Hello
There is a Pump which has to deliver water from a Reservoir to several Junctions. The Junctions have dissimilar Elevations and Demands. There is no any Tank or Reservoir at the end point of network. How can define a sufficient Pump? How can calculate ONE Elevation and ONE Demand to select sufficient Pump from manufacturer product catalogs?
Sim
Please have a look at example 3 in the sample models.
Regards,
Sushma Choure
Bentley Technical Suppport
If I'm understand your question correctly, you may want to look at this Support Solution on system head curves for systems with no downstream storage (you can find a lot of previous forum discussions on this subject, too.)
communities.bentley.com/.../15371.system-head-curves-with-no-downstream-storage-solution-500000056093.aspx
You may also want to take a look at our Advanced Water Distribution Modeling and Management book for general modeling advice.
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Jesse
Thank you very much. I will focus on this Wiki page.
Would you tell me which page or section of the book you referred to it?
Simbaa,
You may also want to have a look at this wiki entry which explains how you can estimate the desired head for your pump given you know the flow rate you want.
communities.bentley.com/.../16879.estimating-a-pump-curve-for-a-model.aspx
Mark
Thank you very much. This is a good idea. But:
I used it for a closed system and some problems occurred. The model and the photos are attached:
Total Demand is 20.9 l/s.
After running the model, first error is ‘Node is not connected to a boundary’. I set a reservoir at the end point of the network which has lowest Elevation, to remove this error (this reservoir can not deliver flow to network).
After running again, it shows that all Junctions have negative pressure.
If you define a Pump as you said (with a single point:Flow=20.9 l/s & Head=3.05-.34 m), pressures remain negative.
What is the problem. How can define pump for a closed system like this?
Negative pressure can be due to several reasons, please see this support solution. It doesn't say that pump can’t deliver the flow or head.
Sushma
Is inserting a useless reservoir to remove the Error Message (as I did above) correct or a better option can be suggested?
Inserting a 'dummy' reservoir is likely to give incorrect results. Better to use 'pressure dependent demands' and then create a system head curve at the pump that you are trying to design. See the link that Jesse provided earlier for more details.
Mal
Dear Mall
Thank you very much for your good responses. I read below Wikis carefully:
Now I know how to draw System Head Curve for any network (Closed or non-closed). But my first question is unanswered yet:
Assume there is a network with just one Reservoir which has lower Elevation against Junction Elevations. Now I want to select a sufficient Pump for entire network. It needs at least one head and one flow to use ‘Design Point’ Type or so. How can I get these two points? I did what Wiki communities.bentley.com/.../16879.estimating-a-pump-curve-for-a-model.aspx mentions, but for my closed-system, it does not run, because there is no any Boundary in the network and ‘Node is not connected to a boundary’ error occures. Either PDD has been defined or not, this error message occures, I insert a dummy Reservoir to remove this error. You says it causes incorrect results.
Please guide me how I must do to solve the problem with defining and selecting a good Pump for this condition. All what you and others say is related to AFTER selecting pump. Graphing System Head Curve (PDD or so) is related to AFTER selecting Pump and my question is about SELECTING Pump itself.
Once you have the system head curve (which is independent of the pump curve), you can overlay some candidate pump curves to select the one that intersects the system head curve near optimal efficiency. Here are some sections of the Advanced Water Distribution Modeling and Management book that you should check out:
Chapter 8.6: Developing System Head Curves for Pump Selection/Evaluation
Page 312: Pumping into a Closed System with No Pressure Control Valve
Chapter 10.8: Power Consumption
Page 438: Determining Pump Operating Points
Dear Jesse
Let me read above references. Ill come back then.
I took a look at your references. Non of them mentioned this situation that is selecting a sufficient pump for a Closed-System according to what Chapter 8.6 explains. If you intercept the pipe between Boundary and other elements (in a Closed-System) to do what Chapter 8.6 suugests (I mean to set two Junctions as a Suction side and Discharge side), then the error ‘Node is not connected to a boundary’ will occured.
What has to do to remove this problem? If this problem be removed, then I know how select a good pump for the model.