Abstract
In many Mediterranean countries, users store water resources in private tanks, which are typically located on rooftops. These local reservoirs are generally connected directly to the water distribution network (WDN). This installation scheme causes a disconnection of the WDN from the users, and thus, the users’ water supply is no longer linked to their consumption, which changes the network operating conditions from the designed conditions. For WDNs characterized by the presence of several private tanks, specific models have to be developed to correctly simulate the operation of the WDN while accounting for reservoirs located between the hydraulic network and users. Some mathematical models that are able to reproduce the tank emptying/filling cycles have already been developed, which combine a tank continuity equation with a float valve emitter law. In the present work, a new emitter law is proposed that improves the predictability of actual models. The new formulation takes into account the variation of the emitter coefficient and of the discharge area during the phases of the filling process of private tanks. Specifically, hyperbolic tangent laws were adopted. A comparison between the proposed mathematical model and the experimental data demonstrated the ability of the new law to estimate the flow discharging into private tanks independently of the float valve branch and of the pressure in the network. The developed model can easily be implemented in hydrodynamic models to take private tanks into account.
Highlights
Water distribution networks (WDNs) should be able to deliver a required quantity of water at sufficient pressure under different design and operational situations
The majority of the hydraulic models for WDNs developed for design and management generally account for customer demands as water withdrawal concentrated in nodes and assume that these demands are fixed a priori in the model [1], independent of nodal heads, and are fully supplied
The analytical results from the hyperbolic tangent law, obtained considering a constant discharge area av = cost, were compared to the results achieved from the system of Equations (16) and (18), considering the effective reduction of the float valve area
Summary
Water distribution networks (WDNs) should be able to deliver a required quantity of water at sufficient pressure under different design and operational situations. A demand-driven analysis may be satisfactory under normal working conditions, it becomes inadequate when the network operates under pressure-deficient conditions (which may be due to its improper design or insufficient water supply from water sources, unplanned pipe outages or unexpected pipe breaks, valve failures, pump breakdowns or excessive consumption [3]). Under such conditions, the demand-driven formulation leads to unrealistic solutions for the hydraulic analysis of WDNs, and the simulation model has to incorporate a nodal outflow discharge model (head-driven analysis) [1]
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