Average Zone Point and Night Day Factor

 Two important concepts for leakage calculations

Reliable leakage calculations need to take account of Zone pressures, so an ‘Average Zone Point’ (AZP) needs to be identified, for representative measurements of average pressure. Because Zone pressure (and therefore leak flow rate) varies over 24 hours, an average ‘Night Day Factor’ (NDF) is also needed to convert night leakage per hour to daily leakage (& vice versa).

The NDF concepts are explained in more detail in Concepts section of this website and the practical application of the AZPandNDFCalcs software is explained in Presentation 2016J. There is also a guideline on calculating average pressure in Influences of Pressure info hub.

This free software explains how to identify and record the location of the Average Zone Point, and how to calculate the Night Day Factor by analysing pressure measurements taken at the Average Zone Point.


An Excel Workbook with colour coded Worksheets tabs:

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Learn why Inlet Point, Average Zone Point and Target (Critical) Point need to be defined for every Zone

Define these points in the PMSites Worksheet, then show them on a Zone Plan, with contours

Night Day Factor = (Night leakage volume / hour) / (24 hour Leakage volume)

Learn why NDF can be more or less than 24 hours/day, depending on variations in average zone pressure

Learn how to calculate NDF from pressures measured at the Average Zone Point

Night time water pressure management comparison