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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 results, this paper proposes to include the moisture advection transfer in the governing equation. To solve the advection-diffusion or the so-called convection differential equation, it is first proposed two efficient numerical schemes whose efficiencies are investigated for both linear and nonlinear cases. The first scheme, Scharfetter – Gummel , presents a Courant-Friedrichs-Lewy (CFL) condition but it is more accurate and faster than the second one, the well-known Crank – Nicolson approach. Furthermore, the Scharfetter – Gummel scheme has the advantages of being well-balanced and asymptotically preserved. Then, to conclude, results of the convective moisture transfer problem obtained by means of the Scharfetter – Gummel 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. [ABSTRACT FROM AUTHOR]

In this paper, an innovative method to minimise energy losses through building envelopes is presented, using the Proper Generalised Decomposition (PGD), written in terms of space x , time t , thermal diffusivity α and envelope thickness L . The physical phenomenon is solved at once, contrarily to classical numerical methods that cannot create a parameter dependent model. First, the PGD solution is validated with an analytical solution to prove its accuracy. Then a complex case study of a multi-layer wall submitted to transient boundary conditions is investigated. The parametric solution is computed as a function of the space and time coordinates, as well as the thermal insulation thickness and the load material thermal diffusivity. Physical behaviour and conduction loads are analysed for 76 values of thermal insulation thickness and 100 types of load material properties. Furthermore, the reduced computational cost of the PGD is highlighted. The method computes the solution 100 times faster than standard numerical approaches. In addition, the PGD solution has a low storage cost, providing interesting development of parametric solutions for real-time applications of energy management in buildings. [ABSTRACT FROM AUTHOR]

In this paper, the use of Bayesian inference is explored for estimating both the thermal conductivity and the internal convective heat transfer coefficient of an old historic building wall. The room air temperature, as well as the temperatures at the surface and within the wall have been monitored during one year and then used to solve the identification problem. With Bayesian inference, the posterior distributions of the unknown parameters are explored based on their prior distributions and on the likelihood function that models the measurement errors. In this work, the Markov Chain Monte Carlo method is used to explore the posterior distribution. The error of the inadequacy of mathematical model are considered using the approximation error model. The distribution of the estimated parameters have a small standard deviation, which illustrates the accuracy of the method. The parameters have been compared to the standard values from the French thermal regulations. The heat flux at the internal surface has been calculated with the estimated parameters and the standard values. It is shown that the standard values underestimate the heat flux of an order by 10%. This study also illustrates the importance of the preliminary diagnosis of a building with the estimation of the thermal properties of the wall for model calibration. [ABSTRACT FROM AUTHOR]

Abstract: Although the thermal bridge effects on the building energy performance have been presented in the literature, the multidimensional hygrothermal analysis of the building envelope is still a challenge due to many difficulties such as modeling complexity, computer run time, numerical convergence and highly moisture-dependent properties. However, their effects are of paramount importance due to the local increase of heat and mass flux densities so that moisture can be easily accumulated around internal corners, increasing mold growth risk and causing structural damage. Therefore, for analyzing the effects of building lower and upper corners, a multidimensional model has been developed to calculate the coupled heat, air and moisture transfer through building envelopes. The algebraic equations are simultaneously solved for the three driving potentials — temperature, vapor pressure and gas pressure gradients — to improve the numerical stability of the discretized model. In the Results section, the coupling of the upper corner, wall, lower corner (with different types of foundations), ground and floor are analyzed in terms of temperature and relative humidity profiles, vapor flow and heat flux, showing the importance of a detailed hygrothermal analysis for accurately predicting building energy consumption, mold growth and structural damage risks. [Copyright &y& Elsevier]

Abstract: Combined multidimensional analysis of heat, air and moisture transport through porous building elements is barely explored in the literature due to many difficulties such as modeling complexity, computer run time, numerical convergence and highly moisture-dependent properties. In this way, a mathematical model considering a combined two-dimensional heat, air and moisture transport through unsaturated building upper corners is presented. In order to improve the discretized model numerical stability, the algebraic equations are simultaneously solved for the three driving potentials: temperature, vapor pressure and moist air pressure gradients. In the results section, the convective effects caused by air stagnation are analyzed in terms of heat flux and mould growth risk for different boundary conditions, showing the importance of a detailed hygrothermal analysis – which is normally disregarded by simulation tools – for accurately predicting building energy consumption, indoor air quality, thermal comfort or mould growth risk. [Copyright &y& Elsevier]

Abstract: The combined heat, air and moisture transfer in building hollow elements is of paramount importance in the construction area for accurate energy consumption prediction, thermal comfort evaluation, moisture growth risk assessment and material deterioration analysis. In this way, a mathematical model considering the combined two-dimensional heat, air and moisture transport through unsaturated building hollow bricks is presented. In the brick porous domain, the differential governing equations are based on driving potentials of temperature, moist air pressure and water vapor pressure gradients, while, in the air domain, a lumped approach is considered for modeling the heat and mass transfer through the brick cavity. The discretized algebraic equations are solved using the MTDMA (MultiTriDiagonal-Matrix Algorithm) for the three driving potentials. Comparisons in terms of heat and vapor fluxes at the internal boundary are presented for hollow, massive and insulating brick blocks. Despite most of building energy simulation codes disregard the moisture effect and the transport multidimensional nature, results show those hypotheses may cause great discrepancy on the prediction of hygrothermal building performance. [Copyright &y& Elsevier]

Abstract: The present study aims to evaluate the importance of wind turbulence when performing droplet trajectory numerical simulations. Turbulence effect on Wind-Driven Rain is studied by calculating the specific catch ratio of 1 mm droplets for an isolated low-rise building windward surface under a 5 m/s normal wind. An Eulerian Second Moment Closure and a Lagrangian one-way coupling models are used to calculate the airflow field and the droplet trajectories respectively. Results show that turbulence has a negligible effect considering the whole windward wall but can substantially modify the value of the specific catch ratio in the case of Wind-Driven Rain gauges. [Copyright &y& Elsevier]

Despite split-type systems for cooling purposes became popular in countries such as China, Japan. India, Indonesia and Brazil, their use commonly promote high gradients of both temperature and air velocity in rooms which may cause considerable thermal discomfort. Hence, this work aims at developing a simplified thermal comfort index, based on temperature and air speed, in order to develop controllers for those types of air conditioning systems, replacing the traditional on-off temperature set-point control by an effective and inexpensive thermal-comfort based control. The work is focused on the assessment of comfort in classrooms by carrying out measurements according to ISO 7730 and ASHRAE 55 Standards, which defines the thermal satisfaction in occupied environments based on the PMV index. Specifically, the speed, temperature and relative humidity of the air and the mean radiant temperature of the room were measured at eight positions within the space. The field experiments were performed considering two 10.5-kW cooling capacity appliances installed in different positions relatively to the layout of the room, considering three levels of supply airflow (high, medium and low) and three set-point temperatures (23, 24 and 25 °C). An analysis of uncertainties is presented for PMV measurements and a regression analysis was applied to the measured data to determine a simplified correlation between thermal comfort (by means of the PMV index) air temperature and air velocity, aiming at developing afterwards a control device based on thermal comfort instead of temperature setpoint only. Results are shown in terms of distribution of air speed, air temperature and PMV index for the two configurations of equipment installation, as well as the resulting empirical model correlating thermal comfort index with both temperature and air speed. In addition, thermal comfort opinions from a survey are contrasted with the simplified thermal comfort model. • Field study of thermal comfort assessment in a classroom conditioned by a split unit. • Uncertainty analysis on the PMV model. • Development of a simplified empirical model. [ABSTRACT FROM AUTHOR]

Highlights • A detailed mathematical model for the heat, air and mass transfer is achieved. • An efficient numerical model is proposed to save computational efforts. • Demonstration of numerical model efficiency (cpu time, accuracy) for a case study. • Evaluation of the reliability of the model by confronting to experimental results. Abstract 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 L uikov '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 D u F ort –F rankel explicit and unconditionally stable scheme for the exclusively diffusion equation. It is combined with a two–step R unge –K utta scheme in time with the S charfetter –G ummel 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. [ABSTRACT FROM AUTHOR]

This paper presents an experimental validation procedure of two solar shading calculation techniques - pixel counting (PxC) and polygon clipping (PgC) - and an inter-software comparison to highlight the capabilities and efficiency of each solar shading calculation method. For the first purpose, digital images were taken from the surfaces of small-scale mock-ups specially constructed to generate experimental data for validating simulation results obtained by cases using three different tools: EnergyPlus (PgC based), Shading II SketchUp plug-in (PxC based) and Domus (PxC based). This first task has shown, for prototypes with simple geometries, that all techniques present results in good agreement with the experimental data. However, for a prototype with a hollowed shading device, the PgC-based technique produced results far from the experimental ones since it is not appropriated to simulate multi-hollowed polygons. In order to further explore the capabilities of the two shading calculation techniques, an inter-software comparison has also been carried out for a complex case, considering different building shading solutions, including non-planar trees. The results, in general, have shown that the PxC technique is not limited to geometrical complexities and leads to an accurate and a very fast assessment of sunlit surface fraction. It has also been shown a difference as high as 10 times on the prediction of a daily-integrated solar heat gain by using the two different techniques. [ABSTRACT FROM AUTHOR]

In the context of estimating material properties of porous walls based on in-site measurements and identification method, this paper presents the concept of Optimal Experiment Design (OED). It aims at searching the best experimental conditions in terms of quantity and position of sensors and boundary conditions imposed to the material. These optimal conditions ensure to provide the maximum accuracy of the identification method and thus the estimated parameters. The search of the OED is done by using the Fisher information matrix and a priori knowledge of the parameters. The methodology is applied for two case studies. The first one deals with purely conductive heat transfer. The concept of optimal experiment design is detailed and verified with 100 inverse problems for different experiment designs. The second case study combines a strong coupling between heat and moisture transfer through a porous building material. The methodology presented is based on a scientific formalism for efficient planning of experimental work that can be extended to the optimal design of experiments related to other problems in thermal and fluid sciences. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to validate and improve three cross and single-sided natural ventilation models implemented in a whole-building hygrothermal and energy simulation program. The tested models are the British Standard for cross ventilation, the de Gids and Phaff's and Larsen's for single-sided ventilation. Airflow rates obtained by those models have been compared to the measurements performed in two full-scale buildings: one single room house located in a wind tunnel facility and one real three-storey building. Results show a large variation of airflow rates provided by the different models. The Larsen's model can be improved if coupled to the CPCALC algorithm, providing better results for both wind tunnel and on-site experiments. [Copyright &y& Elsevier]

A precise hygrothermal model is essential to predict the energy performance of building envelopes providing coupled transport of mass (moisture and air) and heat through porous elements, considering phase change and all heat transfer modes, including the radiative transfer through fibrous materials. Therefore, a new mathematical model, called CAR-HAM (Conductive, Advective, and Radiative Heat, Air and Moisture), is proposed to include the radiative transfer equation to calculate the thermal radiation effects within the porous materials to be taken into account in the energy balance. The moisture and the energy conservation equations are simultaneously solved using a fully implicit scheme and the MTDMA algorithm. The comparison of the proposed model considering some case studies such as attic insulation, bar drying, convection and high humidity (rain load) - showed a good agreement with experimental data available in the literature. [ABSTRACT FROM AUTHOR]

Highlights • Pixel counting technique for interior sunlit area calculation is experimentally validated. • Simulation skillfulness for complex geometries of the pixel counting is investigated. • Pixel counting has good agreement with the experiments. • The impact of internal sun patch position on surface temperature is highlighted. • Importance of computer graphic development to modernize solar energy assessment. Abstract Pixel counting (PxC) emerged as a powerful technique for external solar shading calculations of buildings, providing accurate results with great computational efficiency even for dense geometries. Motivated by this fact and because the technique can be also adapted to cope with interior surfaces without further ado, this paper aims at experimentally evaluating the PxC technique implemented in Domus software for calculating sun patch distribution within building enclosures. For the validation purpose, digital images were taken from the surfaces of an experimental house to compare with the simulation results obtained by using EnergyPlus and two PxC based tools: Domus and Shading II SketchUp plug-in. This first task has shown that the PxC presents results in good agreement with the experimental data, in terms of both location and area of the sun patch. Also, a second case study was constructed to evaluate the capability of PxC for simulating non-convex zones with perforated shading elements. The results, in general, have shown that the PxC can provide accurate results in situations where polygon clipping based algorithms cannot be applied. [ABSTRACT FROM AUTHOR]

This work presents an alternative view on the numerical simulation of diffusion processes applied to the heat and moisture transfer through porous building materials. Traditionally, by using the finite-difference approach, the discretization follows the Method Of Lines (MOL), when the problem is first discretized in space to obtain a large system of coupled Ordinary Differential Equations (ODEs). Thus, this paper proposes to change this viewpoint. First, we discretize in time to obtain a small system of coupled ODEs, which means instead of having a Cauchy (Initial Value) Problem (IVP), we have a Boundary Value Problem (BVP). Fortunately, BVPs can be solved efficiently today using adaptive collocation methods of high order. To demonstrate the benefits of this new approach, three case studies are presented, in which one of them is compared with experimental data. The first one considers nonlinear heat and moisture transfer through one material layer while the second one considers two material layers. Results show how the nonlinearities and the interface between materials are easily treated, by reasonably using a fourth-order adaptive method. Finally, the last case study compares numerical results with experimental measurements, showing a good agreement. [ABSTRACT FROM AUTHOR]

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 ϕ = 10–75%, with one sensor located at the position X between 4 and 6 cm, for the estimation of moisture permeability coefficients, while from ϕ = 75 % to ϕ = 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 ( ϕ = 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental characteristic curves for two room air conditioners are presented. [•] These results can be implemented in building simulation codes. [•] The energy consumption under different conditions can numerically determine. [•] The labeled higher energy efficiency product not always provides the best result. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, several intensive studies have been carried out in order to reduce the energy consumption of buildings. One solution lies on whole building energy simulation that permits to enable the heat (and moisture) transfer through the building envelope and, consequently, is a way to understand how to improve the building performance. This article aims to analyze the modeling level needed to successfully evaluate the heat transfer through glazing parts of windows in such whole-building simulations as it is well-known that windows are the thermally weakest elements of the building envelope. In this way, predictions of glazing surface and zone air temperatures and energy demand obtained using both resistive and finite-volume based models are compared. Results show that for common window glazing structure and outdoor/indoor perturbations, differences between the two models are small. However, in the case of glazing presenting higher solar absorption and thermal inertia, the use of the finite-volume based model is required to accurately predict the glazing internal surface temperature and avoid errors up to 50% for energy consumption in the studied case. Those results put into relief a clear limitation of current whole energy simulation programs to correctly predict the energy consumption of buildings where high thermal inertia double- or triple-glazing windows are installed. [Copyright &y& Elsevier]

Abstract: Studies on the dynamics of temperature and moisture content distributions in porous soils have provided important insight on their effect on the building hygrothermal behavior, where the interaction between both building and soil can contribute to reduce building thermal gains or looses. Hygrothermal aspects can be related to many attributes such as energy consumption, occupants'' thermal comfort and health, and material deterioration. Recently, a great variety of mathematical models to predict thermal and moisture content profiles in porous media have been presented in the literature. Most of those models are based on analysis of multilayer measurements or on Fourier analysis. The development and validation of such mathematical models facilitate the understanding of heat and moisture flows at different soil depths. In this research, a radial basis function neural network (RBF-NN) approach, combined with Gath–Geva clustering method in order to predict the temperature and moisture content profiles in soils, has been presented. A set of data obtained from the computation of the coupled heat and moisture transfer in porous soils for the Curitiba city (Paraná State, Brazil) weather data file has been used by the RBF-NN modeling method. Simulation results indicate the potentialities of the RBF-NNs to learn, for the one step ahead identification, the behavior of temperature and moisture content profiles in the media at various depths. [Copyright &y& Elsevier]

• A multi-criteria method for designing shading devices of buildings is presented. • The method is based on: search of non-dominated solutions and physical programming. • Physical programming allows finding a ranking containing the preferred solutions. • Design objectives are related to Energy Efficiency, Daylighting and Fading Protection. • A Pixel Counting based tool allows evaluating more complex shading devices. Multi-criteria design techniques applied to the analysis of shading devices of buildings have arisen as useful tools for architects. Even though several techniques have been applied to shading devices with simple geometries, they usually require numerous simulations to suitably complete the analysis, making the optimization process time-consuming. Since shading devices should prevent damage to furnishings and materials, performance indicators may not be related exclusively to thermal comfort, energy consumption and daylight performance, but also to other important criteria, such as fading protection. To overcome these limitations, this study aims to present a multi-criteria method for the design of shading devices, including fading protection as an evaluation criterion, regardless of geometry complexity. The method is applied to perforated shading devices of a room office, considering as the design objectives the energy savings, daylight availability on the work plane and solar beam incidence on interior surfaces. As a novelty, a more practical approach is proposed based on two main steps: search process, for obtaining a set of non-dominated solutions, and physical programming method, in which the solutions are ranked according to the preferences of decision makers. Besides, the solar beam incidence on interior surfaces is evaluated by using a pixel counting based method, which was emerged as a powerful algorithm due its capacity to simulate any geometry with accuracy and low computational cost. The results have shown that the proposed method is an effective process in designing of the optimal shading devices to reduce energy consumption, and improve the daylight use and the fading protection, regardless of the geometry complexity. [ABSTRACT FROM AUTHOR]