In recent years Computational Fluid Dynamics (CFD) has been extensively used in the study of the indoor environment and the thermal comfort conditions for the design of modern buildings, however, there remains the need to thoroughly evaluate the accuracy of the results given by CFD methods. In the present work, numerical investigations of the indoor thermal environment in the atria of two existing buildings and in a simple three-storey atrium building design have been undertaken using CFD techniques. The initial work involved the evaluation of various turbulence models and a radiation model used in CFD simulations for the prediction of the thermal environment in atria of different geometrical configurations in two buildings for which experimental data is available. The airflow patterns and temperature distributions were determined, under both forced and hybrid ventilation conditions and thermal comfort conditions were evaluated. The numerical predictions were compared with the available experimental measurements and, in general, good agreement was obtained between the numerical and experimental results. After the evaluation of the adequacy of available turbulence models and the validation of the accuracy of the CFD model used, a simple full-scale three-storey atrium building was modeled to explore the potential of using buoyancy-driven natural ventilation. The validated CFD model was used to determine the ventilation flow rates, airflow patterns, and temperature distributions in the building. The dynamic effect of the thermal mass of the external walls on the performance of the building was also investigated using transient CFD simulations. Atria with various geometrical configurations were studied in order to investigate the effect of atrium design changes on the air flow and temperature distributions in the simple atrium building considered. A parametric study was carried out to assess the sensitivity of the ventilation performance to the change in various geometric and solar parameters. On the basis of this parametric study, a few changes were carried out in the design of the building to examine their effect on ventilation performance. Finally, the use of night ventilation in the atrium building was explored and it was found that night ventilation can be increased by using hot water circulation in the chimney walls. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2012-07-22 12:57:00.947

In this thesis electromagnetic wave propagation is investigated in an indoor environment. The indoor environment is a furnished office building with corridors, corners and rooms. Particularly, there is an atrium through the building in the center. For the study there were measurements available from real building in the 2.1 GHz frequency band. One objective is to design a propagation model that should be simple but reflect the trend of the propagation measurements. Furthermore, a system performance evaluation is carried out based on the implemented model. The proposed 3D model is a combination of the Free Space Path Loss model, the Keenan-Motley model and the recursive diffraction model. The channel predictions from the 2D Keenan-Motley algorithm are quite different from the measurements. Therefore, the 3D Keenan-Motley algorithm is designed to depict the atrium effect and speed up the simulation at the same time. Besides a buttery radiation diagram is created to mimic Kathrein 80010709 antenna installed in the building. Finally, a diffracted path is added to improve the received signal strength for the users around the atrium areas. With all the above procedures, the final results from the model are in good quantitative agreement with the measurement data. With the implemented propagation model, a further analysis of the system performance on the Distributed Antenna System (DAS) is performed. A comparison for the system capacity between the closed building and the atrium building is conducted, showing that the former one benefits more when the number of the cells increases. The reason is the atrium cells suffer severe interference from neighbor cells during high traffic demand scenarios. Then some further cell configurations show that the number of the cells, the geometry performance and the balance of the user fraction should be considered to improve the system capacity.