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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 92
Edited by: B.H.V. Topping and Y. Tsompanakis
Paper 39

A Fuzzy Approach to the Analysis of Natural Ventilation considering the results of Computational Fluid Dynamics

L.Y. Cheng and F.K. Motezuki

Department of Construction Engineering, Escola Politécnica, University of São Paulo, Brazil

Full Bibliographic Reference for this paper
L.Y. Cheng, F.K. Motezuki, "A Fuzzy Approach to the Analysis of Natural Ventilation considering the results of Computational Fluid Dynamics", in B.H.V. Topping, Y. Tsompanakis, (Editors), "Proceedings of the First International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering", Civil-Comp Press, Stirlingshire, UK, Paper 39, 2009. doi:10.4203/ccp.92.39
Keywords: fuzzy, natural ventilation, computational fluid dynamics, dwelling design, comfort, sick building syndrome.

In a tropical country such as Brazil, the natural ventilation is an economical and effective option to improve thermal comfort. If well investigated during the dwelling design, it also contributes to mitigate sick building syndrome and improve indoor air quality. Aiming to provide a practical tool for this analysis, this paper proposes an approach that uses fuzzy systems theory to identify the best configurations for openings of a given layout.

In the present study, the idea used by Givoni [1] in his experimental study on room ventilation is adopted. The inner space of a room is divided into sub-domains whose mean air velocities under different opening configurations are recorded. As the mean air velocities reflect the effectiveness of the ventilation in the sub-domain, an index is created and defined as a mean modular velocity index (MMVI). Nevertheless, instead of experimental results, the MMVI is obtained by means of the simulations based on computational fluid dynamics (CFD).

Since the dimensions and the aspect ratio of the rooms in a typical dwelling does not vary too much, it is possible to define some typical patterns or configurations for the location of the openings such as windows and doors of the rooms. Thus, it is also possible to create a database of typical opening configurations with the CFD results, which are represented as distributions of MMVI in the sub-domains of the rooms.

On other hand the desirable air flow index (DAFI) is used to represent the requirements for ventilation in the sub-domains, which in turn is related to the function of each sub-domain of the room, and may be defined based on a sketch of the layout, the use and the existence or not of obstacles in a sub-domain. The assignment of a DAFI in the sub-domains may also be done directly by the architect or engineer.

With the DAFI and the MMVI indexes, strategies based on fuzzy logic [2] are applied to assess and to select the best matches between the layouts established by the design and the opening configurations. In the present study, three selection strategies were tested: least squares, conformity index and maximum similarity in a generalized Lukasiewicz structure. The last one has two variations: with equal weights and with differentiated weights for the sub-domains.

The results of the tests show that amount the selection strategies, maximum similarity in a generalized Lukasiewicz structure with differentiated weights gave very good results and is able to identify the best opening configuration for a layout. Thus, the approach might be applied to the analysis of the ventilation in the early stage of the architectural design without carrying out complex and time-consuming CFD simulations.

B. Givoni, "Basic study of ventilation problems in housing in hot countries: Final report, sponsored by the Ford foundation", Haifa Technion - Building Research Station, Israel Institute of Technology, 1962.
L.A. Zadeh, "Similarity Relations and Fuzzy Orderings", Information Sciences, 3(2):177-200, 1971. doi:10.1016/S0020-0255(71)80005-1

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