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Old Dominion University (2004)

Analysis of Human Thermal Comfort Using a Coupled Model for Predicting Human Body-Environment Heat and Mass Exchange

Al-Mogbel, Ahmed M..

Titre : Analysis of Human Thermal Comfort Using a Coupled Model for Predicting Human Body-Environment Heat and Mass Exchange

Auteur : Al-Mogbel, Ahmed M..

Université de soutenance : Old Dominion University

Grade : Doctor of Philosophy (PhD) 2004

Résumé
Recent advances in computational fluid dynamics (CFD) make it possible to accurately predict many features of airflow within ventilated spaces. The present study investigates thermal comfort aspects of an occupant in a conditioned space, using a CFD code. The heat and mass transfer between the human body and the surrounding environment is analyzed by a coupled model that accounts for dispersal of metabolically generated heat in the body to the surroundings by the combined mechanisms of radiation, convection, respiration and evaporation. A two-node model in which two coupled non-linear algebraic equations govern the skin temperature and the body core temperature analyzes heat transfer inside the body. The energy interaction between the body and the surroundings is modeled by coupled equations for mass, momentum and energy transport. Since energy and mass (water vapor) interactions between the body and surroundings modify the air temperature and humidity, the numerical algorithm adopted incorporates the coupling between the body and the surroundings, using interfacial boundary conditions for temperature and humidity at the skin surface. A segmented body model has also been developed to take into account the spatial variation of body skin temperature. The proposed segmented model shows more details and incorporates wider variations of body properties. Thermal comfort indices namely, Effective Draft Temperature (EDT), Predicted Mean Vote (PMV) and Percentage of People Dissatisfied (PPD) are used to map the regions of thermal comfort and discomfort. Results presented for several supply air conditions and metabolic activity rate show that of all the variables considered in this study the supply air temperature most strongly influences thermal comfort conditions, followed by the metabolic activity rate. The supply air relative humidity has the least effect. The body skin and core temperatures are most influenced by the metabolic activity rate, followed by the supply air temperature. Simulations with varying supply air turbulence intensity show that it has minimal effect on thermal comfort conditions in the room. Regions of thermal comfort and discomfort mapped on PMV-EDT diagrams show that out of 20 supply air and metabolic activity conditions considered in this study, the room averaged PMV index predicted 15 of them to be in the thermal comfort zone and remaining five were shown to lie in the thermal discomfort zone. The EDT index predicted 18 of the 20 conditions as belonging to the comfort zone. Although in the majority of cases both indices are in agreement regarding their prediction, the PMV index provides a conservative estimate of thermal comfort conditions. The segmented body model points to the fact that results predicted by it provide a more conservative estimate of thermal comfort as compared to the regular (unsegmented) model.

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