Experimental and numerical analysis of heat trasnfer at chimney-roof penetration in relation to the overheating of flammable materials

Chimneys convey exhaust gas produced in domestic heating appliances to the external ambient and to do this they have to pass through roofs and oors. The increasing attention to sustainability and energy saving has led to better insulated buildings, with roofs made up of combustible materials. From the point of view of re, a critical point for safety is where chimneys penetrate roofs or walls made of these materials. Currently, chimneys are tested according to the European standard EN 1859, that prescribes the heat stress test and the thermal shock test for verifying the safety distance from combustible materials to avoid overheating. Despite the certi cation, in some European countries the number of roof res due to the presence of chimneys is high. The goal of the study presented in the thesis is to understand heat transfer between chimneys and roofs, and to propose a solution to roof res problem. A rst result of this work has been the identi cation of the weaknesses of the current certi cation procedure, which can lead to the overheating of ammable materials and re hazard in some real installations. For this, modi cations to the standard will be proposed. With the aim to respond to the needs of the installers, by means of a 2D and a 3D numerical models designed to estimate the steady-state temperature on ammable materials and validated by means of experimental tests, it has been possible to identify all the variables a ecting the heat transfer between chimney and roof, and to collect data to study the problem statistically by means of the ANOVA technique. The results of the statistical analysis have been represented in the form of tables by means of which it is possible to identify the characteristics of the chimney to be installed in a given roof for avoiding the overheating of ammable materials. Also a heating curve model for the estimation of the steady-state temperature from the temperature-time curves measured in experimental tests is proposed in the thesis. Finally, the characteristics of a device to be installed between chimney and roof to prevent the overheating of ammable materials have been identi ed, and the principle on which it is based is the coupling of conductive and insulating materials. The device should guarantee limited temperature on ammable materials also in conditions more critical than those prescribed by the EN 1859 standard.