Thermal Conductivity Of Building Materials Research Articles

Experimental Thermal Conductivity Measurement of Hollow-Structured Polypropylene Material by DTC-25 and Hot Box Test

In this study, experimental measurements of porous polypropylene (PP) using the DTC-25 TA laboratory equipment and a hot box test are compared. The thermal conductivity of building materials indicates their insulation capability. Excellent building materials will have a lower thermal conductivity value as well as other building insulator performance metrics. While results show that increasing the volume fraction of fluid in porous PP has an inverse association with the thermal conductivity of the material, as predicted by porous media theories, there is a marked difference in the measured values of thermal conductivity using the two methods. The thermal conductivity values of porous PP from the DTC-25 and the hot box test were 0.21 and 0.0033 W/mK, respectively. The difference in the thermal conductivity values was due to the misapplication of the Fourier’s guarded heat flow model in the DTC-25 device to a convective fluid porous medium.

INTEGRATED APPROACH TO ENERGY EFFICIENT BUILDING DESIGNING BASED ON BIM

Problem statement. The design of energy efficient buildings requires compliance with a number of criteria. The use of energy efficient constructions and building materials, the use of energy efficient engineering solutions and high performance equipment can more than halve a building's resource consumption. But it is important to select and define the characteristics individually. A real estate object must therefore, first of all, be designed correctly. Calculated designs, reasonably selected building materials and correct calculations from thermal engineering calculators do not guarantee obtaining a heat-insulating and vapor-insulating envelope without gaps. Due to the complexity of the construction object, it is problematic to identify thermal bridges and take into account weak points without an integrated approach to the design of the future building. The climate, geographical location and terrain must also be taken into account. In order to carefully select the optimal design solution, it is necessary to take a large array of data related to energy efficiency indicators. In classic design systems, such information is not displayed or analyzed. It is very difficult to assess the energy efficiency of the project. The technology of building information modeling, or BIM, makes it possible to radically simplify the task of designing energy efficient buildings. The purpose of the article is to substantiate the use of modern programs based on VIM technologies at the stage of energy efficient building design, to determine the criteria for selecting a software complex that will allow you to perform building simulation, calculate energy efficiency indicators, analyze thermal bridges, visualize the results, and issue a package of working documentation within the framework of one program. Demonstrate a highly detailed three-dimensional model of the building enriched with maximum information: data on the thermal conductivity of building materials and technical characteristics of equipment.

Refinement of thermal engineering calculations results taking into account actual materials characteristics

The article presents the laboratory studies results of building materials thermophysical characteristics used in the construction of experimental wooden buildings. In the framework of laboratory experiments, the thermal conductivity and humidity of structural and thermal insulation materials samples were evaluated. The analysis and comparison of the results obtained with the characteristics of the materials declared by the manufacturers and in the reference data is carried out. The results of thermal engineering calculation refinement of the of the enclosing structures of experimental wooden buildings, taking into account the results of laboratory studies of the thermophysical characteristics of building materials used in construction, are presented. The thermal engineering calculation of the enclosing structures of the frame part of experimental buildings has been refined taking into account the actual thermal conductivity of building materials. The influence of the actual thermophysical characteristics of building materials on the results of thermal engineering calculation in comparison with the design values was evaluated. Further directions of research are presented in terms of the influence of cold bridges and inhomogeneities of structures on the thermal characteristics of the thermal contour of the building.

The effect of moisture transfer on heat transfer of roof-wall corner hygrothermal bridge structure

Due to effects of moisture transfer, the hygrothermal bridge could be developed at building corners, and increase the thermal conductivity of building materials. Three different types of roof-wall corners (ring beam, double beam column and shear wall structure) were studied. When considering moisture transfer, effects of different air states, structural types and wall materials on the thermal performance of the hygrothermal bridge were evaluated and heat losses of the structure were compared. Given the periodic boundary conditions, the dynamic thermal response of the hygrothermal bridge after moisture transfer was analysed. Among three types of corners, the increase of heat flow through the most detrimental point of the ring beam structure corner was the largest (34.7%) after considering moisture transfer. The heat flow loss rate of the shear wall structure was the lowest (15.2%). When clay brick was used at the corner rather than aerated concrete for walls, a lower proportion of latent heat flow and higher (8.6%) heat flow loss rate were shown after considering moisture effects. Furthermore, the dynamic thermal response was influenced by multi-dimensional and moisture effects. The time lag was reduced with increasing humidity, while the thermal bridge effects increased the deterioration of the time lag.

Optimization of the thermal conductivity test for building insulation materials under multifactor impact

The thermal conductivity of building materials is an important parameter in building thermal engineering and energy conservation. When building thermal insulation materials are placed in the real environment, they are affected by dynamic temperature and humidity conditions, and most materials have certain moisture content. However, moist materials have a different thermal conductivity than dry materials, and an inaccurate estimation of thermal conductivity will cause errors in the energy conservation calculation of the building envelope. To accurately measure the thermal conductivity under a controllable environment and reduce energy conservation calculation errors, the effects of the measuring apparatuses, drying temperature, specimen size, specimen moisture content, ambient temperature and humidity on the thermal conductivity of the building thermal insulation materials are studied. The sensitivity of thermal conductivity to various influencing factors is analyzed, and the thermal conductivity value of moist building thermal insulation materials is determined as the basis to select or design products for building envelopes. In addition, the test method of thermal conductivity for building thermal insulation materials is optimized.

Thermal Conductivity of Building Materials in Iraq

Thermophysical Properties of Building Materials are Considered to have high importance in predicting building thermal performance, calculating thermal loads inside building, and optimizing the use of a building and insulating materials. Due to the lack of measurements of local building materials properties, designers and air- conditioning engineers have no choice but to use the published foreign data, which probably leads to inaccurate predictions of thermal loads and may give a false thermal performance. At the same time, it leads to an over-designed capacity of air- conditioning systems that lead to increased energy consumption in the building. Thus, it is clear that it was important to conduct this research to evaluate the thermal conductivity and thermal resistance of Iraqi building materials. The number of the local building materials were listed, and specimens were collected from their sites, factories, and suppliers such as bricks, stones, concrete products, gypsum, etc. Those samples were dimensioned to the specific size required when a measurement was conducted by the Hot Wire method. All measurements were carried out at room temperature. The relationship between thermal conductivity, density, moisture content, and pressure for a number of materials was Studied. A comparison between the measurements of the Iraqi building materials and results published in the ASHRAE, CIBS Guide, Australian Specifications, and Jordanian Specifications was made. However, the availability of such data is important for the climatic design of buildings, thermal load calculations for air- conditioning, and choosing the insulating materials.

Effect of recycled concrete aggregate (RCA) on mortar's thermal conductivity susceptibility to variations of moisture content and ambient temperature

Temperature and moisture are two factors that affect the thermal conductivity of building materials. Furthermore, the use of recycled concrete aggregate (RCA) in cementitious composites reduces their thermal conductivity due to increased porosity. However, this increase in porosity may affect the material's thermal conductivity susceptibility to changes in environmental conditions. No studies were found on the effect of RCA on thermal conductivity's susceptibility to moisture content and ambient temperature variations in cement mortars . To study these effects, a total of 135 thermal conductivity tests were performed on mortars with three levels replacement of natural aggregate by RCA, at different saturation degrees and temperatures within the range of expected service-life values. Compressive and flexural strength, permeable porosity, and bulk density were also evaluated. Remarkably, the use of RCA reduces the thermal conductivity's susceptibility to changes in ambient temperature. Besides, RCA increases the porosity, magnifying the susceptibility of thermal conductivity to moisture variations. These variations should be considered when thermal insulation is used as a factor for the environmental impact assessment of cement mortars. Finally, a combination of response surface method models was used to formulate a prediction equation that accurately estimates (error <5%) the thermal conductivity of cement mortars as a function of accessible porosity , saturation degree, and ambient temperature. This research contributes to a deeper understanding and more accurate prediction of RCA's effects on thermal conductivity of cementitious composites as a function of the environmental conditions, which is key to assessing RCA mortars' environmental impact during service life as part of a building component. • RCA reduced the thermal conductivity's susceptibility to ambient temperature changes. • Thermal conductivity's susceptibility to moisture content increases with RCA. • The increase on this susceptibility is related to the increase of porosity. • Thermal conductivity depends on porosity, moisture content and ambient temperature. • An equation that accurately estimates thermal conductivity of mortars is proposed.

Effect of using natural and local environment contents on the thermal conductivity of building materials; case in Medina, Saudi Arabia

The previous literature indicated that thermal characteristics of the local environment of Medina were not addressed despite its apparent importance and abundant availability. The aim of this study is to investigate the use of local environment contents in buildings, its thermal effect and obtain the optimum content that minimizes energy cost. Experimental investigation on thermal conductivity of building materials was conducted on seven different samples at 60 °C hot plate temperature. Thermal conductivity values of volcanic tuff, rose, green and limestone rocks were found between 0.12 and 0.211 W/m k, 0.5195–1.1035 W/m k, 0.21–0.334 W/m k and 0.209–0.5582 W/m k respectively. It was concluded that the thermal conductivity of the mixture of cement with stones and sand extracted from the Medina region varied between 0.388 and 0.4155 W/m k, which showed a decrease of 37.75%–49.74% when compared with the reference value of cement at 0.78–1.1 W/m k.

Effects of Black Scoria on Mechanical Properties and Thermal Insulation Properties of Building Materials

The effect of fine black scoria on the mechanical properties and thermal conductivity of building materials was investigated in this study. Black scoria was used to replace cement in concrete with various percentages. Four concrete samples containing 0%, 10%, 20%, and 30% black scoria were prepared. Characterization black scoria was performed via X-ray powder diffraction, X-ray fluorescence, scanning electron microscopy, thermogravimetric analysis, and differential scanning calorimetry analysis. Then, the compressive strength of the samples was investigated after 14, 21, 28, and 91 days of curing at room temperature. Finally, the thermal conductivities of the samples were measured after 28 days. Based on the experimental results, the highest compressive strength among the samples was 45.3 MPa, obtained from the mixture containing 10% black scoria after 91 days of curing. It was also observed that the average thermal conductivity of the concrete samples decreased with an increase in the fine black scoria content from 1.8 to 0.193 W m−1 K−1. Thus, black scoria is an appropriate substitute for commercial admixtures in cement composites in thermally insulating building materials due to its low density, excellent compressive strength, and good heat insulation properties.

The Influence of Salts’ Presence in the Materials on their Moisture and Thermal Conductivity

Energy saving in buildings is largely determined by the energy efficiency of the external building envelopes. The latter, as a rule, are the multilayer and incorporate structural and heat-insulating layers. The presence of individual hygroscopic salts and their mixtures in building materials changes their physical and chemical properties. Due to the increase in the sorption properties of building materials and changes in the inter-pore substance composition, humidity increases and the heat-protective properties decrease. This paper presents the results of the experimental and theoretical studies on the salts’ effect assessment on the change in moisture content and thermal conductivity of building materials due to the salt solutions and crystals’ presence in the pore space. To study the saline building materials’ thermal conductivity, the mathematical modeling methods using the theory of flow and bringing the materials’ structure to a unit cell are used. It is shown that the change in thermal conductivity occurs due to the crystalline salt precipitation from the solutions in the material’s pores, to the changes in their initial chemical properties, to the changes in the properties of the vapor-air mixture above the salt solutions due to diffusion. The results obtained make it possible to establish the hygroscopic salts’ influence significance in solid and liquid phases on the building materials’ thermal conductivity. A scheme for determining the thermal conductivity of building materials is proposed, taking into account salt effects, including the determination of: the components’ volume concentrations; sequentially the thermal conductivity of the material’s shell; salt crystals, a solid phase consisting of the material’s shell and crystalline salt, a binary and multicomponent saline solution, the pore space and the pore substance inside. The general formula for determining the thermal conductivity of a saline building material is given.

Features and results of assessment the thermal conductivity of building materials and products by the active method of thermal non-destructive testing

Thermal control (passive and active) is a non-destructive testing method. During passive thermal control, the test object is characterized by a temperature field formed during its operation. In active thermal control, the test object is additionally thermally stimulated. This technique is widely used in various areas of construction, energy, mechanical engineering, transport. This paper proposes a variant of active thermal non-destructive assessment of the thermal conductivity coefficient of building materials and products on the example of a fragment of a building structure made of silicate bricks. The test object is subjected to thermal stimulation by an external source of thermal energy before reaching a steady-state thermal regime. Thermography of the test object surfaces is carried out. The average integral temperatures of surfaces or individual sections of the test object are calculated. The coefficient of thermal conductivity of the test object is determined, which is used to calculate its thermal resistance (resistance to heat transfer). After that, the coefficient of heat transfer is calculated. The method was implemented in laboratory conditions. It can be used in natural and operational conditions for accurate and quick determination of the key thermophysical properties of building materials and products.

Rice husk incorporated foam concrete wall panels as a thermal insulating material in buildings

The major segment for energy consumption is found in industry, transport, agricultural, residential and commercial sector. The main part of the energy consumption in residential and commercial buildings is due to the use of mechanical devices to maintain a comfortable indoor environment. Thermal conductivity of building materials is one of the factors which influence the heat transfer in buildings. Thermal conductivity can be reduced by the use of materials with low density. The present paper reports the development of a sustainable thermal insulating external wall panel and its mechanical, thermal and durability properties. The wall panel was prepared using foam concrete and rice husk and replacing the cement by fly ash. Strength of panel was tested by conducting in plane bending test and compressive strength test. Thermal conductivity was tested using guarded hot plate apparatus. Durability properties were tested by conducting water absorption test, drying shrinkage and acid resistance test. The test results showed that the rice husk and fly ash content had a major influence on the thermal conductivity and durability properties of the developed wall panels.

Comprehensive correction of thermal conductivity of moist porous building materials with static moisture distribution and moisture transfer

Accurate determination of the thermal conductivity of building material is key to calculating its heating/cooling loads and energy consumption. The thermal conductivity of building material is not only related to the pore structure characteristics but also the internal static moisture distribution and moisture transfer characteristics, and the mechanisms of both differ in how they affect the internal heat transfer performance. This paper analyzed the influential quantitative relations between the static moisture distribution and moisture transfer with respect to the thermal conductivity of building materials in different hygrothermal environments. The analysis is based on the additional thermal conductivity calculation method derived from static moisture distribution and moisture transfer proposed by us. The results show that the static moisture distribution has a notable influence on the thermal conductivity under the heating conditions in winter, whereas the influence of moisture transfer is negligible. Nonetheless, the influence of both factors on the thermal conductivity should be considered during air-conditioning in summer. The comprehensive correction rate of the thermal conductivity of building materials in typically hot and humid areas in China are determined, and the influence of the thermal conductivity of moist building materials on the heat transfer coefficient of enclosure structures is analyzed.

On the Problems of Determining the Thermal Conductivity of Building Materials

On the Problems of Determining the Thermal Conductivity of Building Materials

Experimental Investigation on Thermal Conductivity of Building Materials Manufactured from Paper Wastes

Experimental Investigation on Thermal Conductivity of Building Materials Manufactured from Paper Wastes

Thermal conductivity of insulations approached from a new aspect

In the literature, several definitions can be found for the thermal conductivity; however, many of them are not clearly explained. The easiest explanation is the following: the property of a material to conduct heat. It is evaluated primarily in terms of Fourier’s Law for heat conduction. Nowadays, the examination of the thermal conductivity of building materials is very important both for the manufacturers and for the consumers. Nonetheless in real, confusing definitions and interpretations can be found regarding the exact meaning of the thermal conductivity of the materials. In physics and in engineering practice, the following appellations are used as heat conductivity, thermal conduction coefficient, design and declared values of the thermal conductivities as well as the effective thermal conductivity. In this article we would give an overview about the correct explanations of the above-mentioned values. At first thermal conductivity measurements of four different types of expanded polystyrene materials (EPS, 80, 100, 150, 200) will be presented by using Holometrix Lambda 2000 type Heat Flow Meter after drying them in a Venticell 111 type laboratory oven to changeless mass.

Using the heat flow plate method for determining thermal conductivity of building materials

The heat flow plate method is used to determine thermal conductivity of a building material sample made of Rohacell (insulating foam). Experimental technique consists in placing the sample with a reference material on top (polystyrene sample) in a calorimetric chamber and heating from underside. Considering that the heat flux which passes through the two layers is constant and knowing thermal conductivity of the reference material, the sample thermal conductivity is determined. The temperature difference between the two opposite sample’s sides is recorded only when the steady state is achieved (constant heat flux).

Nonlinear Effect of Moisture Content on Effective Thermal Conductivity of Building Materials with Different Pore Size Distributions

Understanding the quantitative relationship between the effective thermal conductivity and the moisture content of a material is required to accurately calculate the envelope heat and mass transfer and, subsequently, the building energy consumption. We experimentally analyzed the pore size distributions and porosities of common building materials and the influence of the moisture content on the effective thermal conductivity of building materials. We determined the quantitative relationship between the effective thermal conductivity and moisture content of building materials. The results showed that a larger porosity led to a more significant effect of the moisture content on the effective thermal conductivity. When the volumetric moisture content reached 10 %, the thermal conductivities of foam concrete and aerated concrete increased by approximately 200 % and 100 %, respectively. The effective thermal conductivity increased rapidly in the low moisture content range and increased slowly in the high moisture content range. The effective thermal conductivity is related to the moisture content of the materials through an approximate power function. As the moisture content in the walls of a new building stabilizes, the effective thermal conductivity of normal concrete varies only slightly, whereas that of aerated concrete varies more significantly. The effective thermal conductivity of the material is proportional to the relative humidity of the environment. This trend is most noticeable when the wall material is aerated concrete.

A correction factor to approximate the design thermal conductivity of building materials. Application to Spanish façades

The thermal conductivity of building envelope materials varies according to the conditions of temperature and moisture content. Precisely determining the thermal conductivity is a primary challenge in developing more appropriate, realistic thermal designs for buildings. However, a detailed implementation of environmental conditions requires either the use of sophisticated software programmes and the collection of a large set of climate data at each location or a laborious analytical calculation. To simplify the thermal design of buildings, regulations use normative conductivity values based on constant, standardised conditions of temperature and moisture content, which are independent of ambient conditions. This article proposes a correction factor that considers these conditions to functionally approximate the design thermal conductivity of materials based on their normative values. For this calculation, a procedure that simplifies the standard ISO 10456:2007 using the mean annual temperature and relative humidity data for each location is proposed. The procedure is applied in 52 Spanish cities to correct the conductivity values established by the Spanish regulation for façade materials. A correction map of Spain is presented. Finally, by using the ISO standard, the corrections are validated by comparing the values with the design thermal conductivities calculated for different case studies.

Inconsistency in Russian and international standards in the determination of the design values of thermal conductivity of building materials and products

Inconsistency in Russian and international standards in the determination of the design values of thermal conductivity of building materials and products