legitimate night use component of minimum night … · introduction to the initiative • aim and...

Water Loss 2010 - June 06 - 09, 2010 São Paulo/SP

Marco Fantozzi, MIYAAllan Lambert, ILMSS Ltd

Legitimate Night Use component of Minimum Night Flows Initiative:

Report by Marco Fantozzi

Introduction to the Initiative

• Aim and Objectives assigned

• Progress to date

• A Practical terminology for analysis of Minimum Night Flow components– Night Use, Customer Night Leakage and Utility Night Leakage – Terminology for Components of MNF, with Influence of Pressure– Typical FAVAD N1 and N3 values for Components of Minimum

Night Flow– Relationships between Average Zone Pressure and Leak Flow

Rate, and between Average Zone Pressure and Consumption Rate

• Conclusions

• It has been recognised by many WLTF members and others that there is a need for utility personnel to have a common terminology for night flow components and to have guidelines on how to calculate legitimate night use for their own water systems taking into consideration the specific circumstances applicable to each utility.

• Consequently, this Initiative has been developed by the Water Loss Task Force to address this need. Marco Fantozzi was asked to lead the Initiative and to help develop guidelines on this topic.

• A team has been assembled from various countries to work on this initiative, and include representatives from the UK, Italy, Cyprus, France, Croatia, Austria, Australia, Brasil, Iran, USA, and Canada.

Aim and Objectives assigned

As there is as yet no IWA recommended 'best practice' standard international terminology for night flow components, initial targets for this WLTF initiative are to:– a) define a practical terminology for analysis of minimum

night flow components (to be the foundation for further analysis)

– b) prepare and present the initial proposal for terminology and ask for comments (to be provided before a fixed deadline) by interested parties at Water Loss 2010.



– c) develop and propose guidelines on how to define when an approximate estimate is satisfactory and when further investigation is needed (depending mainly on night flow figures)

– d) Investigate relationship between leakage and assessed night use.

– e) Develop a matrix which will be the basis for calculating assessed night use under any operating regime in any geographical location

– f) It is expected that output from the Water Loss Task Force on this subject will include guidance on minimum night flow analysis.

Progress to date

• First meeting of people interested in participating in the Initiative took place in September 2008 in Vienna at IWA World Congress.

• Second meeting took take place in April 2009 in CapeTown during WaterLoss2009.

• Presentation in June 2010 in Sao Paolo during WaterLoss2010.

• It is expected this initiative will span over a period of around 36 months.

• This Interim Report relates to Objectives (a) and (b). • The terminology for MNF components is developed, for the

reader, on a step-by-step basis, with 5 Grades of detail. Grade 1 is the simplest, Grade 5 the most detailed. Each of these Grades could be appropriate in different circumstances internationally, depending upon how high or low the night leakage is, and what the night leakage estimate is being used for. This approach, based on Grades, will permit Objective © above to be related to an appropriate Grade (probably Grade 1)

• Comments are sought not later than June 30th on the draft approach of using ‘Grades’ and on the terminology used in the development of Grades 1 to 5.

Progress to date

A Practical terminology for analysis of Minimum Night Flow components

• Although the IWA Best Practice Water Balance, published in 1999/2000, has been widely adopted internationally (with some minor local modifications), there is no equivalent standard international terminology for minimum night flow components.

• This may be because, in quite a large proportion of countries, real losses are only assessed from water balances; district metered areas do not exist, and night flows are not measured.

• In the UK, where metering of all customers has not been traditional, estimates of real losses based only on water balances are likely to less reliable. Accordingly, around 1980, techniques to assess leakage from night flow measurements, and to identify zones with high leakage, began to be developed.

• An increasing number of countries now use these techniques, but as there has been no standard terminology, the interpretation of data and reports based on night flows can be confusing.


Minimum Night Flow consists of Night Leakage and Night Use

Figure shows an example of a 24-hour profile of inflow and Average ZonePressure for a Zone supplied by gravity. In the early hours of the morning(normally sometime between 1 am and 4 am) customer night use is at aminimum, and leakage is at a maximum because of the higher averagepressures at night.

Source: R. Liemberger

If an estimate can be made of the customer night use, at the time of minimum night flow, then what remains (if the measured night flow is reliable) will be leakage.

Delivery Point• However, some of the leakage

will be occurring on the customer’s underground pipes and plumbing systems, so it becomes necessary to separate ‘Night leakage’ into ‘Utility leakage’ and ‘Customer leakage’.

• This means that it is necessary to define a ‘delivery point’ on service connections, after which any leakage becomes part of ‘consumption’ (as in the IWA Water Balance) and is attributed to customers, rather than to the Utility.


Leaks between the meter and reservoir

Direct pressure use Consumption afterthe reservoir

Meter

Road

House

Not affected by pressure but by roof tank

Affected by pressure

Main

Service

Delivery Point• Logic suggests that the ‘delivery

point’ at which ‘consumption’ is measured should be the point on the service connection where ownership and responsibility for the service connection passes from the Utility to the customer.

• Ideally, customer meters should be located at the delivery point, but often, for various reasons, the meter is located some distance after the delivery point. There are many international variations, so each Country or Utility will need to define the Point of Delivery that is most appropriate to its own circumstances.


Leaks between the meter and reservoir

Direct pressure use Consumption afterthe reservoir

Meter

Road

House

Not affected by pressure but by roof tank

Affected by pressure

Main

Service


• Splitting of Minimum Night Flow into Components can be done using several different Grades of detail, depending upon the purpose of the analysis. These are shown as Grades 1 to 5.

GRADE 1 Terminology for Components of Minimum Night Flow

• The Grade 1 (simplest) terminology for components of Minimum Night Flow is shown in Figure, with the Point of Delivery as a red line.

• Note that Night Consumption may include some use of water at night by the Utility itself, especially if the Utility is operated by the Municipality.

Utility Night Leakage UNL is derived by deducting estimates of Night Consumption (NC) from the Minimum Night Flow (MNF). Although MNFs are usually measured in litres/second, for component analysis of night flows it is more appropriate to specify them in m3/hour.

Utility Night Leakage UNL (m3/hour) = MNF - NC


• In the Grade 2 terminology of MNF components, the estimate of Night Consumption is obtained by adding separate estimates of Night Use and Customer Night Leakage as shown in Figure.


• In the Grade 3 analysis of MNF components, Night Use, Customer Night Leakage and Utility Night Leakage are each split into two principal components as shown in Figure.

Night Use is split into:‘Exceptional’ use – the sum of individual uses above a threshold (100 litres/hour?)‘Assessed’ use – the sum of all small uses individually less than the threshold flow rateCustomer Night Leakage is split into:‘Inside Buildings’ – the sum of all leaks inside buildings (usually smaller leaks)‘Outside Buildings’ – the sum of all leaks outside buildings (often larger leaks)Utility Night Leakage is split into:‘Detectable Bursts Leakage’ – visible, or not visible but detectable by acoustic methods‘Undetectable Background Leakage’ – not visible, not detectable by acoustic methods


• In the Grade 3 analysis of MNF components, Night Use, Customer Night Leakage and Utility Night Leakage are each split into two principal components as shown in Figure.

It is appropriate to mention here two terms which originated in the UK in 1980:‘Net Night Flow’ (NNF) is the Minimum Night Flow MNF minus Exceptional Night Use ENU; it can be applied internationally and is retained in this recommended international terminology for night flow components.‘Legitimate Night Use’ (usually specified in litres/property/hour in the UK) is approximately the equivalent of ‘Assessed Night Use’ in Figure, but cannot be easily applied internationally as the method and numerical value of Assessed Night Use will vary widely in different circumstances (single residences, apartment blocks, persons per household, toilet cistern sizes etc.) and would be traditionally specified in different ‘non-transferable’ units from country to country. Accordingly, we recommend that the term ‘Legitimate Night Use’ is not included in the IWA International Night Flow Terminology.


• A Grade 4 terminology of MNF components is shown in Figure. As previously mentioned, Night Consum-ption may include some use of water at night by the Utility itself especially if the Utility is a Municipality – for example, irrigation systems for recreational areas.

‘Exceptional’ Night Use splits into ‘Utility’, ‘Non-Residential’ and ‘Residential’ components‘Assessed’ Night Use splits into ‘Non-Residential’ and ‘Residential’ components

typical sources of Customer Night Leakage ‘Inside’ and ‘Outside’ Buildings can be mentioned‘Detectable Bursts Leakage’ splits into Unreported Bursts and Reported Bursts (not yet repaired)‘Undetectable Background Leakage’ splits into components on service connections and mains


• The difference between Background Leakage, Reported Bursts and Unreported Bursts is summarised in Figure.

• Note that this concept applies to service connections as well as to mains.


- When deciding on an active leakage control intervention: it is useful to first estimate the background leakage (which is sensitive to pressure but not detectable), so that the Detectable Bursts Leakage (DLU in Figure) can be estimated before the intervention is made.

Why a basic understanding of pressure:flow rate relationships is needed :

In a Grade 5 analysis, the influence of pressure on the components of MNF is also included.


- When relating Utility Night Leakage (m3/hour) to Real Losses in m3/day:the Utility leakage rate varies over 24 hours as the average Zone pressure changes, so it is not correct to multiply the Utility Night Leakage (in m3/hour) by 24 hours/day, unless the Average Zone Pressure is uniform throughout the day.

Why a basic understanding of pressure:flow rate relationships is needed:

Source: R. Liemberger

Variation of Utility Leakage Components with Average Zone


Typical FAVAD N1 and N3 values for Components of Minimum Night Flow

Most discharges from pressurised pipelines – whether they are components of leakage or components of consumption – vary with pressure, to a greater or lesser extent. The most appropriate concept to predict these discharges is the FAVAD(Fixed and Variable Area Discharges) concept.

The two equations used for predictions are:

Leak Flow Rate L (volume/hour) varies with Average Zone Pressure to the power N1L varies with AZPN1, where 0.5 < N1 < 1.5

Consumption C (volume/hour) varies with Average Zone Pressure to the power N3C varies with AZPN3, where 0.0 < N3 < 0.5


Typical FAVAD N1 and N3 values for Components of Minimum Night Flow

Figure shows the range of values of N1 and N3 which typically apply to different components of minimum night flow MNF, which enable graphs to be created from component analysis of Minimum Night Flows, and continuous measurements of Zone inflow and Average Zone Pressure.


Figure shows how changes in Average Zone Pressure influences the different components of Leak Flow Rates and Consumption. Leak Flow Rates and Consumption are:• most strongly influenced by pressure when N1 or N3 values are high• least influenced by pressure when N1 or N3 values are low

Relationships between Average Zone Pressure and Leak Flow Rate, and between Average Zone Pressure and Consumption Rate

Conclusions

A Practical terminology for analysis of Minimum Night Flow components has been defined

Comments are sought not later than June 30th on:

• the draft approach of using ‘Grades’ and on • the terminology used in the development of

Grades 1 to 5 !!• if you have comments to contribute, please

contact: [email protected]

Thanks !

mailto:[email protected]

legitimate night use component of minimum night … · introduction to the initiative • aim and...

Documents