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...multi-element physiological model established Smith is investigated. The sensible heat transfer from the surface of human body placed in uniform and front-back asymmetric radiant environments, with ambient air temperature of 28[degrees]C, was calculated using the coupled simulation method. According to the results, the microclimate around the human body and its thermal characteristics changed in response to the radiant conditions. However, compared with the results of the human subject experiments, which were measured under the same thermal conditions, in terms of skin temperatures, it is indicated that the simulation cannot accurately predict the skin temperature at the limbs, even in a uniform environment. Finally, measures for improving the prediction accuracy of the present coupled simulation method are suggested based on examination of the cause of the discrepancy.
INTRODUCTION
In recent years, task/ambient air-conditioning systems and radiant heating systems have been developed for high performance, with thermal comfort and energy saving simultaneously, by making the best use of nonuniform environmental conditions (Song and Kato 2004; Cermak et al. 2006). In order to evaluate the thermal sensation of the people in a room equipped with such air-conditioning systems, it is important to determine the heat transfer distribution over the whole body in detail, as the local thermal characteristics of body parts, which are directly heated or cooled, may be pivotal factors. Experiment using full-sized human-shaped manikins, with the surface covered by heating wires and temperature sensors, is a common method to measure the realistic pattern of heat transfer over the whole body (Tanabe et al. 1994). However, as it is difficult to divide a thermal manikin into a large number of partitions, due to the limitations in production, it is almost impossible to measure the detailed distribution of skin temperature and heat transfer over the body surface. Moreover, such measurements are unable to account for the independent effects of convection and radiation, as a number of different types of sensors are required for their determination.
A more recent approach is to use simulation coupled with mathematical human thermal physiological models on thermal transport processes in a virtual environment, which is becoming more efficient and attractive as an analytical tool owing to the increased calculation capacity of modern computers. The computational thermal manikin, based on the coupled simulation of convection, radiation, moisture transport, and human thermal physiological model, was first defined and proposed by Murakami et al. (1997). By using the computational thermal manikin, it became possible to independently calculate and examine in detail the heat transfer owing to convection, radiation, and sweating. However, in their studies, a simply shaped human body with feet and arms put together close to the body was used for the calculation of convective and radiant heat transfer; Fanger's model or Gagge's two-node model, which dealt with whole-body heat balance rather than local balance, was adopted for calculating the heat transfer inside the human body (Fanger 1972; Gagge et al. 1971). Therefore, the analytical tool is considered inapposite for people in a nonuniform environment, where thermal sensation is highly dependent on local heat transfer characteristics. More recently, a number of studies have been conducted to develop the computational thermal manikin (Tanabe et al. 2002; Sorensen and Voigt 2003; Nilsson 2004), but to the authors' knowledge, there have been no successful reports concerning a human body placed in various nonuniform environments to date.
Hence, the primary goal of this study was to develop a new computational thermal manikin that can simulate detailed heat transfer distribution over the entire body surface and can be used to evaluate the thermal sensation of a person in typical multifarious nonuniform environments. To achieve this objective, a human body model with a complex shape, which had feet, arms, a jaw, and breast, was used in the convection and radiation simulation; multi-element human thermal physiological models, which have a three-dimensional shape and can produce the three-dimensional temperature and heat transfer inside a body, are considered in this study. In this paper, the coupled simulation of convection, radiation, and Smith's human thermal physiological model was applied to investigate the local thermal characteristics of a human body located in uniform and front-back asymmetric radiant environments with an ambient air temperature of 28[degrees]C. Moreover, the predictive accuracy of the simulation method is verified by comparing the simulation results with the experimental results, which were obtained under the same thermal conditions by human subject experiments, in terms of skin temperature. Based on the comparison, the deficiencies of the present simulation method are examined, and measures for improving its predictive accuracy are proposed. If sufficient prediction is available for heat transfer in detail by the coupled simulation method, it can be enabled to evaluate the thermal perception in nonuniform environments by incorporation with a proper comfort model.
OUTLINE OF COUPLED SIMULATION METHOD
Smith's Human Thermal Physiological Model
Smith (1991) developed a three-dimensional, transient multi-element human thermal model with detailed control functions applied to the human thermoregulatory system. As shown in Table 1 and Figure 1, in this model the whole body is approximated geometrically by 15 cylindrical body parts (head, neck, torso, upper arms, thighs, forearms, calves, hands, and feet), which are connected together with both central and superficial vessels. These connections transfer heat between the body parts by blood circulation. By using Benzinger's experimental data (Benzinger 1970), the variation of blood vessel radii during vasomotor response, the sweat rate, and the shivering metabolic rate are modeled as functions of core and skin temperatures.Moreover, the model is made up of 6907 elements, of which 338 elements have surfaces exposed to the external environment. Three kinds of elements are used in the model, as shown in Figure 2. Triangular and rectangular three-dimensional shapes are used for tissue elements, which are assigned as specific types, such as brain, abdomen, bones, muscle, or fat and skin and given the corresponding physical property, according to anatomical data and other reported information. One-dimensional elements, which are located between the three-dimensional elements,...
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