Economic design of water distribution systems in buildings

Once the design flows and geometric characteristics of the circuits are known, the sizing of a water piping system should be found by computing the most adequate diameters for the various sections in order to guarantee the fulfilment of boundary conditions, based upon limits and restrictions related to velocities and pressures. This paper describes a new criterion for the sizing of water distribution piping in buildings, called the economic sizing criterion, which seems to be of particular interest for systems of large dimensions with extensive critical circuits. These characteristics can be found in several buildings, such as hospitals, hotels, shopping centres and airports. In systems that are conditioned by pressures, this criterion requires the computation of the values of the diameters to be applied to the various sections of the water distribution piping that minimize the overall installation cost according to some boundary conditions. So this criterion leads to a nonlinear optimisation problem that should be processed by an appropriate solver. A description of the new criterion and corresponding optimisation model is first introduced and discussed in detail. A practical problem related to a large hospital is also considered in order to illustrate the importance of the proposed criterion in practice. The associated optimisation problem is processed by the well-known GAMS/MINOS nonlinear optimisation solver. Computational results for this special instance are included and indicate the advantages of using the new criterion over traditional criteria for finding sizing of piping systems.