Analysis of heat transfer in a building structure accounting for the realistic effect of thermal radiation heat transfer

Abstract

A computer code BERHT (Building Energy with Radiative Heat Transfer) is developed to simulate the effect of heat and mass transfer in a building structure. The code uses many of the programming structure of a well-known whole-building energy analysis code, ENERGY-PLUS. A realistic model for interior longwave radiative heat transfer is implemented. The model accounts for the absorption/emission of participating species (CO₂, H₂O, and small particles) in a building environment and the geometric effect of a building structure. Spectroscopic data from RADCAL, a narrow band model, is used to simulate the absorption effect of the two participating gases. Neural network is utilized to provide accurate and efficient correlations which can be readily implemented in a heat and mass transfer calculation for a three-dimensional building structure. A series of numerical studies for a single room building structure are conducted. Numerical data are generated. For nominal concentration of CO₂, H₂O, and small particles, results show that the presence of an absorbing/emitting medium has important effects on the distribution of the total heat transfer between convection and radiation. The presence of a participating medium, however, has only a minimal effect on the overall heat transfer and the temperature of the interior air. It is shown that the overall energy balance is strongly influenced by external parameters. The "greenhouse" effect is simulated numerically. Results confirm that the absorption of short-wave radiation by the surface and the subsequent heat transfer from the surface to the air mixture in the room is the primary mechanism for the greenhouse effect. To study the effect of radiation in a higher temperature environment, a computer code FRTF-RAD (Fire Resistance Test Furnace with Radiation) is developed. The radiative heat transfer in a fire resistance test furnace is simulated. Results show that emission and reflection from the wall boundaries have major effects on the radiative heat flux measurement in a test sample. The data which demonstrated the scalability of the test furnaces are shown to be limited to isothermal furnaces only. From the perspective of a compartment fire, numerical data also shows that particle emission and emission from the wall are essential in the initiation of flashover.