work in a hot environment for a long time,the working efficiency may be reduced due to thermal discomfort and even produce heat stress,thus endangering their physiological health.Garments with cooling or heating functions were initially applied to the physiological protection of the human body in special environments,such as aerospace and firefighting.Such garments can cool or heat the human body directly,which helps users maintain normal physiological thermal regulation.In order to improve the thermal comfort of workers,cooling garments are considered to be used to cool them in hot environments.With the continuous development of science and technology,and the improvement of people’s requirements for thermal comfort,most of the research objects targeted by existing studies are people with low activity levels,such as office workers,etc.The application of cooling garments can improve their thermal comfort while reducing energy consumption.Current research on athletes or people working outdoors at high temperatures and intensities is mainly aimed at using cooling garments to reduce the heat stress of personnel and to protect them physiologically.In contrast,less research has been conducted for workers with low to moderate activity levels in factories.Therefore,based on the physical activity level of workshop workers,this paper proposed a cooling garment using phase change materials and conducted an experimental study to systematically analyze the subjective perception,physiological parameters,cognitive ability and working efficiency of personnel.In this study,paraffin wax solution with a phase change temperature of 22°C was used as the phase change material to produce phase change cooling garments covering a total of seven parts of the human body: forehead,back,abdomen,waist,upper arm,forearm,and thigh.Twenty healthy university students(10 male and 10 female)were recruited as subjects,wearing normal working garment and phase change cooling garment respectively in an artificial climate chamber at 31°C.Subjects were asked to perform two typical factory working activities,one was standing(1.2met)and the other was packing while standing(2.5met).Subjective questionnaires(including thermal sensation,thermal comfort,thermal satisfaction,thermal preference,sweat feeling and cold stimuli sensation)were collected from the subjects with relevant physiological parameters(involving heart rate,blood pressure,oxygen saturation,skin temperature and ear temperature),and subjects completed cognitive ability tests and their working efficiency was counted.The improvement effect of the phase change cooling garment was evaluated by comparing the parameters when wearing the normal working garment with the phase change cooling garment.The main findings were as follows:The phase change cooling garment can improve the subjective feelings of thermal sensation and thermal comfort of personnel in a hot environment.The subjects’ overall thermal sensation when wearing the cooling garment was reduced from 2.8 to 1.4 in the packing stage and from 3 to 0.7 in the standing stage,and the overall thermal comfort was reduced from 1.9 to 0.9 in the packing stage and from 2.4 to 0.4 in the standing stage.The subjects no longer perceived the environment as very hot,but felt more comfortable and satisfied,with reduced expectations of a cooler environment and sweat feelings.There was no excessive cold stimuli and discomfort due to cooling.The phase change cooling garment could significantly reduce the mean and local skin temperature,and the mean skin temperature decreased by 1℃ and 1.6℃ under the two activities of packing and standing,respectively;the cooling garment could maintain the personnel’s skin temperature between 33.7～34.3℃ when packing and a comfortable and near-comfortable state of about 33.5℃ when standing;there was no significant effect of the cooling garment on ear temperature,which was mainly influenced by the environment temperature;the cooling garment also did not cause significant changes in the heart rate and blood pressure of the subjects,both of which were mainly related to the activity level;there was a tendency for the oxygen saturation to increase when wearing the cooling garment,but the increase was not significant.The completion time for personnel to answer the cognitive tests was significantly lower when wearing the cooling garment.The speed of answering the Stroop test improved by about 9% and 6.3% under both packing and standing activities,respectively,and the Image finding test improved by about 19% and 12% under both activities,respectively,but the error rate of the tests remained essentially the same.There was a significant improvement of 19% in working efficiency during the packing condition.Further analysis showed that the improved effect of the phase change cooling garment on both skin temperature and thermal sensation decreased slightly with increasing activity level,and there was a significant correlation between skin temperature and overall thermal sensation at each activity level.The phase change cooling garment proposed in this paper can improve the thermal comfort of factory workers in a hot environment to some extent,help reduce skin temperature,and improve the cognitive ability and working efficiency of personnel.The results of the study provide relevant data and underlying theory for the application of such wearable cooling devices in manual laborers.