A THEORETICAL APPROACH TO ESTIMATE THE TIME LAG OF BUILDING ENVELOPES

The investigations of the building elements from the point of view of energy engineering became very important since the last 50 years. Insulation of the building envelope is one of the keys to reduce the heating energy loss. The mainly used thermal insulating materials are Expanded Polystyrene (EPS), Extruded Polystyrene (XPS) and mineral wool materials, moreover the nano-sized insulators (e.g.: aerogel, vacuum insulations etc.) are requiring spaces for themselves also. Aerogels are nanoporous lightweight materials that were discovered more than 70 years ago. Nowadays their applications are truly widespread. In this article measurement results and theoretical backgrounds are presented. Thermal parameters of building envelope, such as heat storage capacity, heat-loss coefficient, time constant, time lag, heat transfer coefficient etc. are very useful during the analysis of thermal behavior of building's. This paper describes a methodology developed to calculate the time lag based on our previous measurement results. The thermal diffusion and time lag calculations are based on the Onsager-equations and atomic diffusion rules.