Device for Limiting the Temperature at Chimney-Roof Penetration in Very Critical Chimney Operating Conditions

In recent years, numerous roof fires have occurred due to the presence of a chimney, and also certified chimneys were involved. Chimneys installers and chimney producers are disoriented because the chimney certification does not guarantee safe installations, and also the performance of devices for limiting the roof temperature is uncertain. Results reported in this paper will help them to accomplish safe chimney installations. The paper describes the main features of a device to be installed at chimney-roof penetration for limiting flammable materials temperature and, consequently, the roof fires risk. The device is composed of elements made of insulating material to reduce the heat transfer from the chimney towards the roof, and elements made of conductive material to facilitate the heat transfer from the device itself towards the ambient. The features of the device have been investigated by means of 32 numerical simulations performed with a CFD code: in each numerical test a variable has been changed and the conditions that have determined the lowest roof temperature have been considered the most suitable. If compared to the temperature measured when only insulating material is installed at chimney-roof penetration, the conductive elements reduce the roof temperature of more than 1000°C. The optimal version of the device, that is, 100 mm thick and made of two conductive elements ensures a roof temperature lower than 85°C when the exhaust gas temperature in the chimney is 1000°C in steady conditions. In addition, the device avoids the formation of thermal bridges between indoor and external ambient, and it engenders heat recovery in indoor ambient.