The traditional approaches to determine the design flow rates in building water supply system can be classified into probabilistic and empirical ones [2]. The probabilistic ones are more suitable because they take into account more realistic conditions of each design condition, which is represented as random variables intervening in the use of the water inside the buildings. Nevertheless, the probability theory only considers random variables, which depend on future events. It does not treat fuzzy variables that better represent the behavior of the user, which is required in a more accurate assessment of flow rates in the feeding branches.

The amount of all the sanitary appliances used in multifamily buildings the shower generates the largest impact in the value of the design flow rate of the apartment's feeding branch. This is because of its longer duration of usage and its larger unitary flow rate. Moreover, the duration of the usage of the shower is strongly affected by the subjective behavior of the users, which may be modeled by means of a fuzzy approach, instead of the probabilistic ones.

In this way, as the first step to develop a more accurate method to establish the design flow rate for the water submetering system of the residential buildings, the aim of this work is to apply the fuzzy logic to determine the duration of shower usage, especially of a typical family of three persons: father, mother and a teenager son. As it is very difficult to carry out flow rate measurements for a family, the results of the approach present herein is firstly validated by using the measurements obtained from the apartment of three students.

The results of the validation show good agreements between the measured and calculated ones. The application of the approach to the estimation of the duration of the shower in a typical small family clearly shows the behaviour of each family member. Thus, one of the great advantages of the approach is the ability to take into account the influence of the subjectivity of the user on the usage of the sanitary appliances.

1

L.H. Oliveira, M.S.O. Ilha, O.M. Gonçalves, "Design flow rate simulation using probabilistic and empiric method for water sub metering system in Brazilian multifamily buildings", in "Proceedings of the 33rd International Symposium on CIB W062 Water Supply and Drainage for Buildings", Brno University of Technology, Brno, Czech Republic, B99-B109, 2007.

2

O.M. Gonçalves, "Contribuições para a Economia e Qualidade dos Sistemas Prediais", Memorial circustanciado (Livre-docência junto ao Departamento de Engenharia de Construção Civil) - Escola Politécnica da Universidade de São Paulo, Brasil, 1997.

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