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 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

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

The paper presents the modeling and simulation of 2D heat and moisture transport with and without air movement for a building construction. 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 it might have much more impact on the moisture characteristic as presumed so far. Our results indicate that especially vapor transport is in our case study very sensitive for air movement. As much as 40% Rh change at the inner surfaces of the building constructions are observed if we take air movement into account. Concerning the simulations tool, it is concluded that the use of the COMSOL Multiphysics software enables and simplifies the research of possible important effects that are not included in other standard heat and moisture simulation tools

The mapping of climate-dependent simplified thermal systems using state-spapce models

Performances of thermal systems 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 system. This paper presents a methodology for obtaining maps of performances of simplified thermal systems that are virtually spread over whole Europe using state space models. It is concluded that these maps are useful for finding regions at the EU where systems have the highest expected performances

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

Integrated heat air and moisture modeling and simulation

An overall objective of our work is to improve building and systems performances in terms of durability, comfort and economics. In order to predict, improve and meet a certain set of performance requirements related to the indoor climate of buildings, the associated energy demand, the heating, venting and air conditioning systems and the durability of the building and its interior, simulation tools are indispensable. In the field of heat, air and moisture transport in building and systems, much progress on the modeling and simulation tools has been established. However, the use of these tools in an integrated building simulation environment is still limited. Also a lot of modeling work has been done for energy related building systems, such as solar systems, heat pump systems and heat storage systems. Often, these models focus on the systems and not on the coupled problem of building and systems. This thesis presents the development and evaluation of an integrated heat, air and moisture simulation environment for modeling and simulating dynamic heat, air and moisture processes in buildings and systems. All models are implemented in the computational software package MatLab with the use of SimuLink and Comsol. The main advantages of this approach are: First, the simulation environment is promising in solving both time and spatial related multi-scale problems. Second, the simulation environment facilitates flexible linking of models. Third, the environment is transparent, so the implementation of models is relatively easy. It offers a way to further improve the usage and exchange of already developed models of involved parties. More than 25 different heat, air and moisture related models are included in this work. Most of the models are successfully verified (by analytical solutions or by comparison with other simulation results) and/or validated (by experimental data). The use of the simulation environment regarding design problems is demonstrated with case studies. Overall is concluded that the simulation environment is capable of solving a large range of integrated heat, air and moisture problems. Furthermore, it is promising in solving current modeling problems caused by either the difference in time constants between heating venting and air conditioning components and the building response or problems caused by the lack of building simulation tools that include 2D and 3D detail simulation capabilities. The case studies presented in this thesis show that the simulation environment can be a very useful tool for solving performance-based design problems