HEAT TRANSFER COEFFICIENT OF THE INTERNAL SURFACE OF THE EXTERNAL WALL AND THERMOMETRIC METHOD

Abstract

coefficient, heat, convection, radiation, measurement, temperature, wall, building

A method for determining the heat transfer coefficient of the inner surface of the outer wall is proposed. The method takes into account real conditions. The heat transfer coefficient is presented as the sum of the radiative and convective parts. The radiative part takes into account the surface emission coefficients, the temperature of the outer wall surface, and the average radiation temperature, which is taken equal to the weighted average temperature of the inner surfaces. The average surface temperature is proposed to be determined using infrared thermography. The convective component of the heat transfer coefficient is determined according to the values of certain dimensionless parameters. To assess the dominant mechanism of air movement near the surface, the speed of movement is measured with hot-wire anemometer. A formula is obtained to determine the transition point from the laminar flow regime to the turbulent one. A choice of equations is proposed to determine the local values of the Nusselt number, and accordingly, the convective component of the heat transfer coefficient. A ratio for the average values of the convective component is obtained. Field studies were performed for real multi-stored residential buildings. The local and averaged values of the heat transfer coefficient of wall surfaces were obtained. This can be useful both for determining the average value of the wall U-value and for comparison with the results of local experimental measurements by other methods. Using the determined heat transfer coefficients and the thermometric method (THM), of the wall U-value were obtained. For conditions of low temperature in the room and a well-insulated wall, a significant decrease in the heat transfer coefficient of the wall surface, and accordingly, of the wall U-value, was obtained in comparison with the results obtained using the standard constant value of the heat transfer coefficient.

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