Modelling cavity ventilation behind brick veneer cladding : how reliable are the common assumptions?

Throughout the years, different numerical HAM-simulation tools have been developed to assess and predict the heat, air and moisture response of building components. But, though commercially available and commonly applied in building practice, still, several simplifications and shortcomings exist in the common models. Probably the most important one, is the fact that most tools neglect or strongly simplify air transport, focusing only on heat and moisture transport. Especially for the analysis of wood frame constructions, these simplified models may cause a large discrepancy between simulation results and real performance. This study aims at a comparison of the outcomes of numerical HAM -simulations for wood frame constructions with experimental data of real test cases. In particular, the focus of this paper is on cavity ventilation behind brick veneer. Therefore, a simplified version of a wood frame wall with brick veneer cladding is studied in this paper. Different common modelling assumptions are compared. Furthermore, a detailed measuring campaign has been conducted at the VLIET test building of the KU Leuven to validate the different modelling approaches. By verifying the results of the numerical simulations by the data of real test cases, the reliability of the modelling assumptions can be analysed. The results of this study clearly show that simplified assumptions on cavity ventilation in HAM-models might cause large discrepancies between simulation results and in-situ measurements

A comparison of model order reduction methods for the simulation of wall heat transfer

In this paper, the potential of model order reduction for simulating building performance is assessed, via a case study of modelling heat transfer through a massive masonry wall. Two model order reduction techniques – proper orthogonal decomposition and proper generalized decomposition – are investigated and compared. Moreover, to illustrate the performance of model order reduction techniques, the accuracies of the two model order reduction techniques are respectively compared with a standard finite element method. The outcomes show that both of the two model order reduction techniques are able to provide an accurate result, and the proper generalized decomposition tends to be more versatile than the proper orthogonal decomposition method

Neural networks to predict the hygrothermal response of building components in a probabilistic framework

In recent years, probabilistic assessment of hygrothermal performance of building components has received increasing attention. Given the many uncertainties involved in the hygrothermal behaviour of building components, a probabilistic assessment enables to assess the damage risk more reliably. However, this typically involves thousands of simulations, which easily becomes computationally inhibitive. To overcome this time-efficiency issue, this paper proposes the use of much faster metamodels. This paper focusses on neural networks, as they have proven to be successful in other non-linear and non-stationary research applications. Two types of networks are considered: the traditional multilayer perceptron (with and without a time window) and memory neural networks (LSTM, GRU). Both are used for predicting the hygrothermal behaviour of a massive wall. The results showed that all networks are capable to predict the temperature profiles accurately, but only the LSTM and GRU networks could predict the slow responses of relative humidity and moisture content. Furthermore, the LSTM and GRU network were found to have almost equal predicting accuracy, though the GRU converged faste

Impact of wind-driven rain on historic brick wall buildings in a moderately cold and humid climate: Numerical analyses of mould growth risk, indoor climate and energy consumption

This paper gives an onset to whole building hygrothermal modelling in which the interaction between interior and exterior climates via building enclosures is simulated under a moderately cold and humid climate. The focus is particularly on the impact of wind-driven rain (WDR) on the hygrothermal response, mould growth at interior wall surfaces, indoor climate and energy consumption. First the WDR load on the facades of a 4×4×10 m3 tower is determined. Then the hygrothermal behaviour of the brick walls is analysed on a horizontal slice through the tower. The simulations demonstrate that the impact of WDR loads on the moisture contents in the walls is much larger near the edges of the walls than at the centre. The obtained relative humidity and temperature at the interior wall surfaces are combined with isopleths of generalised spore germination time of fungus mould. The results show that WDR loads can have a significant impact on mould growth especially at the edges of the walls. Finally, for the case analysed, the WDR load causes a significant increase of indoor relative humidity and energy consumption for heating.status: publishe

Hygrothermal behaviour of timber frame walls finished with a brick veneer cladding

In this study, two typical timber frame walls with brick veneer cladding have been constructed at KU Leuven to investigate the hygrothermal response of these constructions in a moderate sea climate. Main topic of research is the contradictory criterion for the wind barrier when it comes to the risk on interstitial condensation for winter and summer conditions: in winter a vapour open wind barrier is appropriate, in summer a more vapour tight. Therefore, similar walls but with different types of wind barrier have been investigated. In one set-up a vapour open bituminous impregnated wood fibre board is used as wind barrier, whereas in the second set-up a more vapour tight wood fibre cement board is used. The study shows that a high relative humidity can be expected at the interface between insulation and wind barrier during winter conditions, leading to a high mould growth index. In contrast, the relative humidity at the interface between insulation and inner vapour retarder during summer is lower than expected. This can be caused by the buffering capacity of the hygroscopic materials in the wall

Characterising the Actual Thermal Performance of Buildings: Current Results of Common Exercises Performed in the Framework of the IEA EBC Annex 58-Project

AbstractSeveral studies have shown that actual thermal performance of buildings after construction may deviate significantly from that anticipated at design stage. As a result, there is growing interest in full scale testing of components and whole buildings. The IEA EBC Annex 58-project ‘Reliable Building Energy Performance Characterisation Based on Full Scale Dynamic Measurements’ is developing the necessary knowledge and tools to achieve reliable in-situ dynamic testing and data analysis methods that can be used to characterise the actual thermal performance and energy efficiency of building components and whole buildings. The research within this project is driven by case studies. As a first simple case, an experiment on testing and data analysis is performed on a round robin test box. This test box can be seen as a scale model of a building, built by one of the participants, with fabric properties unknown to all other participants. Full scale measurements have been performed on the test box in different countries under real climatic conditions. The obtained dynamic data are distributed to all participants who have to try to characterise the thermal performance of the test box's fabric based on the provided data.This paper presents the first results obtained on the round robin exper ment. It is shown how different techniques can be used to characterise the thermal performance of the test box, ranging from a simple stationary analysis to advanced dynamic data analysis methods