Abstract:

Objective Cold environments threaten the life and health of the human body, and active heating of the human body can reduce heat loss from the body in a cold environment. This research aims to explore the influence of local heating of various body parts on the local thermal sensitivity and overall thermal comfort in a cold environment, which provides a theoretical basis for the design of local electric heating garment against cold environment.

Method For the first part of the experiments, 12 subjects were invited to apply 8 body parts thermal stimulation (chest, back, abdomen, waist, hands, elbows, knees and feet) separately using carbon fiber heating patches in a chamber with temperature of 5 ℃ and relative humidity of 50%. The local skin temperature, the scores of thermal and comfort sensations were collected during the tests to calculate the local thermal sensitive level of each body part. The second part of the study were carried out by heating simultaneously two body parts located at the same sensitive level to examine the differences between single-area heating and two-areas heating.

Results The results of local electrical heating showed a significant difference in the heating demand among eight body parts (P<0.05), the order of influencing degrees on the overall thermal sensation (OTS) was ranked from highest to lowest as feet / back / chest / abdomen / waist / elbows / knees / hands, and heating the feet has the greatest influence on the OTS (the impact factor is 0.112). In terms of heating temperature, the skin temperature of each body part finally converged to 39.8 ℃ at the end of local heating, indicating that the local skin temperature tolerance value is 39.8 ℃ under the experimental conditions. The heating temperature of the heating patches at the end of local heating was defined as the local preference temperature, which was found in the range of 46-49 ℃ for the limbs and 43-46 ℃ for the torso. The eight body parts can be divided into three sensitive regions, namely the highly sensitive regions (upper back and feet), the medium sensitive region (chest, abdomen and waist) and the low sensitive region (elbows, knees and hands). The results of two-area heating revealed a significant effectiveness of combined heating two parts in highly sensitive regions over that of low sensitive regions, and the combined heating of high sensitive regions can achieve the full-body thermal comfort. The heating energy consumption of each part was abdomen (11.1 W), chest and back (11.5 W), waist (11.6 W), elbow (16.9 W), knee (17.0 W), hand (17.1 W) and foot (17.2 W), more energy was consumed to heat the limbs than torso for the same heating duration.

Conclusion For local heating of the stationary standing human body, heating the feet alone is the most effective way to improve the comfort of the human body in a cold environment, while heating other single body part cannot make the whole body reach thermal comfort. This finding suggests the necessity of the combined heating. Among them, the combination of heating the feet and back, chest and waist, waist and abdomen demonstrated a better effect in achieving the full-body thermal comfortable and satisfactory state. For comprehensive consideration of energy consumption, it is recommended heating the chest and waist, or waist and abdomen to save electricity. To avoid local scalding, the local skin temperature of 39.8 ℃ has been suggested as the reference for designing the local electric heating garment. The number of subjects can be further increased in subsequent studies, more heating sites will be selected, and the influences of gender, age, occupational characteristics on human local thermal sensitivity and heating preference will be comprehensively considered.

Key words: carbon heating sheet, heating patch, electrically heated clothing, local thermal sensitivity, thermal comfort