Monroe L. Weber-Shirk S chool of Civil and Environmental Engineering AguaRed

Algorithms  Distribution System  Simulation  Design  Transmission Line  Simulation  Design

Distribution System: Central vs Distributed Storage  If storage is centralized, then distribution system must be sized to handle fluctuating demand  If storage is distributed, then distribution system can be sized to meet average demand

Distribution System Simulation: Centralized storage  Design such that tap flow rates meet a specified minimum flow rate that is much larger than the average flow rate  Model taps as emitters turned on and off randomly  Requires many simulation trials to characterize the system performance  Display flow rate performance of each node using color mapping

Simulation algorithm  Each tap has a specified total demand for a day  The probability of being open is a function of time in the day  The length of time that the tap needs to be open is unknown at the beginning of the analysis  Open time could be calculated based on average flow rates from repeated runs. After each run the open time would be adjusted to get closer to the total demand.

One run for centralized storage  For each tap the probability that it is open is a function of  Time of day (time peak factor)  Mean value of 1  Property of community water usage pattern  emitter flow/(average demand times time peak factor)  Value greater than 1  Property of each tap  Order 20!  Probability of open= 1/pf emitter This is made up data

More detailed steps…  Assigning emitter values  Maximum emitter value – K =1 and D is pipe diameter  The program should check and warn (or prevent entry) if the emitter values are greater than the theoretical maximum  These will be assigned by the software eventually  Determining how many emitters to open  Setting the time step  We must have check valves at all emitters to prevent reverse flow

Determining how many emitters to open  Plot system response curve with total system flow rate as a function of emitter value  100% is all emitters open  10% is all emitters set to 10% of their set value  User selects design peak factor  Determine fraction open  Set all emitter values to original values

Measure the emitter peak factor  Open all emitters x% and measure their flow rates  Divide the emitter flow rates by x% to get their flow rates if they were fully open  Calculate the 100% emitter flow rate divided by the design flow rate (per capita demand times people per household times ) =  The probability that an emitter is open is equal to This factor is a function of time of day!

Random emitters  Are time steps independent or does an emitter’s chance of being on increase if it wasn’t on recently?  How do we guarantee that all emitters get tested?  Run enough tests so that all emitters were turned on at least 10 times

Display of results  Display designated parameter for each emitter using color ramp  Potential parameters  Minimum flow rate  Average flow rate  Fraction of times that flow was zero  Total volume delivered during 1 hour period?

Setting the time step  Could be based on the need to have every emitter tested many times

Distribution System Simulation: Distributed storage  Each household has a storage reservoir that is approximately equal to their daily demand (perhaps 0.25x to 2x)  Float valve controlled  Distribution system only needs to provide average demand (perhaps modified by a peak factor of approximately 2 to provide a margin of safety for potential for system expansion)  Taps could be modeled as a set demand  Taps could be modeled precisely as small storage tanks with float valve and faucets as emitter

Design  What flow must each pipe be designed to handle (centralized storage)?  The design question reduces to determining where the pipe size changes

Distribution system design algorithm  Install pressure breaks  Measure design flows in all pipes (necessary for loops) using EPANET  Find critical taps (smallest values of hf/L)  Assign hf/L to each pipe based on  L = shortest path between distribution tank (or pressure break) and most critical downstream tap  h f = difference between static head and minimum head at the tap  Choose pipe diameter based on hf/L and Q for each pipe  Install orifices in emitters to get desired flow rate at the taps (is this based on static pressure or on the design dynamic pressures?)  Calculate

Distribution system design algorithm  Pressure break  Install large pipes everywhere (perhaps 12” diameter)  Turn off all taps  Measure the static pressure everywhere in distribution system  Install pressure breaks where needed to get pressure within design range

Measure design flows in all pipes (necessary for loops) using EPANET  Set the demand at all taps to (peak hour factor) x (per capita demand) x (number of individuals/household)  Using large pipes everywhere, run EPANET simulation to determine flows in all pipes  Start at a known pressure point  Identify all taps in the pressure zone (upstream from the next pressure break)  Measure the path length and elevation difference between the known pressure point and each tap

Designing for future growth  Future growth will increase the demand on the mains, but not on the household connections.  Therefore the mains need to be designed to handle the future flow.  It may be necessary to specify where growth is most likely to occur  Add the increase in flow to all distribution pipes (very conservative)  Multiply the flow in each distribution pipe by a factor (not conservative enough if the new growth is all at one end of the system)

Future growth 2  If we make the distribution pipes larger to accommodate future growth, then when we test the system response to turning on taps it will tend to perform well.  However, the true test is when taps are turned on and off at the end of its design life. How can we best simulate this?

 Where do we get each term in the equation for pipe diameter?  What is wrong with the slope of my lines? Transmission Line Design Critical point

Designing the next section Actual HGL given real pipe size Pipelines can have multiple critical points or a single critical point (the end of the line!) We are finding the HGL that meets the requirement “HGL must be above the pipeline”

Pipe Size Selection Procedure  Given design flow rate, calculate for each pipe  Given the required ratio of pipe length to elevation drop select a pipe from the appropriate schedule that has a value of that is greater than the required value

Mix pipe sizes to get design flow  We could mix a large pipe and a small pipe to more closely deliver the design flow  Given total pipeline length (L) and total elevation difference (h f )  Select a pipe with smaller (L/h f ) 1 and a pipe with larger (L/h f ) 2  Calculate length of each pipe required subject to total length and total head loss constraints

Two Pipe Size Mix Head loss constraint Length constraint

Mixing pipe sizes  If you install the small pipe upstream from the large pipe it is possible that the HGL will drop below the pipeline  If there aren’t any other constraints, install the large pipe diameter upstream  If possible, use the small pipe where higher pressure rating PVC or galvanized iron pipe is required

Pressure Constraints  Different “schedules” of pipe can withstand different pressures (higher pressure means thicker walls means more money)  The system must be designed so that a valve can be closed right at the distribution tank and the pipes must withstand the resulting static pressure (p=  gh)

PVC Schedules ScheduleMax pressure (psi) Max Static Head (m) SDR SDR SDR SDR and 80f(diameter)

Schedules 40 and 80

Different pipe materials  Galvanized iron pipe is more expensive than PVC and is rougher (has more head loss)  So it can be logical to use smaller galvanized iron pipe than PVC pipe even though the head loss will be much greater through the iron pipe!

Goal is to get design flow rate at minimum cost  I am not sure what the correct algorithm is!  The available energy can be “spent” as head loss wherever you like  Goal is to use the energy where it reduces the project cost most  Use smaller diameter pipes for high pressure sections of PVC pipe or for galvanized iron pipe  Head loss changes rapidly as pipe size changes, so it will only be possible to use slightly smaller pipes.

Hydraulic Gradeline HGL Static HGL 112 m 1.5” 2”

Pressure Break  A small tank (with a free surface) in a pipeline used to prevent high pressure downstream from the pressure break  Inflow can be regulated by a float valve  If inflow is unregulated excess water will exit through an overflow  Pressure breaks can be installed to make it possible to use cheaper pipes