Why do you need N1 tests for effective pressure management modelling?

What is N1?
N1 is a power law that simplifies the relationship between changes in pressure and leak flow rates in both rigid and flexible pipes. By utilizing a specific N1 value, you can model how leak flow rates change with changes in average pressure.

Fixed vs. Variable N1 Values
While many practitioners use a fixed N1 value between 0.5 to 1.5 for ease in leakage calculations, it is important to recognize that the N1 value can vary with Average Pressure, particularly at lower pressures.

Each DMA may exhibit a unique N1:AZP relationship as shown below, based on its specific characteristics, so it is essential not to assume that the same N1 value applies to all zones and DMAs.

Implications of Using a Constant N1 Value
Using a constant N1 value may simplify calculations, but it implies that the percentage of Fixed and Variable Area Leaks remains unchanged, regardless of pressure fluctuations. This reasoning may hold for minor pressure changes, but significant drops in pressure can alter the dynamics.

See what happens to the proportion of Fixed and Variable Area Leaks when N1 changes, in the table below

If you use Hour Day/Night Day factors, it is essential to perform an N1 test, as they will also be influenced by substantial pressure changes.

Determining which Zones and DMAs need an N1 Test
Not all your Zones and DMAs may need an N1 test, but how do you know which ones do and which ones don’t?

• How do you identify DMAs that would benefit from an N1 test, ranked in order of priority?
• How can you quickly determine which DMAs would not benefit from an N1 test, allowing you to continue using the current assumed N1 values?

N1 Triage – identify and prioritise zones for N1 testing