The effect of micro air movement on the heat and moisture characteristics of building constructions

The research focuses on the effect of air movement through building constructions. Although the typical air movement inside building constructions is quite small (velocity is of order ~10-5 m/s), this research shows the impact on the heat and moisture characteristics. The paper presents a case study on the modeling and simulation of 2D heat and moisture transport with and without air movement for a building construction using a state-of-art multiphysics FEM software tool. Most other heat and moisture related models don’t include airflow or use a steady airflow through the construction during the simulation period. However, in this model, the wind induced pressure is dynamic and thus also the airflow through the construction is dynamic. For this particular case study, the results indicate that at the internal surface, the vapor pressure is almost not influenced by both the 2D effect and the wind speed. The temperatures at the inner surface are mostly influenced by the 2D effect. Only at wind pressure differences above 30 Pa, the airflow has a significant effect. At the external surface, the temperatures are not influenced by both the 2D effect and the wind speed. However, the vapor pressure seems to be quite dependent on the wind induced pressure. Overall it is concluded that air movement through building materials seems to have a significant impact on the heat and moisture characteristics. In order to verify this statement and validate the models, new in-depth experiments including air flow through materials are recommended

Chaotic Behavior of the Airflow in a Ventilated Room

Chaotic systems may lead to instability, extreme sensitivity and performance reduction. Therefore it is unwanted in many cases. Due to these undesirable characteristics of chaos in practical systems, it is important to recognize such a chaotic behavior. The existence of chaos has been discovered in several areas during the last 30 years. However, there is a lack of studies in relation with buildings that also can be regarded as complex dynamic systems. In this paper the chaotic behavior of the airflow in case of an ordinary ventilated room is researched. Chaotic behavior is already observed in the simulations by changing the supply air temperature from 22 oC into 21.9 oC. In the case when no buoyancy is taking into account, minor chaotic behavior is observed by a small in the air supply control parameters

The Exploration of an Inverse Problem Technique to Obtain Material Properties of a Building Construction

The main goal of this work is to investigate whether material properties can be obtained using an inverse problem technique. The inverse problem technique used in this paper consists of three main parts: First, a set of input data (time series and parameters) and the objective data (time series) to be reproduced. Second, a model capable of simulating the requested data. Third, optimisation of the modeling parameters by filling simulated data with the objective data. The suggested methodology of the inverse problem tcchnique seems promising for estimating material properties but requires that: (I) All measurements errors must be known; (2) The (measured) signals itself should deliver enough input power into the system; (3) The simulated objeeti\'e data should be sensitive enough for changes in material properties

The mapping of simulated climate-dependent building innovations

Performances of building energy innovations are most of the time dependent on the external climate conditions. This means a high performance of a specific innovation in a certain part of Europe, does not imply the same performances in other regions. The mapping of simulated building performances at the EU scale could prevent the waste of potential good ideas by identifying the best region for a specific innovation. This paper presents a methodology for obtaining maps of performances of building innovations that are virtually spread over whole Europe. It is concluded that these maps are useful for finding regions at the EU where innovations have the highest expected performances

Simulation and Experimental Validation of Chaotic Behavior of Airflow in a Ventilated Room

Chaos may lead to instability, extreme sensitivity and performance reduction in dynamic systems. Therefore it is unwanted in many cases. Due to these undesirable characteristics of chaos in practical systems, it is important to recognize such a chaotic behavior. In this paper the chaotic behavior of the airflow in case of an ordinary ventilated room is researched. Computational chaotic behavior is already observed in the simulations by changing the supply air temperature from 22 oC into 21.9 oC.However, it could be the case that, despite all efforts, the chaotic behavior is a numeral artifact. Therefore laboratory experiments using a scale model were performed. It is concluded that the computational model of the experimental scale model has to be improved to simulate the experimental results more accurately.Furthermore, the presented method seems promising in detecting chaotic behaviour

Implementation of comsol in simuLink S-functions, revisited

Comsol has standard facilities to export models to SimuLink. Normally, the standard export works well if the solvers, available in SimuLink, can handle the problem. However, if a model in Comsol needs special solvers, for example airflow or other non-linear problems, the standard export to SimuLink is often not suitable, because the standard solvers of SimuLink cannot handle such a problem efficiently. This can cause long simulation duration times and even leads to no solution at all. The paper presents a possible solution to this problem by implementing Comsol code in the discrete section of a SimuLink S-Function The advantage of this approach is that the special solvers of Comsol can be used in the SimuLink environment. This can lead to significant improvement of the simulation duration time

The Use of System Identification Tools in MatLab for Transfer Functions

This report introduces the system identification toolbox in MatLab as a tool to produce the required transfer functions

EU maps of climate related building performances using state-space modeling

Performances of building energy innovations are most of the time dependent on the external climate conditions. This means a high performance of a specific innovation in a certain part of Europe, does not imply the same performances in other regions. The mapping of simulated building performances at the EU scale could prevent the waste of potential good ideas by identifying the best region for a specific innovation. This paper presents a methodology for obtaining maps of performances of building innovations that are virtually spread over whole Europe. It is concluded that these maps are useful for finding regions at the EU where innovations have the highest expected performances