AVERAGE ZONAL PRESSURE
In order to assess if pressure management will be suitable for a
particular system, it is necessary to identify the Average Zonal
Point (AZP) and Critical Pressure Point (CPP). The Average Zonal
Pressure (AZP) is the hydraulic head in the network that best
represents the typical pressure within a zone. This can be weighted
by properties or connections to give a typical pressure that customers’ experience. Some water companies identify an Average Zonal Point as a specific location in the network that is representative of the network and can be logged to monitor the AZP over time. This removes the need to log the whole network to calculate the AZP. The AZP can be used to aid in the comparison between zones and help direct pressure management activities. AZPs or an average AZP across multiple zones can be monitored by water companies to track improvements or for regulatory or other reporting purposes.
In leakage (and burst) calculations investigating the effects of pressure management, the AZP is often used. An alternative is to calculate the Maximum Average Zonal Pressure (MAZP) or the Average Night Zonal Pressure (ANZP). This is the average pressure in the network at the lowest flow condition, which normally occurs at night. This then correlates to estimates on leakage utilising the minimum night flow, when consumption is assumed to be at its lowest.
Knowing the location of the AZP means that a utility can track a single location as an indicator for the entire network. The AZP is a quick and easy indication of pressures across a zone and can be tracked and reported over time. Reductions in the AZP can be used to calculate expected reductions in leakage levels and burst rates.
Identifying the AZP can be complicated. Often, it is done through a full logging exercise across a pressure managed area that then guides a network model. This requires logged data and a good understanding of the pipe network. An indication of the AZP (or at least the AZNP) can be calculated by logging a few points in a network and then using the elevations to guide the calculations.