Search Results (11)

This paper concerns measurements and CFD simulations of vacuum-insulated glazing (VIG), which consists of two glass panes separated by a narrow gap from which air has been removed. Distancers, e.g., in the form of small balls, are inserted into this gap every few centimeters to prevent the glass from deflecting. In the first part, simulations of two-pane VIG thermal transmittance with the Ansys Fluent program are described, resulting in thermal transmittance of VIG without the network of distancers equal to 2.18 W/(m²K) and with the distancers equal to 2.29 W/(m²K). The influence of the supports on the thermal transmittance of VIG is also determined. The CFD results show that the supporting balls increase the two-pane VIG thermal transmittance by about 0.15% with respect to the glazing without the distancers. Then, VIG is analyzed both numerically and tested in two measurement stands. Firstly, the tests are performed in a guarded hot-plate apparatus, according to the EN ISO 8302 standard. The two-pane glazing with one low-emissivity coating has a measured thermal transmittance equal to 1.75 W/(m²K). Other measurements were undertaken in the calorimetric chamber equipped with the hot-box apparatus. The results of the numerical assessment are then compared to the measurements of the existing three-pane vacuum-insulated glazing with two low-emissivity coatings, the same as simulated. The procedure follows the EN ISO 8990 standard. Measurement results of 1.10 W/(m²K) are compared to the simulation results of VIG thermal transmittance equal to 1.09 W/(m²K). A satisfactory agreement is reached. Additionally, this paper considers a new correction coefficient to thermal transmittance according to standard EN 673 in order to achieve a proper calculation of vacuum-insulated glazing in the center-of-glass region. The authors propose to use an adjustment coefficient of 1.05 when calculating the thermal transmittance of vacuum-insulated glazing without taking into account convection in the vacuum space and the thermal influence of distancers. Full article

Europe calls for a transition to the circular economy model based on recycling, reuse, the proper design of products, and repair. Recycling requires energy and chemical products for waste processing; on the contrary, reusing reduces the impact of transportation and expands the life of materials that cannot be recycled. This article highlights the characteristics of selected end-of-life materials; it aims to raise awareness among manufacturers to consider products’ conscious design to facilitate their reuse in different sectors. Panels 7 cm thick, realized by assembling cardboard packaging, egg boxes, bulk polyester, and felt, have been experimentally tested to understand whether they can be installed indoors to improve thermal and acoustic comfort. The panels’ equivalent thermal conductivity ${\lambda }_{eq}$ measured through the guarded hot plate method is 0.071 W/mK. Acoustic tests have been performed in a sound transmission room and a reverberation room. The weighted sound reduction index $R_w$ is 19 dB, the weighted sound absorption coefficient ${\alpha }_w$ is 0.30, and the noise reduction coefficient $NRC$ is 0.64. The measured properties have been compared to those of commercial materials, and the results show that the panels have interesting properties from the thermal and acoustic points of view. They could be employed in the building sector and in disadvantaged contexts where low-income people cannot afford commercial insulating materials. Although other factors, such as fire resistance, need to be evaluated, these results show that the proposed approach is feasible. Full article

Plaster is one of the most used and studied materials in the building process. This paper shows the result of the characterisation of a new plaster-based material enlightened and reinforced with polymers and end-of-life tyres’ recycled materials. As far as end-of-life tyres are a common waste item, this paper offers new recycling possibilities, as well as significant improvements in new building materials. Mechanical, thermal conductivity, sound absorption, fire reaction and environmental impact are studied and analysed. Three different end-of-life tyres’ recycled materials are used, two size rubber and textile fibres. A significant density reduction up to 17% was achieved mainly due to end-of-life materials lower density. Two thermal conductivity measurement methods, heat flux meter and guarded hot plate, were conducted and then compared. A 20% improvement with respect to the reference was achieved in those samples with textile fibre. The two methods’ measurements got a 1% difference in all samples analysed except textile fibre. Thus, this allowed to validate these methods and assure these measurements. Sound absorption was also measured. These materials reached α = 0.32 in high frequencies. Performance in low frequencies were lower. Fire tests led to no ignition results and no fire propagation. Finally, a basic global warming potential impact study based on environmental product declaration (EPD) is conducted. The most relevant result of this study is the potential 20–34% reduction of CO₂ emissions with the elaboration of these composites. Full article

The evolution of bio-based composites in the building industry is strongly linked with the growing demand for sustainable development, which is relevant nowadays. Hemp shives are a large group of organic residues that are obtained in the process of oil extraction as well as straw processing. These residues could be utilized along with a binder as constituents in the manufacture of bio-based building composites. This study is focused on the impact of density and relative humidity on the effective thermal conductivity of hemp shive-based bio-composites with a magnesium binder. For this reason, a series of samples with variable densities was manufactured and subjected to conditioning in a climatic chamber at a constant temperature and different relative humidity settings. As soon as samples were stabilized, the guarded hot plate method was applied to determine their thermal conductivities. Before each measurement, great care was taken during sample preparation to ensure minimum moisture loss during long-lasting measurements. The results showed that an increase in sample density from 200 kg/m³ to 600 kg/m³ corresponded to up to a three-fold higher composite thermal conductivity. In the case of sample conditioning, a change in relative humidity from a very low value to 90% also resulted in almost 60% average higher thermal conductivity. Full article

In many cases of heat treatment of steel products, the heated charge has a porous structure. The examples of such charges include bundles of long steel components e.g., bars. The basic thermal property of the charge in this form is effective thermal conductivity k_ef. This paper presents the results of experimental examinations of effective thermal conductivity of the porous charge, which is composed from various types of steel long components. Due to the specific nature of the samples, a special measurement stand was constructed based on the design of a guarded hot plate apparatus. The measurements were performed for sixteen different samples across a temperature range of 70–640 °C. The porosity of the samples, depending on the type of components used, ranged from 0.03 to 0.85. Depending on these factors, the effective thermal conductivity ranged from 1.75 to 8.19 W·m⁻¹·K⁻¹. This accounts for 0.03 to 0.25 of the value of thermal conductivity of the solid phase of the charge, which in the described cases was low-carbon steel. It was found that the effective thermal conductivity rises linearly with temperature. The intensity of this increase and the value of coefficient k_ef depend on the transverse dimension of the components that form the charge. The results may represent the basis for the validation of various models of effective thermal conductivity with respect to the evaluation of thermal properties of the porous charge. Full article

This study examined the moisture vapor permeability and thermal wear comfort of ecofriendly fiber-embedded woven fabrics in terms of the yarn structure and the constituent fiber characteristics according to two measuring methods. The moisture vapor permeability measured using the upright cup (CaCl₂) method (JIS L 1099A-1) was primarily dependent on the hygroscopicity of the ecofriendly constituent fibers in the yarns and partly influenced by the pore size in the fabric because of the yarn structure. On the other hand, the moisture vapor resistance measured using the sweating guarded hot plate method (ISO 11092) was governed mainly by the fabric pore size and partly by the hygroscopicity of the constituent ecofriendly fibers. The difference between the two measuring methods was attributed to the different mechanisms in the measuring method. The thermal conductivity as a measure of the thermal wear comfort of the composite yarn fabrics was governed primarily by the pore size in the fabric and partly by the thermal characteristics of the constituent fibers in the yarns. Lastly, considering market applications, the Coolmax^®/Tencel sheath/core fabric appears useful for winter warm feeling clothing because of its the good breathability with low thermal conductivity. The bamboo and Coolmax^®/bamboo fabrics are suitable for summer clothing with a cool feel because of their high thermal conductivity with good breathability. Overall, ecofriendly fibers (bamboo and Tencel) are of practical use for marketing environmentallyfriendly high-performance clothing. Full article

The use of renewable and natural materials characterized by the low environmental impact is nowadays a key issue for the sustainable development of the construction industry. For this reason, the interest for natural fibers, to be used as reinforcement in composites as an alternative to other fibers, is continuously growing. In this paper, the use of hemp for reinforcing lime mortar used as plaster is considered with a multidisciplinary approach, taking into consideration the structural and thermal performance. Natural fibers have several advantages compared to industrial ones, such as low cost, low environmental impact, biodegradability, renewable nature. Moreover, these can show remarkable mechanical performance in relation to specific weight, and sometimes, as in the case of hemp fibers, these can improve the thermal insulation capacity of the plaster. However, the experimental results on the mechanical features are still lacking, especially to assess their durability, and the variability of thermal parameters with the mechanical characteristics. Therefore, this paper proposes an experimental program, developed at Laboratory of Materials and Structures (LAMAS) of the University of Sannio (Italy), aimed at investigating the main mechanical properties (compression strength, flexural strength) of lime mortar reinforced by hemp fibers and subjected to various environmental exposures and aging processes. The characterization is completed with the measurement for the produced samples of the thermal conductivity by means of the standardized guarded hot plate technique. Full article

Insulation performance in older buildings is usually poor, so retrofitting the insulation in these buildings would reduce the energy required for heating, resulting in cost and energy savings. Windows account for a significant amount of the heat loss, therefore, we have developed vacuum layer type vacuum insulation panels (VIPs) with a frame structure that is also slim and lightweight. The developed VIPs are inexpensive and easy to install, as well as being slim and translucent, so retrofitting the window insulation of existing buildings can be easily performed. In this paper, we propose a frame covering with a low emissivity film and a gas barrier envelope coating, with a focus on a reasonable design method. Firstly, a structural model was created to evaluate the safety and specifications of the frame using element mechanical analysis. Next, a finite element model (FEM) was created to predict the insulation performance. Subsequently, experimental validation was completed and the insulation performance was evaluated with the measured thermal conductivity by a guarded hot plate (GHP) apparatus. Finally, case studies were used to evaluate the insulation performance under different conditions. The optimum design included a reasonable frame-structure to hold the vacuum layer with a high insulation thermal conductivity performance of approximately 0.0049 W/(m·K). Full article

The authors develop slim and light-weight vacuum insulation panels (VIPs) by producing vacuum layers with spacers and plastic plates. The developed VIPs have the advantages of a low cost and easy installation, thus facilitating retrofitting insulation of existing buildings. In addition, one of the developed VIPs is slim and translucent so it can be easily used for windows in an internal installation. In this paper, the authors first propose a vacuum layer type slim translucent VIP and focus on a reasonable design method. Next, the authors introduce the design process in which the structural design is obtained with element mechanical analysis and a three-dimensional analysis is conducted for the VIP element. In the study, a heat transfer model is used to predict the insulation performance through finite element analysis (FEA). Subsequently, the authors perform an experiment to measure the thermal conductivity in a guarded hot plate apparatus to validate the performance prediction. Finally, case studies are performed to confirm how the different design conditions affect the insulation performance. The optimum design of the vacuum layer type slim and translucent VIP will have a sufficient structural strength to hold and maintain the vacuum layer. The thermal conductivity is approximately 0.007 $\mathrm{W}/\left(\mathrm{m}·\mathrm{K}\right)$ , which can effectively improve the insulation performance in applications. Full article

The thermal conductivity of soils and rocks constitutes an important property for the design of geothermal energy foundations and borehole heat exchange systems. Therefore, it is interesting to find new alternatives to define this parameter involved in the calculation of very low enthalpy geothermal installations. This work presents the development of an experimental set-up for measurements of thermal conductivity of soils and rocks. The device was designed based on the principle of the Guarded Hot Plate method using as heat source a laboratory heater. The thermal conductivity of thirteen rocky and soil samples was experimentally measured. Results are finally compared with the most common thermal conductivity values for each material. In summary, the aim of the present research is suggesting a procedure to determine the thermal conductivity parameter by a simple and economic way. Thus, increases of the final price of these systems that techniques such as the “Thermal Response Test” (TRT) involvs, could be avoided. Calculations with software “Earth Energy Designer” (EED) highlighted the importance of knowing the thermal conductivity of the surrounding ground of these geothermal systems. Full article

The thermal conductivity of straw bales is an intensively discussed topic in the international straw bale community. Straw bales are, by nature, highly heterogeneous and porous. They can have a relatively large range of density and the baling process can influence the way the fibres are organised within the bale. In addition, straw bales have a larger thickness than most of the insulating materials that can be found in the building industry. Measurement apparatus is usually not designed for such thicknesses, and most of the thermal conductivity values that can be found in the literature are defined based on samples in which the straw bales are resized. During this operation, the orientation of the fibres and the density may not be preserved. This paper starts with a literature review of straw bale thermal conductivity measurements and presents a measuring campaign performed with a specific Guarded Hot Plate, designed to measure samples up to 50 cm thick. The influence of the density is discussed thoroughly. Representative values are proposed for a large range of straw bales to support straw-bale development in the building industry. Full article