Publications

Despite the importance of thermal conductivity for a range of modern glass applications, its compositional dependence and structural origins in modified oxide glasses remain poorly understood. In particular, the thermal conductivity of oxide glasses with network formers other than silica remain almost unexplored and no thorough connection with structural characteristics of glasses has been made. In this work, we study the thermal conductivity of binary lithium borate glasses using both experiments and classical molecular dynamics (MD) simulations. This glass system is chosen due to the nonmonotonic evolution in the boron coordination number as a function of composition and because glasses may be made in a wide compositional window. Specifically, we show that thermal conductivity exhibits a clear boron anomaly effect, as observed in both experiments and MD simulations. Thermal conduction is thus believed to mainly be promoted by the presence of fourfold coordinated boron. However, simulated vibrational density of states for the studied series suggests that the thermal conductivity is also influenced by the presence of the modifier ions based on an observed overlap between Li and O modes. Overall these results provide insights into the connection between thermal conductivity and structure of modified oxide glasses, which is the first step toward developing a model for predicting the composition dependence of thermal conductivity.

The goal of the project CleanTechBlock 2 is to develop and test a durable and sustainable construction wall element which complies with the building regulations of 2020, and has a certain aesthetics attractiveness. The CleanTechBlock (CTB) prefabricated elements consist of cellular glass insulation blocks mounted in between two layers of brick masonry [1] [2].

The aim of this technical document is to report the results of the different experimental investigations performed on the CTB and other commercial cellular glass samples to determined their thermal conductivity. These experimental investigations have been carried out at the Laboratory of Building Energy and Indoor Environment at the Department of Civil Engineering of Aalborg University (Denmark).

The aim of this technical report is to provide a large collection of the main thermos-physical properties of various common construction materials and materials composing the elements inside the indoor environment of residential and office buildings. The Excel file enclosed with this document can be easily used to find thermal properties of materials for building energy and indoor environment simulation or to analyze experimental data.

In recent years, research has identified some bio-based, porous building materials as good or excellent regulators of moisture in buildings. The ability of a material to absorb, release and store moisture is described by vapour sorption isotherms. It is necessary input to simulations of indoor environmental parameters in regards to human comfort, and nowadays it can be determined by a number of laboratory experiments, each of which characterized by specific specimen size, equilibration time and methodology.

The purpose of this study is to experimentally derive isotherms for three bio-based, porous building materials by a standardized testing method, using saturated salt solutions. Furthermore, results from the standard method are compared to values of moisture content for the same materials, obtained by air-drying at different relative humidity. This is done with the aim to compare the findings from the two methods with respect to time and repeatability of the results.

Derived isotherms are further used as direct input in the building simulation software BSim, which is capable of predicting indoor environment parameters by solving coupled, transient heat and moisture transport equations using finite volume method discretization. Indoor air relative humidity and moisture content distribution in the construction are compared for the experimented materials and conventional building materials.

Results show better agreement between isotherms obtained by standard method and air-drying for low density materials. Simulation results suggest that bio-based, highly porous building materials are comparable to conventional building materials in respect to air relative humidity variations, compared to conventional building materials.

The understanding of the thermal transport mechanism of foam glass is still lacking. The contribution of solid- and gas conduction to the total thermal conductivity remains to be reported. In many foam glasses, the solid phase consist of a mix of an amorphous and a crystalline part where foaming agents can be partially dissolved into the glass structure. We investigate the influence of incorporation of residues from foaming agents (MnO2 and Fe2O3) on the solid conductivity of cathode ray-tube (CRT) panel glass. We have prepared samples by sintering and melt-quenching technique to obtain samples containing glass and crystalline foaming agents and amorphous samples where the foaming agents are completely dissolved in the glass structure, respectively. Results show that the samples prepared by sintering have a higher thermal conductivity than the samples prepared by melt-quenching. The thermal conductivities of the sintered and the melt-quenched samples represent an upper and lower limit of the solid phase thermal conductivity of foam glasses prepared with these foaming agents. The content of foaming agents dissolved in the glass structure has a major impact on the solid thermal conductivity of foam glass. Hence, the solid thermal conductivity of foam glass can be optimized by altering the foaming agent and its content.

The increasing share of intermittent renewable energy on the grid encourages researchers to develop demand-side management strategies. Passive heat storage in the indoor space is a promising solution to improve the building energy flexibility. It relies on an accurate control of the transient building temperature. However, many of the current numerical models for building energy systems assume empty rooms and do not account entirely for the internal thermal inertia of objects like furniture. This review article points out that such assumption is not valid for dynamic calculations. The furnishing elements and other internal content can have a significant impact on the indoor thermal dynamics and on the occupants’ comfort. There is a clear lack of guidance and studies about the thermo-physical properties of this internal mass. Therefore, this paper suggests representative values for the furniture/indoor thermal mass parameters and presents the different available modelling technics. In addition, the large exposed surface area of furniture pieces offers a good potential for the integration of phase change materials. It can highly increase the effective thermal inertia of light frame buildings without any construction work.

Many numerical models for building energy simulation assume empty rooms and do not account for the indoor content of occupied buildings. Furnishing elements and indoor items have complicated shapes and are made of various materials. Therefore, most of the people prefer to ignore them. However, this simplification can be problematic for accurate calculation of the transient indoor temperature. This article firstly reviews different solutions to include the indoor content in building models and suggests typical values for its characteristics. Secondly, the paper presents the results of a numerical study investigating the influence of the different types of thermal inertia on buildings energy flexibility. Although the insulation level and thermal mass of a building envelope are the dominant parameters, it appears that indoor content cannot be neglected for lightweight structure building simulations. Finally, it is shown that the integration of phase change materials in wallboards or furniture elements can appreciably improve the energy flexibility of buildings.

In order to fit low energy building policies and reduce environmental impact of buildings, construction materials must have good balance between thermal properties and embodied energy. By using such materials, reduction of both operational and embodied energy are achieved simultaneously.

Hemp concrete is a bio-based building material composed of the woody core of industrial hemp and lime based binder. It is a non-load-bearing material, which can be used as floor and around structural frames for walls and roof. The material is characterized by relatively low environmental impact, moderate thermal properties and, high air and moisture permeability. The properties vary with binder composition, mixing and casting techniques, as well as intended application.

This research presents preliminary heat and moisture building simulations of single family house made out of hemp-lime composite. To evaluate the performance of hemp-lime, it is compared to models with common external walls, upon defined parameters.

The article also determines the variation of thermal conductivity for hemp-lime commercial plaster and wall mix, as a function of moisture content. The most promising binder composition and mixing proportions for the wall mixture are identified through literature review; thereafter samples for the experiment are prepared and tested in laboratory environment. Thermal conductivity is found by using Hot Plate Apparatus λ-meter EP500, while moisture dependence is established upon testing samples with different moisture content.

Results from the experiments show non-linear increase in thermal conductivity with increase in moisture content. The results and potential benefits of using hemp-lime are discussed and conclusions are drawn.