Effects of the coupling of insulating and conductive materials to limit the temperature at chimney-roof penetration

Recently, many roof fires have occured in Europe due to the presence of a chimney. Since also certified chimneys were involved in the fires, chimneys producers have attempted to propose some solutions. However, these latter may sometimes not be effective, especially if the chimney operating conditions are more severe than those in the chimney certification procedure. Consequently, given the relevance of the problem, the scientific community was asked to identify the causes of the fires, and many studies presented in the literature have shown some points to be taken into account when designing and testing a chimney. Since heat transfer at chimney-roof penetration depends on many variables, recently, it was proposed to limit the temperature at this point by means of a device. The device should limit the temperature in very thick and insulated roofs, and in any chimney operating condition, that is, in normal chimney operating conditions and during soot fire events. Such a device is called CEIL and its features were identified in a numerical study presented in the literature. Differently from the device in the market, the CEIL device is made of conductive elements and insulating materials. The function of the insulating layer is the limitation of the heat flux from the chimney to the roof, whereas the function of the conductive elements is the facilitation of the heat transfer from the device to the surrounding. In other words, the conductive elements act like fins that dissipate heat to the ambient. Given that no experimental test was performed, this paper presents the results of an experimental campaign performed to assess the efficacy of the CEIL device and to investigate aspects not taken into account in the preliminary numerical investigation. The experimental campaign has taken into account the most critical chimney operating conditions identified in the literature and it has consisted into three phases. Firstly, it has been investigated whether a device of fixed dimension can effectively be installed in any roof. In the second phase it has been investigated whether a conductive element installed in the clearance can actually limit the roof temperature in very critical operating conditions represented by high exhaust gas temperature in the chimney and small air infiltration in the materials at the chimney-roof penetration. Finally, the effectiveness of a device 200 mm thick in height and 100 mm thick in width has been assessed in different operating conditions. Results show that the coupling of an appropriate number of conductive elements and insulating layers can limit the roof temperature effectively. For example, the presence of a conductive element reduces the roof temperature from 140°C to 70∘C with a device 5 cm thick when the exhaust gas temperature is 500∘C. A device made of an insulating layer 100 mm width and two conductive elements keeps the roof temperature at 61∘C when the exhaust gas temperature is maintained at 650∘C until the achievement of the steady condition and it is risen at 970∘C for 30 min.