1,720,987 research outputs found
Device for Limiting the Temperature at Chimney-Roof Penetration in Very Critical Chimney Operating Conditions
No full textIn 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
Thermal characterization of a multilayer coating for seismic and energy building renovation
Full text linkMany buildings built in Italy in the 60s and 70s need an energy requalification and at the same time an improvement of the seismic behaviour. A non-invasive method for a joint requalification consists of an anti-seismic plaster layer and a thermal coating. In this work, a multi-layer package of 3 cm of SFRM coating and 8 cm of wood fiber placed on a 20 cm masonry wall is analyzed. Numerical and experimental analysis allowed to characterize the wall, and to determine the influence of the connecting elements
Data on temperature-time curves measured at chimney-roof penetration
Full text linkData on temperature-time curves measured at chimney-roof penetration are reported here. The tests were performed in different configurations in order to reproduce all the possible conditions in which a chimney may operate. To do this, a chimney was installed in a corner test structure and in an axi-simmetric test structure, and in three roofs of different thickness, thermal resistance, and layers position. The space between chimney and roof was left open, sealed with metal sheets, sealed with insulating panels, and filled of insulating material respectively
Towards large-scale simulation of indoor thermal conditions in buildings supplied with district heating: Model evaluation based on experimental data
No full textUtility companies are studying ways to improve the energy efficiency of district heating networks and promote flexible solutions. However, the impact of any modification must be verified, especially when dealing with existing buildings whose heating systems were originally sized based on different design conditions. Predictive simulations are carried out for this scope. Several building energy simulation options are available, computational effort and availability of input data being the strictest constraints for their adoption. In this preliminary work, real temperature measurements from a multi-family house in a demo site supplied by an experimental district heating branch have been used to assess the performances of dynamic energy models of different complexity. Images, local registries and literature studies have been used as sources of input information. Despite the high degree of approximation of the available data, encouraging results are found, with a root mean squared error below 1.5 °C over the heating season for a single dwelling, while inertial effects need to be better modelled when the whole building is simulated. The opportunity of improving the consistency and coordination between public databases is also discussed as a way to increase energy mapping possibilities
Influence on energy demand of thickness, thermal conductivity, and volumetric heat capacity of ladle working lining in secondary steel-making process
Full text linkThe secondary steel-making process involves several steps during which steel is kept in a
ladle, that is, a vessel made of an outer steel layer (carpentry), an intermediate refractory layer, and
an internal refractory layer. Unlike the intermediate layer, the internal layer undergoes a progressive
reduction in thickness and a periodic restoration. Traditionally, it is made of alumina or magnesite.
During the process, the ladle undergoes unsteady heating and cooling; therefore, heat transfer
depends on thermal conductivity and heat capacity. This study aims to identify the ladle internal layer
characteristics that affect the energy demand. This analysis investigates the effect of the internal layer
thickness S, volumetric heat capacity C, and thermal conductivity λ. Through the Design Of the
Experiments (DOE), different scenarios have been selected and analyzed by means of numerical
simulations performed on a numerical model defined in COMSOL Multiphysics. The energy demand
as a function of the internal layer properties has been estimated, and it has emerged that low thermal
conductivity and heat capacity values require a lower amount of energy
Performance analysis of a large TES system connected to a district heating network in Northern Italy
Full text linkThe addition of storage capacity to district heating systems increases flexibility and expands the range of usable heat sources. Despite their apparently simple nature, thermal energy storage (TES) tanks display a wide range of performances due to different construction and operation choices, as proven by numerous literature studies. However, most of the investigations focus on domestic-size tanks of few cubic metres or, on the other hand, very large seasonal storages of hundreds of thousands of cubic metres. In this work, the performances of a 5000 m3 TES recently introduced in a district heating network in Brescia, Italy, are experimentally analysed using temperature and flow rate measurements acquired over two months in the heating season. First-law efficiencies, exergy, and stratification parameters are calculated and discussed. Energy and exergy efficiencies computed for all examined cycles are above 90%, in line with literature values for smaller and larger TESs. The thermocline profile is generally stable through the cycle unless anomalous events occur, and its average thickness is below 4% of the water height. The combined analysis of single-point indicators, thermocline profiles, and qualitative temperature heatmaps shows that short partial charge/discharge events followed by long stand-by periods negatively affect performances. Stratification efficiency and stratification number give further time-dependent information on the vertical distribution of temperatures in the TES. Heat losses towards the outside are also estimated and discussed in the light of integrative measurements performed on other TESs with similar characteristics, showing that particular care must be paid to the top, where dissipation could be increased by evaporation phenomena if the water surface is not protected
Energy- and exergy-based analysis for reducing energy demand in heat processes for aluminum casting
No full textIn this paper, energy- and exergy-based analysis is used to analyze a factory with high energy demand for the production of aluminum discs. The analysis is focused on heat processes that take place in a melting furnace, a casting machine, a heat treatment oven, and a drying oven. Energy and exergy efficiencies are computed to assess the room for the improvement of the energy efficiency processes. The analysis shows that a large amount of energy is lost due to heat losses to the environment, and solutions for reducing energy demand and emissions have been identified. Instead of changing the equipment of a factory, significant improvements and consequent reduction of fossil fuels consumption can be obtained by increasing the thermal insulation of some components and by means of waste heat recovery performed by heat exchangers, with a consequent energy demand reduction of 15%
Experimental Analysis of Chimneys in Wooden Roofs
No full textThe number of fires in roofs crossed by chimneys is high. According to the manufacturers' prescriptions, chimneys can be installed in direct contact with roof combustible materials or be spaced from them. In this paper, the influences of the installation mode and of the roof characteristics on the temperatures reached by the combustible materials are investigated by means of twelve experimental tests. Three roofs and four installation modes are analyzed to investigate whether and how they influence the temperatures of the materials surrounding the chimney and, hence, the consequent fire hazard. One roof is representative of the setup currently used in certification procedure, and the other two are representative of roofs in energy-saving buildings. The space between chimney and roof (clearance) has been left open to reproduce the condition in the certification procedure. Then, for reproducing the installation modes that may occur in real installations, the clearance has been sealed with metal sheets, sealed with insulating panels, and filled with insulating materials. Results show that temperatures are strongly affected by these variables, and in real installations, temperatures can be much higher than those measured in the certification procedure. For this, the existing standard should be reviewed accordingly
Dynamic approach to evaluate the effect of reducing district heating temperature on indoor thermal comfort
No full textTo reduce energy consumption for space heating, a coordinated action on energy supply, building fabric and occupant behavior is required to realize sustainable improvements. A reduction in district heating supply temperature is an interesting option to allow the incorporation of renewable energy sources and reduce distribution losses, but its impact on the final users must be considered. This aspect is especially critical as most European countries feature an old building stock, with poor insulation and heating systems designed for high-temperature operation. In this study, a complete methodology is devised to evaluate the effect of district heating temperature reduction on the end users by modeling all the stages of the system, from the primary heat exchanger to the indoor environment. A dynamic energy performance engine, based on EN ISO 52016-1:2017 standard and completed with a heat exchanger model, is implemented, and its outputs are used to calculate thermal comfort indicators throughout the heating season. As a practical application, the method is used to evaluate different scenarios resulting from the reduction of primary supply temperature of a second-generation district heating network in Northern Italy. Several building typologies dating back to different periods are considered, in the conservative assumption of radiator heating. The results of the simulations show that the most severe discomfort situations are experienced in buildings built before 1990, but in recent buildings the amount of discomfort occurrences can be high because of the poor output of radiators when working at very low temperatures. Among the possible measures that could help the transition, actions on the primary side, on the installed power and on the building fabric are considered. The investigation method requires a limited amount of input data and is applicable to different scales, from the individual building to entire urban areas lined up for renovation
Flow models of perforated manifolds and plates for the design of a large thermal storage tank for district heating with minimal maldistribution and thermocline growth
No full textLarge water tanks are used as thermal energy storage components in district heating systems to store sensible heat produced by intermittent energy sources and to decouple the production of thermal energy from its demand. Good thermal stratification is crucial for energy storage efficiency, thus flow maldistribution and mixing of water layers at different temperatures should be minimized. This paper proposes an innovative internal flow distribution configuration for a large-size thermal energy storage, and develops new simplified analytical models for the choice of its design parameters. In the novel configuration, water is injected into (and collected from) the cap volumes of the tank by flowing radially inward (outward) through several small orifices of a peripheral toroidal manifold. Two horizontal perforated plates cover the full cross sections downstream of the manifolds and rectify the vertical flow, thus reducing mixing. Uniform perforation pitch was analytically demonstrated to be the most reasonable solution both for the toroidal distributors and for the rectifying plates. A 1D model was developed to predict the time evolution of the vertical temperature distribution in the tank. The turbulence-related parameters that could not be inferred from the existing fluid-mechanics literature were initially estimated with CFD simulations. The results of CFD-calibrated model were then compared to experimental data obtained from a full-scale large water-tank facility recently built in Brescia according to the proposed design. After a re-calibration of the exponent defining the decay of homogeneous turbulence downstream of the perforated plates, good agreement was found between measured and predicted vertical temperatures. With the novel inlet design, a thermocline of about 0.5 m is established immediately downstream of the perforated plate, and remains practically constant along time. The model is important to minimize and control the thermocline thickness so as to maximize the recoverable thermal energy, not only at the tank design stage but also to identify optimal loading and unloading protocols
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