Housing Project (English Units)

Housing Project (Metric Units)


The objective of this example is to model a pipeline system to supply water to a new housing development. As the engineer you will evaluate the design to find the smallest pipe size that will still meet the water supply requirements.

No Fire Conditions:

Each house requires 10 gal/min at a minimum of 60 psig.

Fire Conditions:

Each house requires 2 gal/min with no minimum pressure. One fire hydrant may be open at a time and requires 100 gal/min at 90 psig static.

Topics Covered

  • Using Scenario Manager

Required Knowledge

This example assumes the user has already worked through the Beginner: Three Reservoir Problem example, or has a level of knowledge consistent with that topic. You can also watch the AFT Fathom Quick Start Video Tutorial Series on the AFT website, as it covers the majority of the topics discussed in the Three-Reservoir Problem example.

Model File

This example uses the following file, which is installed in the Examples folder as part of the AFT Fathom installation:

Step 1. Start AFT Fathom

From the Start Menu choose the AFT Fathom 12 folder and select AFT Fathom 12.

To ensure that your results are the same as those presented in this documentation, this example should be run using all default AFT Fathom settings, unless you are specifically instructed to do otherwise.

Step 2. Define the Fluid Properties Group

  1. Open Analysis Setup from the toolbar or from the Analysis menu.

  2. Open the Fluid panel then define the fluid:

    1. Fluid Library = AFT Standard

    2. Fluid = Water (liquid)

      1. After selecting, click Add to Model

    3. Temperature = 60 deg. F

Step 3. Define the Pipes and Junctions Group

At this point, the first two groups are completed in Analysis Setup. The next undefined group is the Pipes and Junctions group. To define this group, the model needs to be assembled with all pipes and junctions fully defined. Click OK to save and exit Analysis Setup then assemble the model on the workspace as shown in the figure below.

The fire hydrants are both turned off to begin the problem. Select the Optional tab in the Assigned Flow Properties window and select Flow Off to close the hydrant. Do this for both hydrants.

The Workspace for the Housing Project example.

Figure 1: Model for Housing Project Example

Pipe Properties

All the mains are to be the same size. We will try 3, 3 ½ , and 4 inches to see which one meets the requirements. Enter 3-inch pipe for the main and hydrant supply lines in the base case.

  1. Pipe Model tab

    1. Pipe Material = PVC - ASTM

    2. Pipe Geometry = Cylindrical Pipe

    3. Size = Use table below

    4. Type = schedule 40

    5. Friction Model Data Set = Standard

    6. Lengths = Use table below

Pipe Size Length (feet)
1 3 inch 2000
10 & 20 3 inch 300
101-105 & 201-205 3 inch 200
199 & 299 3 inch 10
206 1 inch 150
108 & 207 1 inch 125
106, 110, 208, & 210 1 inch 100
107, 109, & 209 1 inch 75

Junction Properties

  1. J1 Reservoir

    1. Name = West Lake

    2. Liquid Surface Elevation = 235 feet

    3. Liquid Surface Pressure = 0 psig

    4. Pipe Depth = 0 feet

  2. Branches

    1. Elevation = Use table below

Branch Elevation (feet)
203 -10
102-105 & 204 -5
101, 106, 202, & 205 0
201 & 206 5
  1. Assigned Flows

    1. Elevation = Use table below

    2. Type = Outflow

    3. Flow Specification = Volumetric Flow Rate

    4. Flow Rate = Use table below

Assigned Flow Name Elevation (feet) Flow Rate (gal/min) Special Conditions
107 Browns 10 10 None
108 Peters 20 10 None
109 Chambers 35 10 None
110 Fords 15 10 None
111 Kellys 20 10 None
199 North Hydrant 5 100 Flow Off
207 Norths 20 10 None
208 Stewarts -15 10 None
209 Coles 30 10 None
210 Allens 10 10 None
211 Burns 5 10 None
299 South Hydrant 0 100 Flow Off

ØTurn on Show Object Status from the View menu to verify if all data is entered. If so, the Pipes and Junctions group in Analysis Setup will have a check mark. If not, the uncompleted pipes or junctions will have their number shown in red. If this happens, go back to the uncompleted pipes or junctions and enter the missing data.

The flows will be varied based on the different scenarios examined. To do this, we need to create child scenarios. We will use the Scenario Manager to create the designs we need to evaluate.

Step 4. Manage the Scenarios

  1. In the Scenario Manager, create a child of this scenario by right-clicking on the Base Scenario and selecting Create Child. Name this child scenario 3 inch Pipe. This will be the parent scenario for all the runs with 3 inch main pipes. Alternatively, you can select the Create Child icon on the Scenario Manager on the Quick Access Panel to create this child scenario.

  2. Select the 3 inch Pipe scenario and create another child, this one named Fire Flow. set the flow rate at each house to 2 gal/min instead of 10 gal/min. This will be the flow rate demand that needs to be met at the houses when either hydrant is open.

  3. Next, create two children of this scenario named North Hydrant Fire and South Hydrant Fire. Load the North Hydrant Fire scenario from the Scenario Manager. Open the properties window of the North Hydrant and on the Optional tab, toggle the flow on by changing the special condition to None.

  4. Now load the South Hydrant Fire scenario turn on the South Hydrant.

  5. You now have all the scenarios that need to be evaluated for each pipe size but we still have two more pipe sizes that we need to investigate.

  6. Right-click the 3 inch Pipe scenario and select Clone With Children.

  7. Name this scenario 3.5 inch Pipe.

  8. Repeat this process to create another set of scenarios named 4 inch Pipe. The Scenario Manager on the Quick Access Panel should look like Figure 2.

The Scenario Manager in the Quick Access Panel for the model.

Figure 2: Scenario Manager for Water Supply to Housing Project

After creating the scenarios for the 3.5 inch pipe and 4 inch pipe, we need to open these scenarios and change the pipe sizes. This is accomplished most quickly with the Global Pipe Edit window.

  1. Load the 3.5 inch Pipe scenario.

  2. Select Global Edit then Global Pipe Edit from the toolbar or Edit menu.

  3. Click the radio button for Pipe Template at the top, if not already selected, and click Select Pipe Data.

  4. Change the Size to 3-1/2 inch, click OK.

  5. In the Parameters to Change (Select in List) area, check the box next to Nominal Size 3-1/2 inch.

  6. Since we only want to apply this to certain pipes, select Special above the Pipe List.

  7. Change the Selection Type to Pipe Input Properties.

  8. For Pipe Property, select Pipe Inner Diameter.

  9. For Range, enter From 3 To 3.5 inches.

  10. Click Select Pipes and note that 15 of 25 pipes were selected, these are all the pipes that are currently 3 inches. Click OK.

  11. Click Apply Selections. A message should appear to inform you that changes were successively applied.

  12. Click OK.

Repeat this process for the 4 inch Pipe scenario but changing the pipe Size to 4 inch. Return to the 3 inch Pipe scenario when finished.

Step 5. Specify Output

Before running the model, load the Base Scenario to set the Output Control. Open the Output Control window by selecting Output Control from the toolbar or Tools menu. This window allows the user to specify the output from the Fathom simulation. The window starts with a default set of outputs. Often the default output is sufficient. You may also specify a title for the model. Click on the General tab and add a title of Housing Project Example. On the Display Parameters tab, select the Junctions button and change the static and stagnation pressure units to psig. Click OK to save and close the Output Control

Now load the 3 inch Pipe scenario.

Step 6. Run the Model

Click Run Model on the toolbar or from the Analysis menu. This will open the Solution Progress window. This window allows you to watch as the AFT Fathom solver converges on the answer. This model runs very quickly. Now view the results by clicking the Output button at the bottom of the Solution Progress window.

Step 7. Examine the Output

The output from this model is shown in Figure 3. For the 3 inch Pipe scenario, with no hydrants open, the flow to each house is 10 gal/min and the stagnation pressure must be at least 60 psig. The pressure at each house is above 60 psig, so the system with 3 inch mains would be sufficient.

The Assigned Flow tab of the Output window for 3 inch mains with no fire.

Figure 3: Output window for 3 inch mains with no fire

On the Scenario Manager, load the North Hydrant Fire scenario under the 3 inch Pipe scenario. Run the model, and look at the output. This output is shown in Figure 4. Although the hydrant receives 100 gal/min, the supply pressure is less than the required 90 psig.

The Assigned Flow tab of the Output window for 3 inch mains with north hydrant fire conditions.

Figure 4: Output window for 3 inch mains with north hydrant fire

Because we know that 3 inch is sufficient for No Fire conditions, we only need to test the Fire conditions for each pipe size. After testing all the fire conditions, 4 inch pipe is the only size that will deliver 90 psig to the North Hydrant during fire conditions. Therefore, the housing development mains must be 4 inch pipe.