Verifying Pressure Dependent Demand Modeling

While most water distribution system models are demand driven, there are situations where the ability to model pressure dependent demands (PDD) is essential. These models incorporate some function relating nodal demand to pressure. While the underlying logic behind PDD is sound, there has not been a study to verify PDD modeling.In this study, a laboratory scale water distribution system was constructed where orifice opening and flow could be accurately controlled and measured. Data were collected over a wide range of flow patterns, orifice opening and source heads. In all 109 runs were made with multiple readings for each run.These data were compared with a calibrated hydraulic model of PDD and the results showed that the lab model and computer model agreed well with the average orifice exponent just slightly greater than the theoretically expected value of 0.5. The study showed that for correctly calibrated orifices in steady conditions, PDD modeling is accurate.