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Abstract

When comparing measurements to numerical simulations of moisture transfer through porous materials a rush of the experimental moisture front is commonly observed in several works shown in the literature, with transient models that consider only the diffusion process. Thus, to overcome the discrepancies between the experimental and the numerical models, this paper proposes to include the moisture advection transfer in the governing equation. To solve the advection-diffusion differential equation, it is first proposed two efficient numerical schemes and their efficiencies are investigated for both linear and nonlinear cases. The first scheme, Scharfetter-Gummel (SG), presents a Courant-Friedrichs-Lewy (CFL) condition but is more accurate and faster than the second scheme, the well-known Crank-Nicolson approach. Furthermore, the SG scheme has the advantages of being well-balanced and asymptotically preserved. Then, to conclude, results of the convective moisture transfer problem obtained with the SG numerical scheme are compared to experimental data from the literature. The inclusion of an advective term in the model may clearly lead to better results than purely diffusive models.

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... Numerous studies state similar observations. Interested readers may consult [9,10] for a preliminary introduction to this investigation. ...
... (3)-(6), is solved using a finitedifference standard discretisation. An embedded adaptive in time RUN-GE-KUTTA scheme, combined with a SCHARFETTER-GUMMEL spatial discretisation approach, is used [10]. It is adaptive and embedded to estimate local error in time with little extra cost. ...
... This hypothesis is assumed considering the slight variation of temperature observed in the ambient facility and in the material, as illustrated in Fig. 2(a) and (b). In [10], the mass average velocity in the material was estimated around = 5 mm/s v , where the facility imposed an air flow at one face of the material. In the current study, no air movement are imposed. ...
Article
This paper presents a practical application of the concept of Optimal Experiment Design (OED) for the determination of properties of porous materials with in-situ measurements and an identification method. First, an experimental set-up was presented and used for the measurement of relative humidity within a wood fibre material submitted to single and multiple steps of relative humidity variation. Then, the application of OED enabled to plan the experimental conditions in terms of sensor positioning and boundary conditions out of 20 possible designs. The OED search was performed using the Fisher information matrix and a priori knowledge of the parameters. It ensures to provide the best accuracy of the identification method and thus the estimated parameter. Optimal design results have been found for single steps from the relative humidity phi = 10 to 75%, with one sensor located at the position X between 4 and 6 cm, for the estimation of moisture permeability coefficients, while from phi = 75% to phi = 33%, with one sensor located at X° = 3 cm, for the estimation of the advection coefficient. The OED has also been applied for the identification of couples of parameters. A sample submitted to multiple relative humidity steps (phi = 10-75-33-75%) with a sensor placed at X° = 5 cm was found as the best option for determining both properties with the same experiment. These OED parameters have then been used for the determination of moisture permeability and advection coefficients. The estimated moisture permeability coefficients are twice higher than the a priori values obtained using standard methods. The advection parameter corresponds to the mass average velocity of the order of v = 0.01 mm/s within the material and may play an important role on the simulation of moisture front.
... The Scharfetter-Gummel numerical scheme was proposed in 1969 in [36] with very recent theoretical results in [18,19]. In the context of building porous media, it is successfully applied in [5] to water transport and then in [6] to combined heat and moisture transfer. The contributions of the present paper is two fold. ...
... The contributions of the present paper is two fold. First, the model proposed in [5] is extended by including the air transport equation. Then, the extension of the Scharfetter-Gummel approach to a system of three coupled advection-diffusion equations is proposed. ...
... The moisture and heat equations are advection-diffusion types. The Scharfetter-Gummel approach has shown great efficiency in preliminary studies for a single equation [5] and a system of two coupled equations [6]. Therefore it will be used for the spatial discretisation of the moisture and heat equations. ...
Preprint
This work presents a detailed mathematical model combined with an innovative efficient numerical model to predict heat, air and moisture transfer through porous building materials. The model considers the transient effects of air transport and its impact on the heat and moisture transfer. The achievement of the mathematical model is detailed in the continuity of Luikov's work. A system composed of two advection-diffusion differential equations plus one exclusively diffusion equation is derived. The main issue to take into account the transient air transfer arises in the very small characteristic time of the transfer, implying very fine discretisation. To circumvent these difficulties, the numerical model is based on the Du Fort-Frankel explicit and unconditionally stable scheme for the exclusively diffusion equation. It is combined with a two-step Runge-Kutta scheme in time with the Scharfetter-Gummel numerical scheme in space for the coupled advection-diffusion equations. At the end, the numerical model enables to relax the stability condition, and, therefore, to save important computational efforts. A validation case is considered to evaluate the efficiency of the model for a nonlinear problem. Results highlight a very accurate solution computed about 16 times faster than standard approaches. After this numerical validation, the reliability of the mathematical model is evaluated by comparing the numerical predictions to experimental observations. The latter is measured within a multi-layered wall submitted to a sudden increase of vapor pressure on the inner side and driven climate boundary conditions on the outer side. A very satisfactory agreement is noted between the numerical predictions and experimental observations indicating an overall good reliability of the proposed model.
... Numerous studies state similar observations. Interested readers may consult [9,10] for a preliminary introduction to this investigation. ...
... (3)- (6), is solved using a finitedifference standard discretisation. An embedded adaptive in time RUN-GE-KUTTA scheme, combined with a SCHARFETTER-GUMMEL spatial discretisation approach, is used [10]. It is adaptive and embedded to estimate local error in time with little extra cost. ...
... This hypothesis is assumed considering the slight variation of temperature observed in the ambient facility and in the material, as illustrated in Fig. 2(a) and (b). In [10], the mass average velocity in the The samples are cylindrical, with a 10 cm diameter and 8 cm thickness. The size of the samples has been chosen in order to avoid borders effects and to minimize the perturbation of sensors inside the sample. ...
Experiment Findings
Full-text available
This is a first instance where my concerns led to a retraction of the paper concerned. I contacted the editor with my comments, he contacted the authors, but they obviously did not succeed in refuting my arguments. It continued with a retraction discussion by the publisher, which indeed led to the official retraction of the article by the journal. This is however the exception the confirms the rule, as typically the resistance against a request for retraction is strong.
... "It must be stated that there is absolutely no constructive proposal in the submitted article.", and "Instead of criticizing the community [4][5][6][7], the author should be encouraged to bring constructive proposals." (wherein [4][5][6][7] refer to earlier comments from my side). ...
... and "Instead of criticizing the community [4][5][6][7], the author should be encouraged to bring constructive proposals." (wherein [4][5][6][7] refer to earlier comments from my side). It should however be noted that none of the reviews actually countered my arguments, instead relying mainly on rejecting the core idea of scientific discussion via journal comments. ...
... This same methodological error was also present in a related prior article from the same authors [2], which has recently been retracted for that reason [4]. [1]'s authors were moreover aware of this matter when submitting [1], as it was brought to their attention by the discusser early in 2017, with respect to another publication of theirs that makes the same mistake [5]. ...
Experiment Findings
Full-text available
This is the first time where I explicitly encountered hostility by editor and reviewers with respect to corrections, critiques and comments. It took me a year to get a response from the editor, and it took several months before the reviews came in. These were all outrightly negative and hostile, perhaps a consequence of the proper selection by the editor, who has co-authored with the disputed authors. The editor did however obviously not consider that a conflict of interest in this matter.
... In that paper, hygrothermal properties of wood-based products were measured, including the sorption isotherm and vapour permeability of wood-fibre insulation. In the four years since that publication, these results have been referenced frequently [2][3][4][5][6][7][8][9][10][11]. The present author contends though that the study in [1] contains flaws in the measurement, calculation and presentation of the vapour permeability of woodfibre insulation. ...
... The present author contends though that the study in [1] contains flaws in the measurement, calculation and presentation of the vapour permeability of woodfibre insulation. These have led to the wider adoption of incorrect permeabilities [2][3][4][5][6][7][8][9][10][11], which in turn have resulted in debateable claims, on the inaptitude of stationary vapour diffusion experiments [8,10] and on the importance of advection in hygroscopic ad-/desorption [9,11]. The goal of this discussion is to reveal the erroneous measurements, calculations and presentations in [1] as well as to discuss the ramifications for the investigations [2][3][4][5][6][7][8][9][10][11] making use of [1]'s outcomes. ...
... These have led to the wider adoption of incorrect permeabilities [2][3][4][5][6][7][8][9][10][11], which in turn have resulted in debateable claims, on the inaptitude of stationary vapour diffusion experiments [8,10] and on the importance of advection in hygroscopic ad-/desorption [9,11]. The goal of this discussion is to reveal the erroneous measurements, calculations and presentations in [1] as well as to discuss the ramifications for the investigations [2][3][4][5][6][7][8][9][10][11] making use of [1]'s outcomes. ...
Experiment Findings
Full-text available
My investigations of the papers concerning impossible advection during hygroscopic adsorption experiments on wood fibre insulation led me to the publication that presents its hygroscopic properties. On this, I showed that its measurement, interpretation, and presentation of the vapour permeability is flawed, and moreover that its outcomes are being incorrectly adopted by other researchers. This is then finalised by sketching the potential consequences for these analyses making use of the flawed data.
... The Scharfetter-Gummel numerical scheme was proposed in 1969 in [36] with very recent theoretical results in [18,19]. In the context of building porous media, it is successfully applied in [5] to water transport and then in [6] to combined heat and moisture transfer. The contributions of the present paper is two fold. ...
... The contributions of the present paper is two fold. First, the model proposed in [5] is extended by including the air transport equation. Then, the extension of the Scharfetter-Gummel approach to a system of three coupled advection-diffusion equations is proposed. ...
... The moisture and heat equations are advection-diffusion types. The Scharfetter-Gummel approach has shown great efficiency in preliminary studies for a single equation [5] and a system of two coupled equations [6]. Therefore it will be used for the spatial discretisation of the moisture and heat equations. ...
... Some improved explicit schemes, enabling to overcome the stability restrictions of standard Euler explicit schemes, have been proposed in [13,14]. An accurate and fast numerical scheme based on the Scharfetter-Gummel idea has been proposed in [15] to solve the advective-diffusive moisture differential equation. Some attempts based on model reduction methods have been also proposed with an overview in [8]. ...
... Another issue arises while comparing the numerical model results and experimental data. Some discrepancies were observed as reported in several studies [15,21] and illustrated in Figure 1. A material, with an initial moisture content U 0 , is submitted to adsorption and desorption cycles. ...
... The convection process designates both diffusion and advection transfer. Thus, the fluxes can be expressed as [15,31,32]: ...
Article
This paper aims at estimating the sorption isotherm coefficients of a wood fiber material using experimental data. First, the mathematical model, based on convective transport of moisture, the Optimal Experiment Design (OED) and the experimental set-up are presented. Then, measurements of relative humidity within the material are carried out, after searching the OED using the computation of the sensitivity functions and a priori values of the unknown parameters. It enables to plan the experimental conditions in terms of sensor positioning and boundary conditions out of 20 possible designs, ensuring the best accuracy for the identification method and, thus, for the estimated parameter. After the measurements, the parameter estimation problem is solved. The determined sorption isotherm coefficients calibrate the numerical model to fit better the experimental data. However, some discrepancies still appear since the hysteresis effects on the sorption capacity are not included in the model. Therefore, the latter is improved proposing an additional differential equation for the sorption capacity to consider the hysteresis effects. The OED approach is developed for the estimation of five of the coefficients involved in the hysteresis model. To conclude, the prediction of the model with hysteresis have better reliability when compared to the experimental observations.
... In that paper, hygrothermal properties of wood-based products were measured, including the sorption isotherm and vapour permeability of wood-fibre insulation. In the four years since that publication, these results have been referenced frequently [2][3][4][5][6][7][8][9][10][11]. The present author contends though that the study in [1] contains flaws in the measurement, calculation and presentation of the vapour permeability of woodfibre insulation. ...
... The present author contends though that the study in [1] contains flaws in the measurement, calculation and presentation of the vapour permeability of woodfibre insulation. These have led to the wider adoption of incorrect permeabilities [2][3][4][5][6][7][8][9][10][11], which in turn have resulted in debateable claims, on the inaptitude of stationary vapour diffusion experiments [8,10] and on the importance of advection in hygroscopic ad-/desorption [9,11]. The goal of this discussion is to reveal the erroneous measurements, calculations and presentations in [1] as well as to discuss the ramifications for the investigations [2][3][4][5][6][7][8][9][10][11] making use of [1]'s outcomes. ...
... These have led to the wider adoption of incorrect permeabilities [2][3][4][5][6][7][8][9][10][11], which in turn have resulted in debateable claims, on the inaptitude of stationary vapour diffusion experiments [8,10] and on the importance of advection in hygroscopic ad-/desorption [9,11]. The goal of this discussion is to reveal the erroneous measurements, calculations and presentations in [1] as well as to discuss the ramifications for the investigations [2][3][4][5][6][7][8][9][10][11] making use of [1]'s outcomes. ...
Article
Full-text available
In 2014, this journal published the paper “Characterization of hygrothermal properties of wood-based products – Impact of moisture content and temperature” presenting among others the vapour permeability of wood-fibre insulation. This discussion demonstrates that the measurement, the calculation and the presentation of this vapour permeability has suffered from various errors, invalidating the obtained intrinsic vapour permeabilities of wood-fibre insulation. This discussion moreover demonstrates that several subsequent authors have furthermore misinterpreted their air-gap-corrected vapour permeabilities as intrinsic vapour permeabilities, which in turn invalidates, at least in part, these authors’ challenges to the state-of-the-art on the measurement and simulation of hygroscopic moisture transport in porous materials.
... In the case of the above mentioned experimental studies, the air velocity is probably induced by a difference in the boundary vapor pressure. In Berger et al. (2017), the physical model was improved by considering moisture transfer by diffusion and advection. However, the coupling with heat transfer through porous material was neglected. ...
... This assumption certainly needs to be reconsidered, particularly in the context of building physics, where the temperature has daily and seasonally variations. Therefore, the first objective of this work is to improve the physical model proposed in Berger et al. (2017), by including the energy conservation equations, and analyze the effect of this improvement when comparing it to the experimental data from James et al. (2010). ...
... To address this issue, the second objective of this work is to explore the use of the innovative Scharfetter-Gummel numerical scheme for a system of coupled parabolic differential equations. This scheme was studied in Berger et al. (2017) and interesting results were shown with a very accurate solution obtained at a low computational cost. Since these results were obtained for a single nonlinear equation, it is necessary to extend them for the case of a system. ...
Article
Full-text available
Comparisons of experimental observation of heat and moisture transfer through porous building materials with numerical results have been presented in numerous studies reported in the literature. However, some discrepancies have been observed, highlighting underestimation of sorption process and overestimation of desorption process. Some studies intend to explain the discrepancies by analysing the importance of hysteresis effects as well as carrying out the sensitivity analysis on the input parameters as convective transfer coefficients. This article intends to investigate the accuracy and efficiency of the coupled solution by adding advective transfer of both heat and moisture in the physical model. The efficient Scharfetter-Gummel numerical scheme is proposed to solve the system of advection-diffusion equations, which has the advantages of being well-balanced and asymptotically preserving. Moreover, the scheme is particularly efficient in terms of accuracy and reduction of computational time when using large spatial discretization parameters. Several linear and nonlinear cases are studied to validate the method and highlight its specific features. At the end, an experimental benchmark from the literature is considered. The numerical results are compared with the experimental data for a purely diffusive model and also for the proposed model. The latter presents better agreement with the experimental data. The influence of the hysteresis effects on the moisture capacity is also studied, by adding a third differential equation.
... As a matter of fact, in several cases, the advection moisture transfer phenomenon should also be considered in the context of porous media. Moisture advection is the transport of water vapor by the air and is included as an additional term in the equation of the process (4) (details are not reported here, the reader can see [28,29] as recent references). Berger et al. [28] show the inclusion of an advective term in the model and results in the context of moisture transfer in porous building elements, whereas Gasparin et al. [29] discuss numerically efficient methods for moisture diffusion, with a reduced computational effort. ...
... Moisture advection is the transport of water vapor by the air and is included as an additional term in the equation of the process (4) (details are not reported here, the reader can see [28,29] as recent references). Berger et al. [28] show the inclusion of an advective term in the model and results in the context of moisture transfer in porous building elements, whereas Gasparin et al. [29] discuss numerically efficient methods for moisture diffusion, with a reduced computational effort. Azeem et al. [30] focused recently on a review on the liquid moisture transport behavior of fabric, stating that transportation of liquid water in the fabric cannot be defined at only one condition, but a range of conditions that should be measured regarding the ability to transport liquid moisture. ...
Article
Full-text available
The aim is to develop soft sensors (SSs) to provide an estimation of the laundry moisture of clothes introduced in a household Heat Pump Washer–Dryer (WD-HP) appliance. The developed SS represents a cost-effective alternative to physical sensors, and it aims at improving the WD-HP performance in terms of drying process efficiency of the automatic drying cycle. To this end, we make use of appropriate Machine Learning models, which are derived by means of Regularization and Symbolic Regression methods. These methods connect easy-to-measure variables with the laundry moisture content, which is a difficult and costly to measure variable. Thanks to the use of SSs, the laundry moisture estimation during the drying process is effectively available. The proposed models have been tested by exploiting real data through an experimental test campaign on household drying machines.
... As the analytical solution of the advection-dispersion solute transport equation remains useful for a large number of applications in science and engineering, several studies have concentrated in this direction. Berger et al. (2017) [11] proposed to solve the advection-diffusion differential equation trough two numerical schemes, Scharfetter-Gummel and Crank-Nicolson approach, whose efficiencies were investigated for both linear and nonlinear cases. Li et al. (2011) [12] have studied analytical solutions for advection and dispersion of a conservative solute in a onedimensional double-layered finite porous media are presented. ...
... As the analytical solution of the advection-dispersion solute transport equation remains useful for a large number of applications in science and engineering, several studies have concentrated in this direction. Berger et al. (2017) [11] proposed to solve the advection-diffusion differential equation trough two numerical schemes, Scharfetter-Gummel and Crank-Nicolson approach, whose efficiencies were investigated for both linear and nonlinear cases. Li et al. (2011) [12] have studied analytical solutions for advection and dispersion of a conservative solute in a onedimensional double-layered finite porous media are presented. ...
Conference Paper
Full-text available
In recent years, the evaluation of water quality in distribution systems has generated enormous interest in the scientific community due to the increasing concentration of population in urban areas and frequent issues connected with supply water quality. Following the wave of bioterrorism subsequent the events of September 11 th 2001, a need can be foreseen to seek adequate preventive measures to deal with contamination in water distribution systems that may be related to the accidental contamination and deliberate injection of toxic agents of any origin in the distribution networks. Therefore, it is very important to create a sensor system that detects contamination events in real time, while maintaining the reliability and efficiency of the measurements, limiting the cost of the instrumentation. A reliable monitoring system, for this kind of problems, cannot be deployed without realistic modelling support. The current state-of-the-art in water distribution systems analysis usually adopt a simplified approach to water quality modelling, neglecting dispersion and diffusion and considering simplified reaction kinetics. Even if such simplifications are commonly acceptable in fully turbulent flows, they may take to relevant errors in transition flows with low velocity thus taking to unreliable interpretation of the contamination in complex networks. The present paper aims to compare different modelling approaches to the evaluation of contaminant dispersion in two distribution networks: one laboratory network in which contamination experiments were carried out in a controlled environment (Enna, Italy) and a full-scale real distribution network (Zandvoort, Netherlands).
... As the analytical solution of the advection-dispersion solute transport equation remains useful for a large number of applications in science and engineering, several studies have concentrated in this direction. Berger et al. (2017) [11] proposed to solve the advection-diffusion differential equation trough two numerical schemes, Scharfetter-Gummel and Crank-Nicolson approach, whose efficiencies were investigated for both linear and nonlinear cases. Li et al. (2011) [12] have studied analytical solutions for advection and dispersion of a conservative solute in a onedimensional double-layered finite porous media are presented. ...
... As the analytical solution of the advection-dispersion solute transport equation remains useful for a large number of applications in science and engineering, several studies have concentrated in this direction. Berger et al. (2017) [11] proposed to solve the advection-diffusion differential equation trough two numerical schemes, Scharfetter-Gummel and Crank-Nicolson approach, whose efficiencies were investigated for both linear and nonlinear cases. Li et al. (2011) [12] have studied analytical solutions for advection and dispersion of a conservative solute in a onedimensional double-layered finite porous media are presented. ...
Conference Paper
In recent years, the evaluation of water quality in distribution systems has generated enormous interest in the scientific community due to the increasing concentration of population in urban areas and frequent issues connected with supply water quality. Following the wave of bioterrorism subsequent the events of September 11th 2001, a need can be foreseen to seek adequate preventive measures to deal with contamination in water distribution systems that may be related to the accidental contamination and deliberate injection of toxic agents of any origin in the distribution networks. Therefore, it is very important to create a sensor system that detects contamination events in real time, while maintaining the reliability and efficiency of the measurements, limiting the cost of the instrumentation. A reliable monitoring system, for this kind of problems, cannot be deployed without realistic modelling support. The current state-of-the-art in water distribution systems analysis usually adopt a simplified approach to water quality modelling, neglecting dispersion and diffusion and considering simplified reaction kinetics. Even if such simplifications are commonly acceptable in fully turbulent flows, they may take to relevant errors in transition flows with low velocity thus taking to unreliable interpretation of the contamination in complex networks. The present paper aims to compare different modelling approaches to the evaluation of contaminant dispersion in two distribution networks: one laboratory network in which contamination experiments were carried out in a controlled environment (Enna, Italy) and a full-scale real distribution network (Zandvoort, Netherlands).
... It is based on the Scharfetter-Gummel numerical scheme. This approach is particularly efficient for so-called advection-diffusion equations as highlighted from a mathematical point of view in [16] and illustrated in [17] and [18] for the case of heat and moisture transfer in building porous materials. In our work, the proposed numerical model is compared to the standard methods in the context of capillary adsorption phenomena. ...
Article
Rising damp is one the main causes of moisture damages in historical buildings. The goal of this study is to propose an efficient numerical model for the predictions of capillary adsorption phenomena in porous material. The Scharfetter-Gummel numerical scheme is proposed to solve an advection-diffusion equation with gravity flux. Its advantages such as accuracy, relaxed stability condition and reduced computational cost are discussed along with the study of linear and nonlinear cases. Last, the reliability of the numerical model is evaluated by comparing the numerical predictions with experimental observations of liquid uptake in bricks. A parameter estimation problem is solved to adjust the uncertain coefficients of moisture diffusivity and the hydraulic conductivity and thus improve the predictions. The efficient numerical model enables to solve the inverse problem two times faster than standard approaches. A very satisfactory reliability of the proposed numerical model is observed.
... It is based on the Scharfetter-Gummel numerical scheme. This approach is particularly efficient for socalled advection-diffusion equations as highlighted from a mathematical point of view in [12] and illustrated in [2,3] for the case of heat and moisture transfer in building porous materials. In our work, the proposed numerical model is compared to the standard methods in the context of capillary adsorption phenomena. ...
Preprint
The goal of this study is to propose an efficient numerical model for the predictions of capillary adsorption phenomena in a porous material. The Scharfetter-Gummel numerical scheme is proposed to solve an advection-diffusion equation with gravity flux. Its advantages such as accuracy, relaxed stability condition, and reduced computational cost are discussed along with the study of linear and nonlinear cases. The reliability of the numerical model is evaluated by comparing the numerical predictions with experimental observations of liquid uptake in bricks. A parameter estimation problem is solved to adjust the uncertain coefficients of moisture diffusivity and hydraulic conductivity.
... Within this framework, attention has generally focused on the development of modelling approaches that could suitably relate material structure to water vapour permeability. While various models have been proposed to generically account for the flow of gases and vapours in several porous materials [9][10][11][12][13][14], the relationship between the structure of porous materials and their permeability to gases and vapours remains an open question. ...
Article
This work focuses on the relationship between water vapour permeability and porosity in earthen materials. Earth blocks have been suitably fabricated and their pore size distribution evaluated along with water vapour permeability. Experimental results are compared with theoretical predictions obtained from a fractal model relating porosity to transport processes. Experimental and modelling outcomes compare remarkably well, thus making the fractal model show promise for addressing the design of earth materials with tailored properties.
... Then, for the heat and mass advection-diffusion Equations (2a) and (2b), the SCHARFETTER-GUMMEL numerical scheme is used. Preliminary studies 23,24 showed the efficiency of the approach to extend the stability conditions and the accuracy of the solution. As a last step of the proposed methodology, the time discretisation of these two equations, an innovative two-step RUNGE-KUTTA approach is used of the time discretisation of these two advection-diffusion equations, enabling to extend further the stability region of the numerical scheme. ...
Article
Full-text available
This article proposes an efficient explicit numerical model with a relaxed stability condition for the simulation of heat, air and moisture transfer in porous material. Three innovative approaches are combined to solve the system of two differential advection-diffusion equations coupled with a purely diffusive equation. First, the DuFort-Frankel scheme is used to solve the diffusion equation, providing an explicit scheme with an extended stability region. Then, the two advection-diffusion equations are solved using both the Scharfetter-Gummel numerical scheme for the space discretisation and the two-step Runge-Kutta method for the time variable. This combination enables to relax the stability condition by one order. The proposed numerical model is evaluated on three case studies. The first one considers quasi-linear coefficients. The theoretical results of the numerical schemes are confirmed by our computations. Indeed, the stability condition is relaxed by a factor of 40 compared to the standard Euler explicit approach. The second case provides an analytical solution for a weakly nonlinear problem. A very satisfactory accuracy is observed between the reference solution and the one provided by the numerical model. The last case study assumes a more realistic application with nonlinear coefficients and Robin-type boundary conditions. The computational time is reduced 10 times by using the proposed model in comparison with the explicit Euler method.
... Results highlighted that experimental data is in compliance with the literature. Also, a comprehensive mathematical model was established by Berger et al. [71] for evaluating the moisture behaviour by including the air transport, vapour pressure, and temperature in their previous model [72] for predicting the HAMT through porous building materials. They revealed that this model could reduce the computational effort by 16 times in comparison to standard approaches. ...
Article
In today’s world, energy efficiency is the most sought characteristic. Enhancing energy efficiency and hence moving towards sustainability is considered as the primary requirement. Buildings are the places where we spend most of our time and thus they consume more than one-third of the energy consumption. This forces the stakeholders to think about the new ways to strike a dynamic balance between comfortable human dwelling, efficient resource management, and protecting our environment. Uncontrolled heat and moisture transport impact the building physics, occupant’s health and comfort, and energy efficiency significantly. This can be controlled by modeling the nonlinear and complex hygrothermal behaviour of the structures in an early phase. Several researchers are working to improve the hygrothermal dynamics of buildings which makes it necessary to succinctly review the progress in the field. The present communication signifies the study to assess the hygrothermal dynamics by considering the role of building materials and ventilation systems for improving the building hygrothermal characteristics and thus making it more energy-efficient. The CIMO and PRISMA approaches have been utilized to synthesize the literature comprehensively. The results reported that building performance is subjected to appropriate hygrothermal dynamics which can be optimized by selecting the less sensitive, sustainable, and heat resistant building materials in the pre-construction phase. Also, utilizing appropriate ventilation can also aid in improving the hygrothermal dynamics. Finally, this article can also be considered as a benchmark for modern professionals (e.g. designers, energy auditors, researchers, conservators, buildings’ owners, and policymakers) and can drive them towards suitable and reliable retrofit and maintenance interventions by considering the effect of hygrothermal dynamics.
... As mentioned before, hysteresis of moisture sorption is one of the possible phenomena. Some studies [8,12] seem to show that taking into account the air advection could improve the comparison between measurement and simulation. Moreover, in the standard characterization method (cup method) advective vapor transfer are overlooked, this could imply an underestimation of the vapor permeability in case of highly air permeable material [8]. ...
Article
Full-text available
In order to improve understanding of heat and mass transfer, two studies, at material and room scale are carried out. At the material scale, a dynamic experimental method has been developed and applied to a wood fiber previously characterized with classical steady-state methods. Several samples were subjected to successive steps of relative humidity at constant temperature. Relative humidity inside the material was continuously recorded and samples were weighed regularly. This dynamic measurement method enables to identify hygrothermal properties by an inverse methods. The measurements are compared with a numerical model both in terms of relative humidity and of moisture content. Then the development of a new facility to study the influence of wood wall on building comfort and to validate numerical results at room scale is presented.
... Some building models and applications for accurate assessment of moisture impact in building materials using different software are reported in (Woloszyn e Rode 2008), showing how numerical analysis are also essential tools at the building moisture estimation. However, the interaction between measurements and numerical simulations frequently present discrepancies (Berger et al. 2017), besides being restricted to MC values, and no electric resistance, capacitance is simulated. In this sense, creating numerical models in WUFI and DELPHIN software and using the experimental data to compare directly MC and impedance results, thus validating the models. ...
Conference Paper
Full-text available
Non-destructive measures regarding building dampness assessment plays a vital role within the constructions health evaluation. In this sense, this research investigates the relationship between impedance measurements and moisture content inside building porous materials. 1D simulations involving computational modelling of coupled heat and moisture transport in Delphin and WUFI software were carried out using data from a three-year test that investigated the electric current behaviour considering five types of sandstones under temperature-and humidity-controlled experimental conditions. The simulated results showed that impedance measurements have a direct and clear inverse response to the moisture content and, with further research, could be a reliable alternative for quantitative in-situ building dampness estimations.
... As mentioned before, hysteresis of moisture sorption is one of the possible phenomena. Some studies[8,12]seem to show that taking into account the air advection could improve the comparison between measurement and simulation. Moreover, in the standard characterization method (cup method) advective vapor transfer are overlooked, this could imply an underestimation of the vapor permeability in case of highly air permeable material[8]. ...
Conference Paper
In order to improve understanding of heat and mass transfer, two studies, at material and room scale are carried out. At the material scale, a dynamic experimental method has been developed and applied to a wood fiber previously characterized with classical steady-state methods. Several samples were subjected to successive steps of relative humidity at constant temperature. Relative humidity inside the material was continuously recorded and samples were weighed regularly. This dynamic measurement method enables to identify hygrothermal properties by an inverse methods. The measurements are compared with a numerical model both in terms of relative humidity and of moisture content. Then the development of a new facility to study the influence of wood wall on building comfort and to validate numerical results at room scale is presented.
... For the present study, the energy and economic performance of the electric radiant floor heating system in a residential building were assessed through the measurement and energy simulation. According to the Act on the Promotion of the Development, Use, and Diffusion of New and Renewable Energy, Korea Ministry of Trade, renewable energy systems should be designed for newly constructed residential buildings in South Korea [18]. Therefore, the electricity consumption for electric radiant floor heating systems can be offset by renewable energy systems such as electricity generated by solar PV panels. ...
Article
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In South Korea, radiant floor heating has been used from old housing to the recently constructed residential buildings, which is called “Ondol”. The Ondol system is generally a water-based system and it uses hot water as a heat medium provided by boilers fueled by natural gas. With great effort to reduce greenhouse gas emissions, electric Ondol panels have been increasingly applied to the recent residential buildings for floor heating. While the prefab electric Ondol panels were developed with the demand for dry construction method, the information about the prefab electric Ondol system is not sufficient. For the present study, the thermal performance of the prefab electric Ondol panels was investigated through field measurement. In addition, the heating energy and economic performance of the electric panel were compared with the conventional Ondol system. As a result, a significant surface temperature difference was observed. Moreover, the heating cost for the prefab electric Ondol system was more expensive than the conventional system, even though a heat loss was observed by the operation of the conventional system.
... An important issue concerns the estimation of other important hygrothermal properties as the liquid conductivity. Some parallel preliminary study showed the importance of advection phenomena [35,49,50], therefore we plan to investigate it in further works. ...
Article
The standard methods to determine the vapour permeability and the moisture sorption curve may lack of accuracy since discrepancies are observed when comparing numerical predictions to experimental data. Moreover, these properties are determined in steady state conditions while the numerical predictions are carried in transient regime. Thus, this paper presents an experimental design to estimate these properties using dynamic measurements and identification method. The experimental facility is presented, enabling to measure at the same time the relative humidity within the material and the total moisture content. The performance of the facility and protocol in terms of reproducibility, uncertainty and direction of heat and moisture transfers are checked, confirming the abilities of the set-up. Then, experimental results are used to determine the hygrothermal material properties using a trust-region algorithm. Investigations are done to analyse important issues as the choice of the observation: relative humidity and/or mass measurements, to solve the parameter estimation problem. The estimated properties are finally validated by comparing the numerical predictions with experimental data for other boundary conditions.
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Hemp concrete is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities behavior, which are known to strongly depend on the amount of water contained in wall pores and its evolution. In this context, the aim of this paper is to study the experimental determination of sorption-desorption curves of hemp concretes following two methods and at two temperatures (23 �C and 40 �C). The former considers the total sorption-desorption loop, from the dried state to a relative humidity of 85%, while the second one is based on partial relative humidity cycles between 23% and 85%. At first, the difference between the curves obtained through these two methods were analysed. They were then implemented in a simple hygrothermal model to simulate dynamic hygroscopic and hygrothermal loadings. The comparison between the theoretical calculations and the experimental results eventually allows to scan which of these relations is more representative of the real dynamic behaviour of the tested hemp concretes.
Article
Models for the prediction of heat and mass transfers in building porous materials have been developed since the 90’s with simulation programs such as MATCH, UMIDUS, DELPHIN and Wufi. These models are used to analyze the physical phenomena occurring and particularly the impact of moisture on buildings’ energy performance and durability. With this goal in mind, it is important to validate the representation of the physical phenomena made by the numerical models. This article reviews recent studies comparing the results obtained with numerical models and experimental data. An overall trend can be observed for most of these studies, highlighting that the experimental front always rushes faster than the simulation results. Therefore, this study analyses theses comparisons to explain these discrepancies based on the effects of (i) the type of materials, (ii) the boundary conditions, (iii) the scale of the design facility, (iv) the model used to describe the physical phenomena and (v) the influence of the model input parameter. The general trend shows that discrepancies are observed most particularly for highly hygroscopic or bio-based materials. These discrepancies are also greater for time dynamic boundary conditions, particularly at the scale of the wall. Moreover, some of the assumptions on the properties of the materials used as input in the models are questioned. Indeed, the models considering the hysteresis effects and temperature dependency of the moisture storage capacity show better agreement with experimental data. Finally, the physical phenomena used in the models only consider diffusive transport while it appears that the advective of moisture through the porous material may play an important role.
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In this work, combined experimental and fractal nature analysis procedures are proposed in order to both model and design mechanical properties of porous ceramics. Several porous ceramics samples have been considered both from an in-situ experimental campaign and from the literature. Microstructural information concerning pore size distribution has been approximated by the Intermingled Fractal units (IFU) approach and effective mechanical properties are derived by a simple discrete model. The capability of the proposed methodology to reproduce high-scattered mechanical properties is fully shown and a comparison with classical bounds and estimates is also reported. Finally, the combined experimental, fractal nature analysis and homogenisation scheme is implemented as a design procedure for the technological production of advanced porous ceramics.
Article
The hygroscopic performances of building materials have a considerable effect on the humidity of indoor environments, and this performance depends on various factors on the material (physical properties), system (ambient airflow), and room (moisture load profile in the indoor environment) levels. Thus, these three levels should be considered to comprehensively evaluate the hygroscopic performances of building materials. The effective moisture penetration depth (EMPD) model assumes a layer of constant thickness with uniform relative humidity on the material surface subjected to a periodic sine wave variation in indoor humidity. The EMPD model is commonly used by simulation software such as EnergyPlus to characterize hygroscopic performance. The computational speed of the EMPD model used in EnergyPlus is fast compared to other models such as the combined heat and moisture transfer model; however, it can provide inaccurate results. By considering the effect of the ambient airflow velocity on materials and changing the relative humidity variation from a periodic sine wave to a periodic square wave, a series of evaluation indexes is proposed to adapt the EMPD model to more practical situations. The calculated evaluation indexes are then verified through a theoretical analysis and experimental calculations. A simpler and faster method is thus proposed by modifying the original EMPD model to consider airflow velocity and square wave modification. This method is then verified using several gypsum-based materials. The optimized EMPD model is shown to provide a more realistic prediction of the hygroscopic performances of building materials in different areas, functional building types, and under different airflow velocities.
In recent years, there has been a need to seek adequate preventive measures to deal with contamination in water distribution networks that may be related to the accidental contamination and the deliberate injection of toxic agents. Therefore, it is very important to create a sensor system that detects contamination events in real time, maintains the reliability and efficiency of measurements, and limits the cost of the instrumentation. To this aim, two problems have to be faced: practical difficulties connected to the experimental verification of the optimal sensor configuration efficiency on real operating systems and challenges related to the reliability of the network modelling approaches, which usually neglect the dispersion and diffusion phenomena. The present study applies a numerical optimization approach using the NSGA-II genetic algorithm that was coupled with a new diffusive-dispersive hydraulic simulator. The results are compared with those of an experimental campaign on a laboratory network (Enna, Italy) equipped with a real-time water quality monitoring system and those of a full-scale real distribution network (Zandvoort, Netherlands). The results showed the importance of diffusive processes when flow velocity in the network is low. Neglecting diffusion can negatively influence the water quality sensor positioning, leading to inefficient monitoring networks.
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Well-balanced schemes, nowadays well-known for 1D hyperbolic equations with source terms and systems of balance laws, are extended to strictly parabolic equations, first in 1D, then in 2D on Cartesian computational grids. The construction heavily relies on a particular type of piecewise-smooth interpolation of discrete data known as ℒ-splines. In 1D, several types of widelyused discretizations are recovered as particular cases, like the El-Mistikawy-Werle scheme or Scharfetter-Gummel’s. Moreover, a distinctive feature of our 2D scheme is that dimensional-splitting never occurs within its derivation, so that all the multidimensional interactions are kept at the discrete level. This leads to improved accuracy, as illustrated on several types of drift-diffusion equations.
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Well-balanced schemes, nowadays mostly developed for both hyperbolic and kinetic equations, are extended in order to handle linear parabolic equations, too. By considering the variational solution of the resulting stationary boundary-value problem, a simple criterion of uniqueness is singled out: the $C^1$ regularity at all knots of the computational grid. Being easy to convert into a finite-difference scheme, a well-balanced discretization is deduced by defining the discrete time-derivative as the defect of $C^1$ regularity at each node. This meets with schemes formerly introduced in the literature relying on so--called $\EL$-spline interpolation of discrete values. Various monotonicity, consistency and asymptotic-preserving properties are established, especially in the under-resolved vanishing viscosity limit. Practical experiments illustrate the outcome of such numerical methods.
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Detailed modelling of air leakage paths through complex building wall assemblies is a challenging task. It requires transient modelling of diffusion and advection phenomena through fluid and solid domains, including porous materials and air channels. In this article, the development of a numerical model coupling heat air and moisture transfers (commonly called HAM transfers) is presented. The model is able to deal with non-isothermal air flow through complex 2D (two-dimensional) geometries, combining air channels and porous media, air permeable or not. A stepwise 1D validation of the model is achieved with numerical benchmarks. The model is then tested on a 2D air leakage configuration subjected to infiltration and exfiltration scenarii.
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This paper presents experimental hygrothermal data of an hemp concrete wall of dimensions 0.9×0.9×0.1 [m3]. The wall is instrumented with sensors to monitor temperature, relative humidity at the middle of the wall and incoming heat flows at the external surfaces. It is placed in a double climatic chamber that allows the regulation of temperature and relative humidity on each side of the wall, independently to each other. The experimental results leads to a clear identification of the coupling between the variation of the relative humidity inside the wall and its temperature. The validity of the commonly adopted assumptions for hygrothermal simulation are finally analyzed in the light of these experimental results. The material parameters used for the simulations are measured separately on decimetric samples of the same hemp concrete, which comes from the same mix and with the same apparent density.
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The mathematical semiconductor device model, consisting of the po-tential equation and the current continuity subsystem for the carriers, is studied from the standpoint of its decoupling fixed point map and the numerical approximate fixed point map. Variational principles will be discussed for this process and for discretizations achieved by use of gen-eralized splines. By the choice of trial space, these capture the upwinding associated with Scharfetter-Gummel methods. An approximation calcu-lus will be introduced in conjunction with the numerical fixed point map.
Book
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Substantial effort has been drawn for years onto the development of (possibly high-order) numerical techniques for the scalar homogeneous conservation law, an equation which is strongly dissipative in L1 thanks to shock wave formation. Such a dissipation property is generally lost when considering hyperbolic systems of conservation laws, or simply inhomogeneous scalar balance laws involving accretive or space-dependent source terms, because of complex wave interactions. An overall weaker dissipation can reveal intrinsic numerical weaknesses through specific nonlinear mechanisms: Hugoniot curves being deformed by local averaging steps in Godunov-type schemes, low-order errors propagating along expanding characteristics after having hit a discontinuity, exponential amplification of truncation errors in the presence of accretive source terms... This book aims at presenting rigorous derivations of different, sometimes called well-balanced, numerical schemes which succeed in reconciling high accuracy with a stronger robustness even in the aforementioned accretive contexts. It is divided into two parts: one dealing with hyperbolic systems of balance laws, such as arising from quasi-one dimensional nozzle flow computations, multiphase WKB approximation of linear Schrödinger equations, or gravitational Navier-Stokes systems. Stability results for viscosity solutions of onedimensional balance laws are sketched. The other being entirely devoted to the treatment of weakly nonlinear kinetic equations in the discrete ordinate approximation, such as the ones of radiative transfer, chemotaxis dynamics, semiconductor conduction, spray dynamics of linearized Boltzmann models. “Caseology” is one of the main techniques used in these derivations. Lagrangian techniques for filtration equations are evoked too. Two-dimensional methods are studied in the context of non-degenerate semiconductor models.
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Simulation models for moisture transfer in building materials are highly incongruent with respect to the moisture potential used. Often the relatively better numerical efficiency and accuracy of a certain moisture potential is put forward as motivation. Various claims are made in that respect, but factual evidence is typically lacking. This paper aims at providing such support by assessing simulation efficiency and accuracy for capillary pressure, relative humidity and -log(-capillary pressure). To that goal, a suite of benchmark simulations are performed with those three potentials and performances are compared, based on deviations from reference solutions and on numbers of iterations required. The study initially reveals mixed results, showing no consistent advantages for either potential. Further analysis uncovers though that -log(-capillary pressure) suffers from a strongly nonlinear moisture capacity near saturation. This finally results in a decision in favour of capillary pressure and relative humidity, at least for general-purpose moisture transfer simulation.
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This paper presents the Umidus program which has been developed to model coupled heat and moisture transfer within porous media, in order to analyze higrothemal performance of building elements when subjected to any kind of climate conditions. Both diffusion and capillary regimes are taken into account, that is the transfer of water in the vapor and liquid phases through the material can be analyzed. The model predicts moisture and temperature profiles within multi-layer walls and low-slope roofs for any time step and calculates heat and mass transfer. Umidus has been built in an OOP language to be a fast and precise easy-to-use software.
Article
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A whole building hygrothermal model has been developed on the basis of an existing detailed model for thermal simula- tion of buildings. The thermal model is a well-proven transient tool for hour-by-hour simulation of the thermal conditions in multizone buildings. The model has been expanded with new capabilities for transient simulation of indoor humidity condi- tions, taking into account the moisture buffer capacity of build- ing components and furnishings and the supply of humidity from indoor activities. Also integrated in the model are tran- sient calculations of the moisture conditions in the layers of all the external building envelope components. The advantage of the new model is that both the boundary conditions for the envelope and the capacity of building mate- rials to buffer the indoor humidity are considered in the same calculation. The model considers the latent heat effect asso- ciated with the absorption or evaporation of moisture, and it takes into account the way in which moisture in the building materials affects their thermal conductivity. The paper presents the principles for the model and some applications and calculation results. The model is validated against experimental data from a full-scale test cell. In the test cell, it is possible to control the release or withdrawal of humidity from the indoor space and measure the response in humidity of the air and the moisture content of building materials in the room. A sequence of exper- iments has been conducted using different interior materials to provide source data for the effect of moisture absorption and release. Examples of comparisons between simulated and measured data are presented.
Article
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Humidity of indoor air is an important factor influencing the air quality and energy consumption of buildings as well as durability of building components. Indoor humidity depends on several factors, such as moisture sources, air change, sorption in materials and possible condensation. Since all these phenomena are strongly dependent on each other, numerical predictions of indoor humidity need to be integrated into combined heat and airflow simulation tools. The purpose of a recent international collaborative project, IEA ECBCS Annex 41, has been to advance development in modelling the integral heat, air and moisture transfer processes that take place in “whole buildings” by considering all relevant parts of its constituents. It is believed that full understanding of these processes for the whole building is absolutely crucial for future energy optimization of buildings, as this cannot take place without a coherent and complete description of all hygrothermal processes. This paper will illustrate some of the modelling work that has taken place within the project and present some of the simulation tools used.
Article
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Performance and service life of building components are to a large extent determined by their hygrothermal behaviour. Since experimental examinations, apart from being expensive, can cover only small aspects of the real phenomena, the demand for computational tools has increased in recent years. In contrast to previous moisture calculations depending on sophisticated material parameters which were difficult and sometimes impossible to measure, new investigations have led to rather simple yet very accurate models requiring mostly standard material properties. Numerous applications have already proven the validity of the described calculations, which are based on physically plausible formulations.
Book
This book intends to stimulate research in simulation of diffusion problems in building physics, by first providing an overview of mathematical models and numerical techniques such as the finite difference and finite-element methods traditionally used in building simulation tools. Then, nonconventional methods such as reduced order models, boundary integral approaches and spectral methods are presented, which might be considered in the next generation of building-energy-simulation tools. The advantage of these methods includes the improvement of the numerical solution of diffusion phenomena, especially in large domains relevant to building energy performance analysis.
Article
Implicit schemes have been extensively used in building physics to compute the solution of moisture diffusion problems in porous materials for improving stability conditions. Nevertheless, these schemes require important sub-iterations when treating nonlinear problems. To overcome this disadvantage, this paper explores the use of improved explicit schemes, such as Dufort–Frankel, Crank–Nicolson and hyperbolization approaches. A first case study has been considered with the hypothesis of linear transfer. The Dufort–Frankel, Crank–Nicolson and hyperbolization schemes were compared to the classical Euler explicit scheme and to a reference solution. Results have shown that the hyperbolization scheme has a stability condition higher than the standard Courant–Friedrichs–Lewy condition. The error of this schemes depends on the parameter τ representing the hyperbolicity magnitude added into the equation. The Dufort–Frankel scheme has the advantages of being unconditionally stable and is preferable for nonlinear transfer, which is the three others cases studies. Results have shown the error is proportional to O(dt). A modified Crank–Nicolson scheme has been also studied in order to avoid sub-iterations to treat the nonlinearities at each time step. The main advantages of the Dufort–Frankel scheme are (i) to be twice faster than the Crank–Nicolson approach; (ii) to compute explicitly the solution at each time step; (iii) to be unconditionally stable and (iv) easier to parallelize on high-performance computer systems. Although the approach is unconditionally stable, the choice of the time discretization remains an important issue to accurately represent the physical phenomena.
Article
Non-Fickian diffusion in native and thermally modified wood was analyzed by the inverse method. A low quality of the identified diffusivity values was found for the diffusivity which was either constant or varying with water content. This was explained by the non-Fickian behavior. It was especially distinct for thermally modified wood for which an increased delay in obtaining the hygroscopic equilibrium was clearly shown. Such a delay was explained by time required for molecular reorganization to produce new sorption sites. This phenomenon was accounted to improve the physical model by modifying the convective boundary condition. A relaxation mechanism was used for this purpose with an adequate time constant.
Article
Presents introductory skills needed for prediction of heat transfer and fluid flow, using the numerical method based on physical considerations. The author begins by discussing physical phenomena and moves to the concept and practice of the numerical solution. The book concludes with special topics and possible applications of the method.
Article
Implicit-explicit (IMEX) schemes have been widely used, especially in conjunction with spectral methods, for the time integration of spatially discretized partial differential equations (PDEs) of diffusion-convection type. Typically, an implicit scheme is used for the diffusion term and an explicit scheme is used for the convection term. Reaction-diffusion problems can also be approximated in this manner. In this work we systematically analyze the performance of such schemes, propose improved new schemes, and pay particular attention to their relative performance in the context of fast multigrid algorithms and of aliasing reduction for spectral methods. For the prototype linear advection-diffusion equation, a stability analysis for first-, second-, third-, and fourth-order multistep IMEX schemes is performed. Stable schemes permitting large time steps for a wide variety of problems and yielding demonstrate that weak decay of high frequency modes can lead to extra iterations on the finest grid when using multigrid computations with finite difference spatial discretization, and to aliasing when using spectral collocation for spatial discretization. When this behavior occurs, use of weakly damping schemes such as the popular combination of Crank-Nicolson with second-order Adams-Bashforth is discouraged and better alternatives are proposed. Our findings are demonstrated on several examples.
Article
Excessive levels of moisture in buildings lead to building pathologies. Moisture also has an impact on the indoor air quality and the hygrothermal comfort of the building's occupants. A comprehensive list of the possible types of damage caused by moisture in buildings is discussed in the present paper. Damage is classified into four types: damage due to the direct action of moisture, damage activated by moisture, damage that occurred in a moist environment and deterioration of the indoor environment. Since moisture pathologies strongly depend on the hygrothermal fields in buildings, integrating these factors into a global model combining heat air and mass transfers and building energy simulation is important. Therefore, the list of moisture damage types is completed with a proposal of factors governing the risk of occurrence of each type of damage. The methodology is experimented on a simple test case combining hygrothermal simulations with the assessment of possible moisture disorders.
Article
To assist with the correct design of buildings, many computational models have been developed to assess the transient heat, air, and moisture (HAM) transfer within building walls. Validation of these computational models is essential to gain confidence in the codes. This paper provides datasets for validating 1-D heat and mass transfer models step by step, gradually increasing the complexity of a multilayer wall with hygroscopic components. The experiments were performed using a double climatic chamber. The climatic conditions on either side of the wall progress from the simplest boundary conditions (isothermal) to more complex ones with oscillations that mimic the mid-season period. To assess the hygrothermal response of the tested walls under such climatic conditions, the conditions of ambient air and the temperature and humidity profiles within the wall thickness are monitored during the test. This paper gives some detailed information on the chamber design, the instrumentation, the materials, and the climatic conditions so that other researchers can use the collected data for validation of their models or to build future test facilities. The results obtained with the test facility highlight the coupling that exists between heat and mass transfers across multilayer walls using hygroscopic components. The heat release by moisture adsorption is observed in the temperatures profiles. During the mid-season period, the results show the differences of the phase shift and the amplitude attenuation of the temperature and the water vapour pressure across the wall thickness.
Article
An experimental wooden-frame house was designed, instrumented and tested to provide measurements suitable for the study of coupled vapour and heat transfer under real climate conditions. In this paper, six different wall assemblies were tested under complex temperature and humidity boundary conditions over more than 3 years. The main objective is to take advantage of the strong outdoor and indoor stresses to emphasise the dynamic coupling between vapour and heat transfer for different wall assemblies. Measurements showed that the heat flux crossing the vertical walls was significantly influenced when a vapour flow crossed insulating materials with high hygroscopic inertia. To further explain this result, a classical numerical model was selected. It was designed to compute coupled transfer at the building scale. A good agreement was obtained for temperature measurements, while higher differences were observed with humidity measurement. An uncertainty analysis was achieved on both experimental and numerical results. It appeared that the uncertainty of the simulation results was one order of magnitude lower than the experimental uncertainty. Finally, the numerical model was used to break down the coupling of vapour and heat transfers. The latent heat effect occurred as the most sizeable effect, which was consistent with the experimental observations.
Article
This paper presents the experimental results on spruce plywood and cellulose insulation using the transient moisture transfer (TMT) facility presented in Part I [P. Talukdar, S.O. Olutmayin, O.F. Osanyintola, C.J. Simonson, An experimental data set for benchmarking 1-D, transient heat and moisture transfer models of hygroscopic building materials-Part-I: experimental facility and property data, Int. J. Heat Mass Transfer, in press, doi:10.1016/j.ijheatmasstransfer.2007.03.026] of this paper. The temperature, relative humidity and moisture accumulation distributions within both materials are presented following different and repeated step changes in air humidity and different airflow Reynolds numbers above the materials. The experimental data are compared with numerical data, numerical sensitivity studies and analytical solutions to increase the confidence in the experimental data set.
Article
A standard for binary floating-point arithmetic is being proposed and there is a very real possibility that it will be adopted by many manufacturers and implemented on a wide range of computers. This development matters to all of us concerned with numerical software. One of the principal motivations for the standard is to distribute more evenly the burden of portability between hardware and software. At present, any program intended to be portable must be designed for a mythical computer that enjoys no capability not supported by every computer on which the program will be run. That mythical computer is so much grubbier than almost any real computer that a portable program will frequently be denigrated as "suboptimal" and then supplanted by another program supposedly "optimal" for the real computer in question but often inferior in critical respects like reliability. A standard --- almost any reasonable standard --- will surely improve the situation. A standard environment for numerical programs will promote fair comparisons and sharing of numerical codes, thereby lowering costs and prices. Furthermore, we have chosen repeatedly to enrich that environment in order that applications programs be simpler and more reliable. Thus will the onus of portability be shared among hardware manufacturers and software producers.
Article
An experimental investigation has begun concerning the hygrothermal behaviour of wooden frame houses. The experimental set-up, consisting in a full-scale wooden frame house exposed to natural exterior climate is presented in the paper. It is located in Grenoble (South-East of France), and is equipped with over 150 sensors in order to collect a large amount of data (temperatures, relative humidity). The experimental data presented in the paper enable to get better understanding of coupled hygrothermal phenomena, and can be used to allow the validation of numerical models for heat, air and moisture transfers in wooden frame buildings. The analysed results demonstrate the importance of temperature-driven moisture diffusion from hygroscopic panelling.
Article
The presence of hygroscopic materials has a large impact on the moisture balance of buildings. Nowadays, HAM (Heat, Air and Moisture) models are widely used to investigate the role of hygroscopic materials on the performance of buildings, i.e. on the building envelope, the indoor climate and valuable objects stored within the building. Recently, these HAM models are being coupled to CFD (Computational Fluid Dynamics) models to study the moisture exchange between air and porous materials on a local scale (microclimates), or to BES (Building Energy Simulation) models which focus on the interaction between air and porous materials at building level. Validation of these numerical codes is essential to gain confidence in the codes. However, available experimental data are rather scarce.This paper describes the design of a new test facility for humidity experiments. A dedicated AHU system is used to provide well-controlled air (constant temperature and RH) to an airtight and well-insulated room-size test chamber. In one of the walls of the chamber a calcium silicate sample is installed. A step in RH of the supply air is imposed. Temperature and RH of the supply air, the room air and on various depths inside the sample are continuously registered during the experiments. Two types of experiments were carried out to validate a coupled CFD–HAM model and a coupled BES–HAM model. The temperature outside the test chamber was controlled and there was no temperature difference imposed across the chamber walls. Comparing the models with the measured data gave satisfactory agreement.
Article
As numerical models of heat and moisture transfer in porous building materials advance and numerical investigations increase in the literature, there remains a need for simple accurate and well-documented experimental data for model validation. The aim of this two part paper is to provide such experimental data for two hygroscopic building materials (cellulose insulation and spruce plywood) exposed to 1-D and transient boundary conditions. Part I of this paper describes the transient moisture transfer (TMT) facility used to generate the experimental data as well as the uncertainty and repeatability of the measured data. The measured material properties are also presented to fully document the experimental data set and permit its use by other researchers.
Article
The processes of mass transfer in the material influence not only the conditions within the material but also inside the connected air spaces. A new module for precise representation of mass transfer in materials in contact with the indoor air, called Humi-mur, was elaborated and validated in this work. It allows for the precise representation of sorption isotherm and vapour permeability dependence on relative humidity. Also the sorption curve hysteresis has been implemented. The new module was then applied to estimate the sensitivity of the results to uncertainty in measured material properties and the impact of hysteresis effect. Reasonable estimation of experimental uncertainty resulted in the deviation of approximately 6% in the calculated results. Hysteresis quite strongly influences the dynamic behaviour of materials. Concerning hysteresis in the sorption isotherm, we showed that the average of the adsorption and desorption equations is a reasonable approximation of mean behaviour for coarse calculation. In case when precise results of the relative humidity (absolute humidity) are needed, the hysteresis effect should be taken into account.
Article
Most building materials are porous, composed of solid matrix and pores. The time varying indoor and outdoor climatic conditions result heat, air and moisture (HAM) transfer across building enclosures. In this paper, a transient model that solves the coupled heat, air and moisture transfer through multilayered porous media is developed and benchmarked using internationally published analytical, numerical and experimental test cases. The good agreements obtained with the respective test cases suggest that the model can be used to assess the hygrothermal performance of building envelope components as well as to simulate the dynamic moisture absorption and release of moisture buffering materials.
Article
This paper presents experimental data measured in a bed of gypsum boards in the transient moisture transfer (TMT) facility at the University of Saskatchewan. The relative humidity and temperature were measured at two depths in a gypsum bed and the moisture accumulation was measured for the entire bed. Experiments were conducted for both coated (acrylic and latex paint) and uncoated gypsum. These experimental data are compared to simulated data from eight different numerical models. The agreement between the experimental and numerical data is good and often within the experimental uncertainty bounds. A sensitivity analysis was performed to show the influence of material properties such as sorption, vapour permeability and the transfer coefficients on the simulated results. One model examines hysteresis of the sorption isotherm.
Article
A stability analysis of the classical Crank–Nicolson–Galerkin (CNG) scheme applied to the one-dimensional solute transport equation is proposed on the basis of two fairly different approaches. Using a space-time eigenvalue analysis, it is shown, at least for subsurface hydrology applications, that the CNG scheme is theoretically stable under the condition PeCr ≤2, where Pe and Cr are the mesh Péclet and Courant numbers. Then, to assess the computational stability of the scheme, the amplification matrix is constructed, and its norm is displayed in the ( Pe, Cr ) space. The results indicate that the norm of the amplification matrix is never smaller than unity and exhibits a hyperbolic nature analogous to the above theoretical condition.
Article
This paper presents theoretical calculations of the large-signal admittance and efficiency achievable in a silicon p-n-v-ns Read IMPATT diode. A simplified theory is employed to obtain a starting design. This design is then modified to achieve higher efficiency operation as specific device limitations are reached in large-signal (computer) operation. Self-consistent numerical solutions are obtained for equations describing carrier transport, carrier generation, and space-charge balance. The solutions describe the evolution in time of the diode and its associated resonant circuit. Detailed solutions are presented of the hole and electron concentrations, electric field, and terminal current and voltage at various points in time during a cycle of oscillation. Large-signal values of the diode's negative conductance, susceptance, average voltage, and power-generating efficiency are presented as a function of oscillation amplitude for a fixed average current density. For the structure studied, the largest microwave power-generating efficiency (18 percent at 9.6 GHz) has been obtained at a current density of 200 A/cm<sup>2</sup>, but efficiencies near 10 percent were obtained over a range of current density from 100 to 1000 A/cm<sup>2</sup>.
Physical Analysis and Hygrothermal Caracterisation of Construction Materials: Experimental Appraoch and Numerical Modelling
  • D Samri
D. Samri, Physical Analysis and Hygrothermal Caracterisation of Construction Materials: Experimental Appraoch and Numerical Modelling (In French), PhD thesis, INSA de Lyon, Lyon, France, October 2008.
International Energy Agency Energy Conservation in Buildings and Community Systems Programme Heat, Air and Moisture Transfer through New and Retrofitted Insulated Envelope Parts
  • M Kumar Kumaran
M. Kumar Kumaran, International Energy Agency Energy Conservation in Buildings and Community Systems Programme Heat, Air and Moisture Transfer through New and Retrofitted Insulated Envelope Parts: [IEA] (Hamtie), Annex 24 Task 3/Final report: Material properties. Laboratorium Bouwfysica, Dep. Burgerlijke Bouwkunde, K.U.-Leuven, 1996.
An analysis of moisture accumulation in walls subjected to hot and humid climates
  • D M Burch
D.M. Burch, An analysis of moisture accumulation in walls subjected to hot and humid climates, ASHRAE Trans. 93 (16) (1993).
Simulation Program for the Calculation of Coupled Heat, Moisture, Air, Pollutant, and Salt Transport
  • B C Bauklimatik Dresden
B.C. Bauklimatik Dresden, Simulation Program for the Calculation of Coupled Heat, Moisture, Air, Pollutant, and Salt Transport, 2011. http://www. bauklimatik-dresden.de/delphin/index.php?aLa¼en.
Analysis aequationum universalis seu adaequationes algebraicas resolvendas methodus generalis, et expedita, ex nova infinitarum serierum doctrina deducta ac demonstrata. Microfilm copy: University Microfilms
  • J Raphson
J. Raphson. Analysis aequationum universalis seu adaequationes algebraicas resolvendas methodus generalis, et expedita, ex nova infinitarum serierum doctrina deducta ac demonstrata. Microfilm copy: University Microfilms, Ann Arbor(MI), 1690. 17
Development of a Response Factor Approach for Modeling the Energy Effects of Combined Heat and Mass Transfer with Vapor Adsorption in Building Elements
  • R J Liesen
R.J. Liesen, Development of a Response Factor Approach for Modeling the Energy Effects of Combined Heat and Mass Transfer with Vapor Adsorption in Building Elements, PhD Thesis, Mechanical Engineering Department, University of Illinois, Illinois, USA, 1994.
Air, and Moisture Control in Building Assemblies-Material Properties. In ASHRAE Handbook-Fundamentals, page 1000
  • Ashrae Chapter
ASHRAE. Chapter 26: Heat, Air, and Moisture Control in Building Assemblies-Material Properties. In ASHRAE Handbook-Fundamentals, page 1000. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2013. 19
  • M Van Belleghem
  • M Steeman
  • A Willockx
  • A Janssens
  • M De Paepe
M. Van Belleghem, M. Steeman, A. Willockx, A. Janssens, M. De Paepe, Benchmark Exp. moisture Transf. Model. air porous Mater. 46 (4) (2011) 884e898.
The Handbook of Groundwater Engineering
  • J W Delleur
J.W. Delleur, The Handbook of Groundwater Engineering, Second Edition, CRC Press, New York, 2006.