Developing a PDA Head-Outflow Relationship from a Microscale Analysis

Pressure-driven analysis (PDA) frequently is adopted for water distribution system hydraulic simulation under pressure deficient conditions. Wagner's equation is the most used head-outflow relationship (HOR) to represent the supply rate as a function of the available pressure. PDA simplifies the multiple outflow fixtures for spatially distributed customers represented by a node as a single orifice. It also assumes that all demands are flowrate based, neglecting the volumetric limits. This work demonstrates a methodology for developing HOR functions by building nodal demands from a microscale fixture by fixture analysis and determining actual supply at the hydraulic model node according to the responses in a small neighborhood of homes. Results are shown for a base case and for sensitivity tests of the number of homes, the value of the emitter coefficients, and human factors. Additional research is needed to precisely simulate fixture relationships and human responses at the household level and to identify the applicable range of pressures under which a PDA is necessary.