Latest Practical Advances in Pressure Management

Transcription

1 North American Water Loss Conference 2017 SAN DIEGO - December 3-5, 2017 Latest Practical Advances in Pressure Management Allan Lambert, Water Loss Research & Analysis allanlambert@wlranda.com Marco Fantozzi, Studio Marco Fantozzi, marco.fantozzi@ .it Kobus van Zyl, University of Cape Town, Kobus Van Zyl, kobus.vanzyl@uct.ac.za Mark Shepherd, JOAT Consulting, South Africa, Julian Thornton, Thornton International, thornton.julian@gmail.com 1 19/12/2017 1

2 Overview of Presentation Pressure:leak flow rate relationships 1994: John May: Fixed & Variable Area Discharges 1995 to date: N1 Power Law approximation 2017: Van Zyl et al prove FAVAD hydraulically valid 2017: Lambert fast-tracks FAVAD for practitioners Step 1: Calculate N1 from N1 night test (simple spreadsheet) Step 2: Identify Fixed and Variable area leaks %s at AZPave in N1 test (easy) Step 3: Show how N1 changes with pressure (equation, graph) Step 4: Calculate leak flow rate vs AZP equation (with graph) Step 5: Calculate leak flow rates from AZP pressures (graph) Step 6: Improve Night Day Factor calculations (graphs, equation) 2 19/12/2017 2

3 John May (1994) Pressure Dependent Leakage (World Water and Environmental Engineering, October 1994) The original article that explained the FAVAD concept (Fixed and Variable Area Discharges) for pressure:leak flow rate relationships Free download from LEAKSSuite website at: SEMINAL-1994-ARTICLE-4.pdf with permission of Water Environment Federation (USA), which now holds the copyright. 3 19/12/2017 3

4 Fixed and Variable Area Leakage Paths Fixed area leakage Lf varies with P 0.5 Includes ring cracks, corrosion holes. Variable area leakage Leak area varies with P Velocity varies with P 0.5 Leak flow varies with P 1.5 includes background leakage at joints and fittings, and splits in flexible pipe materials 4 19/12/2017 4

5 N1 Power Law approximation of FAVAD Leak flow rate L varies with P N1 Initial average pressure Po Initial leak flow rate Lo Assume Lo = A x Po N1 (1) New average pressure P 1 New leak flow rate L 1 L 1 = A x P 1 N1 (2) For small changes in pressure, assume A and N1 almost constant Divide 2 nd eqn by 1 st eqn A cancels out L 1 /Lo = (P 1 /Po) N1 Numerous tests show that N1 usually lies within the range 0.5 to /12/2017 5

6 A 2-step N1 Night Test on Zone Vila Maria, SABESP, Brazil (1998) Experimentos - Relacao dentre Vazao e Pressao Zone inflow rate m 3 /hr Average Zone Night Pressure (m) Flowrate m3/hr Pressure m AZNPo Vazao M3/hora AZNP 1 AZNP 2 Increased inflow to roof storage tanks mca :00 0:25 Lo 0:50 1:15 1:40 2:05 2:30 2:55 3:20 3:45 4:10 L 1 L 2 4:35 5:00 5:25 5: /12/ :15 Hora Customer night use 6:40 7:05 7:30 7:55 8:20 8:45 9:10 9:35 10:00 10:25 10:50 11:15 11:40 L 1 /L 0 = (AZP 1 /AZP 0 ) N1 so N1 = ln(l 1 /L 0 )/ln(p 1 /P 0 )

7 Current use of N1 by Practitioners Since 1994, the N1 power law FAVAD is being widely used by practitioners internationally Most users tend to assume a constant N1 1.0 (linear), or 1.15 (Japan) Some users try to predict N1 using component analysis, or pipe materials and snapshot ILI Some consultants carry out N1 tests but most practitioners have never done so and more systematic training is needed 7 19/12/2017 7

8 Pressure Control expands after 1995 Thousands of pressure control schemes installed internationally since 1995 to reduce leakage; justified economically due to better methods to predict reductions in leak flow rates (FAVAD, simplified to N1 Power Law) advanced pressure control with flow modulation methods to predict reductions in new burst frequency on mains, and services, and extend infrastructure life As a consequence many systems now are operating at lower and more variable pressures It became necessary to review concepts used for calculations 8 19/12/2017 8

9 Recent collaborative research on FAVAD By Prof. Kobus van Zyl, Allan Lambert, Amanda Cassa, Dr Richard Collins and post-grad University of Cape Town students Leakage Numbers for lab tests on pipe samples: Leak Area vs pressure relationships Influence of low/negative pressure on leak flow rates Open Access paper on hydraulic analysis by van Zyl, Lambert and Collins ASCE Journal of Hydraulic Engineering / Vol 143 Issue 9 - Sept 2017 ( downloads) summarised in Presentation 2017S on LEAKSSuite Allan Lambert has now applied FAVAD concepts to N1 tests, to get fast-track methods for practitioners to use 9 19/12/2017 9

10 The Leakage Practitioner Concept For valid results, Zonal N1 tests must follow rules, just like taking a blood pressure test at the Doctor s Step 1: Pressure MUST be measured at the correct place At Doctor s: sitting, on upper arm at the same level as the heart not the neck and not the ankle! In Zone: at the Average Zone Point AZP not the inlet point and not the critical point! Step 2: Change the pressure Doctor: when patient is relaxed, raise pressure to a maximum, then allow to fall back to minimum Zone: wait for steady inflow and AZP pressure at night; reduce pressure to achieve lower steady minimum flow and pressure Step 3: Summarise results of analysis quickly and clearly in units and format the patient/utility can easily understand 10 19/12/

11 Inlet Point Critical Point NOT ENOUGH! Average Zone Pressure (AZP) 11 19/12/

12 Fast track approaches for practitioners Use Fast-track FAVAD calculations, customised for practitioners, for improved leakage calculations WLR&A s Leakage Practitioner fast-track approach for Utilities using FAVAD in 6 steps: 1. Calculate N1 from an N1 test, or assume N1, at a specified Average Zone Pressure 2. Identify % split of Fixed and Variable Area leaks from N1 3. Then calculate N1 vs Average Zone Pressure equation 4. Use N1 test to define Leak Flow Rate vs AZP equation 5. Predict zonal leakage from AZP pressures in real time 6. Improve reliability of assessment of Night-Day Factors 12 19/12/

13 N1 Leakage Practitioner test: Fast track Steps 1 to 3 Test Data N1 Night Test for Anyzone on Sunday 7th May 2017 No. of Properties 1000 Population 2000 MNF Night Use Leakage Rate L Start 01:30 to 02:15 AZNPo = 64.0 psi USgpm 8.80 USgpm USgpm Finish 02:30 to 03:15 AZNP1 = 51.2 psi USgpm 8.80 USgpm USgpm Step 1 At Average AZNP = 57.6 psi N1 = ln(l 1 /L 0 )/ln(aznp 1 /AZNP 0 ) = 1.29 Lave = 69.3 USgpm Step 2 Fixed Leakage Area FAL% = 1.5 -N1 = 0.21 Variable Leakage Area VAL% = N1-0.5 = 0.79 Step 3 Average Zone Pressure AZP when N1 = 1.0 is AZP N1 =1 = AZPave x FAL/VAL = 15.4 psi General Equation for N1 vs AZP is N1 = AZP /(AZP + AZP N1 =1 ) where units of AZP are in psi Equation for N1 vs AZP is N1 = AZP /(AZP ) where units of AZP are in psi CAUTION If you extrapolate the N1 vs AZP equation to higher AZP pressures than the maximum in the N1 test, you risk creating new leaks which may change the N1 vs AZP relationship For methodology and derivation of N1 vs AZP equations, see FAVAD Pressure & Leakage: How does pressure influence N1? (Lambert, Fantozzi, Shepherd, 2017) at Paper 2017L and Presentation 2017K 13 19/12/

14 Step 3: General relationship between N1 and AZP: N1 reduces as average zone pressure reduces N1s from individual Zonal tests can be plotted on this graph Always quote N1 with its corresponding Average Zone Pressure N1 always reduces as Average Zone Pressure decreases Rate of change increases as Average Zone Pressure decreases 14 19/12/

15 Step 4. Derive Leak Flow Rate vs AZP pressure from N1 test Leak Flow Rate in USgpm Day and Date of N1 Test Initial Steady State Lowered Steady State Calculations by A.N.Other Sunday 07-May-17 01:30 to 03:36 02:30 to 03:15 Date 03-Jun-17 AZNPo = 64.0 psi MNFo = USgpm Night Consumption 8.80 USgpm Night Leakage Rate Lo = USgpm AZNP1 = 51.2 psi MNF1 = USgpm Night Consumption 8.80 USgpm Night Leakage Rate L1 = USgpm FAVAD equation is Leak Flow Rate L in USgpm = x AZP x AZP 1.5 AZNPave = 57.6 psi MNFpred USgpm Night Consumption 8.80 USgpm Predicted Leakage Rate = USgpm N1 at 57.6 psi = 1.29 with 79% variable area leaks and 21% Fixed Area Leaks Average Zone Pressure at N1 = 1.0 is AZNPave x % Fixed /% Variable Area = 15.4 psi N1 = AZP/(AZP ) Predict current Leak Flow rate vs AZP equation direct from reliable N1 test Using FAVAD, L (volume/unit time) = A x AZP B x AZP 1.5 From N1 test, we know L 0 and AZNP 0, and L 1 and AZNP 1 Solve simultaneous equations, derive A, B in units to suit user s data Extrapolate L vs AZP equation from N1 test to full range of lesser AZPs This defines the current L vs AZP equation at the time of the N1 test 80.0 Leak Flow Rate in USgpm 70.0 Pressure at Average Zone Point in psi /12/ Leak Flow Rate L in USgpm vs AZP in psi L = 1.91 x AZP x AZP 1.5 Pressure at Average Zone Point in psi N1 Test Calibration Point Predicted Variable Area Leak flow Predicted Fixed Area Leak Flow

16 Step 5: Calculate leak flow rate profile from AZP pressures Example: Zone in Mexico with roof tanks: continuous measurement at AZP point Recovering from intermittent supply with pressure management, AZP 12 to 18 m Derive L vs AZP equation using automated N1 test every Sunday morning Use L vs AZP equation to predict 96 x 15 min leak flow rates, add for daily leakage Check: predict 15 min leak flow rates from N1 vs AZP equation + Sun night leak rate Check: predicted night leak rates agree and do not exceed MNF on any week night 16 19/12/

17 Night Day Factor Hours per day Step 6a: Overview of Night-Day Factor Calculate ratio of AZPave/AZP at time of mnf, for X-axis Read off possible range of Night-Day Factors from Y-axis Measure or assess N1 at daily AZPave for Zone if more accurate estimate of NDF is needed NDF vs AZPave/AZPmnf, with Fixed + Variable Area correction Ratio of 24 hour Average AZP/AZP at time of Minimum Night Flow N1 =1.49 at AZPave N1 = 1.40 at AZPave N1= 1.30 at AZPave N1 = 1.20 at AZPave N1 = 1.10 at AZPave N1 = 1.00 at AZPave N1 = 0.90 at AZPave N1 = 0.80 at AZPave N1 = 0.70 at AZPave N1 = 0.60 at AZPave N1 = 0.51 at AZPave 17 19/12/

18 Correction Factor Cf Step 6b: NDF using Correction Factor method Calculate ratio of AZPave/AZP at time of mnf, for X-axis NDF = CF x 24 x AZPave/AZPmnf, where CF is a Correction Factor Derive CF from graph below; CF varies with AZPave/AZPmnf and N1 at AZPave The equation which defines the graph below is used for automatic data processing Night Day Factor = CF x 24 x AZPave/AZPmnf N1 at AZPave = 1.49 N1 at AZPave = 1.40 N1 at AZPave = 1.30 N1 at AZPave = 1.20 N1 at AZPave = 1.10 N1 at AZPave = 1.00 N1 at AZPave = 0.90 N1 at AZPave = 0.80 N1 at AZPave = 0.70 N1 at AZPave = 0.60 N1 at AZPave = Ratio of Average AZP/AZP at hour of Minimum Night Flow: AZPave/AZPmnf 18 19/12/

19 Summary and Conclusions FAVAD concept remains best available, now hydraulically validated N1 Power Law simplified FAVAD, assuming constant N1 for small pressure range, but N1 decreases as pressures reduce Leakage Practitioner approach: use Fast-Track FAVAD to quickly identify Fixed and Variable components from N1 night test quickly calculate N1 vs AZP Type Curves, to check assumed N1s quickly calculate Zonal L vs AZP equation derived from N1 test derive continuous leak flow rate profile from recorded AZP pressures split Zonal 15 minute inflows into leakage and consumption check validity of Night-Day Factor calculations, improve where needed Combination of Academics and Practitioners is mutually beneficial if the different approaches, experiences and communication needs of both communities are recognised when disseminating the outcomes Additional free references are available at /12/

20 Acknowledgements John May, for laying the foundations of these studies 23 years ago Prof. Kobus van Zyl, Richard Collins and post-graduate students of University of Cape Town for reinvigorating Fixed and Variable Area concepts. Many other colleagues in the Pressure Management Team of the IWA Water Loss Specialist Group, for ongoing successful international promotion of the benefits of well targeted pressure management. The LEAKSSuite website for making so much material available, free to all; now over 26,000 users worldwide 20 19/12/

21 North American Water Loss Conference 2017 SAN DIEGO - December 3-5, 2017 Latest Practical Advances in Pressure Management Allan Lambert: Water Loss Research & Analysis allanlambert@wlranda.com Marco Fantozzi, Studio Marco Fantozzi, marco.fantozzi@ .it Kobus van Zyl, University of Cape Town, Kobus Van Zyl, kobus.vanzyl@uct.ac.za Mark Shepherd, JOAT Consulting, South Africa, Julian Thornton, Thornton International, thornton.julian@gmail.com Thanks for your attention! 21 19/12/