Control Valve - ANS (English Units)

Summary

This example will show how to use AFT Arrow ANS module to size a system based on pipe weight. For many systems the necessary cost data is not available to directly minimize cost, so minimizing system parameters such as weight or flow volume is useful. By minimizing parameters such as these we minimize pipe diameter, which directly correlates to minimizing pipe costs.

We will create a system that feeds water from an elevated reservoir to a lower reservoir at a specified flow rate. A control valve will be used to control the flow rate and can be placed anywhere within the line. We will need to determine what size of piping to use in order to achieve a minimum pressure drop of 140 kPa across the control valve.

Note: This example can only be run if you have a license for the ANS module.

Topics Covered

• Sizing using pipe weight

• Creating a Common Size Group

• Defining Control Valve Design Requirements

Required Knowledge

This example assumes the user has already worked through the Beginner: Air Heating System example, or has a level of knowledge consistent with that topic.  You can also watch the AFT Arrow Quick Start Video (Metric Units) on the AFT website, as it covers the majority of the topics discussed in the Beginner: Air Heating System example.

In addition, it is assumed that the user has worked through the Beginner: Three Tank Steam System - ANS example, and is familiar with the basics of ANS analysis.

Model Files

This example uses the following files, which are installed in the Examples folder as part of the AFT Arrow installation:

• Metric - Control Valve.aro

• Metric - Control Valve - ANS.aro

Step 1. Start AFT Arrow

From the Start Menu choose the AFT Arrow 9 folder and select AFT Arrow 9.

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

Open the Metric - Control Valve.aro example file listed above, which is located in the Examples folder in the AFT Arrow application folder. Save the file to a different folder.

Make sure the "With Insulation" scenario is the active scenario by double clicking on that scenario in the Scenario Manager. The workspace should look like Figure 1

Step 2. Define the Modules Group

Navigate to the Modules panel in Analysis Setup. Check the box next to Activate ANS. The Network option should automatically be selected, making ANS enabled for use.

Step 3. Define the Automatic Sizing Group

In this model we are going to perform sizing to minimize the pipe weight (therefore minimizing cost), while maintaining a minimum pressure drop of 140 kPa across the control valve.

To do this, first go to the Sizing window by clicking on the Sizing tab, or from the Windows menu.

A. Sizing Objective

The Sizing Objective panel should be selected by default from the Sizing Navigation Panel along the bottom of the window.

Set the Sizing Option as Perform Sizing.

For the Objective, choose Pipe Weight, and select the Minimize option from the drop-down list if it is not already selected.

B. Sizing Assignments

On the toolbar at the bottom of the window select the Sizing Assignments button.

In this case we are sizing a new pipeline, so we want to size all pipes in the model.

ØUnder Automatically Size select Always Include in Weight next to each of the pipes.

For this system it is required that both pipes be the same size. We will need to add both pipes to a Common Size Group to specify this. To do this:

1. Click New above Pipe Grouping, and give it new Common Size Group the name Main Pipes

2. A new section will now appear with the Main Pipes group listed under Common Size Groups. Add both pipes to this group by clicking the corresponding radio buttons (Figure 2).

Note that as many Common Size Groups as necessary can be created. Selection tools are available at the bottom of the window to help assign multiple pipes to a Common Size Group for larger models. Additionally, pipes can only be assigned to a group once they are set to be included in sizing.

C. Candidate Sets

Click on the Candidate Sets button to open the Candidate Sets panel.

To select a discrete pipe size, ANS needs a list of candidates from which to choose. This list is called a Candidate Set. To create a Candidate Set, do the following:

1. Under Define Candidate Sets, click the New button.

2. Give the set the name STD Pipes and click OK.

3. From the drop down list choose Steel - ANSI.

4. In the Available Material Sizes and Types on the left, expand the STD pipe sizes list.

5. Double-click each of the sizes from 1 to 10 inches to add them to the list on the right.

6. In the Select Pipe Sizes window, click the OK button.

The STD Pipes set will now appear, and will be automatically defined as a Discrete set.

We now need to define which pipes will use this Candidate Set during the sizing calculation.

ØUnder Assign Candidate Sets to Pipes, set the Main Pipes Common Size Group to use the STD Pipes Candidate Set. The Candidate Sets are now fully defined and assigned to the appropriate pipes, as can be seen in Figure 3.

D. Design Requirements

Select the Design Requirements button.

For this model we only have one Design Requirement, which is for the minimum pressure drop across the Control Valve. To define this requirement:

1. Select the Control Valves button at the top of the window.

2. Click the New button under Define Control Valve Design Requirements.

3. Enter the name Min Pressure Drop.

4. For the Parameter, select Pressure Drop Static.

5. For the Max/Min, select Minimum

6. For the Value and Units, select 140 kPa.

Now we need to apply the defined Design Requirement to the Junction.

ØCheck the box next to the Control Valve Junction J2 in the Assign Design Requirements to Control Valves section.

Note: It is strongly recommended that flow control valves have a Design Requirement specified for the minimum pressure drop/head, or the maximum Cv/percent open at the valve. If no Design Requirements are applied, the ANS module will allow the control valve to control to any pressure required to meet the control setpoint, even if this requires the control valve to add pressure to the system for design purposes. To avoid this behavior in the final solution, a Design Requirement should be applied.

E. Assign Cost Libraries

When the Sizing Objective has been defined as monetary cost, it is necessary to create and assign cost libraries for the automated sizing, which can be done in the Assign Cost Library panel. Since we have defined the objective as Pipe Weight, we will not need to assign any cost libraries, and this button is disabled.

F. Sizing Method

Select the Sizing Method button to go to the corresponding panel.

Select Discrete Sizing, since we are sizing based on commercial pipe sizes.

For the Search Method in a simple model such as this one, the MMFD or SQP method should be appropriate since there is only one Design Requirement, and only one pipe size is being varied. Choose the default Modified Method of Feasible Directions (MMFD).

Step 4. 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 Arrow solver converges on the answer. Once the solver has converged, view the results by clicking the Output button at the bottom of the Solution Progress window.

Step 5. Examine the Output

The output is shown below in Figure 4. We have shown all three sections of the output window with the General, Pipes, and Junctions sections. In the General Section, we have selected the Cost Report tab that shows the variable that was sized for this run. The pipe weight in each pipe was minimized.

In the pipe section, we have selected the Sizing tab that shows the final pipe sizes chosen. We can see that the ideal pipe size was found to be 3 inch pipe. In the Junction section, we have selected the CV Design Requirements tab that shows how we have satisfied the Design Requirement set on the control valve. The only Design Requirement was on pressure drop and we are above the minimum pressure drop of 140 kPa.

Conclusion

This example has demonstrated how simple it is to perform an automated sizing to design a system for a set of requirements. Pipe weight may not be directly proportional to pipe cost but it can be implemented very quickly when cost data is not available.