Jiří Maděra

Computational analysis of hygrothermal performance of renovation renders

A combined computational-experimental approach for service life estimate of surface layers of historical building made from renovation renders is presented in the paper. The experimental part is aimed at estimation of the durability of two commercial systems of double layered renovation renders in terms of their frost resistance. The computational part includes calculation of number of freeze-thaw cycles that may occur in surface layers during a reference year. To achieve this, a diffusion-type model of coupled heat and moisture transport is used. The computations are performed on historical load-bearing structure made of sandstone, brick or arenaceous marl, finished by two different hydrophobic renovation render systems.

Service Life Assessment of Historical Building Envelopes Constructed Using Different Types of Sandstone: A Computational Analysis Based on Experimental Input Data

Service life assessment of three historical building envelopes constructed using different types of sandstone is presented. At first, experimental measurements of material parameters of sandstones are performed to provide the necessary input data for a subsequent computational analysis. In the second step, the moisture and temperature fields across the studied envelopes are calculated for a representative period of time. The computations are performed using dynamic climatic data as the boundary conditions on the exterior side of building envelope. The climatic data for three characteristic localities are experimentally determined by the Czech Hydrometeorological Institute and contain hourly values of temperature, relative humidity, rainfalls, wind velocity and direction, and sun radiation. Using the measured durability properties of the analyzed sandstones and the calculated numbers of freeze/thaw cycles under different climatic conditions, the service life of the investigated building envelopes is assessed. The obtained results show that the climatic conditions can play a very significant role in the service life assessment of historical buildings, even in the conditions of such a small country as the Czech Republic. In addition, the investigations reveal the importance of the material characteristics of sandstones, in particular the hygric properties, on their service life in a structure.

Parallel modeling of hygrothermal performance of external wall made of highly perforated bricks

Abstract Coupled heat and moisture transport in highly perforated bricks is indispensable part of design of energy efficient buildings. Geometry of the perforated bricks is very complicated which results in large number of nodes and elements in numerical analysis. Moreover, material model of the coupled heat and moisture transport leads after discretization to nonsymmetric systems of algebraic equations which need large computer memory. In order to reduce the computational time or to solve problems with many degrees of freedom, parallel computers are employed. Parallelization is based on the Schur complement method which is able to deal with nonsymmetric systems. Example of the coupled heat and moisture transport in a perforated brick of HELUZ company is showed. Real climatic boundary conditions for two different locations are used.

Modification of the computational model of coupled heat and moisture transport: The transition between the liquid and gaseous phases of water

An adjustment of the Kunzel´s mathematical model of coupled heat and moisture transport is presented. The balance equation of moisture is rearranged using additional parameters, introduced for a modification of the description of liquid and gaseous moisture transport in the transition zone between the hygroscopic and overhygroscopic moisture ranges. The adjustment is accomplished by a special weighing function to put fast liquid water transfer and slower vapor diffusion into balance in accordance with the real observations. A simple numerical experiment illustrates the advantage of the modification of the model and the results are discussed.

Computational prediction of hygrothermal conditions in innovated AAC-based building envelopes

Hygrothermal conditions in innovated AAC-based building envelopes are studied in the paper, using computational analysis with exactly measured hygric and thermal transport and storage properties as input parameters. The applied computational model of heat and moisture transport in multi-layered systems of porous materials is based on the Galerkin finite element approach. The computer code written in C++ is used in a series of computational simulations. Climatic data corresponding to the test reference year for Prague are used as boundary conditions, so that cyclic wetting and drying occurs in the envelope. The results of computer simulations of moisture and temperature fields are then utilized in the subsequent service life analysis. On the basis of changes of moisture and temperature, particularly the number of wetting-drying cycles and frost cycles the durability of the AAC envelopes is assessed.

Application of waste ceramic dust as a ready-to-use replacement of cement in lime-cement plasters: an environmental-friendly and energy-efficient solution

A potential application of waste ceramic dust as cement replacement in lime-cement plasters is studied using both experimental and computational approaches. A comprehensive experimental analysis of the material properties of lime-cement plaster and three lime-pozzolan plasters containing different amounts of waste ceramics is performed at first. The results show that compressive strength of ceramics-containing plasters can be up to three times higher as compared with the lime-cement plaster but their thermal conductivity is higher as well. In the second part of the study, the hygrothermal and energy performance of a characteristic building envelope provided with the four analyzed plasters as surface layers is analyzed. The results of numerical simulations reveal that the application of waste ceramic dust in lime-pozzolan plasters does not have a negative effect on both the hygrothermal and energy performance of the building envelope, as compared with the use of lime-cement plaster. Taking into account the energy demand and environmental load related to cement production, the application of waste ceramic dust as a ready-to-use replacement of cement in lime-cement plasters represents the right step toward sustainable development.

A material database for computational models of heat, moisture, salt and momentum transport: Construction of the code as an input module and example of application

Most currently used computational models of heat, moisture, salt and momentum transport can be considered appropriate for predicting the performance of building envelopes providing that the input data have a sufficient quality. However, the standard lists of parameters given by the producers or built-in packages for simulation tools often do not meet the demand of accurate numerical prediction (for instance, the dependency of heat and moisture transport and storage parameters on moisture or temperature is not included). In this paper, we present a material database suitable for application in most current computational models. It contains fundamental physical properties and heat, moisture and salt transport and storage parameters of building materials used in the contemporary buildings with some of them having the mentioned dependency. Selected mechanical parameters are included as well. The database is designed as an open system with secured online access.

Determination of moisture-dependent moisture diffusivity using smoothed experimental data

Application of large sets of experimental data containing measurement errors in computational analyses without any preprocessing can lead to distortion of results. Therefore, transformation of these data from point-wise given values to smooth curves is one of the key factors allowing their proper utilization. In this paper, determination of moisture diffusivity of autoclaved aerated concrete as a function of moisture content using measured moisture profiles, which are processed by smoothing, is presented. For the processing of experimentally measured data smoothing splines are used.

Water transport parameters of autoclaved aerated concrete: Experimental assessment of different modeling approaches:

The water-permeability, moisture-diffusivity, and sorptivity concepts of modeling liquid water transport in porous building materials are analyzed. An overall assessment of the particular models is performed using the moisture profiles measured for two types of autoclaved aerated concrete. The water-permeability and moisture-diffusivity modeling approaches are found suitable from a point of view of accuracy of moisture-transport simulation but they have certain limitations. While the water-permeability concept is advisable for compact materials, the moisture-diffusivity concept should be preferred for materials with a high water penetration rate. Therefore, a combination of both these approaches in a single laboratory is beneficial. The sorptivity concept, on the other hand, can be recommended for a basic assessment of water transport capabilities of building materials only.

Identification of Water Diffusivity of Inorganic Porous Materials Using Evolutionary Algorithms

Two evolutionary algorithms are introduced as universal approaches for the identification of water transport characteristics of inorganic porous materials in both absorption and desorption phases. At first, genetic algorithm and genetic programming are applied for the inverse analysis of water content profiles measured in an absorption experiment. A comparison of results with the output of the commonly used Boltzmann–Matano approach shows that the calculated diffusivities can reproduce experimental data with a similarly good or even slightly better accuracy. In the second part of investigations, a water desorption experiment is realized for autoclaved aerated concrete, a typical representative of inorganic porous materials used in the construction sector. The genetic algorithm and genetic programming exhibit an excellent performance also in this case. Both approaches can thus be considered as viable, more universal alternatives to the traditional methods.