A micro-scale analysis of pressure dependent analysis: Impacts on network scale pda

Several authors have proposed pressure driven analysis (PDA) algorithms to model water distribution networks (WDN) under pressure deficient conditions. All assume supply follows a physical relationship between pressure head and flow from outlets as represented as orifices. However, in a WDN model a node demand represents users that are distributed and uses are further distributed within a premise. Further, WDN analysis is conducted over time-steps much longer than any typical premise use. This spatial and temporal lumping makes the PDA pressure-flow relationship subject to debate. In this study, the validity of this relationship is examined by studying the actual delivery pattern for individual premise uses for a single family residences using a distributed hydraulic model. The desired demand pattern was generated by a stochastic end-use simulator, while the actual supply is determined by a pressure driven method considering each household fixture as a node. The actual demand pattern is almost identical to the desired one for the lumping times used in the practice until a low pressure head threshold is reached. Below that threshold human factors likely change as a result of the hydraulic conditions that alter the demand pattern. Implications of this result on PDA modeling is discussed.