Evaluation of the non-steady thermal behaviour of materials used in typical Argentinean and Mexican buildings

MUÑOZ VASQUEZ, NATALIA; THOMAS, LUIS P; MADIROLAS, ADRIAN

Temixco, Mexico

Simposio; SIERyS Third International Symposium on Renewable Energy and Sustainability; 2015

Materials employed in the buildings walls constitute an essential factor in the estimation of heat gains and losses by conduction across the envelope. If the temperature on each side of a wall is considered constant, a uniform and steady heat flow is established, and then the relationship between the energy transferred and the temperature difference is obtained in a simple way. Here, the thermal conductivity of the material relates both variables. Consequently, a maximum energy flux results when the temperature difference is maximum; that is to say, the curves of temperature and heat flux evolution are in phase under thesteady flow hypothesis. Due to the increase of the thermal insulation required by regulations that consider the geographic location, new materials, local types of construction, etc., it is also convenient to analyse the thermal behaviour of materials with respect to the daily temporary changes of the external temperature. These variations produce two important effects: the attenuation of the energy flux as function of the distance (or decrement factor), and a time lag between the maximum temperature difference and the heat flux. The material response is given by its thermal admittance, which depends on its conductivity, density and heat capacity. The admittance method offers a useful way to calculate those factors and allow obtaining the periodic solution of the heat non-steady equation by means ofcomplex numbers. The matrix multiplication makes possible the calculation for multiple layers walls and the obtaining of significant physical information during the procedure. In this work, the admittances, time lags and decrement factors are estimated and compared for many types of walls that are typical in Argentinean and Mexican buildings. Additionally, the more adequate dispositions according with the use of the walls are analysed, and the influence of these characteristics on the whole construction is assessed.