Investigation into the dynamic heat and moisture transfer through clothing systems using a perspiring fabric manikin

Abstract

Clothing thermal comfort is not only important to survival for people in extreme environments, but also important to improve the living condition in every day life. Thermal comfort should be considered in two related aspects: thermal comfort under steady-state conditions and thermal comfort under transient conditions. Considerable research work has been or is being carried out on clothing thermal comfort under steady-state conditions. Comparatively, little work has been reported on the transient heat and moisture transfer through actual clothing ensembles, although some work is reported on the transient heat and moisture transfer through clothing materials or assemblies. Attempts had been made to establish models for estimating thermal transient comfort, these models however included either the steady-state properties of clothing ensembles, viz. clothing thermal insulation and moisture vapour resistance, or the dynamic heat and moisture transfer through layered fabrics, but not the dynamic behaviour of real clothing ensembles. Clothing properties specific to transient conditions should be defined and investigated. In this study, a new transient thermal model, integrating the dynamic heat and moisture transfer through clothing as well as the two-node human physiological model, is proposed to predict the human physiological responses. The model considered clothing ventilation and moisture accumulation on the surface of the skin and inner surface of the underwear. The numerical results of the model are validated with a set of previously published experimental data and another set of data obtained from current experimental investigation. Very good agreement was found. The model has also been applied to better understand the complex interaction of the various human, clothing and environmental factors and their effects on the human thermal physiological response. In order to quantify the dynamic thermal properties of clothing using the sweating fabric manikin-Walter, a novel test method has also been developed and an associated index was proposed in this test method, the sweating manikin was used to simulate human body's experience in the thermal transient changing from resting to exercising. The average changing rate of mean skin temperature of the manikin in the first hour of simulated 'exercise' (STCR) was taken as an index to provide a measure of the dynamic thermal properties of clothing ensembles. Seven clothing ensembles (Five of them consists of sports T-shirts made of different fabrics and the same shorts; one consists of a business suit, long-sleeve underwear, shorts and long trousers; another consists of a coat long-sleeve underwear, shorts and long trousers) were tested repeatedly on the sweating fabric manikin according to the proposed test procedure. The tests showed good precision and reproducibility. The coefficient of variation is generally less than 4%. It was further found that the index STCR was significantly different among the four clothing ensembles consisting of sports T-shirts made of different fabrics and the same shorts, despite of the fact that the thermal insulation and water vapour resistance of the four clothing ensembles are very close. On the other hand, although the thermal insulation and water vapour resistance of the clothing ensemble with a business suit and a coat are very different from those of the clothing ensemble with two sports T-shirt, their STCR values are very close. Through the theoretical analysis of the dynamic heat and moisture transfer within the clothing-manikin-environment system, it becomes clear that STCR is an integrated parameter which reflects the dynamic heat and moisture transfer through clothing ensembles during the thermal transients from standing to walking. Human physiological experiments were also conducted to investigate the relationship between the new index measured from the manikin tests and the physiological responses in terms of changes of body temperature. The present study showed that a test method can be developed based on the sweating fabric manikin-Walter to provide an objective measure of such dynamic properties. From the present study, it was shown that the changing rate of the mean skin temperature of the clothed manikin-Walter when changing from the "resting" to "exercising" mode is related to the changing rate of the body temperature of a wearer wearing the same type of clothing and undergoing a similar change of body activities, it is therefore reasonable to use the changing rate of the mean skin temperature of the clothed manikin-Walter as an objective index for quantifying the dynamic thermal properties of clothing ensembles. The use of the objective index from tests on the sweating manikin-Walter is clearly advantageous, since tests involving human subjects are time consuming, expensive and poor in reproducibility. A higher value of the index means faster rate of change of body temperature, and shorter duration before the wearer approaching a dangerous thermo-physiological state. Clothing should therefore be designed to reduce the value of the index.