Paper Conference

Proceedings of BSA Conference 2013: 1st Conference of IBPSA-Italy


The effect of material uncertainties on envelope heat transfer simulations

Alessandro Prada, Paolo Baggio, Marco Baratieri, Andrea Gasparella

Abstract: In this paper, the influence of thermo-physical properties on the heat flux transmitted through the envelope is investigated. In fact, the retrieval of reliable thermophysical properties is one of the major difficulties in the early stage of energy simulations. This issue is further emphasized if the model refers to existing buildings, when usually reference thermo-physical properties are used in lieu of declared and certified values (i.e. 90 % fractile). Moreover, the thermal characteristics, especially for porous media, are closely related to the water content and, to a lesser extent, to temperature and age. In addition to this, the uncertainties due to simplifying assumptions, commonly made in thermal analysis, should not be forgotten. For instance, the material apparent conductivities, as well as the other thermophysical properties, are the macroscopic results of various basic mechanisms such as the solid and gas conduction, the gas convection and the long wave radiation. The question then addresses to what extent the uncertainties of thermo-physical properties affect the reliability of the heat transfer through envelope and, consequently, of the energy simulation predictions. In order to answer this question, an uncertainty analysis has been carried out by means of a Monte Carlo approach. This procedure is applied for the recursive numerical solution of the partial differential equation of the heat conduction. Different Italian climates (i.e. Trento and Palermo) and typical wall typologies are adopted in order to broaden the representativeness of the results. Furthermore, two methods widely used in hourly simulation code (i.e. Conduction Transfer Function and Finite Difference Method) are herein analysed.
Pages: 283 - 292