Davide Luscietti

Analysis of the temperatures measured in very thick and insulating roofs in the vicinity of a chimney

Chimneys convey exhaust gas produced in domestic heat appliances to the external environment and to do this they have to pass through elements such as roofs and floors. If these elements are made up of flammable materials the fire hazard may occur. In some European countries the number of roof fire is very high and they affect also certified chimneys, that is, tested following the prescription of the related standards. The aim of this paper is to highlight that the certification procedure does not allow to test chimneys in the worst condition, therefore, chimney installed following the manufacturer prescriptions may in some cases cause the overheating and subsequent roof fire. To do this, experimental tests have been performed for measuring the temperature on roofs in the vicinity of a certified chimney. The results show that the certification procedure should be revised.

Comparison between European chimney test results and actual installations

European standards regulate the certification procedure for determining chimney class temperature and the distance at which to install chimneys from combustible materials. These standards prescribe the heat stress test and the thermal shock test. The high number of roof fires due to the presence of a chimney that have recently occurred in European countries seems to be due to a weak certification procedure. In this article, experimental tests and numerical simulations have been performed to highlight the major differences between real and test conditions to identify critical aspects of the current certification procedure. The influence of the position of the chimney in the test structure, the thermocouples’ positioning and the thermal shock test initial condition have been investigated. It has been shown that flammable materials’ temperatures measured in the certification procedure can be lower than those in real installations, and this is mainly due to the fact that exhaust gas temperature in the certification procedure of chimneys can be even 350°C lower than in real installations. Then, real installations represent a more severe condition.

Computation of linear transmittance of thermal bridges in precast concrete sandwich panels

Precast concrete lightened sandwich panels are widely used building elements. They are made by two concrete wythes separated by a layer of lightweight material: the central layer is inhomogeneous due to the presence of concrete ribs which tie the external wythe and act as thermal bridges. Computation of thermal transmittance of sandwich panels is clearly described in European Standards, but in many cases it requires numerical simulations to determine the linear transmittance ψ associated with lightweight material-concrete interfaces in the inhomogeneous layer. Although simple, these simulations represent a critical issue for many panel manufacturers and they would much rather prefer correlations to compute ψ. In this work we present a correlation based on an artificial neural network (ANN) to estimate linear trasmittauce values for current Italian sandwich panel production. Five input parameters are considered: rib width, lightweight material conductivity, and thickness of the three panel layers. To obtain the data which are necessary to train and test the ANN, a fast and accurate Spectral Element Method is used to solve Laplace equation in the neighborhood of a rib. 5460 ψ values are collected which ensure an accurate network response.

Computing the exergy of solar radiation from real radiation data

The decrease of fossil fuels availability and the consequent increase of their price, has led to a rapidly evolution of renewable market and policy frameworks in recent years. Renewable resources include solar radiation which is of considerable interest as it is inexhaustible, free and clean. In order to calculate how much work can be obtained from solar radiation, several methods have been proposed in the literature. The aim of this work has been to calculate the exergy content of solar radiation in Italy. To do this, we have analyzed real radiation data and we have treated direct and diffuse radiation separately. We have proposed a single exergy factor valid on the Italian area, which is to be applied to the total radiation measured on horizontal surface.

Point Thermal Transmittance of Rib Intersections in Concrete Sandwich Wall Panels

ABSTRACT Concrete sandwich panels are building elements made by two concrete wythes separated by a layer of lightweight material: the central layer is inhomogeneous due to the presence of concrete ribs which tie the external wythes and act as thermal bridges. This paper deals with the problem of determining point thermal transmittance associated with rib intersections. Together with previous results by the authors, it allows accurate calculation of thermal transmittance of sandwich panels according to current International Standards. A dataset of 1080 point transmittance values is obtained upon use of a spectral element method, varying systematically material conductivities and thickness of panel layers, for the most common pairs of rib widths in current panel production. To limit the computational cost, a solution strategy based on the use of low-order polynomials on three grids of increasing refinement, coupled with Richardson extrapolation is adopted. Finally, a power law correlation is proposed that allows to estimate point transmittance within a relative error of 10%.