Coupled tridimensional heat and moisture transfer in soils under buildings / Transferência tridimensional acoplada de calor e de umidade em solos sob edificações

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

After the wide world crisis of energy in the 70#s and the interest in energy consumption reduction, some computational programs had been developed to simulate the building energy performance. However, these codes present some simplifications on their calculation routines of heat transfer through the ground. In this way, we have described a mathematical model applied to building hygrothermal behavior analysis. We have used a lumped approach to model the room air temperature and humidity and a multi-layer model in finite differences for the building envelope. The capacitance model allows studying the dynamic performance of both humidity and temperature of a building zone when it is submitted to the different climatic factors. In order to evaluate the building performance, a C program has been written, which includes solar radiation (direct and diffuse), air infiltration, conduction loads, internal gains of people, lights and equipment. In the results section, we show the influences of simulation time step on temperature profiles within the building envelope and room air temperature and humidity ratio. Then, different numerical methods to integrate in time, the energy and mass conservation equations of the room air domain, were compared in order to speed up simulations without loosing accuracy. In the sequence, models for the pure conduction heat transfer through the ground and its influence on room air temperature were described. In these models, the heat diffusion was calculated by the Fouriers law, by using the finite difference method, considering three approaches (1-D, 2-D and 3-D formulation). A validation of these models were carried out by comparing with results obtained from the commercial CFX-5 package. To conclude, the moisture effects on the heat and mass transfer through the floor and ground were discussed. Firstly, sensitivity analyses of time step, grid size and warm-up period (to reduce initial condition) were carried out for the soil physical domain, considering the presence of moisture. The methodology presented was based on the Philip and De Vries theory, using the thermophysical properties for dissimilar soils with transport coefficients highly dependent on moisture content. The governing equations were discretized in finite volumes and a 3-D model was used for ground and floor.

ASSUNTO(S)

mechanical engineering soil moisture engenharia mecânica - dissertações solos - umidade engenharia hidraulica calor - transmissão heat

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