Effect Of Local Thermal Sensation On Human Responses In Non-uniform Thermal Environment

With the growth of building energy consumption, new approaches to improve thermal comfort have been constantly proposed. New forms of air-conditioning appeared such as floor air supply system, task-ambient air conditioning, etc, whose applications also resulted in non-uniform indoor thermal environments. In addition, non-uniform thermal environment exists widely in our daily life. Therefore, research on non-uniform thermal environment not only has strong application significance, but also aids discovering the principles of human thermal responses. Through subjective survey, explorative investigations on human responses were performed when single body parts were thermally stimulated.At the room with temperatures ranging from 26 to 30℃, cooling airflow is sent to seven body parts: head, chest, back, arm, hand, leg and foot. The air velocity was fixed at 1.5m/s, while its temperature is 20℃. Overall 93 samples are tested, which includes boys and girls with equal numbers. All of the subjects were randomly selected from college students. During the test, they are required to vote thermal responses on voting scales within fixed time intervals, including local thermal sensations, local thermal acceptability of each body part, overall thermal sensation, overall thermal acceptability and overall thermal comfort.Because of the obvious multicollinearity of thermal sensation among body parts, principal component regression approach is proposed for the first time, so as to obtain principal components under different experimental conditions. By regression and analysis of principal components, effect weights of the 7 body parts are gained. The results show that effect weights are unaffected by ambient or local air temperatures. However, different characteristics of trunk and limb are clearly seen. Local stimulation on limb ends has no significant influence except for areas near the stimulation points, while that on trunk brings obvious responses in all parts, which contributes to non-uniform local thermal sensation. Prediction model on overall thermal sensation is obtained base on the effect weights. Excellent agreement is shown between predictions and measurement. The model shows that the weights of local thermal sensation on the overall thermal sensation are fixed values, and little difference is among the weights of different body parts. Through discussion on thermoregulatory reaction principles, it is revealed that thermoregulatory reaction to local reaction is the physiological mechanism of thermal sensation in non-uniform thermal environment, while inner heat transfer caused by blood circulation is the intrinsic cause of non-uniform local thermal sensation.Correlations and distinctions among overall thermal sensation, overall thermal comfort and overall thermal acceptability are analyzed under non-uniform environment. Maximum thermal sensation difference among body parts is raised in order to measure the difference of the thermal sensation. In addition, mathematical relationship between overall thermal acceptability and maximum thermal sensation difference among parts is deducted, based on which evaluation model is proposed.