This collection of exercises has over 320 images designed to walk you step-by-step towards the modeling of water distrib...
Epanet and Development A progressive 44 exercise workbook
First English Edition. November 2011.
Santiago Arnalich
Epanet and Development A progressive 44 exercise workbook First English Edition. November 2011.
ISBN: 978-84-612-6088-1 © Santiago Arnalich Castañeda All rights reserved. You can photocopy this manual for your own personal use if you are unable to purchase it due to your economic situation. Otherwise, consider buying a copy to support these initiatives. If you would like to use part of the contents of this book, contact us at:
[email protected]. Errata at: www.arnalich.com/dwnl/xepaxen.doc Cover photo: Proja Jadid, Afghanistan. Revised by: Maxim Fortin and Mary Brown.
DISCLAIMER: The information contained in this book has been obtained from credible and internationally respected sources. However, neither Arnalich - Water and Habitat nor the author can guarantee the precision of the information published here and are not responsible for any errors, omissions, or damage caused by the use of this information. It is understood that the information published herein is without a specific purpose and under no circumstances intends to provide professional engineering services. If these services are required, the assistance of a qualified professional is necessary.
Table of contents 1. Before you begin
1
Some important points before you get started ............................................... 2 How this book is organized ............................................................................. 3 Downloading the program and the manual .................................................... 5 Installing Epanet ............................................................................................. 6 Sticking to units and shaking off errors ........................................................... 8
2. Taking a seat
9
Work space and configuration ...................................................................... 10 Exercise 1. Introductory tutorial .................................................................... 12 Exercise 2. An indispensable ritual ............................................................... 14 Exercise 3. Drawing a network diagram ...................................................... 16 Exercise 4. Saving time configuring .............................................................. 18 Exercise 5. Inconsolable diameters .............................................................. 20 Exercise 6. Keeping your eyes sharp ........................................................... 25 Exercise 7. Recalling with help ..................................................................... 28 Exercise 8. Getting over stage fright ............................................................. 29
3. Drawing the network
37
Maps, objects and sketches ......................................................................... 38 Exercise 9. A simple topographic survey ...................................................... 41 Exercise 10. A branched topographic survey ............................................... 46 Exercise 11. An abrupt case ......................................................................... 50 Exercise 12. Loading a backdrop.................................................................. 53
iv
Epanet and Development. A progressive 44 exercise workbook
Exercise 13. A simple emergency ................................................................. 56 Exercise 14. Finding out dimensions ............................................................ 62 Exercise 15. Loading Google Earth images .................................................. 64
4. Demand
69
Demand in time and space ........................................................................... 70 Spreadsheet crash course ............................................................................ 74 Exercise 16. Building a daily consumption pattern ....................................... 77 Exercise 17. Nodes with different consumer types ....................................... 84 Exercise 18. No data ..................................................................................... 87 Exercise 19. Yield evaluation ........................................................................ 89 Reservoir sizing ............................................................................................. 96 Exercise 20. Peeping into the future ............................................................. 99 Exercise 21. Population density limits ......................................................... 100 Exercise 22. Regression ............................................................................. 102 Exercise 23. Computing time-varying demands ......................................... 105 Exercise 24. Total allocation ....................................................................... 108 Exercise 25. Per node allocation................................................................. 110 Exercise 26. Per street allocation................................................................ 111 Exercise 27. Per loop allocation .................................................................. 113
5. Quality
115
Chlorine residual, ageing and treatment by dilution .................................... 116 Exercise 28. Chlorine decay ....................................................................... 118 Exercise 29. Chlorine decay II .................................................................... 122 Exercise 30. Ageing .................................................................................... 124 Exercise 31. Two sources ........................................................................... 127
6. Scenarios
131
Scenarios .................................................................................................... 132 Exercise 32. Reservoir between distribution and pump .............................. 135 Exercise 33. Springs and tail tanks ............................................................. 141 Exercise 34. Pressure zones ...................................................................... 145 Exercise 35. Adding a pump ....................................................................... 152 Exercise 36. Modeling a borehole ............................................................... 157 Exercise 37. Skeletonization ...................................................................... 165
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
Index of contents
7. Economics
v
169
Economic issues ......................................................................................... 170 Exercise 38. The investment bill ................................................................. 173 Exercise 39. Pumping costs ........................................................................ 174 Exercise 40. Comparing alternatives .......................................................... 175 Exercise 41. Volatile countries .................................................................... 178 Exercise 42. Economic diameter ................................................................ 179 Exercise 43. Economic diameter II ............................................................. 182 Exercise 44. Using Epanet .......................................................................... 183
In way of farewell ..................................................................................... 184 About the author ....................................................................................... 186 Bibliography ............................................................................................. 188
www.arnalich.com
Helping improve Development Aid through training and consultancy.
1 Introduction Some important points before you get started How this book is organized Downloading the program and the manual Installing Epanet Sticking to units and shaking off errors
Often, a few hours of trial and error can save you a few minutes of reading manuals. (Anonymous)
2
Epanet and Development. A progressive 44 exercise workbook
Some important points before you get started ● This manual has been designed for use in Development Cooperation projects. The particular context means that many components and procedures that are so necessary in projects for rich countries make no sense. ● Many exercises have been included that are not strictly Epanet exercises. This is because it is very easy to waste time with Epanet calculating things that do not make a lot of sense and which can put the projects in danger. Epanet works with the data that we give it and it is very important to be clear how it has been obtained. ● This manual has been created for use in development projects and therefore some procedures will not be suitable for use in developed countries. ● This manual is limited to the design of a network. Analysis of existing networks needs a more complicated approach and more elaborate techniques. ● There are not many people who work in development full-time for a long period, and as such this is not intended to be a cutting edge manual, but one that you can return to when you need it. ● If you find any errors, please let us know at:
[email protected]
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 1. Introduction
3
How this book is organized 1. It is progressive. The exercises follow a logical order for the calculation of a network and they increase in difficulty. You are free to utilize it how you see fit; bearing in mind that if you follow the order presented you will probably scratch your head less often. 2. It is complementary to Epanet and Development. How to calculate water networks by computer, where you can find additional explanations to the quick theory here. Without it you’ll probably struggle to follow if you are not familiar with water networks. You can consult it free online, or buy a printed copy or pdf at www.arnalich.com/en/books.html. It has online content. You can download the items needed in each exercise or get it all at www.arnalich.com/dwnl/epaxen/epaxenall.zip 3. It has warnings:
ATTENTION! In Epanet it is easy to make some mistakes that are difficult to detect. This symbol indicates the most common ones to avoid them "exploding in your face”.
BEWARE, GREAT WASTE OF TIME! As in all IT programs and in real life, it is very easy to be swamped by useless work that can result in even "the snails getting ahead of you”.
4. It has routes that look like this: “>Project/ Defaults”. The forward slash indicates that there is a jump in the menu, so that this route is equivalent to selecting “Project” in the general menu and “Defaults ” in the drop-down menu:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
4
Epanet and Development. A progressive 44 exercise workbook
If the route was >Browser /Data /Pumps, you must go to Browser, the Data tab and select Pumps:
5. It has symbols to make reading easier:
Download necessary. In order to carry out the work in hand you will need to download the file indicated.
Invitation to save the file with the suggested name. This will be used later in another exercise.
The necessary theory is in the book Epanet and Development. How to calculate water networks by computer, referred to from here on as the theory book.
Start of a practical exercise and its number.
6. The printed copies are black and white. Unfortunately color comes at a ridiculous price. You can see graphics in color by going to our website and clicking on “Read online>” next to the book title at: www.arnalich.com/en/books.html
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 1. Introduction
5
Downloading the program and the manual Epanet in English and its manual can be downloaded free of charge from the US EPA website:
www.epa.gov/nrmrl/wswrd/dw/epanet.html#downloads
Alternatively, if this link fails or changes in the future, you can use a search engine to find an updated version. As a last resource, a copy of the program is available at:
www.epanet.es/descargas/EN2setup.exe
www.arnalich.com
Helping improve Development Aid through training and consultancy.
6
Epanet and Development. A progressive 44 exercise workbook
Installing Epanet Once you have downloaded the program, you will find a similar icon to this in the folder of your computer where it was downloaded.
1. Click on the icon to commence installation. You may be asked to provide the administrator password.
2. Press “next” in all the dialogues that follow. The second dialogue allows you to select where you want it to be installed.
3. The installation finishes quickly. If you don’t change anything you will find your program in "C:\Program Files\EPANET2\Epanet2w.exe".
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 1. Introduction
7
4. Press start and follow the route shown in the image, >All programs/ EPANET 2.0/ EPANET 2.0. If you can’t find it, type Epanet in the search box (marked with an asterisk in the image).
Congratulations, you are now ready to do the exercises!
www.arnalich.com
Helping improve Development Aid through training and consultancy.
8
Epanet and Development. A progressive 44 exercise workbook
Sticking to units and shaking off errors To work with Epanet you will have to do some very simple calculations by hand. Although they are simple, many of them are prone to errors and very treacherous like, for example, double negatives or how many days there are between 2 dates. If you have the discipline to stick to the units you will discover many of these errors before they affect your emotional stability. For example, look at these two calculations using the same conversion of units:
A. 14 m3/h = 14
m3 m3 * h 1000l
*
1 3600s 14 * 3600 l 3 3 = * m *m * * 1h 1000 s h*h
= 50,4 l*m6/ h2*s ¡¿ l*m6/ h2*s?! If, like me, you don’t know this unit of flow, something went wrong.
m 3 1000l 14 * 1000 m 3 h l 1h B. 14 m /h = 14 * * = * * * = 3,88 l/s h 3600 3600s m3 h s m3 3
NOTE: To multiply by 1h/3,600s is the same as multiplying by 1/1, given that 1 hour and 3,600 seconds are the same thing. If it is easier for you, you can think of it as "there is 1 hour in every 3,600 seconds". The result is a change of units.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
2 Taking a seat Work space and configuration Exercise 1. Introductory tutorial Exercise 2. An indispensable ritual Exercise 3. Drawing a network diagram Exercise 4. Saving time configuring Exercise 5. Inconsolable diameters Exercise 6. Keeping your eyes sharp Exercise 7. Recalling with help Exercise 8. Getting over stage fright
Computers are useless. They can only give you answers. (Pablo Picasso)
10
Epanet and Development. A progressive 44 exercise workbook
Work space and configuration The first time that you open Epanet you will find a screen similar to this:
The upper horizontal menu lends itself to quick familiarization, nevertheless the majority of options and commands are in the Browser. The Browser is the front door to all the program data and, furthermore, allows you to configure calculation options and ways of representing the results. We will see the use of the Browser as we progress. Meanwhile, do not forget that this is the main gateway of communication with Epanet.
The majority of functions that have an annoying tendency to hide are in the tab “Data” of the Browser. Look for them there first!
Before starting you should make sure that Epanet is using the correct units. When selecting LPS, the units are established as follows:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat • •
Flow: liters/second. Pressure: column meters of water, being 10 meters to 1 bar or kg/cm2.
•
Diameter: millimeters.
•
Length: meters.
• •
Elevation: meters. Dimensions: meters.
11
For convenient calculations use the Hazen-Williams formula with coefficients of friction between 100 and 150.
Nominal diameter, internal diameter and outside diameter In metal pipes the diameter that is specified corresponds with the internal diameter. A pipe of 25 mm has 25 mm of bore, and it is this diameter that is introduced to the model. In contrast, the plastic pipes (PVC and HDPE) are named by their external diameter. The internal diameter is the external one minus the thickness of the wall. At the moment of modeling them you should use this internal diameter. To complicate things even more, the specifications between manufacturers can vary. In practice, it is accepted that approximate whole numbers are used; given the very small differences involved it simplifies the task enormously and avoids errors. You can use this table for an approximate correspondence between the nominal diameters (ND) or how pipe are commercially named and internal diameters (ID):
This book will name pipes after their commercial name (outside diameter in plastic pipes) to make things easier to follow and to help you gain an intuitive idea of the behavior of different pipe sizes. But DO remember to use the internal diameters of the pipes to be installed when facing a real case.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
12
Epanet and Development. A progressive 44 exercise workbook
Exercise 1. Introductory tutorial The best way to quickly familiarize yourself with the location of commands in Epanet is to do the excellent tutorial that comes in the Help menu.
1. Start Epanet as seen in the previous section. 2. >Help /Tutorial. Remember, this route is equivalent to:
3. The screen below will open. Follow the instructions until you have finished the exercise. Have patience when you get stuck
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
13
The Help files are not visible in Windows Vista and above systems because the help program winhlp32.exe that came with them was deprecated. This may be solved in the future, meanwhile to access the help files, you can try to download the winhlp32.exe program from the windows website or install (at your own risk) the update for your system. You can download at www.arnalich.com/dwnl/ayudaVista.zip
www.arnalich.com
Helping improve Development Aid through training and consultancy.
14
Epanet and Development. A progressive 44 exercise workbook
Exercise 2. An indispensable ritual Configure Epanet to use Hazen-Williams and the metric system. This simple ritual will save your scalp.
There are few mistakes more disastrous and embarrassing yet easy to prevent than to think that the length of the piping is in meters when Epanet is taking them as feet, the diameter in inches when they are in millimeters and so on. Networks calculated in certain units and interpreted in others have little possibility of functioning. Follow this ritual each time you start a new project like a pilot’s check list before take-off. 1. With Epanet started, open the configuration dialogue with the route >Project /Defaults. 2. In the tab Hydraulics change the Flow Units to LPS. Upon changing to LPS assure that the units are meters, millimeters, liters and seconds. 3. Change "Head loss Formula", immediately underneath, to H-W. Unless you have specific needs, you do not need to change any other options here.
4. You can set default values for different properties in the Properties' tab. A diameter value of 100 mm, will make any new pipe you draw 100 mm. As most of the pipes you will work with will be plastic, set the roughness value to 140 (it will be explained soon) 5. Check the box Save as defaults for all new projects and click OK.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
15
Repeat this ritual for each new Project, and now and then when you are already in a project to confirm that all is OK, and it will save you many headaches.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
16
Epanet and Development. A progressive 44 exercise workbook
Exercise 3. Drawing a network diagram Draw this network whose pipes measures 456 m in length, 75 mm in diameter. The nodes have an elevation of 23 m. 1. Start Epanet. If you already have it open, close and re-start to start fresh. 2. You are starting a new project. Follow the ritual described in exercise 2, to appropriately configure your new project. 3. Draw the network in the size that you want with the drawing icons as you did in the introductory tutorial: Start with the nodes, the points, and later join them with the pipes. Draw all the vertical pipes first and then the horizontals. Your network should look like this:
4. Double click on a horizontal pipe to open the Properties dialogue. Change the length to 456 m and the diameter to 75 mm: 5. In the same way, change the diameter of all the horizontal pipes.
6. For the verticals we are going to try a different way of changing the data. Look at the browser and in the Data tab, select Pipes (>Browser /Data /Pipes). You will see that a list of numbers appears. Each number is the name of a pipe. As you began to draw the horizontal pipes first, the pipes 1 to 6 will be the horizontals and from 7 to 12 the verticals. 7. Select pipe 7 by clicking on the number 7. The same dialogue box will appear that opened when you double
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
17
clicked on the drawing. These are the two alternatives to open the Properties dialogue for the pipe in question. 8. Using the Browser, change the diameter and length of the remaining pipes. 9. Choose the method that you want to change the elevation of the nodes, either via the Browser or by double clicking on the node itself to open the Properties dialogue for the node.
10. Verify that you have entered all the values and that these are correct. Select the Query icon in the upper horizontal bar:
11. In the box that opens construct the sentence: Find nodes with elevation equal to 23. If there is an error, the junction will not appear highlighted in red. In the example below, the right lower node does not have an elevation equal to 23 m.
12. Repeat the process for length and diameter.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
18
Epanet and Development. A progressive 44 exercise workbook
Exercise 4. Saving time configuring Draw this network whose pipes measures 456 m in length and 75 mm in diameter. The nodes have an elevation of 23 m. It is exactly the same exercise as before, but this time we are going to do it in a much quicker way. 1. Start Epanet and again carry out the configuration ritual for a new project, but don’t close the Defaults box. 2. In the Properties tab, introduce the values: 23 for elevation, 75 for diameter and 456 for length. From now on, everything that you draw will have these properties. 3. Draw a node. Now double click on it to open the Properties dialogue and check that it has in fact incorporated the value of 23 m for the elevation. To gain a lot of time and to avoid errors, try to use the defaults as much as possible. If all the pipes are of PVC and new, introduce the roughness, 140, at the start to avoid having to modify them later one by one. If the network has elements that are repeated, as in this exercise, take advantage and introduce length; if the majority of pipes are 100 mm diameter, introduce this diameter and so on. Keep in mind that some networks can have thousands of nodes and thousands of pipes. If you are a normal mortal, you will probably have put a lot of effort into making sure all the lines were perfectly horizontal or vertical and will have tried to align the nodes. This is a huge waste of time with Epanet. Epanet interprets your drawing as if it was a sketch, never as a plan of construction to scale. Effectively, these two sketches represent exactly the same network:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
19
Draw as though you were drawing on the back of a beer mat!
4. Continue drawing the network with this philosophy in mind. Draw the 7 remaining nodes without worrying too much if they are aligned. The last junction is drawn in exaggerated misalignment:
5. Join the points with pipes.
6. Confirm that in spite of the fact that the two pipes that unite the node have gone astray and are clearly longer than the others, for Epanet they all measure the same. Use Query.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
20
Epanet and Development. A progressive 44 exercise workbook
Exercise 5. Inconsolable diameters Ascertain what diameter of pipe you would need so that this simple system supplies water with 1 bar (10 meters of water column). The reservoir is at 20 m, the pipe has a diameter of 75 mm and 100 m of length and the elevation of the node is 0 m. The demand at this point is 0.2 l/s, the equivalent of a normal tap. 1. Start Epanet and again carry out the configuration ritual for a new project, but don’t close the Defaults box because we are going to introduce an error. Pay attention to this exercise. Using coefficients of friction from one formula with another, is a very frequent mistake and difficult to find for those that are new to Epanet. It is not dangerous, because the results that it leaves are absurd. You will notice it very quickly.
2. In >Project /Defaults /Properties introduce a coefficient of friction (roughness) typical for plastic pipes for the Darcy-Weisbach formula, 0.0015.
3. In the Hydraulics tab, confirm that you have selected the HazenWilliams formula (H-W).
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
21
4. Draw the network sketch and introduce property values inside the objects’ property boxes . The demand, 0.2 l/s is introduced in the property called Base Demand. Remember that to open the Properties dialogue of an object you can double click on it or find it in the Browser. The elevation of the reservoir is introduced in the parameter Total Head.
For a detailed explanation of each property, you can go to Chapter 3 of the theory book where the most common elements found in a Developing context are explained or to the Epanet User Manual, paragraph 6.4, for a description of them all. 5. Calculate the network by pressing the flash icon in the horizontal bar:
6. Press OK in the dialogue that appears, and don’t be intimidated by its content. In a short time you will ask yourself why Epanet forces you to accept this box each one of the umpteen times that you try to optimize a network.
7. The warning message that appears indicates that there are "Negative Pressures at 0:00:00 hours". This is the same as saying that water is not arriving at the point of consumption.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
22
Epanet and Development. A progressive 44 exercise workbook
Stop to think for a moment. In your moderate experience, do you believe that a pipeline of only 100 m with the approximate diameter of a roll of toilet paper is not capable of feeding a single tap from a tank 20 m above? How big is the pipe that feeds your shower? You can already see that something has gone wrong. 8. Enlarge the diameter of the pipe to 200 mm and re-calculate. Again you will have error messages. Go to the Map tab of the Browser and select pressure in the nodes drop-down menu to get a diagram similar to this:
9. Repeat the process again, but this time with 1,000 mm, no less than 1m diameter. Once again the same error message will appear. The water doesn’t arrive at the tap! 10. Carry on increasing the diameter of the pipe. Towards 1.25 m diameter, it begins to obtain pressures close to 10 meters: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
23
Introducing coefficients of friction (Roughness) pertaining to another formula, we obtain exaggerated results. If, as recommended, you always use the Hazen-Williams’ formula, make sure that the coefficients are in the order of a hundred.
Some versions, notably the Spanish language ones, have an irksome tendency to automatically revert to the Darcy-Weisbach coefficients, it being the most used in Europe. In a network when correct coefficients are mixed with erroneous ones, it is not so easy to realize that something has gone wrong and there is a very real danger of believing correct a network that has serious failures. To avoid this happening, each time that you install Epanet and open it for the first time, do >Project /Defaults /Properties and make sure that the value of the coefficient by default is correct. Check the box to “Save as defaults for all new projects”:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
24
Epanet and Development. A progressive 44 exercise workbook
Before deciding a design is acceptable, carry out the following verification: "Find links with Roughness below 100" with Query to locate pipes with erroneous coefficients. The result of such a search is shown below:
The area shown inside the dotted line has been drawn with the coefficients of friction corresponding to another formula by mistake (they are shown in red in the program).
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
25
Exercise 6. Keeping your eyes sharp Change the drawing options on the screen to work with a black background. Before continuing with the examples, it is a good time to learn a custom that will save your eyesight and avoid a few headaches. Perhaps you could add it to the start up ritual. 1. Right click anywhere inside the Network Map screen. Select Options.
2. In the menu that appears, select Background and choose the black option:
The screen will turn black, thus avoiding radiation. In this manual, for printing reasons, we will carry on showing a white background.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
26
Epanet and Development. A progressive 44 exercise workbook
3. Try changing the rest of the available options until you find the best combination for you. If you have eyesight problems or bad aim when clicking this thickened version may interest you:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
www.arnalich.com
Helping improve Development Aid through training and consultancy.
27
28
Epanet and Development. A progressive 44 exercise workbook
Exercise 7. Recalling with help Ascertain the coefficients of friction (Roughness) of the different pipes for the different formulas using the Epanet Help. If any Help is truly useful, it is that of Epanet. We have already seen that Epanet is learned and relearned periodically, and that it is difficult in the context of Development Aid that someone be dedicated full-time to Epanet. Don’t treat the Help with snobbishness. Use it to help you remember.
1. Open Help: >Help /Help topics. Remember that you may have problems with the help files if you are using Microsoft Vista or later (see Chapter 1). 2. Explore the Help until you find this:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
29
Exercise 8. Getting over stage fright The small town of Massawa was in need of a water supply system for some time. Traditionally the water was transported by donkey from a stream 6 km away, but funds are now available to use spring in the hill at an elevation of 36 m. The flow is estimated at 3 l/s. A system is planned to supply 6 public fountains, all of them at 17 m of elevation, except number 6 (22 m) and number 1 (25 m) in accordance with this sketch. Distances: Spring-1 1-2 2-3 3-4 3-6 5-Tee
800 m 400 m 300 m 250 m 500 m 200 m
The system will use PVC pipes to feed 0.2 l/s to each fountain and 1.0 l/s to the school maintaining a minimum pressure of 10 m at all points.
1. Configure the defaults in the way that will save you most work. 2. Draw the nodes of the network. 3. Node 5 will be connected to some intermediate point of the pipe that runs between 3 and 4. In order to represent this, you should draw a node without demand that in reality would correspond with a "T". In the image below this T is shown unearthed and as an extra point in the plan of Epanet.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
30
Epanet and Development. A progressive 44 exercise workbook
4. Join the nodes with the pipes in the way that you think most logical and that uses the least materials. Here it seems logical to follow the main road. The length of the section 3-4 should be divided into two, approximately in proportion to the diagram or reality. For example, we can assign 150 m to the left hand side pipe and 100 m to the right one, giving a total of 250 m.
Epanet will allow you to draw the network in any way you like. But back to the real world, if your design does not respect private zones, military buildings, rugged landscape, etc., you will not have great success beyond your computer screen. You may find all sorts of problematic situations, for example, this mujahedeen cemetery in Afghanistan had to be crossed.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
31
Other obstacles are more unexpected, such as these military remains in the roadway. Due to the explosion risk, this is the last place to lay a pipeline. Always walk along the planned routes to make sure they are OK.
5. Introduce the data for elevations, lengths, demands and frictions where there are no default values (from the last exercise you will have deduced that PVC roughness ranges between 140 and 150). 6. Calculate the network by clicking the flash icon. Most likely you will see a message saying Valid Simulation, signifying that the pipes are sufficiently large. But be careful, sufficiently large can be any diameter between the smallest one that functions up to that of the Solar System! 7. Display pressure results by selecting Pressure in the Node drop-down menu in the Map tab of the Browser. 8. Change the scale of the legend to see the results more clearly. To open the dialogue that permits you to do this, right click on the legend. Double clicking (left click) will make the legend disappear. To see it again >View /Legends /Node.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
32
Epanet and Development. A progressive 44 exercise workbook
In this legend, for example, the additional yellow scale has been ignored:
When we have changed the legend the diagram of the screen is brought up to date: :
This system gives you all the correct values of pressure. But remember that the work is not finished yet; first you must carry out an optimization. Verify that if you change the pipe that runs from the spring to fountain 1 to one with a diameter of 1 km (1.000.000 mm), the system continues to come out correct in spite of the fact that it is complete nonsense. Imagine how much a pipe of 1 km of diameter would cost? Would it even be buildable? Do not forget that the notice "Valid Simulation" is only an invitation to optimize the system and not a green light on the part of Epanet for design. 9. You must therefore reduce the diameter of the pipes to the minimum that maintains the pressure in all the points above 10 m. The first changes, by way of example, are described in the following points, but before this there is an important notice on the philosophy: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
33
The most logical is to start with the zones closest to the source of water. If you begin with those farthest away, you will see that the changes that you later make to the pipe diameter near the source will alter the results of those you had so carefully optimized previously. This will result in a never ending spiral of changes. 10. Change the diameter of the pipe from the spring to fountain 1 to 75 mm and press to calculate. Fountain 1, with 8,26 m 1 of pressure does not reach the 10 m minimum required.
11. Change the diameter to 100 mm. With 10.33 m of pressure, it can be taken as correct.
Notice that we have not used diameters of a type 92,319 mm, which would leave the pressure at point 1 at exactly 10 m. Do not waste time trying adjustments such as these and use only internal diameters of pipes that you can actually buy: 25, 40, 63, 75, 100, 125, 150, 200, 250, 300… Remember that when you order the pipes, the diameter obtained from Epanet is the internal diameter. That is to say that for an internal diameter of 79 mm in a HPDE pipe, you should request 90 mm, as the 11 mm of difference corresponds to the thickness of the walls. This data is provided by manufacturers or you can use the generic one provided at the beginning of the Chapter.
1
Do not worry if the values that you obtain are not exactly the same as those in this book. Slight variations in the introduction of data can cause small differences that barely change anything.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
34
Epanet and Development. A progressive 44 exercise workbook
12. If the pipe that comes out of the spring is now 100 mm, it is more than likely that all the other pipes will also be 100 mm or smaller, otherwise, we would be creating a bottleneck at the source and this is only done in very special cases. 13. Edit all the pipes at the same time to change them to 100 mm diameter. The fastest way to do this is editing by group, >Edit / Select all. Then, >Edit / Group Edit opens a dialogue that you would complete it like this:
Click OK to make the changes to the pipes:
14. Carry on reducing the diameter of the pipes until you obtain the optimum system. There is no unique solution but various possibilities.
Remember to press to calculate after a session of changes so that Epanet takes the modifications into account. If you do not recalculate, Epanet and you could end up working on different networks!
This could be one of the solutions:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 2. Taking a seat
35
For simplicity, we have assumed that the best design is the one that has the smallest diameter pipes and therefore the lowest cost. However, there are many other considerations to keep in mind, for example: Is there a danger that they will block? Does it allow for future extension? Look at Chapter 7 of the theory book to see some criteria.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
3 Drawing the network Maps, objects and sketches Exercise 9. A simple topographic survey Exercise 10. A branched topographic survey Exercise 11. An abrupt case Exercise 12. Loading a backdrop Exercise 13. An emergency intervention Exercise 14. Finding out dimensions Exercise 15. Loading Google Earth images
If I can’t draw it, I don’t understand it. (Albert Einstein)
38
Epanet and Development. A progressive 44 exercise workbook
Maps, objects and sketches To share with Epanet your plans of the future network you need to draw it. For this you will use the objects in the drawing toolbar:
The objects Each icon represents a future object of the network with clearly defined properties that you will need to know.
You can consult section 3.1 of the Epanet Users Manual or “Epanet’s main objects” section in Chapter 2 of the theory book. The greatest confusion is between the reservoir and the tank: The tank is just that, a place of limited storage. The reservoir is a source of water so large in comparison with the network that consumption does not affect its volume. It can be a river, a lake, an aquifer… It can act as a source of water or as a drain. Always include at least one in the network.
Two ways to draw If you have a map, aerial photograph, plan or something similar that is to scale of the area where the network will be built, the easiest thing is to use it as the background in Epanet and to draw the network on top. If you specify the dimensions of the background image, Epanet will calculate the length of all the pipes that you draw. This method is called Automatic Length ON, and is the most convenient and precise method. If do not you have a map of the area for the planned network but instead a topographical study, you will have to draw a sketch without scale with Automatic Length OFF and manually specify the lengths of everything.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
39
Subtracting coordinates One of the fastest ways of determining the area inside a map is to subtract the coordinates of two corners. This is especially useful for maps made by GPS or to determine the scale of existing maps when in doubt. Use UTM coordinates for convenience. Consider these two examples of UTM coordinates: 32S 713000 8033400 and 32S 714000 8033400 You can ignore the first part, 32S. The second part is the horizontal coordinate measured in meters from a point, and the next is the vertical one. To find out the distance between the points, you can subtract, arguing as follows: The point A is at 713,000 m from a point of reference (which doesn’t interest us) and B is at 714,000 meters. Therefore the horizontal distance between them is 714,000 -713,000 = 1,000 m.
There are more explanations and an example in the section “Adding cartography” in Chapter 3 of the theory book.
Topographic studies Even if you have a superb map, you will need to carry out a topographical survey of the areas to know the elevation with precision. In the exercises you will learn to interpret these studies. The way to construct them is very simple. A sight is placed on the horizontal between two calibrated rulers. When looking across it, the horizontal plane of vision will cut each rule at a specific height. The difference between these points on the rulers will be the variation in the height of the land. By measuring the distance with a tape measure, we can work out the slope.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
40
Epanet and Development. A progressive 44 exercise workbook
Editing images In this chapter you will need to modify images. If this presents no problems, use the image editing program that you prefer.
If this is not the case, download for free the Paint.net program. We will be using it to follow the instructions on how to modify images: www.getpaint.net/download.html
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
41
Exercise 9. A simple topographic survey Design the following gravity system in galvanized iron knowing that at point E consumption is 5 l/s and that A is a comparatively infinite source of water.
1. Open Epanet and follow the configuration ritual. 2. Before starting to draw, you should understand fully what each thing is in the topographical survey. The ground plan, the first image, helps to locate us, but in Epanet does not serve much purpose. As you are drawing a sketch of the network, any of these to the right would be correct, but: Although it is a sketch, try to keep a resemblance to the reality so that you and other people who will be using the model can easily relate to it. Remember to be clear and orderly in your filing. As you are not going to spend 30 years after the design in the same job, other people will inherit your files. Don’t waste their time! www.arnalich.com
Helping improve Development Aid through training and consultancy.
42
Epanet and Development. A progressive 44 exercise workbook
3. Besides the points of distribution, locate other points that will be key in the design phase, for example, intermediate high points.
Always place a node in the intermediate highest points. Epanet is based on the abstraction that there are negative pressures. In reality, when there is negative pressure in one place, the pipe is full of air and all the water points below it will be without supply. By placing an extra node in high points you will be able to verify that the pressure is sufficient
4. The key points of the sketch, points A, B, C, D, E, should be represented in Epanet to be able to compare the topographical survey with the diagram. Each one of them, like the rest of the intermediate points, will have an elevation and an accumulated distance (chainage) from the initial point. For example, point B has an elevation of 28 meters and an accumulated distance to A of 445 m. If we had to put a pipe between B and the one immediately before, b', its length would be 100 m. 5. There are six key points, five corresponding to the letters and the intermediate high point of chainage 345 (labeled P345). The second high point, chainage 805 m, coincides with D, so there is no need for an additional node. The distances between the points A, P345, B, C, D, and E, are obtained by subtracting their chainage.
The lengths are shown in the diagram, after verifying that its partial sums correspond to the accumulated length of E: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
43
345+100+330+30+160 = 965 m
6. Introduce the elevation data to the nodes.
7. Introduce the demand at point E, make sure that the roughness corresponds to galvanized iron (120) pipes and calculate the network. Modify the legend so as to see the pressure values clearly:
If all has gone well the simulation will be validated. Once again we must see if we can reduce the pipe diameters. Instead of using trial and error as in the preceding exercises, there is a way of detecting at a glance which pipes are too large. Just like when tightening the end of a hose the water accelerates, when placing pipes with diameters that are too large the water decelerates and will have a lower flow speed. This is due to the Continuity Equation that establishes that flow is constant throughout different sections of a pipe: s 1 * v 1 = s 2 * v 2 = s 3 * v 3 = Constant www.arnalich.com
s : Section, v : Velocity
Helping improve Development Aid through training and consultancy.
44
Epanet and Development. A progressive 44 exercise workbook
The normal range of velocities in a pipe at peak time is from 0 to 2 m/s for water without sediment. Looking at which pipes have lower velocities tells us where to begin to make changes. Remember to always start at the point closest to the source of water. 8. >Browser /Map /Links /Velocity. In the Nodes menu, you could select whatever you want to see simultaneously in the diagram, for example, pressure.
Look for low speed values. For example, the shown value of 0.16 m/s is one of them. Modify the diameter of the first pipe until you obtain a velocity of 0.5 m/s or greater. 9. Observe what has happened to the pressures after changing the diameter of the first pipe to 100 mm. Note that points P345 and E cannot get to 10 m of pressure due to the topography; Point P345 has an elevation of 33 m, only 7 less than the reservoir, and E 32 m, 8 m less than A. At these points we must try to obtain all the pressure that we can without making the network excessively costly. We can accept the minimum pressure in these two points is 6 m.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
45
10. The modification of the first pipe has reduced all the water pressures downstream too much. Try increasing the diameter to 125 mm.
The pressures are now close to the minimum pressure of 10 m, the pipe is correctly sized. Note that this pipe now has a velocity of 0.41 m/s. 11. Repeat the process for the rest of the pipes until you find an acceptable solution. 12. One possibility is this, where all the pipes are of 125 mm diameter:
Although point D is slightly under 10 m of pressure, a gain of only 0.064 bars of pressure does not justify increasing all the diameters and shooting up the cost of the system.
Save the final file as Exercise9.net, and then save it again as Exercise10.net, as it will be the starting point of the next exercise.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
46
Epanet and Development. A progressive 44 exercise workbook
Exercise 10. A branched topographic survey A branch line must be added to the design of the preceding exercise to supply a second town, point G, with 7 l/s. Modify the design according to the new data:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
47
1. Open the file Exercise10.net if you closed it after the previous exercise. 2. Note that the data for the main branch is exactly the same. It is only a matter of adding the second branch. Point C, which is common to both branches and has the same elevation, is the point of union. Decide which points you need to include as nodes in the new branch. Point F has been included to show the change in direction of the pipe although you have learned in the tutorial other ways of doing it.
Keep in mind that this is a very simplified topographical study, a real study can have hundreds or thousands of points, and to represent each one of them can be a Herculean yet not very useful task.
3. Introduce the data of the new junctions, the elevations and the demand (24 m, 33 m and 7 l/s). Make sure that you introduce the demand data in the parameter Base Demand. It is easy to be mistaken and to put it in Demand Pattern. In that case, Epanet would show the following notice:
4. Calculate the network. As you optimized the last exercise for only one consumer, you will now have negative pressures. To see which pipes you need to enlarge, look at the velocity in >Browser /Map /Links /Velocity.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
48
Epanet and Development. A progressive 44 exercise workbook
The common pipes, the first 3, now have to transport more than double the water and the pressure suffers. Try enlarging the diameter of these first. 5. Increase their diameter to 200 mm and see what happens with the pressure. Remember that the three nodes marked on the table cannot have greater pressure that 10 m due to their elevation:
The velocity of the water in the pipes of the new branch is only 0.22 m/s. Note what happens to the pressure at point G if its size is reduced. With a loss of only 0.04 bars, the pipes can be changed to 150 mm diameter. In HDPE, for example, the 200 mm pipes cost 22.4 €/m and those of 150 mm 15.4 €/m. The saving made by changing the pipes would be 345 m * 7 €/m = 2,415 €.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
49
Save the last file as Exercise10.net. Later it will be used to introduce a consumption pattern.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
50
Epanet and Development. A progressive 44 exercise workbook
Exercise 11. An abrupt case The intention is to feed from a lake in the slope of a hill a single point in another nearby hill with 2 l/s. The run through is practically straight. The proximity to petroleum producing countries has led to the selection of HDPE as the material. Choose the diameter of this pipeline. Keeping in mind that the regulation of the country requires that the working pressure of the pipes be, at most, 80% of the nominal pressure, what should the nominal pressure be of the pipes that you install?
1. The diagram for this exercise is very simple, but at the time of deciding the relevant points, take this tip into account:
In the event that the network is uneven between points over 40 meters or there will be pumps, it is necessary to place a junction in the low points to assure that the pressure that the pipes bear is inside the working margins of the pipe. Don’t trust the pipe specifications of certain manufacturers.
2. This system will have an initial point A, a final point B and an intermediate point b' of minimal elevation. At times, it is better visually to make a plan as if in lateral view to display the topography, as in this case:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
51
3. Introduce the data. The roughness of the HDPE, 140, the elevations 116 m, 11 m and 86 m, and the lengths 438 m and 543 m, verifying that its sum is in fact 981 m. Finally, enter the demand of B, 2 l/s. 4. Calculate the system and modify the keys keeping in mind that the pressure in the point of distribution should be between 1 and 3 bars. You will arrive at a point in which the pressure in junction B is smaller than 3 bars. However, the velocity of the water is very low. Reducing the pressure at point B, saves in pipes and reduces the pressure at point b'.
It is very important that water supply systems function at the smallest possible pressures over and above the design range. When the systems carry a lot of pressure the leaks are greater and pipe break more often. 5. In this case, there is little room to maneuver because of the topography. The strategy to follow is to reduce the diameter of the downpipe more than that of the ascending pipe to diminish the pressure at point b'.
A possible solution to the system is presented further on. In it, the downpipe has a diameter of 50 mm. Always consider the risk of pipes becoming blocked when sizing and what precautions you can take. For example, having valves every 300m can help detect the section affected by a block. .
www.arnalich.com
Helping improve Development Aid through training and consultancy.
52
Epanet and Development. A progressive 44 exercise workbook
With regards to the working pressure of the pipe, this should be taken during periods of very low consumption. In the peak times, the network pressure decreases and pressure may be greatly underestimated. 6. Change the demand at point B to 0 l/s and take a reading of the pressure at point b’. The result is 105 meters or 10.5 bars.
7. Adjust the value to the regulations currently in force, increasing it by 20%. 105 m * 1.2 = 126 m or 12.6 bars. When the time comes to order the pipes, PN 10 (10 bars) would not be sufficient and you would have to take the next one up, PN 16 (16 bars).
Not all the pipes need to be PN10, only the reaches that are over 80 m below the water tank, thus exceeding the working pressure of the pipe (80% of 10 bar).
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
53
Exercise 12. Loading a backdrop Incorporate image 12.bmp as a background knowing that it measures 1033 m x 625 m.
To carry out this exercise you need to download the image 12.bmp from: www.arnalich.com/dwnl/epaxen/12.zip.
1. Open Epanet and follow the configuration ritual.
Epanet works with background images with the extension “.bmp". These images barely have any compression, resulting in images of large memory size. Compare the size in bmp (572 Kb) with that of the same image in jpg (45 Kb). To avoid the computer running too slow, try not to use images of more than 4 or 5 Mb. Another big objection to using very large images is that with Epanet you can always expand the view but you can’t reduce it. With a too large image, you will have an expanded view whether you want it or not. 2. Load the background image: >View /Backdrop /Load. Select the image 12.bmp from the folder in which it was extracted from the compressed zip file. This loads a background image, but its dimensions are not specified.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
54
Epanet and Development. A progressive 44 exercise workbook
3. To establish the dimensions, >View /Dimensions. One corner will be (0.0) and the other corner (1033, 625). Select meters as unit.
4. A simple way to verify that all has gone well is to place the cursor in the upper right corner of the image and to see if the coordinates that Epanet displays in the lower horizontal bar coincide with the calibration values. To move the image use the Pan button:
5. To draw pipes in the Auto-Length mode, you should activate it by right clicking in the area Auto-Length Off (lower left corner of Epanet) and accept AutoLength On.
6. If it is correctly activated it will now display “Auto-Length On”. © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
55
When drawing with Epanet the Auto-Length changes easily between On and Off. If you are not aware of this, it is very easy to mix pipes of real length with those of default value length. The resulting design does not serve much purpose. Get used to checking this occasionally. If it happens, you can query for the pipe length default value to detect them, as we are about to do.
7. Places two nodes in the outermost points of the scale inside the image, and join them with a pipeline. Notice that the length of pipe has taken a value close to 200 m. A variation of some meters above or below is normal.
8. Deactivate the Auto-Length mode and draw two nodes just over the previous ones and a pipe to join them. The default value of the pipe is generally 100 m, but you can check it in >Project / Defaults /Properties.
9. A search for pipes with a default value will detail all those that were not drawn with the Auto Length mode activated, as it is highly improbable that you have drawn a pipe that measures exactly 100 m.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
56
Epanet and Development. A progressive 44 exercise workbook
Exercise 13. An emergency intervention Design an emergency system in PVC to supply a refugee population in the deforested area shown in image 13.jpg, in which there will be 5 distribution banks of 6 taps, each one fed from a nearby high point. For this purpose, the local authority has provided an aerial photograph with contour lines and grids of 1 km x 1 km.
To do this exercise you will need to download the zip file containing image 13.jpg: www.arnalich.com/dwnl/epaxen/13.zip
1. Open Epanet and follow the configuration ritual. 2. Open the image with Paint.net and save it as 13.bmp so that Epanet can recognize it. To select the program with which to open the file, right click on the image and >Open with /Paint.NET:
3. Once opened, >File /Save as. Below the file name you have the possibility to choose in which format to save it. Click the lower box and choose .bmp (also called Bitmap or Map of bits) from the dropdown menu that appears:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
57
4. Load the image in Epanet, >View /Backdrop /Load. 5. Establish its dimensions, >View /Dimensions. Since the image is square with four sideways grids of 1km each, the total dimension is 4000 x 4000:
6. The next step is to find your way in the image, locating the high points where the tank can go, the low ones, to allow for the water runoff from the taps, etc. 7. In the lower left corner there is a rectangle that resembles a football pitch. It coincides with the highest point. This would be the ideal place to locate the tank as it has good access and plenty of free space around to set up equipment, storage of material, etc. www.arnalich.com
Helping improve Development Aid through training and consultancy.
58
Epanet and Development. A progressive 44 exercise workbook
8. Look for a pathway for the pipes so that there are neither high nor low points. Some background images make it extremely difficult to see the network drawing. For example, draw a node in the scrub area of this image and how it disappears. In these cases, once you are familiar with the image, you can brighten it up:
To brighten the image in Paint.NET, >Adjustments /Brightness/Contrast:
Brighten up the image and save it in the same folder with the name 13faded.bmp. To change from one to another, simply load one or the other. When you do not want the background image select Unload in the same menu.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
59
9. Activate Auto-length and draw the path through. For example, the one shown below is a possibility. From the 35 m at the reservoir, it goes down abruptly until reaching the 25 m contour line. The idea is to pressurize the system quickly. Once it touches the 25 m contour line it carries on. It deviates from the main North-South direction, so as to gently descend to the 20 m contour. It continues again along this contour and finally descends to 15 m.
10. Work out an approximation of the elevations of the junctions using the contour lines. 11. Once the plan is drawn and you have ascertained the elevations, the background image may hinder the visualization of the results. To unload it, >View /Backdrop /Unload.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
60
Epanet and Development. A progressive 44 exercise workbook
12. Knowing that a normal tap has a flow of 0.2 l/s, a distribution ramp of 6 taps will have a total flow of 1.2 l/s. Note that we have not drawn the 6 taps or the structure of the ramp as in the image, but we have simplified it so that the total consumption will be exact. This process is called skeletonization and we will see it later on.
Take note also of the hand washing into the bucket that takes place whilst holding the tap open. These self-closing taps of low sanitary standard continue to be very popular in emergencies. Although they are outside the purpose of this manual, always have in mind these details in the commencement of a water supply system design. 13. Introduce all the data and calculate the network. 14. See if the system has dangerous pressures in the low consumption periods and then find out the diameter of each pipe. One possible solution to the problem is this:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
61
In an emergency, refugee camp or similar installations, there will be queues during some hours of the day. All the taps will be in use, which is less frequent in a network supplying a population. You have just seen how this type of networks is calculated. The other types of network have a different focus when calculating the demand, as will be seen in the following chapter.
Save this exercise as 13.net. We will use it later to place a pump from the river to the tank in the hill and to see why a tank is modeled into the summit of a hill like a reservoir.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
62
Epanet and Development. A progressive 44 exercise workbook
Exercise 14. Finding out dimensions You have an aerial photo of the area where the network is going to be built but you don’t have the dimensions specified. With the help of a GPS you have determined the position of two points where the streets intersect that you thought you would be able to recognize easily both in the aerial photo and on the land. The coordinates of these two points are: A B
10 S 0559741 4283782 10 S 0564821 4281174
Load and dimension the background image to use it in Epanet.
To do this exercise you need to download the image 14.jpg. www.arnalich.com/dwnl/epaxen/14.zip
1. Open Epanet and follow the configuration ritual. 2. Change the format of the photo from JPG to BMP. 3. Work out the dimensions of the image:
The sign of the distance does not have any practical importance. This image corresponds with 5080 meters in the horizontal (East-West) and 2608 in the vertical (North-South). 4. Epanet only accepts the dimensions of the corners. The next thing to do is to trim the image so that points A and B coincide with the corners. For this use Paint.NET, >Tools /Rectangle Select.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
63
Place the cursor on point A, click and drag to point B.
5. Trim pressing the crop icon and save the image as BMP:
6. Load the background image, >View /Backdrop /Load and dimension it using these distances. Verify that all this is correct by placing the cursor in the right upper corner and reading the coordinates in the lower bar.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
64
Epanet and Development. A progressive 44 exercise workbook
Exercise 15. Loading Google Earth images Obtain and measure a satellite image of the airport of Mogadishu in Somalia with Google Earth.
To carry out this exercise you need to download and install the free program Google Earth. http://earth.google.com/download-earth.html 1. Open Google Earth. The welcome screen is similar to this:
The navigation is carried out in this control board in the top right corner. These controls remain partially transparent unless the mouse is over them. In the case where you want to use the image as background, pay attention to always stay vertical. © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
65
Notwithstanding, by tilting the view you can obtain three-dimensional images that can help you to decide pathways for the pipes.
2. Navigate to the Horn of Africa and you will see Mogadishu:
3. Approach Mogadishu until you have a view of the city and locate the airport. It is in the southwest.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
66
Epanet and Development. A progressive 44 exercise workbook
4. When the two extremes of the airport occupy almost all the screen, do a screen capture. This is done by pressing the "Print screen" key, usually found in the upper right corner of the keyboard.. Once you have done this, you will have copied the screen. 5. Open Paint.NET and press Ctrl and v simultaneously. The image will appear in the program.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 3. Drawing the network
67
6. Now you will need to cut it according to some coordinates. To do this, in Google Earth, place the cursor on an easily distinguishable point near the lower left corner and read the coordinates in the bottom bar.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
68
Epanet and Development. A progressive 44 exercise workbook
7. Repeat in the process near the right upper corner to obtain the second coordinate. You will have two coordinates like these:
8. Crop the image using the points that you have taken. 9. Load the image and enter the values in the Dimensions dialogue as in the previous exercises. The quantity and resolution of the available images in Google Earth grows rapidly. Some years ago there were barely images of large cities; the current coverage is pretty good.
Consult the sections "Bread crumb maps and GPS points", “Net2epa" and "Importing maps from AutoCAD" of the section "Drawing the network", Chapter 3 of the theory book to discover other, less common ways of using maps. If you can get a version of Google Earth Pro, which is free for non-profits, then you can export the satellite images in high resolution in the save menu.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
4 Demand Demand in time and space Spreadsheet crash course (Excel, etc.) Exercise 16. Building a daily consumption pattern Exercise 17. Nodes with different consumer types Exercise 18. No data Exercise 19. Yield evaluation Reservoir sizing Exercise 20. Peeping into the future Exercise 21. Population density limits Exercise 22. Regression Exercise 23. Computing time-varying demands Exercise 24. Total allocation Exercise 25. Per node allocation Exercise 26. Per street allocation Exercise 27. Per loop allocation
Life is what happens while you’re busy making other plans. (John Lennon)
70
Epanet and Development. A progressive 44 exercise workbook
Demand in time and space Up to now we have supposed a constant demand throughout the day. They will consume "7 l/s at point G" or "2 l/s at point B". The reality is that demand varies through time, most notably throughout the day. Another consideration is how to distribute this demand among the different nodes that form a network. To determine the demand and to distribute it spatially is to load the model.
Chapter 4 of the theory book deals with this topic in detail. To understand the nuances, it is important that you read it all. The following shows a daily consumption pattern:
Multipliers The way to take into account these daily variations is to use numbers that multiply to give an average demand for the day, the multipliers. The philosophy is very simple, if the daily average is 10 l/s, and at 16:00 hours 20 l/s is consumed, the multiplier is 2. Thus, Epanet only has to apply the multipliers for each hour to express the change in demand over time. To calculate the multipliers: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
71
Average Demand * Multiplier = Instantaneous Demand That is:
10 l/s * 2 = 20 l/s
Calculation of the total daily consumption This is the sum of all the expected consumption. If I have 2 goats, 3 country people and a donkey, the daily total demand could be: 2 goats x 5 l/goat = 10 l 3 people x 30 l/ person = 90 l 1 donkey x 20 l/donkey = 20 l ---------------------------120 liters per day
Minimum uses (l/un) Urban inhabitant Rural inhabitant Pupil Out patient In patient Ablution Camel (once a week) Goat and sheep Cow Horses, mules
50 30 5 5 60 2 250 5 20 20
Design Period If current data were used to design a network it would become obsolete before the system is even built. To make sure this does not happen, try to ascertain what the situation will be after a specific number of years called the design period. How many actual years to consider is an arbitrary decision. Normally a 30 year period is used, in spite of the fact that the minimum life of PVC, for example, is 50 years. Projecting beyond 30 years increases the uncertainty and puts the initial investment in doubt. With 30 years, sufficient time is given to the population so that they can plan and organize any modifications that they are going to need. Nonetheless, 30 years is not a mathematical period. In any case, try to design networks so that they can be easily enlarged. In various parts of the theory book you can learn how.
Projection formulas Arithmetic: Geometric
Pf , Future Population P0 , Actual Population i , rate of growth in % t , time in years
Exponential
www.arnalich.com
e , Number e, (e=2,718...)
Helping improve Development Aid through training and consultancy.
72
Epanet and Development. A progressive 44 exercise workbook
The geometric projection has a greater field of application. The arithmetic one is not recommended for populations of more than 20,000 people.
Monthly, weekly and non-measured consumption coefficients The monthly and weekly variations are taken into account by multiplying by a coefficient, another multiplier. For example, if the average has been calculated with measurements taken on a Monday and the day of highest demand has double this consumption, the weekly coefficient will be 2. Similarly, using the monthly differences, you can calculate a monthly coefficient. Finally there is a consumption that is difficult to determine: leaks, losses during use, illegal connections, public utilities, etc. The leaks and losses in new networks are around 20% making the coefficient for unaccounted-for water 1.2.
A pessimistic outlook The networks are designed for the worst case scenario: the busiest time of the day during the busiest day of the week of the less favorable month with the biggest population served (30 years out). It is assumed that if it is capable of functioning at the moment of greatest demand, it will do so without problems the rest of the time. The way to represent this mathematically is by multiplying the coefficients: G lobal = D aily x W eekly x M onthly x C onsumption not measured G lobal = 2,39 x 1,15 x 1,37 x 1,2 = 4,52 If the average demand is 10 l/s, in the worst moment of the network it will consume: 10 l/s * 4,52 = 45,2 l/s When you don’t have any data, use a global coefficient between 3.5 and 4.5, depending on the size of the variations you expect. Read the section “Small systems and other approaches to demand” of the theory book to get insight on how to design emergency or public fountain systems.
Demand allocation Read the section with this title in the theory book
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
73
Static Analysis This is what we have been doing so far: considering only the moment of maximum consumption.
Extended Period Analysis This observes a series of intermediate states, which is very useful when considering other moments, like those of minimum consumption. These moments give us an idea of the aging of the water in the network, the leaks, the maximum pressures of the system, etc.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
74
Epanet and Development. A progressive 44 exercise workbook
Spreadsheet crash course (Excel, etc.) In hands-on type courses students appreciate a quick review of the use of a spreadsheet. Here we cover the most common one, Excel. If you are already familiar with the use of Excel, skip this section. 1. Open the program by clicking on the icon:
The program is organized in multiple cells, identified by the letter of the column and the number of the line, in the image the cell highlighted is C4.
2. To introduce a number into the cell, select it and enter the number. Type 10 in cell B2 and 6 in C2. When entering content in a cell, it also appears in the horizontal box above.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
75
3. To perform an operation, click on the cell where you want the result to appear and introduce the symbol “=” followed by the operation. Multiply the two previous cells by typing “=B2*C2” into cell. Alternatively, you can write = and click on B2, type an operation and click on C2.
4. If you wanted to introduce the hours of the day in consecutive cells, it would be very tiring. To speed up the process, write 1 and 2. Next select the two cells where you have entered the numbers. Placing the cursor on the lower right changes the form. Click here and drag. You will see that it produces progressive numbers.
5. Type whatever numbers in the 3 columns below the 10 and the 6.
6. Place the cursor on the lower left corner of cell D2 and below in the same way as described in point 4. Notice that the formula in cell D2 has been extended to the lower cells updating in a way that cell D3 shows B3*C3, D4 shows B4*C4 and so on.
7. This, even though it seems very convenient, can in fact be a nuisance if you want to multiply all the numbers of column C by B2 then you do not want the formulas to be updated automatically. To avoid this, place $ signs in front of the row, the column or both, according to what you want to block. In the proposed case the formula in cell D4 would be “=$B$2*C2". The result using $ signs and that not using them is very different: www.arnalich.com
Helping improve Development Aid through training and consultancy.
76
Epanet and Development. A progressive 44 exercise workbook
8. To find the total of a column, place the cursor in the lower cell, and press the symbol ∑. You can change the selection until you cover what you want to be included.
9. Excel has many functions. You will use some of them frequently such as the powers or logarithms. To find them, press next to the Sum button and choose from the dropdown menu.
With these 9 steps, you have what is strictly necessary for the following exercises. At the beginning it will be confusing, but after five minutes of practice you will be more at ease.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
77
Exercise 16. Building a daily consumption pattern Measurements have been taken in 30 supply points of a nearby network during the 24 hours of July 18th, 2007. Build and apply the daily pattern to the network of exercise 10.
Pay great attention to this exercise, it is fundamental for calculating with Epanet and in it we introduce concepts and forms that will be used repeatedly later. 1. Obtain the total consumption for the day by adding the consumption of each time band: 1,800 + 700 + 200 +…+3,000 = 213,700 l. 2. Obtain the average hourly consumption by dividing the total between 24 hours: 213.700 l. / 24 hours = 8.904 l/h 3. Obtain the multiplier for each hour by dividing the consumption of the hour in question by the average consumption: 0:00 1,800 / 8,904 = 0.20 1:00 700 / 8,904 = 0.08 2:00 200 / 8,904 = 0.02 ….. ….. …… 23:00 3,000 / 8,904 = 0.23 4. To get rid of errors, confirm that the sum of the multipliers is 24: 0.2 + 0.08 + … + 0.34 = 24
Take advantage of your previous work and make spreadsheets that you can reuse. If at this stage and in the following exercises you organize a collection of spreadsheets for reuse you will gain a lot of time and avoid errors.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
78
Epanet and Development. A progressive 44 exercise workbook
5. Once you have constructed the pattern by calculating the multipliers, open the file 10.net. 6. Follow the route >Browser /Data /Patterns. The Browser shows you that it is empty, that you have not yet defined any patterns. To define one, press the Add icon:
The Pattern Editor will open. The following method will be very similar for establishing other curves in Epanet, like pump curves, energy costs, etc. The two remaining icons, shown inactive, serve to erase a curve and to publish it. 7. Enter the multipliers for each hour band. You can assume that the first multiplier is that of 0:00, which seems more logical, or that of 1:00, as in Epanet. The result is the same and for the calculation there is no difference.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
79
Once finished, the editor will show a bar chart of the consumption distribution:
8. Save the consumption pattern as 15.pat. All too often, actual data cannot be measured because the system does not exist yet, measurement equipment is not available or does not work properly. Even in those situations, do not use the
www.arnalich.com
Helping improve Development Aid through training and consultancy.
80
Epanet and Development. A progressive 44 exercise workbook demand patterns showed in this manual unless indicated otherwise. These patterns are fictitious examples used only to meet learning objectives.
9. Change the configuration of Epanet to switch from static analysis to an extended period one. In >Browser /Data /Options /Times, enter a Total Duration of 72 hours:
Do not use durations of less than 3 days. Many tendencies are only revealed after a number of cycles. For example, notice how this tank empties with time. In an analysis of only 24 hours we would not have detected that this tank will always be empty and that it makes no sense to build it.
To avoid having to look at many screens before seeing the peak time, it is a good idea to configure Epanet so that it starts off showing you the results for that hour. In the exercise and in the same menu, select 14:00:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
81
10. You still have to specify that the nodes follow this new pattern. In nodes E and G, introduce the name of the consumption pattern in Demand Pattern:
11. Calculate the network. Now that you are looking at the daily peak consumption, and not just average demand, the network that you so meticulously optimized no longer manages to deliver water to all the points. Negative pressures have appeared. 12. To visualize how behavior changes over time, press Forward of the Browser. Use the controls like those of a video player.
www.arnalich.com
in the Map tab
Helping improve Development Aid through training and consultancy.
82
Epanet and Development. A progressive 44 exercise workbook
13. For the moment forget the rest of the hours and concentrate on optimizing the network for the peak time, 14:00. Before making the necessary changes to the network so that once again they are in the correct range of pressures, add a pipe starting at node B and ending at node F:
Don’t forget that to optimize a network, besides changing diameters, you can also add or remove pipes, tanks, valves, etc. In this case a new pipe has been added in a sketch that is not to scale. To determine its length, you should organize a new topographical survey, find the equipment and the people and wait for the results. Whenever you work on a network in which modifications of this type are planned, try to work with a background image that is to scale. If you do not have one, ask the topographical team to produce something to scale that you can use or, if you have access to a GPS, create it as is explained in the section "Bread crumb Maps and GPS points" of the section "Drawing the network", Chapter 3 of the theory book. 14. Take the length of the new pipe as 428 m and continue making changes to the network until 14:00h when the pressure is greater than 5 m (remember that the difference of elevation at the source of water does not allow us to achieve the normal value of 10 m).
15. Once done, analyze the ageing. To see how much time the water spends in the pipes, do >Browser /Data /Options /Quality. Choose Age in the dropdown menu.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
83
16. Select >Browser / Map / Nodes / Age. Press Forward in the Browser and observe how the water in the network ages with time. At the end of the low consumption period, 7 AM, the greater periods are recorded:
To understand the importance of ageing in the quality of water and chlorination, read the section "What parameters of quality to evaluate with Epanet?” in chapter 5 of the theory book.
Save the file as 16.net without closing it, it will be used in the next exercise.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
84
Epanet and Development. A progressive 44 exercise workbook
Exercise 17. Nodes with different consumer types News of the network project 16 have stimulated the local authorities to build a small nutritious pasta factory at point E. It is forecasted that it will consume 11 cubic meters of water daily, 20% of which will be between 12:00 and 16:00, 50% between 16:00 and 18:00 and the remaining 30% at 18:00. Is it necessary to enlarge the existing system? 1. Construct the consumption pattern of the factory, as per the previous exercise. The result will come out something like this:
The way to construct it is as follows: if between 12:00 and 16:00 there are 4 hours and 20% is consumed, the consumption of each hour is 5% of the total. Between 16:00 and 18:00 there are two hours of which 50% of the consumption is distributed, that is 25% each hour. 5% of 11,000 liters (11 m3) is equivalent to: 11,000 * 0.05 = 550 liters. The average hourly rate is 11.000 liters / 24 hours = 458.3 l/h
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
85
458.3 l/h * 1h/3,600s = 0.127 l/s, this will be introduced in Epanet. To calculate the multipliers, divide the hourly average by the consumption of that hour. Note that regarding units, it’s all the same if you are comparing l/s, cubic meters, loads of rice from the paddy fields, or any another quantity that occurs to you. M 5% = 550 liters / 458.3 liters = 1.2 M 25% = 2.750 / 458.3 = 6 M 30% = 3.300 / 458.3 = 7.2
These calculations, despite being simple, are very prone to error like the double negatives or the days that there are between two dates. It is very good practice to do a verification. In the previous table, there are two marked in red that are very simple to do: the sum of the multipliers is 24 and the total of the liters that arrive each hour is 11,000. Another very silly verification is that if 5% is 1.2, 5 times more (25%) will be 1.2 * 5 = 6. Be advised!
2. Construct in Epanet the corresponding pattern, >Browser /Data /Patterns /Add.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
86
Epanet and Development. A progressive 44 exercise workbook 3. Click on node E to add the new demand. This node will have consumption according to pattern 1 of 5 l/s and the consumption of the factory, according to pattern 2, of 0.127 l/s. In the properties of node E, press Demand Categories and introduce both:
4. Calculate the network and answer the question asked at the beginning of the exercise. Remember that you have to look at all the times. If it turns out to be inconvenient, deactivate the time of the results starting at 14:00.
No, it is not necessary to enlarge it. The peak time, is still at 14:00, and both pressures are above 5 m which we established was the minimum.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
87
Exercise 18. No data The refugee camp at Anagret has long queues to collect water and the leaders established a rotation system for the distribution so that some areas can be supplied in the mornings and others in the afternoons. After 3 years, the departure of the refugees is not foreseen in the near future, and it has been decided to enlarge the production of water and the system of distribution. Establish a pattern of consumption on which to calculate the system of distribution. In this case, there is neither data nor a real possibility to measure it. The population is accustomed to receiving water at certain times. Nevertheless, once they eliminate the restrictions, they will begin to readjust to their normal pattern. 1. Establish a hypothesis for the consumption. In developing contexts, it is frequently the case that the consumption has two peaks, one in the morning when the consumption is 50-60% of the water and the other at mid-afternoon when it is 25%-35%. A pattern constructed like this may look like the following:
2. To calculate the consumption pattern it is easier to refer to 100 liters. In this way the conversion of percentages to liters is direct, 15% is 15 liters. The average flow for each hour would be 100 liters / 24 = 4.16. The multipliers are:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
88
Epanet and Development. A progressive 44 exercise workbook
3. Enter them in Epanet.
Save the pattern with the name generic.pat. To save it, go to Patterns in the Browser and select the Save option.
Read the section “When there is no data” in Chapter 3 of the theory book to learn other ways to overcome lack of data.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
89
Exercise 19. Yield evaluation A small rural settlement of stock farmers has a population of 196 people. It is estimated that an average family is composed of 7 people, 2 cows and 70 sheep. There is no data of consumption for the people, but it is known that the animals drink for three hours at dawn and two at sunset. If the system predicted is fed from a spring of 0.5 l/s in its least productive moment at an elevation of 46 m: Is the flow of the spring sufficient? Would it be resolved by building a tank? Of what size? There is a scale plan of the location.
Area 1, 23 m and 9 families Coordinates A: 23 S 410038 8763991 Area 2, 31 m and 15 families Coordinates B: 23 S 411238 8763091 Area 3, 27 m and 4 families Troughs: 5 at 26 m
1. Calculate the total quantity consumed per person and animal. 196 people / 7 people/family = 28 families. Taking an allowance of 30 liters per person, 20 per cow and 5 per sheep:
People Cows Sheep www.arnalich.com
Family
Total (x28) Allowance Totals 7 196 30 5880 2 56 20 1120 70 1960 5 9800
Helping improve Development Aid through training and consultancy.
90
Epanet and Development. A progressive 44 exercise workbook
Animals: Persons: TOTAL:
10920 liters/day 5880 liters/day 16800 liters/day
2. Build the patterns. In the case of the animals, and supposing that the total consumption is based on 5 homogeneous hours: Average consumption, 10,920 liters / 24 hours = 455 liters/hour Average flow, 455 l/h* 1h/3,600 s = 0.126 l/s Hourly consumption: 10,920 liters / 5 hours = 2,184 l/h Multiplier of each hour of consumption is 2,184 / 455 = 4.8 The pattern of the animals will be:
Given the lack of data on the population and such a small settlement where most of the consumers are animals, use the generic pattern that you built in the previous exercise, >Browser /Data /Pattern /Add /Load.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
91
3. Before drawing the network, follow the configuration ritual. From now on, it will be taken for granted that each exercise is started with this ritual.
Download the file 19.zip to obtain the backdrop: www.arnalich.com/dwnl/epaxen/19.zip
4. Measure and prepare the image. Remember to trim it using the points with known coordinates and to change it to BMP format.
5. Draw the network and make sure that Auto-length is activated.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
92
Epanet and Development. A progressive 44 exercise workbook Unless specified otherwise, all the pipes in the exercises from here on will be of plastic, the most common material in development contexts. 6. Introduce the elevations. Assign an elevation of 26 m to the new node that serves as a junction. 7. Introduce the demands and the consumption patterns of the different points. In the case of the trough, we simulate all 5 as a single node. The average was 0.126 l/s according to the calculation in point 2. In the case of the people, each area will contribute according to the number of families that it contains. The total volume is 5,880 liters / 24h*3,600s = 0.068 l/s. Thus, Area 1 = 0.068 l/s * 9 families / 28 families = 0.022 l/s Area 2 = 0.068 l/s * 15 families / 28 families = 0.036 l/s Area 3 = 0.068 l/s * 4 families / 28 families = 0.01 l/s 8. To answer the first question, “Is the flow of the spring sufficient?” you must see if the flow of the pipe at the outlet of the reservoir is greater at any moment than the flow of the spring. For this, go to analysis in extended period with a duration of 24 hrs >Browser /Data / Options /Time and calculate the network again. Perhaps the quickest way to see if the flow exceeds 0.5 l/s is by means of a graph of flow vs. time. Press the Graph icon:
In the menu that comes up, you have all the options of Epanet to represent results in graph form. They are very simple and they do not need huge explanations. To make the graph of the flow changes select Time Series, Flow and Links. In Links to Represent add the pipe that exits the reservoir in your model. The configuration of the dialogue and the result is shown below. The intermittent line at 0.5 l/s is not drawn by Epanet; it is an addition to facilitate the visualization.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
93
This is the resulting graph:
The answer is NO. From a little before 5:00 until 7:40 there is a deficit of water and also from 18:40 to 20:20. www.arnalich.com
Helping improve Development Aid through training and consultancy.
94
Epanet and Development. A progressive 44 exercise workbook This graph is very interesting and it is going to answer the second question, “Would it be resolved by building a tank?” The areas below the dotted line and outside the pattern curve (blue) correspond with the volume of water from the spring that would end up at the tank in the periods in which the consumption is smaller than the demand. The shaded zones of the peaks (red) correspond to the volume of water that would leave the tank when the demand is greater than the spring produces.
If the blue zone is greater than the red peaks then the source of water is sufficient, it only remains to store the water during the low consumption periods by placing a storage tank for the periods of high consumption.
The mathematical way to answer the second question is to subtract the total consumption from the total production: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
95
0.5 l/s * 24h * 3,600 s/h = 43,200 l – (10,920+5,880)l = 26,400 extra liters It is resolved by building a tank. 9. You can answer the third question mathematically or through a process of trial and error with Epanet. Place a tank next to the reservoir with a slightly lower elevation than the maximum height of the tank to allow for the flow of water, for example at 40 m. 10. Calculate the network. 11. Make a graph of the evolution of the volume stored in the tank. To do it, click on it once to select it and press the Graph icon. There select the parameter height. 12. Repeating this process and modifying the properties of the tank and avoiding errors in the simulation, you can determine the size of the tank. But let’s leave it here.
In my modest opinion, to try and calculate everything with Epanet is a great waste of time. As the complexity of the system grows it is increasingly more difficult to balance. In the majority of cases in a development context, it is a lot faster, more direct and less prone to error to calculate the size of tanks, pumps, etc. by hand. In the following section we see how they are calculated. www.arnalich.com
Helping improve Development Aid through training and consultancy.
96
Epanet and Development. A progressive 44 exercise workbook
Reservoir sizing To determine what volume of water needs to be stored, we do a balance of entrances and exits at the different times of the day. Subtracting the absolute value of the maximum deficit accumulated from the maximum surplus accumulated gives the necessary volume. In the case of the previous exercise: 1. Calculate the hourly consumptions for each type of consumer (animals and people) and add them in the third column. The total consumptions for each hour are calculated by multiplying the multiplier for the hour by the average daily volume. For example, at 05:00 the people will consume: 0.24 * 245 l=59 l.
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 TOTAL liters
© Santiago Arnalich
Mult. People Mult. Animals Total use 0.00 0 0.00 0 0 0.00 0 0.00 0 0 0.00 0 0.00 0 0 0.00 0 0.00 0 0 0.00 0 0.00 0 0 0.24 59 4.80 2184 2243 0.96 235 4.80 2184 2419 3.12 764 4.80 2184 2948 4.32 1058 0.00 0 1058 4.08 1000 0.00 0 1000 1.68 412 0.00 0 412 0.48 118 0.00 0 118 0.24 59 0.00 0 59 0.24 59 0.00 0 59 0.24 59 0.00 0 59 0.96 235 0.00 0 235 2.40 588 0.00 0 588 2.88 706 0.00 0 706 1.44 353 0.00 0 353 0.48 118 4.80 2184 2302 0.24 59 4.80 2184 2243 0.00 0 0.00 0 0 0.00 0 0.00 0 0 0.00 0 0.00 0 0 24 5880 24 10920
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
97
2. The production is greater than the consumption as we have seen previously. The reservoir will be filled and then it will leave so that the surplus water will be lost. To see the number of hours of spring production needed divide the total consumption by the hourly flow from the source: 16,800 liters / 1,800 l/h= 9.33 hours. We then put under the production column: nine cells with 1,800 and in the tenth cell 600, a third of 1,800. Start filling the cells that coincide with a high consumption.
The hour of the day in which you put the entries will determine the size of the tank. When the water enters at a time of higher consumption, less water is stored and the tanks can be smaller. If water is stored and it is not consumed, the tank will have to be of the total volume that is consumed.
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 TOTAL www.arnalich.com
People Animals Total use Production Balance TOTAL 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 59 2184 2243 1800 -443 -443 235 2184 2419 1800 -619 -1062 764 2184 2948 1800 -1148 -2210 1058 0 1058 1800 742 -1469 1000 0 1000 1800 800 -668 412 0 412 600 188 -480 118 0 118 0 -118 -598 59 0 59 0 -59 -656 59 0 59 0 -59 -715 59 0 59 0 -59 -774 235 0 235 0 -235 -1009 588 0 588 1800 1212 203 706 0 706 1800 1094 1297 353 0 353 0 -353 944 118 2184 2302 1800 -502 443 59 2184 2243 1800 -443 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 5880 10920 0 Helping improve Development Aid through training and consultancy.
98
Epanet and Development. A progressive 44 exercise workbook
The volume of the tank is the remainder of the maximum volume accumulated, 1,297 liters, from the minimum, -2.210 liters: 1,297 liters – (-2.210 liters) = 3507 liters. To this quantity it would be necessary to add reserves for fires, storage for contingencies, etc. Notice what happens if the entrances are put in at the moments of smaller consumption:
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 TOTAL
Persons Animals Total use Production Balance TOTAL 0 0 0 1800 1800 1800 0 0 0 1800 1800 3600 0 0 0 1800 1800 5400 0 0 0 1800 1800 7200 0 0 0 1800 1800 9000 59 2184 2243 0 -2243 6757 235 2184 2419 0 -2419 4338 764 2184 2948 0 -2948 1390 1058 0 1058 0 -1058 331 1000 0 1000 0 -1000 -668 412 0 412 0 -412 -1080 118 0 118 0 -118 -1198 59 0 59 0 -59 -1256 59 0 59 600 541 -715 59 0 59 0 -59 -774 235 0 235 0 -235 -1009 588 0 588 1800 1212 203 706 0 706 0 -706 -503 353 0 353 0 -353 -856 118 2184 2302 0 -2302 -3157 59 2184 2243 0 -2243 -5400 0 0 0 1800 1800 -3600 0 0 0 1800 1800 -1800 0 0 0 1800 1800 0 5880 10920 0
In this case, the volume would be: much more.
9,000 liters – (-5,400 liters) = 14,400 liters,
If you used an organized spreadsheet, you will already have the template for the next time.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
99
Exercise 20. Peeping into the future The data of the 1997 census indicates that the population of Mtala was 12,321 people. In the 2007 census, the current population was 17,544 people. If you plan a system for Mtala with a design period of 30 years, for which population would you do it? Compare the results of the different projection formulas.
1. Calculate the annual rate of growth: 100* (17,544 people - 12,321 people) / 10 years * 12,321 people = 4.2 % per year. 2. Apply the geometric projection formula: Pf = P o (1+ i/100) t = 17,544 (1+ 0.042)30 = 60,278 inhabitants
3. Comparison of the different formulas:
Arithmetic Geometric Exponential
39649 60278 61850
By way of example, this is the comparison of formulas for another population where the great leap between the arithmetic one and the others can also be observed.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
100
Epanet and Development. A progressive 44 exercise workbook
Exercise 21. Population density limits The block UV39 is a recently populated, poor zone of Santa Cruz, in which previously were cultivated fields between the airport and the industrial park. The average family size is 6 people. What population would you use for the design if the system is planned for 30 years, bearing in mind the data from the last census?
A99 A100 A101 A102 A103 Map of
A104 A105 A106 A107 A108 Block 39
A109 A110 A111 A112 A113
A114 A115 A116 A117 A118
Plot Fam. Growth A99 36 1.920 A100 35 2.850 A101 33 2.800 A102 36 0.960 A103 34 1.910 A104 36 1.500 A105 35 1.350 A106 32 2.580 A107 36 1.700 A108 36 0.460 A109 10 10.100 A110 9 17.490 A111 29 3.690 A112 35 1.350 A113 36 1.200 A114 12 11.320 A115 3 11.830 A116 4 15.440 A117 9 10.600 A118 8 15.200
In this problem you would be able to use two approaches, both based on the populations having a limited population. The first, simpler and less accurate is described in this exercise. As the population density grows, the motivation to inhabit a specific zone falls. Looking at the chart and the growth rates, we observe that many boxes are of the value 36.
Download the file 21.zip to avoid having to copy all the data at: www.arnalich.com/dwnl/epaxen/21.zip © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
101
1. Deduce what the limit value could be. It is a good idea to discuss with the area’s population whether they think that they are crowded or not to avoid false and excessively low limits. We can take, for example, the value of 36 families per plot as the limit. 2. Deduce the total quantity of people, assuming that all the plots are populated with this density. 20 plots * 36 families/plot * 6 people / family = 4,320 people. 3. If you had used the geometric formula in this case, using for example the average of the growth rates, 5.8%, the result would have been 16,412 people, 3.8 times greater. This is due to the fact that newly occupied areas have very varied growth rates. To find the average, the Excel function AVERAGE() is used.
Don’t forget to pay special attention to the dynamics of the population. In this case, the least populated plots are concentrated in one area: A99 A100 A101 A102 A103
A104 A105 A106 A107 A108
A109 A110 A111 A112 A113
A114 A115 A116 A117 A118
Investigating the cause, it can be a simple question of access to services, but it can also be that the said area becomes flooded periodically or even that it is mined. Providing services encourages settlement and special attention should be paid to making sure that they are not dangerous zones.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
102
Epanet and Development. A progressive 44 exercise workbook
Exercise 22. Regression Repeat the previous exercise trying to draw out a conclusion about how the growth rate varies with respect to density.
Again it is based on the idea that the growth rate will decrease to the extent that the density increases. To verify that this occurs, we use a statistical technique called regression. Look it up in Wikipedia or in google it for more information. Even though it is very simple to do by hand, it is somewhat laborious. We will use the spreadsheet. 1. Select the family and growth rate columns as if you were going to copy them. 2. Create a scatter graph pressing the button in the insert tab:
3. Press next repeatedly until you get a graph similar to this:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
103
4. Add a trend line. Select the graph’s points, right click and select Add Trendline.
5. Select Linear in the dialogue that opens:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
104
Epanet and Development. A progressive 44 exercise workbook 6. At the bottom, tick Show equation in the graph and Show the value R squared in the graph. Also indicate to extrapolate forward so that the trend line cuts the X axis.
The point where the line cuts the axis, where the growth rate is 0, gives us the density limit value.
This point can also be obtained by using the regression 1 equation: Y = -0.4176x + 16.337 0 = -0.4176x + 16.337 → x = 16.337/0.4176 = 39.12 families/lot The value R2 is a measure of the strength of the relationship between the two variables. If it is 0, the variables are independent and, the closer the value is to 1 or -1, the stronger the dependence between the variables. An absolute value of 0.8 or greater is a good closeness. 7. The calculated population is: 20 plots * 39.12 families/plot * 6 people / family = 4,695 people. Note that this value is more logical than that obtained by geometric progression.
1
Note: strictly speaking one should do an ANOVA of the growth rates and a more complicated statistical
analysis. However, it would complicate things considerably without huge benefits. Simply make sure that you do not use this process if you have less than 10 pairs of data.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
105
Exercise 23. Computing time-varying demands On Wednesday 16 of September a series of measures were carried out at intervals of an hour with 39 meters in a population close to the planned extension. During each day of that week the daily output volumes from the main tank were registered. Finally, data of the monthly billing for the last 5 years were obtained. Using the results subsequently summarized, determine what the demand base will be to distribute between the nodes and also the consumption pattern to apply if the population is 43,000 people with an estimated consumption of 50 l/person.
0:00 1:00 2:00 3:00 4:00 5:00 6:00
200 200 300 400 700 1000 4000
7:00 8:00 9:00 10:00
7000 10000 9000 3000
11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00
4000 4000 5000 9000 11000 11000 4000 2000 3000 4000 2000 700
23:00
500
Monday Tuesday Wednesday Thursday Friday Saturday Sunday
86 67 96 91 82 101 116
January February March April May June July August September October November December
75 63 74 63 89 97 100 99 90 78 76 81
Download 23.zip to obtain the data and the network at: www.arnalich.com/dwnl/epaxen/23.zip www.arnalich.com
Helping improve Development Aid through training and consultancy.
106
Epanet and Development. A progressive 44 exercise workbook 1. Calculate the consumption pattern, according to the method in the previous exercises, from the data in index 23.xls. Open the index 23.net; insert it in the pattern and save it with the name 23.pat. 0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 Total
200 200 300 400 700 1000 4000 7000 10000 9000 3000 4000 4000 5000 9000 11000 11000 4000 2000 3000 4000 2000 700 500
0.05 0.05 0.08 0.10 0.18 0.25 1.00 1.75 2.50 2.25 0.75 1.00 1.00 1.25 2.25 2.75 2.75 1.00 0.50 0.75 1.00 0.50 0.18 0.13
96000 4000 Average
2. Calculate the weekly coefficient. For this, take the value of the day with the highest measurement. If the day of the measurement is the highest, the coefficient is 1 and the results would not change. M measurement = M wednesday = 96 V Max = V sunday = 116 C weekly = 116/ 96 = 1.208. Approximately 1.21
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
107
It is not necessary to calculate the rest of the days. What is important is that Wednesday’s measurements must be increased by 21% to convert them to the day of highest consumption. 3. Repeat the process to ascertain the monthly coefficient. M measurement = M september = 90 V Max = V july = 100 C monthly = 100/ 90 = 1.11
4. Determine the coefficient for the non-measured consumption. For lack of data on illegal connections, and assuming the network to be well maintained, we can use 20%, that is 1.2. 5. Calculate the global coefficient without the daily coefficient: C g ’ = Cs * Cm * Cnm = 1.21 * 1.11 * 1.2 = 1.61 6. The average demand to share between the proposed nodes is: 43,000 people * 50 l/person *1.61 / (24 hours * 3,600 s/h) = 40.09 l/s
Save the Epanet file as 23.net and leave it open for the next exercise.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
108
Epanet and Development. A progressive 44 exercise workbook
Exercise 24. Total allocation Assign the average consumption from the previous exercise to the nodes of network 23.net, keeping in mind that each node covers approximately the same area. The water is pumped from a river into a tank that is represented as a reservoir. Optimize the network. Look at file 23.net. The network is drawn as a sketch without losing time making it regular and pretty, but all the distances between the pipes are 100 m.
If the population and nodes are homogeneously distributed in an area, the simplest way to assign the demand is to assume that consumption is equal in all the nodes. 1. Assign 40.09 l/s by the total allocation method: 40.09 l/s / 12 nodes = 3.34 l/s node 2. Incorporate this demand base to all the nodes. Remember, >Edit / Select all and after >Edit / Edit group. 3. Configure Epanet to carry out an analysis in extended period with the start time coinciding with the daily peak (>Browser /Data /Options /Time). 4. Modify the key to adapt to the design interval, 10-30 m, show velocity in the pipes and optimize the network. Start by reducing redundant pipes:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
109
In spite of the fact that the exterior ring is bigger than needed at various points in the left lower corner, it is worthwhile to install a larger size if there is the possibility of future expansions. The diameter of the central pipe can be reduced. 5. A very simple way to optimize this network, if the topography allows, is to set up the tank at a lower elevation. Try, for example, to lower it to 32 m.
In pumped systems, the majority of optimization efforts should be aimed at lowering the water tanks as much as possible. In this case, for example, 43,000 inhabitants are pumped 50 l/h = an average of 2,150 tons of water. Imagine the energy saving if you didn’t have to raise 2,150 tons 4 meters higher on a daily basis!
6. Increase the diameter of the downpipe from the tank. The decrease in losses will allow the tank to be lowered even more. Note that on changing the diameter of the downpipe from 200 mm to 300 mm, the pressure at the most critical point goes from 10.48 m to 14.30 m. This will allow you to lower the tank a few more meters.
Save the exercise as 24.net so you can use it in the ageing calculations.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
110
Epanet and Development. A progressive 44 exercise workbook
Exercise 25. Per node allocation A 20 year design for a population of 10,000 inhabitants that grows at a rate of 3% is being proposed. The total consumption of each street is represented by each pipe. Allocate the demand.
In the absence of large consumers, all the small consumers of a pipe are distributed in equal parts among the nodes on each end. If there was a large consumer, it would be placed on the exact point of the pipe to adequately represent the differential load that it makes on each node. 1. Calculate the population at the end of 20 years and adequately correct the demand. Pf = P o (1+ i/100)t = 10,000 (1+ 0.03)20 = 18,061 inhabitants To know how much we should increase the demand, we can find the multiplier using the traditional way 18,061/10,000 = 1.81 or we could employ the previous formula for only one inhabitant: Pf = 1 (1 + 0.03) 20 = 1.81. 2. Distribute half of the consumption from the different pipes that flow into a node. Bring the demand up to date keeping in mind the population projection. For example, half of 2 l/s is assigned to node 1, that is to say, 1 l/s. The future demand will be 1 l/s * 1.81 = 1.81 l/s. The remainder of the nodes are shown in the table: Demand Node 1 Node 2 Node 3 Node 4
© Santiago Arnalich
Current
1 6 10 1.5
Future
Arnalich. Water and habitat
1.81 10.86 18.10 2.72
l/s l/s l/s l/s
www.arnalich.com
CHAPTER 4. Demand
111
Exercise 26. Per street allocation A 10 year design for a population of 20,000 inhabitants that grows by 2% (geometric) and consumes 0.01 l/s*person is being proposed, allocate the demand if horizontal streets have 160 users/km and the vertical 200 users/km.
1. Calculate the population at the end of 10 years and adequately correct the demand. Pf = P o (1+ i/100)t = 20,000 (1+ 0.02)10 = 24,380 inhabitants Again, we can find the multiplier in the traditional way 24,380/20,000 = 1.219 or we could employ the previous formula for only one inhabitant Pf = 1 (1 + 0.02) 10 = 1.219. Therefore, each inhabitant will consume: 0.01 l/s * 1.219 = 0.01219 l/s 2. Calculate how many inhabitants correspond to each node. For example, half of the pipe between 1 and 2 will correspond to node 1: 50m * 1 km/1000m * 200 people/km = 10 inhabitants
In node 2:
0.05 * 200 0.05 * 200 0.15 * 160 + 0.05 * 160 -----------------52 inhabitants
(Branch 1) (Branch 3) (Branch 4) (Branch 2)
Nodes 2 and 3, and 1 and 4 are symmetrical with one another. The consumption is obtained by multiplying the inhabitants of each node by its consumption then by the projection multiplier: www.arnalich.com
Helping improve Development Aid through training and consultancy.
112
Epanet and Development. A progressive 44 exercise workbook Node 1 and 4: Node 2 and 3:
© Santiago Arnalich
10 inhabitants * 0.01 l/s*inhab * 1,219 = 0.122 l/s 52 inhabitants * 0.01 l/s*inhab * 1,219 = 0.634 l/s
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 4. Demand
113
Exercise 27. Per loop allocation In Mapu the current density of the block where the work is planned is 200 people/km2 and its surface is 2 km2. It has been seen that the population stabilizes at densities of around 250 people/km2. Calculate the demand of the nodes for 30 years if each inhabitant consumes 0.01 l/s.
1. Project the future population. Don’t consider the 30 years design period; in this case you should focus on the density limit in the statement. 2 km2 * 250 people/km2 = 500 people 2. Calculate the corresponding consumption: 500 people * 0.01 l/s = 5 l/s 3. Distribute the consumption between the border nodes of the network. 5 l/s / 7 nodes = 0.71 l/s*node If a node forms part of several loops, the flows that correspond to each one of the loops are added together.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
5 Quality Chlorine residual, ageing and treatment by dilution Exercise 28. Chlorine decay Exercise 29. Chlorine decay II Exercise 30. Ageing Exercise 31. Two sources
There is no job so sim ple that it cannot be done w rong . (Murphy’s Law)
116
Epanet and Development. A progressive 44 exercise workbook
Chlorine residual, ageing and treatment by dilution The two main parameters of design that you can use in Epanet to evaluate the quality of the water are the concentration of chlorine and the residence time of the water in the network or ageing.
Chlorine Tap water should contain a residual quantity of chlorine of 0.2-0.6 ppm (ppm and mg/l are the same thing for water). Chlorine is consumed: a)
In contact with organic matter in the water. To describe the speed in which it breaks down the bulk coefficient is used, calculated by comparing two measurements sufficiently far apart in time.
C Ln n C0 K= t b)
Being: K, bulk coefficient in days-1 C0, initial concentration Cn, conc. at time n of measurement n t, time in days
In contact with the wall of the pipe. This wall coefficient is very difficult to determine. However, if you use plastic pipes, as is frequently the case, it is 0.
Ageing Water quality depends on how long it spends in the pipes. The quality can be deteriorated by intrusions, infiltrations and by internal reactions. If you have opened a tap in a house that had not been inhabited for some time, for example after a vacation, you should know what I am referring to. Try to design a system so that the water does not spend more than 24 hours in the network. The most problematic parts are those furthest from the source and branched networks. On the other hand, chlorine needs to be in contact with water for 30 minutes to have its full effect. You should pay attention to the points where the ageing is less than 30 minutes if the water was not in contact with chlorine before being distributed (chlorination in the tank).
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
117
Dilutions The simplest way to treat water with a too high parameter is to dilute it. Imagine for example that a borehole provides water with an excess of salinity. In another nearby borehole the water is not saline but does not provide water in sufficient quantity to cover all the demand. Mixing both, a sufficient volume with a lower salinity can be obtained. Epanet allows us to see the percentage of water that comes from a given source in each node and to follow the concentration of a chemical in the network.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
118
Epanet and Development. A progressive 44 exercise workbook
Exercise 28. Chlorine decay A sample of water from the river Tuerlo has been taken. It has been placed in a glass container and chlorine has been added to a concentration of 2 ppm. 36 hours later the concentration was 1.4 ppm. What is the bulk coefficient? If water with 1 ppm of chlorine travels 10 km through a pipe of 75 mm from the chlorination station situated at an elevation of 52 m to a single node that consumes 0.6 l/s at an elevation of 0 m, will it arrive with an adequate concentration of chlorine? 1. Calculate the bulk coefficient:
Ln K=
Cn C0 t
1.4 2 1.5
Ln =
= -0.2378 day-1
2. Draw the proposed network off the statement and introduce the data except the coefficient. However, every kilometer place a node without consumption, to be able to see how the concentration of chlorine changes along the way:
Did you remember to use the default values 140, 75 mm and 1 km? 3. Below we are going to configure Epanet to do a quality analysis. Pay attention to the process: 3.1 To see the evolution over time you need to keep in mind a consumption pattern. For lack of data, use a generic one, for example, 16.pat (>Browser /Data /Patterns / Load). 3.2 Go to extended period (>Browser/ Options /Times /Total Duration). 3.3 Specify what type of analysis you want to carry out, selecting Chemical in >Browser/ Options /Quality /Parameter.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
119
3.4 Add the chlorine source. Click on the reservoir and introduce 1 in the parameter Initial Quality (1 ppm).
3.5 Define the chlorine consumptions, introducing the bulk coefficient in pipe properties and leaving the wall coefficient unmarked (equivalent to having 0 value). The quickest way to do it is by Group Edit:
Remember: >Edit / Select all and >Edit / Group Edit).
It may be that Epanet gives you trouble with the minus sign. If that is the case, one way to get around is writing -0.2378 in another program, copying it and pasting it into the dialog box. Use the right click menu to paste, not ctrl + v.
4. Observe the results of the node terminal hour after hour. If you do a graph you will see that Epanet considers the pipe to be full of water with no chlorine at the moment of initiating the simulation. It is not until the 19th hour that the first load of chlorinated water arrives at the node where it is consumed.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
120
Epanet and Development. A progressive 44 exercise workbook
Once the first load arrives, the concentration barely drops from the original. This behavior is normal, and even helpful, since it allows us to maintain the margins of chlorine at great distances from the network and avoiding secondary chlorinators. In this network the chlorination at the source has to be diminished. The values are too high. 5. Change the concentration of chlorine at source to 0,5 ppm and see what happens:
This chlorine concentration at source would maintain the chlorine values within the suitable range of values.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
121
The objective of modeling the chlorine is to discover the need for satellite chlorinators, to detect points of excessive concentration that could cause refusal by the consumers and to guide the operators toward the best working concentrations.
Every job in water supply installations should be followed by a chlorine shock treatment. You can use your model to detect those places that could be problematic at the moment of elimination of the chlorine shock and where to run off the water to wash away the chlorine excess.
Save the index as 28.net and leave it open.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
122
Epanet and Development. A progressive 44 exercise workbook
Exercise 29. Chlorine decay II Two river water samples have evolved in 48 hours as follows: Sample 1 Sample 2
1 ppm→ 0 ppm 2.8 ppm → 0.3 ppm
What conclusions would you make? What evolution does the chlorine follow in the system of the preceding exercise? 1. The first sample is not usable. It is not known if it arrived at 0 ppm after 3 or 7 hours. In any case, they should not be allowed to arrive at a 0 concentration because of problems of precision. 2. Calculate the extinction coefficient for the second sample:
Ln K=
Cn C0 t
Ln =
0.3 2.8 2
= -1.1168 day-1
Evolutions of chlorine of this type should cause you to suspect a high content of organic matter, particularly when the water temperatures are not over 20ºC. Reconsider if the source is appropriate or if it needs a filtration system. In the case of rivers, the variations can be considerable following periods of rain, of growth of algae and plants, floods, droughts, spills, etc. Avoid taking water directly from a river, for example, by excavating a well near the bank.
In some cases, especially those with high water temperature, the coefficients can reach such negative values. 3. Change the bulk coefficient of all the pipes and repeat the simulation. In this case, the variations are more noticeable but they continue are still maintained between 0.2 and 0.6 ppm even in the periods of less consumption when the water takes longer to complete its journey.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
www.arnalich.com
Helping improve Development Aid through training and consultancy.
123
124
Epanet and Development. A progressive 44 exercise workbook
Exercise 30. Ageing Verify that the ageing of water in the network 24 net is correct.
1. Open the file 24.net. 2. Specify what type of analysis you want to do, select Age in >Browser / Options / /Quality /Age.
3. To see Quality on the screen, select it in Nodes from the Browser. Adjust the key scale in order to see significant time intervals; especially 0.5 (30 minutes) in the lower one in order to detect areas with insufficient contact with chlorine, and 24 to detect areas of stagnation.
4. Change the start time for the results to what it was, 0:00 (>Browser /Data /Options /Times / Report Start Time) and calculate the network so as to take in to account the latest configurations. Notice that water is not in the network for very long and the worry would be more the time of contact with the chlorine rather than ageing. Shortly after the moment of maximum consumption the ageing is at a minimum. The residence time is bigger in the most distant zones (left lower corner). © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
125
5. Change the consumption of the nodes to 0.2 l/s and see what happens.
The demand is now much lower, the velocity in the pipes has drastically decreased and the travel times are much greater. 6. Add a lateral branch using the default options (200 mm, 100 m) as shown in the image. Node A has a demand of 0.2 l/s and B is a dead end without demand. Calculate and observe what happens.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
126
Epanet and Development. A progressive 44 exercise workbook In spite of the fact that the road to A is a lot shorter than to other parts of the network, the time of permanence is way off. This is due to this part not being looped. The nodes in branches (A), those more distant from the source (C) and the nodes with very low consumption (B) are the most problematic regarding ageing. If the times are too high you should modify the network to decrease them. To do this, you can decrease the travel distance or close a nearby network.
Save the file as 30.net and leave it open for the next exercise.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 5. Quality
127
Exercise 31. Two sources The original source of exercise 30 has a concentration of 10 ppm of a substance whose limit, in the standards of the country, is 8 ppm. A second source 76 m from point B has been identified with an elevation of 32 m and a concentration of 3 ppm. The substance is inert in the water and with the pipe components. Would it be possible to supply the network feeding from both sources simultaneously and allowing them to mix in the network? In the Northeast corner, what percentage of the water comes from B at 14:00 on the first day? And on the second day?
1. Incorporate the second source into the model.
2. The substance is inert. Eliminate any coefficient of extinction that there was in the pipes using Group Edit. Change the demand to the original one, 3.34 l/s. Verify that the model remains inside the design pressure limits before looking at any parameters of quality. Only one parameter at a time can be calculated.
3. Introduce the concentration of the sources of the substance in the parameter Initial Quality:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
128
Epanet and Development. A progressive 44 exercise workbook 4. Configure Epanet to go from the Age analysis to that of Chemical (>Browser /Data /Options /Quality /Chemical). 5. Calculate the network; change the Browser to Chemical and the legend to detect any value over 8 ppm.
6. The evaluation of all the hours shows that, although for the hours of low consumption and the south part the concentration of the substance is inside limits, in the hours of greater consumption the majority of nodes continue to have illegal values. Modify the network to make the mix more favorable.
As the problems occur in the periods of greater consumption, decreasing diameter of the problematic source (to 150 mm) and increasing that of acceptable one (to 300 mm) manages to maintain all the values below maximum. Do not forget to verify that the pressures are still within appropriate range!
© Santiago Arnalich
Arnalich. Water and habitat
the the the the
www.arnalich.com
CHAPTER 5. Quality
129
7. To see what percentage of water has its origin at B, configure the model to Trace Node >Browser /Data /Options /Quality /Trace Node. In the dialogue you should specify which is the node you want to analyze .In my model, B is reservoir 17.
8. Modify the key to see the results. To make it more visual and so the nodes take their size according to value, right click on any point of the screen and select Options. In Nodes, check the box Proportional to Value.
The first day 55.57% of the water stems from B, however, observe what happens the next day at the same time:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
130
Epanet and Development. A progressive 44 exercise workbook
We had taken as good a model that in reality does not solve much! We need to mix both sources because B is insufficient. Always, but especially in quality analysis, you must become accustomed to let the model run for several days in order to eliminate erroneous results.
If you are interested, get yourself involved in this case until you achieve no more than 75% of the water in the period coming from B without the substance values surpassing the limits.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
6 Scenarios Scenarios Exercise 32. Reservoir between distribution and pump Exercise 33. Springs and tail tanks Exercise 34. Pressure zones Exercise 35. Adding a pump Exercise 36. Modeling a borehole Exercise 37. Skeletonization
If you consult enough experts, you can confirm any opinion. (Anonymous)
132
Epanet and Development. A progressive 44 exercise workbook
Scenarios In this chapter we show some common or practical scenarios.
Pumps A pumped system can be substituted in a great many cases by a reservoir using the pumping head as elevation, as you will see very soon. Unless you see a clear advantage in simulating a pump, avoid placing them in Epanet. You will discover that they have a certain tendency to try your patience. If you place some, first stabilize the network as if it was a pure gravity-flow project and then place and work the pump to avoid having too many variable sources. In the exercises we are going to see simplifications that avoid the use of pumps as well as ways to locate them with fewer problems.
Depressurization in contact with the atmosphere Each time that a pipe flows into in an open container to the atmosphere, the water itself depressurizes and cannot transmit pressure beyond that point. Imagine an inner tube of a bicycle that has a very large hole (open to the atmosphere). We will not be able to fill it with pressurized air for all that we may try. In spite of its simple-mindedness this is an important concept. For example, it is being open to the atmosphere that differentiates aqueducts, which cannot transport water uphill, from pipes that can.
Pressure zones Occasionally a network has points where the elevations have too much difference to be able to reconcile the pressure of them all. To solve it, pressure zones are established and the network is divided into sub networks where the pressure can be maintained within an appropriate range. As a guideline it is not necessary to establish pressure zones for differences less than 37 m. If there is a map with contour lines, the establishment of pressure zones is direct, following the contour lines. In this case, the 400 m line divides the zone of high pressure from the drop.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
133
Dynamic and static level and depth of installation of the pump The distance from the ground to the aquifer surface is called static level (SWL). When a pump in a borehole begins to pump from the aquifer, it forms a cone of air inside the water similar to the swirl of a drain. During the pumping the water level drops considerably until it reaches the dynamic level (DWL). At the moment of establishing the pumping head, the dynamic level is taken and not the depth of installation of the pump (ID), since to raise water among water does not consume energy.
Negative demands as sources of water If a node with positive demand extracts water from the network, one with negative demand contributes water. Thus a node with a demand of -2 is a fixed entrance of 2 l/s in the network. This is probably one of the most convenient ways to represent a spring. A pattern can also be added to this node, in such a way that if it had the following multipliers 000000000000111111111111, water would only enter in the last 12 hours of the day.
Nevertheless, only use these negative demands in high points of the network that work on gravity, since the flow in the pumps changes according to how much pressure they have to overcome to force water into the network.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
134
Epanet and Development. A progressive 44 exercise workbook
Skeletonization Building a model representing each one of the components of a network is tedious work, prone to error, difficult to analyze, that takes effort to update and is extremely expensive. Imagine that in a network that supplies 10,000 dwellings you had to represent the interior network of each one of them! Skeletonization consists of finding models of the equivalent network increasingly more simple. The way to find if they are equivalent or not is to run the two models and see in which measure they produce similar results. In practice this is difficult and laborious to do. In developing projects the networks are rarely excessively complicated. You can apply skeletonization without problems summarizing all the consumption in one unique node in:
1. 2. 3. 4.
The interior network of buildings. Offshoots of small dimensions compared with the total network. Whatever delivery structure, for example, a public fountain with various taps. Nodes on the same pipeline without branches, like you find on a necklace.
If you need to skeletonize to a greater extent or you want a more detailed explanation, you can consult point 3.11 of the book “Advanced Water Distribution Modeling and Management”.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
135
Exercise 32. Reservoir between distribution and pump We want to pump from river Orst at 1.812 m above sea level to a tank with an elevation of 1.892 m. Once there, it is planned to distribute by gravity to 5 public fountains with an average demand of 0.4 l/s each and located on a terrace at 1.822 m. The topographical study has revealed the following distances: River-Tank: 2.300 m Tank-Source 1: 1.340 m Source 1- Source 2: 200 m
Source 2- Source 3: 160 m Source 1- Source 4: 430 m Source 4- Source 5: 90 m
Design the supply system using a general daily consumption pattern.
Topographic profile from the water tank to tapstand 1.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
136
Epanet and Development. A progressive 44 exercise workbook
Observe that the system has a pumped part, from the tank to the left, and a part by gravity, to the right. Upon discharging the pump pipe into a container open to the atmosphere the water will depressurize. This isolates the part on the right from the left. However powerful the pump is, the pressure of the public fountains will not vary. This is the reason why in Exercise 13 it was only modeled from the tank onwards.
1. Construct a model ignoring the pumped part. The selection of the pump and the principal pipe can be done more easily by hand (this is covered later).
2. Introduce the data from the statement and use the general pattern of consumption (16.net). 3. Calculate the network. You will get something like this, and you can probably already sense that the challenge of this exercise is to control the excess of pressure.
4. Try to decrease the pressure by increasing the friction. To do this get Epanet to show you the results at the peak time, 14:00 (>Browser /Data /Options /Times / Report Start Time). A change of the main pipe to 75 mm leaves the pressure within the interval of calculation at peak time:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
137
Nevertheless, in the periods of lower consumption, the friction is not sufficient to decrease the pressure and the system is far from functioning in the correct range.
A way to resolve this system is by the installation of a break pressure tank (BPT). Again, the pipe enters a tank in contact with the air and depressurizes. A break pressure tank is a very small tank with a free exit and an entrance regulated by a floating valve.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
138
Epanet and Development. A progressive 44 exercise workbook
When the consumption is less than the water that arrives from a higher elevation the tank fills with water and cuts the flow from above. Selecting the elevation of installation of this tank to halfway on the slope can regulate the pressure.
In a development context avoid installing pressure reducing valves. Their price and the necessary logistics to acquire them make it very unlikely that they will be replaced once they have deteriorated. Most often they will have to be bypassed and the systems will be dysfunctional and prone to damage. A break pressure tank, on the other hand, is very strong and the only moveable part, the floating valve, is easy to repair or replace.
5. Following this philosophy of not including unnecessary parts in the model, work the model from the pressure break tank. To do this, leave it like this and consider that what was the tank before, is now the break pressure tank. To determine the length of the pipe according to the elevation of the tank, use the topographical profile. The pressure at peak time was 70 m. To work out the elevation of the break pressure tank with which to begin the tests, subtract the maximum pressure of design from the maximum of the system without pressure break tank and then this value from the elevation of the tank: 70 m – 30 m = 40 m
1,892 m – 40 m = 1,852 m
The length of pipe is 1,340 m – 534 m = 806 m
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
139
6. Modify the pipes until the values of design comply in pressure. The pressure curve has the same form as the one that we calculated before, but now all the values are inside range.
7. Check that the water ageing is less than 24 hours (>Browser /Data /Options /Quality /Age).
8. Check that, at peak time, the velocity in the pipes is between 0.5 and 2 m/s, another important design criterion.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
140
Epanet and Development. A progressive 44 exercise workbook Velocities over 2 m/s indicate that the pipe is too small and they rocket the friction. The minimum velocity is 0.5 m/s in the case of water that contains sediments so that the pipes are self cleaning. If the water does not have sediments, there is no minimum velocity. 9. Once the network is stabilized, the diameter of the pipe that goes from the tank to the break pressure tank should be selected. This entrance pipe should be capable of transporting more water than the maximum volume of the departing pipe. Work out the volume of the departing pipe at peak time, 7.18 l/s:
10. To ascertain its diameter quickly, place a reservoir at the elevation of the tank and a node at the elevation of the BPT and join them with a 534 m pipe in a new Epanet project. Assign it a demand of 7.18 l/s, and make sure you don’t apply any consumption pattern. Select the minimum pipe that maintains the pressures above 10 m.
The downpipe from the tank to the BPT should be 75 mm. It remains to determine which pump to choose, the size of the tank and the pipe for the pump. If there is not a great choice in the market, it is the pump that determines the size of the other elements. A 20 m3/h pump needs a smaller pipe than one of 40 m3/h. In the same way, a pump with a greater yield will generally need a smaller tank. The choice of pump remains outside the objectives of this manual and is not complicated. The decision regarding the size of tank has already been looked at and the selection of the diameter of pipe and it is that diameter that keeps the pump expenses low plus depreciation. There is an example in Exercise 42. © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
141
Exercise 33. Springs and tail tanks A topographical study has taken as datum (elevation 0 m) a spring of fixed volume of 2 l/s. From the spring a homogeneous network of 6 public sources at an elevation of 30 m and with an average consumption of 0.3 l/s is fed by gravity flow according to the consumption pattern 16.pat. Below is shown the spatial arrangement of the elements to scale. Calculate the network.
Download the file 33.zip that contains the background image: www.arnalich.com/dwnl/epaxen/33.zip
1. Ascertain the dimensions of the image, modify it and incorporate it as background: A 345761 8734004 B 346452 8733573
691 m x 431 m
2. Draw the network (with the way Auto-Length On!) and introduce the values of the statement. To limit the flow of a reservoir you can use a dummy flow control valve. As this type of valve cannot be connected directly to a reservoir, you will need to place a dummy node without consumption. It is very important to draw the valve in the sense of a flow, that is to say, first in the new node and then in the corner of the network.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
142
Epanet and Development. A progressive 44 exercise workbook
To insert the valve, click on the icon and then click on each extreme node as written previously. Right click on it to open its properties, and choose Valve Type FCV. In Setting, introduce 2 (l/s). 3. Calculate the network and note the error message:
In other words: at 30 hours the flow that the nodes demand is greater than the valve can let through. Ignore this error, it is useful the first time but it quickly becomes tiresome. To obtain more flow you should build a tank where the water is going to stop when the demand is smaller than the capacity of the spring, and which contributes water when the opposite occurs. A good situation is a tail tank that allows the pressures to balance at the most distant points, at the same time as it contributes a flow that circulates in different pipes to the main flow, avoiding saturation.
4. Place a tail tank at 100 m from Source 3. The elevation is a variable that you must work out. Try, for example, 15 m. As it is not practical to build tanks raised to whatever height, introduce values that are possible as if it were a real case. 5. Calculate the size of tank necessary before calculating with Epanet to avoid working with too many variables.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
Mult. Cons. Production Balance TOTAL 0.20 1296 7200 5904 5904 0.08 518 7200 6682 12586 0.02 130 0 -130 12456 0.03 194 0 -194 12262 0.06 389 0 -389 11873 0.13 842 0 -842 11030 0.34 2203 4320 2117 13147 0.90 5832 7200 1368 14515 1.68 10886 7200 -3686 10829 1.35 8748 7200 -1548 9281 0.67 4342 7200 2858 12139 0.56 3629 7200 3571 15710 1.80 11664 7200 -4464 11246 2.58 16718 7200 -9518 1728 3.59 23263 7200 -16063 -14335 2.81 18209 7200 -11009 -25344 1.24 8035 7200 -835 -26179 0.79 5119 7200 2081 -24098 0.90 5832 7200 1368 -22730 1.01 6545 7200 655 -22075 1.12 7258 7200 -58 -22133 1.01 6545 7200 655 -21478 0.79 5119 7200 2081 -19397 0.34 2203 7200 4997 -14400 24 155520 141120 -14400
Volume
41890 liters
For example, this is a cylindrical tank with 4 m in diameter and 3.4 m in height. Introduce this data in the properties dialogue of the tank. Note from the tank graph that we have achieved the appropriate size straight off:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
143
144
Epanet and Development. A progressive 44 exercise workbook
To visualize the operation of the tail tank, right click on the sketch and open the dialogue Options. In Flow Arrows, check the Open option. From this moment, the direction of the water in the pipes is shown by means of arrows. Leave the simulation to run over time and observe how the direction arrow shows an inflow in the hours of low consumption and an outflow at peak time. 6. Begin the process of optimization of the pipes until you find the smallest that maintain the ranges of pressure. In my case, all the pipes are of 50 mm, save the outlet pipe of the tail tank. If the distances were greater, we would have installed larger pipes to avoid problems of blockages. 7. Lower the tail tank to the lowest height that achieves adequate pressure in the network. In reality, an elevated tank of 11 m and of 42 m3 would be so expensive to build that we would have to look for other alternatives. The most logical perhaps would be to build it at the outlet of the spring.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
145
Exercise 34. Pressure Zones After the earthquake of January 24, the construction of a network for a displaced camp is planned that is fed from point D. The slopes of the looped zone are indicated with the arrow showing the direction of the flow of the water. Point A has the coordinate 107342 8435678 and B, 109742 8435078. Build a design knowing that each intersection has 3 Waterhorse type tapstands and that the Sphere Project establishes that the flow of each tap in an emergency is 0.125 l/s.
1. Determine the demand. The tapstand described in the statement is this:
Each point will consume: www.arnalich.com
6 taps/ramp * 3 ramps* 0.125 l/s = 2.25 l/s
Helping improve Development Aid through training and consultancy.
146
Epanet and Development. A progressive 44 exercise workbook 2. Establish the lengths of the pipes. An alternative is to calibrate the image. However, in this case that is so regular, it is probably simpler to calculate the length of the horizontal and the vertical pipes. Horizontals:
107,342 m – 109,742 m = -2400 m 2,400 m / 4 pipes = 600 m/pipe
Verticals:
8,435,678m – 8,435,078m = 600 m 600 m / 3 pipes = 200 m/pipe
3. Establish the elevation of the points. Beginning with A and moving South, apply the 2% in the following way. 200 m * 0.02 = 4 m The elevations at the beginning are:
A, 62 m A1= 62 m – 4 m = 58 m A2= 58 m – 4 m = 54 m A3= 54 m – 4 m = 50 m
Equally, 600 m * 0.023 = 13.8 m The elevations of the next column are 62 m; 62-13.8 = 48.2 m and so on. The elevations at each point are as follows: 62
48.2
34.4
20.6
6.8
58
44.2
30.4
16.6
2.8
54
40.2
26.4
12.6
-1.2
50
36.2
22.4
8.6
-5.2
4. Sketch the network and introduce the data. 5. Try to adjust the pressure of all the points between 10-30 m, in the peak time as well as in those of less consumption (introduce the demand 0 because there is no pattern to apply). When you have given up, turn the page to see what is happening. In this system it is impossible to maintain the pressures between 10 and 30 meters. The problem that you have is similar to that of going to sleep with a blanket that is too short. If it covers your feet your body is left uncovered and vice versa.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
147
The difference in elevation between the point of the highest loop, at 62 m, and the lower one, at -5.2 m is 67.2 m… a lot greater than the design interval! At the moments of less consumption, to have pressure of 0 bars at A, at B there would be 67.2 m of pressure, 37 m above the maximum design limit. To resolve this problem, the network is divided in two, one covering the high parts and the other the lows. The network for the lower part is fed through a break pressure tank.
The break pressure tank isolates the two networks. Take advantage of this to calculate the networks separately which is much simpler. Begin with the Low Network which is much easier, and place the BPT as if was in node A, that is to say in the reservoir at an elevation of 62 m. The length of the pipe will be 1,800 m, three sections of 600 m. As the network is going to be sized according to the capacity of distribution, a consumption pattern is not necessary.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
148
Epanet and Development. A progressive 44 exercise workbook
Nevertheless, avoid working with the minimum indicators in an emergency if your organization has the means for greater things. In my opinion, to use the criteria of the Project Sphere, such as a tap every 200 people with a flow of 0.125 l/s, is best way to ensure endless queues. The people, refugees or not, and above all in an emergency, have better things to do than to wait hours and hours in a queue. They will be worried about the fate of their family and friends, they will want to rescue what remains of their homes, to seek fuel, food…
6. Draw the diagram and introduce the data to the plan of the low network. The best thing is probably to save the file that you have to return to later, and then save it again as Low Network and eliminate the objects that you don’t need.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
149
With the BPT at 62 m of elevation there continues to be too much pressure. If in this sub network, the minimum elevation is -5.2m and the maximum is 20.6 m, the interval of pressures when the demand is 0 is 25.8 m. To avoid breaking up the network into too many pressure zones, increase this amount by slightly more than 10 meters, which will give a pressure of slightly more than 35.8 m when the network in not in use. This pressure is only somewhat greater that the maximum limit of the network. As there is a point with an elevation of 34.4 m the BPT would be placed in the outlet of this point like this:
7. In Epanet, the only thing that you have to do is to change the elevation of the BPT to 36 m and the length of the pipe to 600 m. Note that we only increased it by 10 m. The reason for this is that the water will circulate downhill in the proposed network and it does not need extra pressure from the BPT. 8. Re-introduce the demand in all the nodes and optimize this network. Change diameters, eliminate pipes, add them, or any action that you consider useful. A possible result is shown below.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
150
Epanet and Development. A progressive 44 exercise workbook 9. Open the original file and this time eliminate the lower part. The pipe that descends from Lake D has to supply both networks. To keep in mind the effects, in terms of the consumption of the lower network on the high one, a node is placed that groups all of its consumption: 8 nodes * 2.25 l/s*node = 18 l/s.
Note that the elevation of the lake is excessive and that it is also necessary to place a BPT in this line of descent. 10. Decide the elevation of the BPT and optimize the network (consider that the slope from the lake to A is homogeneous in order to calculate the length of pipe BPT-A). You will need similar compromises to that of the other BPT. I have thought to place it at 72 m, which gives me a pipe length of: 954 m -------------- (94-62) m X -------------- (72-62) m
X = 298.125 ≈ 298 m of pipe
11. Calculate and optimize the network keeping in mind that the point that represents the low network cannot have less than 10 m of pressure. With this pressure the supply to the low network is guaranteed. Greater pressures would imply a cost of unnecessary energy. This solution, for example, would not be valid because it would leave the Low Network without water.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
151
To allow future expansions southwards, it has been decided not to install pipes of less than 100 mm in the ring and one solution would be this:
12. Calculate the pipe that descends from the Lake to the first BPT. Its length is 656 m. See what is the lowest diameter that pipe BPT-A can be, now that it is higher:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
152
Epanet and Development. A progressive 44 exercise workbook
Exercise 35. Adding a pump Four public fountains with an average consumption of 0.5 l/s are to be supplied by pumping from a river at 0 m. The fountains are situated in the corners of a block of 100x100 m, all at 20 m of elevation. There is no data on the variability in the time of the consumption. The distance from the river to the first fountain is 600 m. Calculate the network and determine what pump would be needed.
You can have a look at the section “Modeling a pump station” in Chapter 3 of the theory book. 1. Draw the diagram. You have probably ended up with something like this:
The first thing to notice is the sense in which the pump is drawn. One of the most frequent errors is to draw the pump the wrong way round and to be asking continually why the network doesn’t work. When you draw objects other than pipes in Epanet, always draw them in the direction in which the water is going to circulate. In the case of a pump, imagine it as if it was a canon. If "you shoot" in the right direction then it is correctly positioned.
2. Introduce the data. There is no data on the variability of the consumption. To determine the peak consumption you can multiply the average consumption by a number between 3.5 and 4.5. The global coefficient of water supply systems is usually around these figures. Thus, the consumption is transformed into: 0.5 l/s * 3.5 = 1.75 l/s at each node © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
153
It is a good idea when placing pumps to respect the chronology that is proposed below. Otherwise, you will find yourself wrapped up in a repetitive process that will consume all your energy.
3. Eliminate the pump. The first step is to work and balance the network; then to place the pump. The source of water is going to be the reservoir by gravity. 4. Change the elevation of the reservoir to the highest point of the network, increasing by 10 m more than the maximum pressure limit: Tentative elevation of the reservoir = 20 m + 30 m + 10 m = 60 m
5. Join the reservoir with the network and begin to optimize it. The main objective is to lower the elevation of the reservoir as much as possible. The higher the reservoir, the more energy will be needed. The lower it is, the less pumping expense and the greater the installation costs since the pipes will have to be of a greater diameter. In the next chapter we will see how to determine the costs of each of the alternatives. For the time being use your best judgement. One way to get an idea is by using the friction analysis or unit loss.
You can read the section “Calculation Criterion” in Chapter 6 of the theory book to understand the concept of hydraulic gradient. Unit loss, head loss and hydraulic gradient are synonymous. 6. Work the model until you have low values of unit loss. For the pump pipe, achieve values smaller than 5 m/km and for the others, below 10 m/km. www.arnalich.com
Helping improve Development Aid through training and consultancy.
154
Epanet and Development. A progressive 44 exercise workbook
7. Once you have ensured that the pipes have acceptable frictions you have determined the diameters of the pipes to use. Notice that the pressure is too high. This is the opportunity to achieve the fundamental objective of lowering the elevation of the reservoir (the height that the future pump must overcome). Find out if the elevation is adequate.
Notice that the pipe frictions haven’t changed. You now know the parameters of the pump that you should install. The flow is: 1.75 l/s*node * 4 nodes = 7 l/s * 3,600 s/1h * 1 m3/1,000 l = 25.2 m3/h The head or height of the pump is: Fictitious elevation of reservoir – Real elevation of source = 40 m – 0 m = 40 m 8. Draw the pump. To do this, place a node in the neighborhood of the reservoir, in my network it is node 6.
Right click on the reservoir pipe and in properties in End Node or Start Node, according to the order in which you have drawn the network, change from Reservoir to the new node that you have drawn.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
155
The pipe will change and will be situated between the new node and the start of the loop . The new node allows you to enter the real length of pipe as the pump, although drawn with pipe, doesn’t allow to enter diameters, lengths, etc. Draw the pump between the reservoir and the new node. Don’t forget to change the reservoir elevation to 0 again!
9. Define a curve for the pump, >Browser / Data /Curve Editor /New. Introduce the data indicated with the arrows in the image below and a name if you want something different from "1". The rest of the information is entered by Epanet automatically:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
156
Epanet and Development. A progressive 44 exercise workbook 10. Introduce the name of the curve in the property "Pump Curve" of the pump and calculate the network. Note that the pressures of the fictitious gravitational network and the real pumped one are exactly the same.
And the question remains… why bother including pumps!? Some networks with several interacting pumps and consumption patterns are easier to calculate and analyze using pumps. For the others, avoid them completely because they do not always behave with the same consideration as in this exercise nor are they always so docile.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
157
Exercise 36. Modeling a borehole The laboratory analysis of the river used in the emergency system from Exercise 13 have shown a high content of coliform bacteria. To avoid endangering the health of the population because to chlorination error, it has been decided to reinstate an old borehole at 30 m away from the intake (8 m of elevation). The preliminary trials have shown that the dynamic level is 37 m and that the capacity of the borehole is 5 l/s. In a hill near the second tap a tank of cement of 6x6x2 m has been found at an elevation of 33 m. The tank is in a bad state but is recoverable. Redesign the network including a pump. Is it worthwhile to restore the tank? (Other data: 10,000 people with consumption pattern 16.pat)
1. Open the index 13.net, load the background and locate the tank. Epanet accepts diameters and heights to determine the parameters of a tank. Since the tank is rectangular and not cylindrical, you should find the cylinder that has the same area as that of the real rectangular prism.
A tank of 6 m x 6 m has a surface of 36 m2. You now have to find the diameter of a circle with an area of 36 m2. The equation for this is: A*B= π (D/2)2 = 36 m2
the equivalent diameter to use is 6.77 m.
S = π (D/2)2 = 3.14 * (6.77/2)2 = 36 m2.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
158
Epanet and Development. A progressive 44 exercise workbook
The generic equation, being A and B, width and length is:
D=2
A* B
π
2. Draw the tank, introduce this data and download the background. With AutoLength activated, join the tank to the network.
In this system one must work with a consumption pattern to ascertain if the capacity of the borehole is sufficient and how the existing tank would function as a balancing tank. 3. Decide how many liters per person are going to be distributed. One way to do this is to calculate how much water would be produced in x operation hours of the existing borehole and to divide it among the existing population. In an emergency it is usually necessary to stretch the systems to work to their maximum, say working 22 hours and leaving 2 for maintenance operations. 5 l/s * 3,600 s/h * 22 hours / 10,000 people = 39.6 l/person 4. Calculate average flow and allocate the demand among the nodes: 39.6 l/person * 10,000 people / 24 hours*3,600s/h = 4.58 l/s 4.58 l/s / 5 nodes = 0.92 l/s 5. Load pattern 15.net and have the nodes abide by it. 6. At this point you can see if it is worthwhile to restore the tank, calculating by hand the size that would be necessary. Alternatively, you can see the evolution of the flow in Epanet. The size of the available tank is 6x6x2= 72 m3
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
159
Mult. Cons. Production Balance TOTAL 0.20 3300 18000 14700 14700 0.08 1320 18000 16680 31380 0.02 330 0 -330 31050 0.03 495 0 -495 30555 0.06 990 18000 17010 47565 0.13 2145 18000 15855 63420 0.34 5610 18000 12390 75810 0.90 14850 18000 3150 78960 1.68 27720 18000 -9720 69240 1.35 22275 18000 -4275 64965 0.67 11055 18000 6945 71910 0.56 9240 18000 8760 80670 1.80 29700 18000 -11700 68970 2.58 42570 18000 -24570 44400 3.59 59235 18000 -41235 3165 2.81 46365 18000 -28365 -25200 1.24 20460 18000 -2460 -27660 0.79 13035 18000 4965 -22695 0.90 14850 18000 3150 -19545 1.01 16665 18000 1335 -18210 1.12 18480 18000 -480 -18690 1.01 16665 18000 1335 -17355 0.79 13035 18000 4965 -12390 0.34 5610 18000 12390 0 24 396000 396000 0
Volume
108 m3
However, the necessary size would be greater, 108 m3. 7. Try to see what quantity of water could be distributed per person if the tank is used whilst avoiding negative pressures. In reality, people are going to consume the amount of water that is available. Nevertheless, this type of calculation is useful because the water network will teach people to consume according to a flatter pattern. Some users will avoid peak consumption times when there are more queues and less pressure.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
160
Epanet and Development. A progressive 44 exercise workbook
0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
Mult. Cons. Production Balance TOTAL 0.20 2708 18000 15292 15292 0.08 1083 18000 16917 32208 0.02 271 0 -271 31938 0.03 406 0 -406 31531 0.06 813 18000 17188 48719 0.13 1760 18000 16240 64958 0.34 4604 18000 13396 78354 0.90 12188 18000 5813 84167 1.68 22750 18000 -4750 79417 1.35 18281 18000 -281 79135 0.67 9073 18000 8927 88063 0.56 7583 18000 10417 98479 1.80 24375 18000 -6375 92104 2.58 34938 18000 -16938 75167 3.59 48615 18000 -30615 44552 2.81 38052 18000 -20052 24500 1.24 16792 18000 1208 25708 0.79 10698 18000 7302 33010 0.90 12188 18000 5813 38823 1.01 13677 18000 4323 43146 1.12 15167 18000 2833 45979 1.01 13677 18000 4323 50302 0.79 10698 18000 7302 57604 0.34 4604 18000 13396 71000 24 325000 396000 71000
Volume
73 m3
At 32.5 liters per person per day, the size of the tank is approximately that which is necessary. Although this exercise lends itself to multiple verifications and tests of different solutions, to keep it manageable as a book of exercises, continue calculating the network with this new consumption figure. 32.5 l/person * 10.000 people / 24 hours * 3,600s/h = 3.76 l/s 3.76 l/s / 5 nodes = 0.75 l/s 8. Incorporate the new data in the model. Change the calculation method to an extended period of 72 h with a report start time of 14:00.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
161
9. Initiate the process of simulation of the pump by means of a reservoir. Add 30 m to the pipe of the original reservoir and change the elevation of the reservoir to the height of the highest point of the network increasing by 10 m the maximum limit of pressure: Tentative elevation of reservoir = 25 m + 30 m + 10 m = 65 m
10. The network is completely unbalanced. The pressures are excessive; the friction of some pipes is too low, while that of others reaches values of 40 m/km. Work the network and decrease the elevation of the reservoir. A possible solution is shown below:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
162
Epanet and Development. A progressive 44 exercise workbook
Link ID Pipe 5 Pipe 6 Pipe 7 Pipe 8 Pipe 9 Pipe 1
mm 150 150 125 100 75 100
m/s 0.35 0.2 0.66 0.69 0.61 0.93
m/km 0.94 0.32 3.77 5.28 5.94 12.39
11. Calculate the real elevation of the reservoir and the height of the pump: Real elevation = Topogr. elevation – Dynamic level = 8 m – 37 m = -29 m Pump height = Fictitious elevation - Real elevation = 42 m – (-29 m) = 71 m
12. Draw the network with the pump from the auxiliary node (aux) and change the elevation of the reservoir:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
163
13. Create a curve for the pump with 71 m of head and 5 l/s (>Browser /Data /Curves /New). Introduce the name of this curve in the parameter Curve of the pump. 14. Calculate the network. Normally the simulation is valid. If this message comes up, the pump is operating outside of range, providing more flow than specified:
Rebalance the network without the pump. If the network requires the pump to work above its head or height, Epanet will stop it and will notify you:
You have to rebalance the network yet again. 15. According to the calculation measured in point 6, the pump functions from 6:00 AM to 00:20, a total of 20.33 hours. To specify this you should do an operation pattern similar to the consumption pattern, where 1 signifies ON and 0 OFF (>Browser /Data /Pattern /New).
16. Specify this pattern in Pattern in the Pump’s properties dialog:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
164
Epanet and Development. A progressive 44 exercise workbook 17. Enter the Report Start Time as 0:00 and calculate the network.
If at these heights you thought that pumps were not so complicated, check what sort of message you get if you set the reservoir elevation at -150 m and change a node demand for 10 l/s. However, it is not the amount but the creativity of the errors of pumps that is so intimidating. A great number of these messages are repetitive. 18. By entering an initial quantity in the tank, the messages type "Node 2 is not connected" will disappear. If the pump does not work and there is no water in the tank, the water is not circulating in the network, "it is not connected". For example, you can suppose that it is full; given its Initial Level is 2. This will cause a large number of the original errors to disappear, leaving only a height error. 19. In the behavior curve of the pump enter an excessive height, for example, 200. You will see that the error in your network persists and is not a question of height. Remember this technique of exaggeration. It is particularly useful in creative errors in which the cause of the problem and the error message that Epanet produces are completely independent. It will avoid you losing a lot of time in small progressive adjustments to no aim. Notice that the problem happens at 23:00 hours (corresponding to 0:00, since Epanet begins at 1:00), that is to say, almost at the end of the day. If you change the multiplier 0.33 to 1, you will have no more errors. Entering multipliers of 1 or 0 will avoid many problems. The problems of pumps are many and varied. They are not particularly difficult to solve but they can consume a lot of time and be somewhat exasperating. Remember that the main way to avoid them is to ask if it really contributes something to have the pump in the model. In a development context, the majority of the times the answer is NO.
Save the file as 36.net. © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
165
Exercise 37. Skeletonization A water network is to be installed in the service area where each building permanently consumes 0.1 l/s. There is aerial photography of the area which measures 928 m x 1,425 m. The area is completely flat and is fed by a booster pump set to a minimum pressure of 2 bars located where the roadways merge. Construct and balance the network. Up to what point can it be skeletonized? The pump to which the statement refers has a ball inflated to 2 bars. When the pressure falls below 2 bars, it starts automatically.
Download the file 37.zip to obtain the aerial image: www.arnalich.com/dwnl/epaxen/37.zip
1. Once you have configured Epanet, load the background image and enter its dimensions. Remember to change the format of the image to BMP. You may also have to lighten the background to be able to see your sketch more clearly. 2. Draw the network. You can substitute the pump for a reservoir with a 20 m elevation. The rest of the nodes will have a 0 m elevation. The result is shown on the following page. 3. Introduce the demand for the nodes.
You will have already realized that the most laborious part is doing the model of this very simple network, even if all the elevations are equal, all the consumptions are equal and with Epanet introducing the lengths.
4. To keep the exercise manageable, change the diameter of all the pipes to 75 mm and calculate the network.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
166
Epanet and Development. A progressive 44 exercise workbook
Save the exercise as 37complete.net.
5. Begin the skeletonization process, eliminating the simple branches. The consumption of the branch node passes to the general pipe node to which it was added. Note that the pressure of this node before and after the change remains the same; both models are equal, but the second is now somewhat simpler.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 6. Scenarios
167
6. Before finishing the skeletonizing of all the simple branches, note that there are branches somewhat more complicated than necessary that can also be summarized in one node. By doing this you will avoid work skeletonizing simple branches from which will divide other more complex branches that go on to be skeletonized later. Branch A is summarized as point a, with a consumption of 3*0.1 l/s = 0.3 l/s. Branch B as point b with a consumption of 2*0.1 l/s = 0.2 l/s.
Another way to skeletonize is to eliminate various consecutive nodes, providing that none of them are great consumers. All the nodes in line C convert to a unique node, c, that inherits the total consumption.
Note that the process of skeletonization in itself consumes a lot of time changing demand bases, redrawing pipes, etc. Therefore, in the majority of cases, unless there are obvious doubts, it is better to draw the network already skeletonized. You have already seen two evident cases, small pipelines connected to houses and small branch lines. There is not a lot that can be systematized in the process of skeletonization. Up to now you have seen the process that will save you a lot of work without running great risks. From there, you can experiment, checking the results between the changed model and the original one to see up to what point it can be simplified. However, it will be rare that you skeletonize beyond what you have seen here. The main reason being that, to do a quality analysis, you need the complete model and it is rare for development projects to have a complexity that justifies maintaining two models. www.arnalich.com
Helping improve Development Aid through training and consultancy.
168
Epanet and Development. A progressive 44 exercise workbook
Do not use models more skeletonized than you have seen here to evaluate parameters of water quality! The skeletonized model has less pipe length and unidirectional circulation, and this changes the results to a great extent.
You can continue with this exercise, remembering to continue saving each different stage if you want to compare them.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
7 Economics Economic issues Exercise 38. The investment bill Exercise 39. Pumping costs Exercise 40. Comparing alternatives Exercise 41. Volatile countries Exercise 42. Economic diameter Exercise 43. Economic diameter II Exercise 44. Using Epanet
Money is like manure. You have to spread it around or it smells. (Oscar Wilde)
170
Epanet and Development. A progressive 44 exercise workbook
Economic issues The hydraulic aspects are important so that the service can exist. The economic aspects are determinants and also the difference between a network being another jumble of humane scrap or a key service that empowers the economic and social development of a community.
To gain a better and more complete perspective of the economic aspects read Chapter 7 of the theory book.
Costs All activities have two types of cost. The investment cost is the cost of purchasing the equipment or the network installations. The running cost is the total of the day to day costs. To the extent that the investment cost increases, for example, by enlarging the diameter of a pipe, the operating costs decrease e.g. pump consumption. The most economic solution is that which minimizes the sum of both costs, the lowest point of the Total expenditure curve.
Cost comparison So that the costs are comparable they should be examined at the same point in time, normally at the beginning of the project. The operating cost is easy to determine, except for random costs like damages. Normally they are negligible compared to the
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
171
main costs: pump and water processing. For the investment cost, you must keep in mind both inflation effects and depreciation of money over time. Also bear in mind the amortization during the useful life (design period). Use these formulas successively:
r=
1+ i −1 1+ s
at =
r, real interest rate s, inflation r, bank interest
(1 + r ) T * r (1 + r ) T − 1
F = M * at
at, amortization factor F, annual cost of investment M, inverted total
In a development context, operating costs are assigned a greater importance when the investment costs are taken on by donor. If you are faced with a donor imposed limit, decrease the size of the intervention and make it more modest, but resist the temptation to increase the operation costs. Pumps frequently operate by generator. An average approximately 0.3 liters of diesel per kWh produced.
generator
consumes
Ability to pay Whether a project ends up being abandoned or not, depends on the perception of the system’s users. A system that requires more resources than the users want to invest will be abandoned. It is very important that the operating costs and the investment payback be below what the users are willing to spend. Find out what this is and consider it your main design criterion, over and above pressure, hydraulic gradient lines and all others. Be humble. The decision regarding the amount is not yours; it is a decision of the users.
Cost Ranking The projects which you have worked on have a cost distribution as follows: 1º. Pipes and accessories 2º. Excavations 3º. Sand bed 4º. Valve boxes 5º. Pipe installation www.arnalich.com
36 % 31 % 16 % 11 % 5%
Helping improve Development Aid through training and consultancy.
172
Epanet and Development. A progressive 44 exercise workbook
The conclusion is interesting: Two thirds of the costs are independent of the pipe diameter!
You can read the paragraph “Dry Diametritis” in Chapter 7 of the theory book to see how to benefit from this situation and avoid the most common problems of excessive economic zeal.
Common wasteful mistakes Before approving a design, ensure that it does not fall into one of these categories: •
Gigantism. The placement of pipes much larger than are really necessary, impairing the quality and increasing the investment and maintenance costs.
•
Redundancy. The placement of pipes that do not contribute to the transport capacity in places where they are not needed for the geography.
•
Strangulation of the sources. This is the case in a network where the pipes are too small at the outlet from a tank, reservoir or pump.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
173
Exercise 38. The investment bill The design period of the network in Ceel Dherre is 25 years with a total budget of 100,000 €. The local inflation rate is 3% and the Banks lend Money at 4%. What is the annual investment cost? 1. Calculate the real interest rate. The interest, i=0.04 and inflation, s=0.03, then:
r=
1+ i 1 + 0.04 − 1= − 1 = 0.00097 1+ s 1 + 0.03
2. Calculate the amortization factor:
at =
(1 + r ) T * r (1 + 0.0097) 25 * 0.0097 = (1 + r ) T − 1 (1 + 0.0097) 25 − 1
= 0.04524
3. Calculate the annual cost: F = 100,000 € * 0.04524 years-1 = 4,524 € Notice that it is different from 100,000 €/ 25 years =4,000 €/ year. This is due to the corrected value of the investment, called present value, being F * 25 years = 113,109 € and not simply 100,000.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
174
Epanet and Development. A progressive 44 exercise workbook
Exercise 39. Pumping costs A pump station fills a tank which supplies the city. The pump supplies the tank at a rate of 7 l/s and uses 10 kW per hour according to the manufacturer. The population that it supplies is 1,200 people and it has been established that each inhabitant receives 50 liters daily. The price of a kW is 0.155 € and doesn’t vary during the day. What is the cost of the pump? If the electricity was provided by generator and the cost of diesel was 1 €/l, what would be the new cost?
1. Establish the cost per m3 of water. In an hour, the station will pump: 7 l/s * 3,600 s /h * 1 m3/1,000 l = 25.2 m3/h. The cost per hour of the pump will be: 10 kW * 0.155 € = 1.55 €/h And the cost per m3: 1.55 €/h / 25.2 m3 /h = 0.0615 €/m3 2. Determine the annual cost: 365 d/y * 1,200 inhab * 50 l/inhab*d * 1 m3/1000 l = 21,900 m3/y 21,900 m3/y * 0.0615 €/m3 = 1,347 €/y 3. If the electricity is provided by generator the operating cost will be: 10 kW/h * 0.3 l/kWh * 1 €/ liter = 3 € / h 3 €/h / 25.2 m3 /h = 0.12 €/m3 21,900 m3/y * 0.12 €/m3 = 2,628 €/y.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
175
Exercise 40. Comparing alternatives Sharhjaj is situated 12 km from the river Singag in India, where the Banks lend Money at 2%. There are two alternative proposals: a. A gravity-fed water supply project from the river with a total estimate of 120,000 €. The outlet filters the river water and it has been established that the necessary dosage of chlorine is 1.7 ppm. The price of chlorine HTH at 70% is 7 €/kg. b. The construction of a project based on a borehole with a total cost of 59,000 €. The manufacturers curve (Grundfos) and the pump conditions are shown below. The electricity comes from the town’s network and is charged at 0.2 €/kWh. Which alternative is most cost effective?
1. Find out the data on inflation for India. You can use the World Bank site: http://go.worldbank.org/WLW1HK71Q0 2. Calculate the investment cost of alternative A.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
176
Epanet and Development. A progressive 44 exercise workbook Although there is a tendency to an increase in the last year, it can be said that inflation varies in the region of 4%. The annual cost is: Bank Interest i
0.02
Inflation s
0.04
Period (years)
30
Investment M
120000
Rate of real interest r
-0.0192
Amortization factor at
0.02432472
Annual Cost A
2919
Take a second to observe how the annual bill varies with changing interest rates or inflation. If the interest is greater than inflation, the annual cost grows: Bank Interest i Inflation s Period (years) Investment M Rate of real interest r Amortization factor at
0.02 00 25 100000 0.05 0.070952
Annual Cost
7095
If the interest is less than inflation, the annual cost decreases: Bank Interest i Inflation s Period (years) Investment M Rate of real interest r Amortization factor at
0.02 00 25 100000 0.05 0.070952
Annual Cost
7095
The conclusion is interesting: © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
177
In countries with high inflation investment should be favored. In countries with low inflation the balance shifts towards operating costs. 3. Work out the investment cost of alternative B. Bank interest i
0.02
Inflation s
0.04
Period (years)
30
Investment M
59000
Rate of real interest r
-0.0192
Amortization factor at
0.02432472
Annual Cost B
1435
4. Work out the operating cost of alternative A. 1.7 ppm is the same as 1.7 mg/l. Keeping in mind that the chlorine is at 70%, the quantity that is needed is: 50,000 m3/y * 1.7 mg/l * 1,000 l/m3 * 1kg/1,000,000 mg / 0.7 = 121.43 kg/y 121.43 kg/y* 7 €/kg = 850 €/y 5. Work out the operating cost of alternative B. The data from the manufacturer’s diagram are 38.4 m3/h and 5.96 kWh. The number of operating hours and the cost in kWh are: 50,000 m3/y / 38.4 m3/h = 1,302 h/y 1,302 h/y * 5.96 kW = 7,760 kWh/y 7,760 kWh/y * 0.2 €/kWh = 1,552 €/y 6. Compare the costs:
Option
Gravity
Borehole
Investment
2919
1435
Operating
850
1552
TOTAL
3769
2987
Without other criteria, the borehole alternative is more desirable. www.arnalich.com
Helping improve Development Aid through training and consultancy.
178
Epanet and Development. A progressive 44 exercise workbook
Exercise 41. Volatile Countries Doomborale is located 6 km from the river Shabelle in Ethiopia where the Banks lend Money at 4%. Again, there are two alternative proposals: a. The rehabilitation of the channels to the outskirts of the settlement with a total estimate of 45,000 €. b. The construction of a route from the river to an existing natural depression. The consumption of the pump is estimated at 4,600 € per annum and the investment at 12,000 €. Which alternative is most cost effective?
1. Find out the data for inflation in Ethiopia. According to the World Bank, the change in inflation in recent years is as follows:
Forget the calculator, there is not much to calculate here…
In those countries with variable inflation, prioritize the initial investment over any operating cost. On one hand, the money will quickly lose value. On the other hand, there is a risk that the price of the products, notably the fuel, will rise far above what the users can afford. The system will stop functioning just when the users are most vulnerable. The channels should be renovated.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
179
Exercise 42. Economic Diameters Calculate the economic diameter of a pumping main of 2,600 m for a flow of 10 l/s and 4,000 hours annually of work, if inflation is 2%, the interest is 5%, the wire to water efficiency is 60%, the price per kWh is 0.08 € and the cost of HDPE is: DN 32 40 50 63 75 90
Cost €/m 0.629 0.918 1.445 2.242 3.242 4.518
DN 110 125 160 200 225
Cost €/m 6.757 9.213 14.518 22.400 28.108
It is a matter of finding the cheapest solution as in the preceding period. To simplify, we ignore the price of the pump for the time being. We will look at it in the next exercise. 1. Using the Mougnie formula of optimum velocities you can ascertain a band of diameters. Use the formula on the right, modified for flows and assuming a maximum velocity V max = 1 m/s.
Vmax = 1.5 D + 0.05 Qmax = 0.1πD Vmax 4
0.01 m3/s = 0.1 π D * 1m/s / 4
D= 0.127m
We can carry out the calculations for pipes of 100 mm, of 125 mm and of 150 mm. 2. Presuppose the investment in pipes: 100 mm: 125 mm: 150 mm:
2,600 m * 6.757 = 17,568 € 2,600 m * 9.213 = 23,954 € 2,600 m * 14.518 = 37,747 €
3. Calculate the annual cost of the investment:
www.arnalich.com
Helping improve Development Aid through training and consultancy.
180
Epanet and Development. A progressive 44 exercise workbook
Bank interest i
0.05
Bank interest i
0.05
Inflation s
0.02
Inflation s
0.02
Period (years) Investment M
30
Period (years)
30
17568
Investment M
23954 0.0294
0.0294
Rate of real interest r
Amortization factor at
0.05063209
Amortization factor at
0.05063209
Yearly bill 100mm
890
Yearly bill 125mm
1213
Rate of real interest r
Bank interest i
0.05
Inflation s
0.02
Period (years)
30
Investment M
37747
Rate of real interest r
0.0294
Amortization factor at
0.05063209
Yearly bill 150mm
1911
4. Calculate with Epanet the pressure loss in the 3 scenarios. To do this, set up this system:
5. Calculate the network, ignore the messages about negative pressure and note the pressure value in the node:
The pressure loss by friction is 43.19 m in the case of a 100 mm pipe. 6. Change the diameter of the pipe progressively and make a note of the values:
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
181
7. Calculate the energy cost of each alternative. Assume that the performance of the pump is very similar for the different pumping heights. If you want to be very precise you will have to select a pump for each scenario and use its particular efficiency. The energy consumed for each different meter of height is: E consumed = mgh / µ
m, mass ; g = 9.81 m/s2; h, height and µ, efficiency
E= 4,000 h/y * 10 l/s * 3,600 s/h * 1m / 0.6 =2,354,400,000 j 2,354,400,000 j * 1 kWh/3,600,000 j = 654 kWh/m 100 mm: 125 mm: 150 mm:
43.19 m * 654 kWh/m * 0.08 €/kWh = 2,260 € 14.57 m * 654 kWh/m * 0.08 €/kWh = 762 € 5.99 m * 654 kWh/m * 0.08 €/kWh = 314 €
8. Work out which option has the lowest total cost: Option
Investment
Operating
TOTAL
100 mm
890
2260
3149
125 mm
1213
762
1975
150 mm
1911
314
2225
The diameter to install is125 mm.
www.arnalich.com
Helping improve Development Aid through training and consultancy.
182
Epanet and Development. A progressive 44 exercise workbook
Exercise 43. Economic Diameters II In the previous exercise it was estimated that the pumps last approximately 5 years. The pump necessary for the option with 100mm costs 9,800 €, with the 125mm option it costs 6,300 € and with the 150mm option, 5.800 €. Which is the most economic option? 1. Calculate the investment cost of each pump: Bank interest i
0.05
Bank interest i
0.05
Inflation s
0.02
Inflation s
0.02
Period (years)
30
Period (years)
30
Investment M
9800
Investment M
6300
Rate of real interest r
0.0294
Rate of real interest r
0.0294
Amortization factor at Yearly bill 100mm
0.0506321
Amortization factor at Yearly bill 125mm
0.05063209
Bank interest i
0.05
Inflation s
0.02
Period (years)
30
Investment M
5800
Rate of real interest r
0.0294
Amortization factor at Yearly bill150mm
0.05063209
496
319
294
2. Add the annual cost to each one of the alternatives in the operating cost. Option 100 mm
Investment Operating 496 4396
TOTAL 4892
125 mm
319
2136
2455
150 mm 294
1578
1871
The most economic option is 125 mm without great advantages over the 150 mm. In this case it is probably more advantageous to install the larger pipe to be prepared for future installations. Note that we have not included excavation costs, installation, etc.! Even though there are formulas to work out the economic diameter, like that of Mendiluce, I believe that they are more complicated to use. © Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
CHAPTER 7. Economics
183
Exercise 44. Using Epanet In the area from Exercise 36.net, the electricity costs 0.05 € from 0:00-6:00, 0.15 € from 6:00-18:00, and 0.12 € from 18:00-0:00. The pump has a 60% efficiency. What is the annual cost per pump? 1. Open file 36.net and calculate it. 2. Calculate the multipliers that will determine the variation in electrical costs: 0:00-6:00 6:00-18.00 18:00-0:00
1 0.15 €/h / 0.05 €/h = 3 0.12 €/h / 0.05 €/h = 2.4
3. Create a pattern for the price in the same way that you created the consumption patterns :
4. Do >Browser /Options Configure the box like this:
www.arnalich.com
/Energy.
Helping improve Development Aid through training and consultancy.
184
Epanet and Development. A progressive 44 exercise workbook 5. To get the report, calculate the network and follow >Report /Energy:
The annual cost will be 13.43 €/d * 365 d/y = 4,902 €/y.
Calculate the consumption in the way that is most comfortable for you. However, if you use Epanet, enter the exact data of the pump to avoid the approximations that Epanet uses when there is no precise data. Introduce pump curves at 3 points at least using the manufacturer’s data.
© Santiago Arnalich
Arnalich. Water and habitat
www.arnalich.com
In way of farewell The end of the book has arrived; yet you will still have some questions. Many of them are only resolved with experience. Just like the network models, this book was intended to find the balance between covering everything that is really important with a certain depth and not overwhelming or intimidating with an endless volume of data and situations. I hope I have achieved this. If you believe that the book can be improved in some way or you notice something missing, don’t hesitate to write to me:
[email protected]
And remember, there is life out there… The computer screen should not stop you from meeting the users!
About the Author
Santiago Arnalich At 26 years old, he began as the coordinator of the Kabul Project CAWWS Water Supply, providing water to 565,000 people, one of the biggest projects at the time. Since then, he has designed improvements for more than a million people, including refugee camps in Tanzania, the city of Meulaboh following the Tsunami, and the poor neighborhoods of Santa Cruz, Bolivia. Arnalich Water and Habitat is an organization that helps improve the impact of humanitarian actors through training and consultancy in the fields of Water Supply and Environmental Engineering.
Bibliography 1. Arnalich, S. (2007). Epanet and Development. How to calculate water networks by computer. Arnalich water and habitat www.arnalich.com/en/books.html 2. Cabrera E. y otros (2005). Análisis, Diseño, Operación y Gestión de Redes de Agua con EPANET. Editorial Instituto Tecnológico del Agua. 3. Expert Committee (1999). Manual on Water Supply and Treatment. Government of India. 4. Fuertes, V. S.y otros (2002). Modelación y Diseño de Redes de Abastecimiento de Agua. Servicio de Publicación de la Universidad Politécnica de Valencia. 5. Mays L. W. (1999). Water Distribution Systems Handbook. McGraw-Hill Press. 6. Santosh Kumar Garg (2003). Water Supply Engineering. 14º ed. Khanna Publishers. 7. Rossman, L. (2000). Epanet 2 User’s Manual. Environmental Protection Agency. Cincinnati, USA. 8. Walski, T. M. y otros (2003). Advanced water distribution modeling and management. Haestad Press, USA. Haestad methods. 9. Walski, T. M. y otros (2004). Computer Applications in Hydraulic Engineering. Haestad Press, USA. Haestad methods.
Version 1.0
