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In silico human model for fluid-initiated indoor environmental design

People spend the majority of their time in enclosed spaces like car and commuter train interiors, aircraft cabins and buildings, wherein the indoor air quality (IAQ) greatly influences their quality of life, making IAQ issues increasingly important as far as controlling health risks to residents are concerned. In recent years, indoor air pollution has been recognized a serious social problem. Indoor air pollution is caused by various contaminants in indoor air, e.g. gasphase and aerosol-phase contaminants that are emitted from vehicles/building materials and/or are transported from outdoors to indoors by ventilation. They are exacerbated by the introduction of new materials and new construction methods, and by the growing prevalence of airtight environments, high thermal insulation and insufficient ventilation design. Individuals in indoor environment are at risk of being exposed to gas-phase and aerosol-phase contaminants, and a lot of epidemiological studies indicate that exposure to these contaminants in air is associated with increased risks of lung cancer, asthma and chronic diseases, as well as increased risks of induced mortality and morbidity in residents. A reference concentration (RfC) of target contaminant in indoor environment is generally defined under the assumption of perfect mixing condition. This assumption might be useful for approximate ventilation design. At the same time, the exposure, contaminant concentration and breathing air quality are highly dependent on local contaminant concentration distributions around human body surfaces. The metabolic heat production and effects of breathing could greatly influence the microclimate around the body, which in turn significantly affect the flow and distribution of contaminants and the local heat transfer characteristics of the body. Thus, it is very important to analyse the detailed interaction (heat/moisture and contaminant transfer) between the human body and its surrounding microclimate for sophisticated indoor environmental design for residents. Numerical simulations of airflow, temperature and the contaminant distribution field have been used in the designing of room air conditioning and the analysis of indoor environmental quality. Numerical simulation is significant in the analysis of contaminant distribution field structures and can be used to design a precise control method for indoor environmental quality at local point/domain. In this context, interest in using an in silico human model, i.e. computer-simulated person integrated with computational fluid dynamics (CFD) technique for this purpose in research and design has been growing steadily. To set a threshold concentration value, the use of biological bodies for in vivo studies or tissue and cells for in vitro studies has been required, as animal and biological tests are always needed for toxicology studies. On the other hand, in vivo/in vitro studies involving human subjects and mammal surrogate models for toxicology studies have been facing ethical restrictions. Recently, the use of in silico models as a substitute for in vivo or in vitro studies has been increasing because of the remarkable developments of computer and visualization technology in the medical field. In silico models, with detailed geometry and physiology reproductions of these biological bodies, as substitutes for real humans/animals, are therefore in great demand. The concept and first-stage development of an in silico human model integrated with CFD for indoor environmental design were investigated by Murakami et al. in the late 1990s. They analysed the flow field and temperature distribution around a human model whose simplified geometry was reproduced by CFD. Further studies have used CFD simulation coupled with human body and human-thermoregulation model to investigate the indoor thermal environment and its impact on human thermal comfort. Murakami et al. performed a combined simulation of airflow, radiation and moisture transfer, integrated the results and transferred them into a transient thermoregulation model in order to calculate the human skin surface