| Health,comfort and energy issues are prevalent in the uniform and stable thermal environment created by traditional HVAC systems.Therefore,the academic circle is constantly looking for new ventilation technologies and ventilation strategies in order to solve this problem.Looking at the development trend of indoor airconditioning systems,the size of the target control area of the air-conditioning system has a tendency to range from the entire room to a local area of the room,from the creation of the overall environment of the room to the enhanced adjustment of the microenvironment around the human body.The "personal thermal management system" developed from the "personal environmental control system" has also received more and more attention.However,existing personal thermal management devices have many usage limitations and drawbacks.Therefore,there is a need to find better wearable personal thermal management systems to improve occupant thermal comfort in indoor office environments.Although the human face and neck region has only 5.5% of the total body surface area,face and neck cooling has been found to be very effective in improving thermal comfort during high temperature exercise.This paper will study the actual performance of two wearable head cooling fans to improve the thermal comfort of office workers.These fans are flexible and controllable with low power consumption,and can meet the cooling needs of indoor occupants in warm environments.This study uses two energy-efficient wearable face and neck cooling fans to improve the thermal comfort of occupants under warm indoor conditions.The local skin temperature and thermal perception responses when using two wearable cooling fans were studied and compared by the method of objective parameter measurement and subjective subject experiment.Additional attention was paid to gender differences in the effect of head cooling on overall thermal comfort.Subjective human response experiment were conducted after measuring the actual operating wind speeds of the two fans.A total of 16 subjects,8 males and 8 females,filled in their true thermal sensations at indoor ambient temperatures of 28,30,and 32°C.The experiment was carried out successively in the order of no-cooling comparison phase,fixed wind speed phase and individual control phase.The results showed that both cooling fans could significantly reduce the local skin temperature in the forehead,face and neck region by up to 1.8°C.And the face cooling fan and the neck cooling fan have a better cooling effect on the face and neck respectively.The use of both cooling fans significantly improved the overall thermal sensation and overall thermal comfort vote in a warm environment,with a maximum decrease of 1.5 units in the thermal sensation vote and a maximum increase of 0.85 units in the thermal comfort vote.The subject’s free control can stabilize the overall thermal comfort around "neutral".Both cooling fans can raise the acceptable indoor temperature to 31.0°C,which saves about 42% of summer air conditioning energy consumption compared with the benchmark indoor set point of 25°C.Studies have shown that the use of cooling fans,especially neck cooling fans,can significantly improve the work efficiency of office workers,and also increase the proportion of subjects reporting dry eye symptom and dry lips symptom,but the use of free control strategies can reduce the proportion of discomfort symptoms.Furthermore,the study demonstrates the important role of individual behavior in further improving the personal thermal comfort when using wearable localized thermal comfort devices.In the free control mode,the subjects can prevent excessive cooling and insufficient cooling by adjusting the wind speed of the fan,which improves the overall thermal sensation vote and thermal comfort vote to some extent.From the gender analysis,it can be seen that the average skin temperature of the head and the average overall thermal sensation votes of women are lower than that of men,while the average overall thermal comfort votes of women is significantly higher than that of men at warm indoor temperatures.The results showed that women have a higher sensitivity to cold stress and better heat tolerance to warm environments,but their need for cooling is greater than men.In addition,the use of fans can significantly amplify the differences in the average head skin temperature,thermal sensation and thermal comfort between different sexes in warm environments,but the use of free regulation strategies can reduce this difference.Finally,despite some issues on dry eyes and dry lips associated with those wearable cooling fans,it is concluded that these two highly energy-efficient wearable cooling fans could greatly improve thermal comfort and save energy consumption of HVAC in warm environments. |
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