Experimental comparison of local direct heating to improve thermal comfort of workers

Abstract

This study aims to investigate the effect of wearable local heating devices on the thermal comfort of workers doing handwork in cold environments. Experiments were carried out by using local radiant heating, ankle heating, wrist heating, torso heating, and combined heating, which were compared with no heating conditions. Twenty subjects participated in the experiments under air temperature conditions of 13 and 15 °C. The participants were asked to perform three activities: standing, assembling screws, and assembling small shelves. Subjective questionnaires pertaining to overall thermal sensation, local thermal comfort of hands, and thermal comfort were collected. The mean skin temperature (MST) was measured. The results show that some of the local direct heating improves subjects' overall thermal sensation, local thermal sensation of hands, and thermal comfort significantly. These methods include torso heating and the combined heating. Moreover, subjects’ MST and working efficiency are also increased. The working efficiency is found to be related closely to local thermal sensation of hands. Although wrist heating does not improve the thermal sensation significantly, it improves the thermal sensation of hands and the work efficiency effectively. The analysis shows that local thermal sensation of hands is linearly related to the overall thermal sensation. When the local thermal sensation of hands is neutral, the overall thermal sensation would be slightly warm, and subjects would feel more comfortable. Compared to local radiant heating, these wearable heating devices are more efficient, in that they improve thermal comfort and working efficiency better with a lower energy cost.