BRJ – Volume 61, Number 3, 2014
P. Staňák, J. Sládek, V. Sládek, S. Krahulec:
Numerical evaluation of effective thermal properties for materials with variable porosity ….. 129 – 142
A. Al-Swaidani, S. Aliyan, N. Adarnaly, B. Hanna, E. Dyab:
Influence of volcanic scoria on mechanical strength, chemical resistance and drying shrinkage of mortars ….. 143 – 150
R. Kittler, S. Darula:
The research search for the least beneficial overcast sky and progress in defining its luminance gradation function ….. 151 – 166
B. Mansoury, H. R. Tabatabaiefar:
Application of sustainable design principles to increase energy efficiency of existing buildings. 167-178
Numerical evaluation of effective thermal properties for materials with variable porosity
P. Staňák, J. Sládek, V. Sládek, S. Krahulec
In this paper a computational homogenization technique is applied to thermal analyses in porous materials. A volume fraction of pores on the microstructural level is the key factor that changes the macroscopic thermal properties. Thus, the distribution of thermal fields at the macroscopic level is analysed through the incorporation of the microstructural response on the representative volume element (RVE) assuming a uniform distribution of pores. For the numerical analysis the scaled boundary finite element method (SBFEM) is introduced to compute the thermal response of RVE. The SBFEM combines the main advantages of the finite element method (FEM) and the boundary element method (BEM). In this method, only the boundary is discretized with elements leading to the reduction of spatial dimension by one, similarly as in the BEM. It reduces computational efforts in the mesh generation and CPU time. The proposed method is used to study square RVE with a circular and elliptic pore under the thermal load. Dimensions of the pore are varied to obtain different volume fractions of matrix material. Numerical results for effective thermal conductivities obtained via SBFEM modelling show an excellent agreement with the finite element analysis using commercial software COMSOL Multiphysics.
Keywords: thermal conductivity, effective material properties, representative volume element (RVE), material porosity, scaled boundary finite element method
Influence of volcanic scoria on mechanical strength, chemical resistance and drying shrinkage of mortars
A. Al-Swaidani, S. Aliyan, N. Adarnaly, B. Hanna, E. Dyab
In the study, three types of cement have been prepared; one CEM I type (the control sample) and two blended cements: CEM II/A-P and CEM II/B-P (EN 197-1), each of them with three replacement levels of volcanic scoria: (10 %, 15 %, 20 % wt.) and (25 %, 30 %, 35 % wt.), respectively. Strength development of mortars has been investigated at 2, 7, 28 and 90 days curing. Evaluation of chemical resistance of mortars containing scoria-based cements has been investigated through exposure to 5 % sulphate and 5 % sulphuric acid solutions in accordance with ASTM C1012 & ASTM 267, respectively. Drying shrinkage has been evaluated in accordance with ASTM C596. Test results showed that at early ages, the mortars containing CEM II/B-P binders had strengths much lower than that of the control mortar. However, at 90 days curing, the strengths were comparable to the control mortar. In addition, the increase of scoria significantly improved the sulphate resistance of mortars. Further, an increase in scoria addition improved the sulphuric acid resistance of mortar, especially at the early days of exposure. The results of drying shrinkage revealed that the CEM II/B-P mortar bars exhibited a greater contraction when compared to the control mortar, especially at early ages. However, drying shrinkage of mortars was not influenced much at longer times.
Keywords: strength, chemical attack, drying shrinkage, blended cement, durability, natural pozzolan
The research search for the least beneficial overcast sky and progress in defining its luminance gradation function
R. Kittler, S. Darula
Recently illuminance levels under ISO/CIE homogeneous standard sky types were characterised in their relative terms after ISO/CIE (2004, 2003) standardised as normalised by the luminance in the zenith. Sky luminance and horizontal illuminance based on the gradation and scattering indicatrix functions, including the extreme overcast cases frequently encountered in nature, were recently determined in absolute physical units of luminance in kilocandles per meter square and of illuminance in kilolux. The historical search to find energy and visibility critical sky luminance distributions shows a progression of steps in studying the worst or critical overcast situations. That progression has enabled the determination and evaluation of interior illuminance for comparison of the merits of dual daylighting and artificial lighting under established criteria for comfortable visibility.
Keywords: overcast sky, gradation function, daylighting, sky luminance distribution
Application of sustainable design principles to increase energy efficiency of existing buildings
B. Mansoury, H. R. Tabatabaiefar
This study investigates the effectiveness of different energy retrofitting techniques and examines the impact of employing those methods on energy consumption of existing residential buildings. Based on the research findings, the most effective and practical method of retrofitting has been proposed in order to improve energy efficiency of existing buildings. In order to achieve this goal, an existing residential building has been simulated in FirstRate 5 software so as to determine the existing thermal performance of the building. Afterwards, considering sustainable design principles, different insulation layers, glazing, and construction materials have been employed to conduct a comprehensive thermal performance study. Based on the research outcomes, the best technique for increasing energy efficiency of existing buildings and reducing their environmental impact and footprint has been identified and proposed for practical purposes.
Keywords: energy consumption, residential building, sustainable design principles, thermal performance