For water distribution networks two type of analysis are performed: 1 - hydraulic analysis or the balancing of the network and 2 - technical-economic analysis or the network sizing. In technical-economic analysis the hydraulic condition (the continuity of flow rate at nodes and energy conservation in independent loops) is added and economic conditions (minimum annual expenses for construction and operation). In these conditions, the technical-economic analysis represents a nonlinear programming problem with equality restraint (relation 11-13) which transforms into a nonlinear system (relation 15-17) with which we determine flow rates and head losses on pipelines. This system has in its construction the hydraulic conditions (relation 16,17) and “economical” conditions (relation 18,21) both being written in the same way. In the case when the objective function W (relation 1) is convex the establishing of flow rates and head losses is done directly, but in the case when the same function is concave-convex it is necessary to have an intermediate step. By relation 10 it obtains the theoretical diameters which will be adjusted to meet commercial ones. In the paper is presented a model and a methodology for the application of the technical-economic analysis to the water distribution networks, and a mode of utilization for a practical example.

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