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Stochastic simulation of rain intrusion through small defects due to water rivulet overpressure. Introducing a driving rain leakage potential.
Carl-Eric Hagentoft1, Lars Olsson2
1Chalmers University, Sweden; 2RISE Research Institutes of Sweden
Moisture damages occur in external walls due to rain intrusion. The rain resistance of façades, joints and connecting details has been insufficient. This becomes an issue for moisture sensitive external walls. This paper investigates the pressure build up in water rivulets running down a façade, the friction as well as the counter acting pressure in the curved water surfaces on the backside of the external cladding. Randomized rain events coupled to the buildup of a random number of water rivulets are used in the Monte Carlo simulations. The probability and the severity of rain intrusion is presented based on different climates and building orientations.
4:15pm - 4:30pm
Characterising the effects of wind-driven rain on the thermophysical performance of cavity walls by means of a Bayesian framework
Virginia Gori1, Valentina Marincioni2,3, Hector Altamirano-Medina2,3
1UCL Energy Institute, University College London, United Kingdom; 2UCL Institute for Environmental Design and Engineering, University College London, United Kingdom; 3UK Centre for Moisture in Buildings, United Kingdom
Cavity wall is one of the most common construction types in temperate maritime climates, including the UK. However, water penetration may lead to damp within the structure, freeze-thaw damage at the outer surface and a reduction in thermal resistance. The magnitude of wetting effects on the energy performance of cavity walls is still unclear, with potentially significant implications for climate-change-mitigation strategies. This paper investigates the thermophysical performance of uninsulated and insulated cavity walls and its degradation as the element is wettened. Experiments were performed in a hygrothermal laboratory where two cavity-wall specimens (one of which coated with external waterproofing treatment) were tested under a high wind-driven rain exposure. Changes in the thermophysical performance between dry and wet conditions were evaluated through U-value testing and Bayesian inference. Substantial U-value increase was observed for wet uninsulated specimens (compared to dry conditions); conversely, closer U-value ranges were obtained when insulated with EPS grey beads. Moreover, latent-heat effects through the external masonry leaf of the untreated specimen were predicted by the Bayesian framework. Results suggest a negligible efficacy of waterproofing surface treatments as strategies for the reduction of heat transfer within the element, and possible effects of these agents on the evaporative and drying process.
4:30pm - 4:45pm
Impact of climate change on the wind-driven rain exposure of a historical building
John Bourcet1, Aytac Kubilay1, Dominique Derome2, Jan Carmeliet1
1ETH Zurich, Switzerland; 2Université de Sherbrooke, Canada
Wind-driven rain is a significant moisture source on building facades. The areas over the building envelope that are exposed to high amount of rain usually have a higher risk of deterioration due to moisture. Climate change can have an impact on the wind-driven rain exposure of buildings and thus on moisture-induced damage risks. First, changing rain event patterns and increased average temperatures can lead to an overall increase in rain exposure. Second, increasing temperatures can lead to an increased risk for freeze/thaw damage in northern countries. Therefore, it is critical to take into account the future wind-driven rain load when planning for the preservation and maintenance of buildings.
The present study uses computational fluid dynamics (CFD) simulations of wind-driven rain with a validated Eulerian multiphase model to estimate the rain exposure of a historical building located in an urban area in Victoria, BC, Canada. The current weather data is modified using a simplified weather morphing method to reflect the potential changes in rain events with climate change considering the RCP8.5 Scenario, representing high emission conditions. The analyses are performed for the current weather conditions as reference and the predicted future conditions with climate change.
The results show a wind-driven rain intensity pattern on the exposed facade of the building, which is similar to the current conditions. However, the wind-driven rain exposure increases for almost all locations on the façade by up to 20%. Such changes can result in higher risk of biodegradation and freeze/thaw damage in the future. CFD simulations allow for high spatial resolution of wind-driven rain deposition for the critical time periods in a year, thus, improving the appropriateness of retained boundary conditions for hygrothermal analyses.
4:45pm - 5:00pm
Effects of anisotropy of properties of fired clay materials on strain evolution and results of coupled hygrothermal and mechanical simulations during freezing and thawing
Kazuma Fukui, Chiemi Iba, Daisuke Ogura
Kyoto University, Japan
The evaluation of risks of moisture damages, such as frost damages and salt scaling, of fired clay materials has become more important these days because there are increased risks associated with internal insulation of masonry walls to improve the building’s energy efficiency. Also, the preservation of ceramic bricks and tiles used in historic buildings is still an urgent issue.
Hygrothermal simulations are considered as an effective measure to deal with such challenges. Furthermore, coupled hygrothermal and mechanical models have been developed following the theory of the poroelasticity and poromechanics. These approaches have been also applied to fired clay materials and masonry walls. However, such models often neglect anisotropy of the material properties. Because the properties of fired clay materials are strongly anisotropic as well as heterogeneous, its effects on the hygrothermal and mechanical behaviors should be adequately understood and considered in the simulations.
In this study, we investigated the effects of the anisotropy during freezing and thawing processes as an example. We measured strain evolution during a freeze-thaw experiment using a plate-shaped fired clay material and then conducted coupled hygrothermal and mechanical simulations based on the poromechanics. According to the results of the experiment, the strain in the thickness direction of the material significantly increased as the temperature decreased while the material hardly expanded in the direction normal to the thickness direction, which showed the strong anisotropy of the deformation. The comparison of the experimental and calculation results revealed that an isotropic model and even a model including the anisotropy of the elastic modulus and water permeability could not adequately reproduce the deformation during the experiment. Finally, the effects of the anisotropy of the poroelastic properties were also examined.
5:00pm - 5:15pm
Fundamental Study on the Thermodynamic Non-Equilibrium Freezing Probability Prediction Model Taking into Account the Super Cooling Phenomena in Porous Material
Osaka City University, Japan
It is commonly considered that frost damage is caused by sudden freezing of supercooled water, which is a random phenomenon. Because the supercooling phenomenon is thermodynamic non-equilibrium phenomenon, the previous thermodynamic equilibrium analytical model cannot investigate influence of the supercooling phenomenon.
Therefore, the aims of this study are to establish a prediction model for the probability of freezing until any lowest reached temperature, and to obtain the probability distribution function of the freezing point for the proposed analytical prediction model.
First, theoretical prediction model for the probability of the instantaneous increment of ice content when lowest achieving temperature was known was derived based on these assumptions that building structure is an aggregation of small elements and probability distribution of the freezing point in small elements is independent from each other. The applicability of the proposed model for small continuum will be validated as the future task.
Next, the freezing point measurement was carried out by using saturated mortar samples as the small element. As the results, it could be found that the first freezing due to supercooling occurred from -4 to -11 deg. C and the maximum probability was appeared at -7.5 deg. C. From comparison between the average increment of ice content based on the measurement result and the 40 % volume of pore water until the thermodynamically-based freezing point, there was a good agreement for both of them.
Moreover, the probability distribution of the increment of ice content could be regarded as a normal distribution. And the method that can calculate the probability distributions of the instantaneous increment of ice content for any lowest achieving temperature from pore size distribution was proposed. Because the calculation results of the proposed method had good agreements with the measurement results, it can be concluded that the proposed method has enough validity.