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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. [ABSTRACT FROM AUTHOR]

Abstract Heat and mass transfers are becoming increasingly important in the field of building physics. They should be considered to predict building performance, especially for a wall containing highly hygroscopic materials. The moisture balance at the room scale is influenced by air leakage and moisture sources, by the vapour transfer within the material and by the interaction between the wall and the air volume. Therefore, to study the impact of mass transfers on the indoor climate, experimental data at different scales of study are needed. The present study adopts this approach to validate hygrothermal prediction. At the material scale, the hygric properties of wooden panels are estimated using an inverse method algorithm with transient experimental data. The phenomena within the wall and the interactions between the wall and the air volume are studied by designing an experimental device and characterising it in terms of air leakage to validate predictions obtained with model. The values of the material properties are validated at the wall scale by correctly simulating the hygrothermal behaviour before characterising the exchange between the wall surface and the air volume by estimating the convective transfer coefficient. Using this information, the indoor moisture level is correctly predicted by the developed model as well as the heat and mass flows through the walls. Finally, this numerical model highlights that taking into account coupled transfers has only a slight effect on the average energy consumed, while the heating power at the beginning of moisture steps is greatly decreased due to moisture adsorption. [ABSTRACT FROM AUTHOR]

Available throughout the world and used in construction for thousand years, earthen materials are known to improve indoor air quality while keeping the internal temperature relatively stable. In Rhône-Alpes, France, the rammed earth technic is the most spread and consists in compacting layers of earth, one by one, within a framework. Current thermal standards, which are mainly based on thermal resistance of the material, urge to insulate walls. However, due to its interaction with its environment, and its couplings between heat and moisture transfers, the observed thermal behaviour of uninsulated rammed earth can be above the expectations. The objective of the paper is to highlight the living comfort provided by non-insulated rammed earth walls, for different orientations, from in-situ measurements performed over more than two years. Winter, with low energy use for heating, and summer, with no cooling device, are studied. The study points out the important role of solar irradiance on the thermal balance of the house, and thus the importance of a good architecture. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper proposes the application of the covariance matrix adaptation (CMA) evolution strategy for the identification of building envelope materials hygrothermal properties. All material properties are estimated on the basis of local temperature and relative humidity measurements, by solving the inverse heat and moisture transfer problem. The applicability of the identification procedure is demonstrated in two stages: first, a numerical benchmark is developed and used as to show the potential identification accuracy, justify the choice for a Tikhonov regularization term in the fitness evaluation, and propose a method for its appropriate tuning. Then, the procedure is applied on the basis of experimental measurements from an instrumented test cell, and compared to the experimental characterization of the observed material. Results show that an accurate estimation of all hygrothermal properties of a building material is feasible, if the objective function of the inverse problem is carefully defined. [ABSTRACT FROM PUBLISHER]

This paper proposes a reduced order model to simulate heat and moisture behaviour of material based on proper general decomposition (PGD). This innovative method is ana priorimodel reduction method. It proposes an alternative way for computing solutions of the problem by considering a separated representation of the solution. PGD offers an interesting reduction of numerical cost. In this paper, the PGD solution is first compared with a finite element solution and the commercial validated modelDelphinin an 1D case. The results show that the PGD resolution techniques enable the field of interest to be represented with accuracy, with a relative error rate of less than 0.1%. The study remains in the hygroscopic range of the material. As the numerical gain of the method becomes interesting when the space dimension increases, this resolution strategy was then used on a 2D multi-layered test case. The dynamics and amplitude of hygrothermal fields are perfectly represented by the PGD solution. Temperature and vapour pressure modelled with PGD can be used for post-processing and analysing the behaviour of an assembly. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]

Innovative and efficient ways to carry out numerical simulations are worth of investigation to reduce the computational complexity of building models and make it possible to solve complex problems. This paper presents a reduced order model, based on Proper Generalised Decomposition (PGD), to assess 2-dimensional heat and moisture transfer in walls. This model is associated with the multizone model Domus using an indirect coupling method. Both models are co-simulated to perform whole-building hygrothermal simulation, considering 2D transfer in walls. The whole-building model is first validated with data from the IEA Annex 41. Then, a case study is considered taking into account a 2-zones building with an intermediary shared wall modelled in 2 dimensions to illustrate the importance of the technique to analyse the hygrothermal behaviour of the wall. It has been highlighted that the whole model enables to perform more precisely analyses such as mould growth on the internal surface. In addition, important theoretical numerical savings (90%) are observed when compared to the large original model. However, the effective numerical savings are not so important (40%) due to the limitations of the co-simulation method. [ABSTRACT FROM AUTHOR]