Selecting VSP for EPS

Simbaa,

What type of VSP do you have in the real system? Is it a fixed head, fixed flow, or one that is pattern based that changes based on the time of day?

There are a few things that you should note based on your question. If you're talking about pumps following demand patterns then you need to understand that a pump is going to deliver whatever flow and head it needs to in order to satisfy the demands in the system because WaterCAD\GEMS is a demand driven software, which means demands always need to be satisfied. With that being said, if you want a pump to follow a demand pattern assigned to a particular junction then I don't think you need to use a VSP at all because a non-VSP pump will already do that, which should get you to your defined goal of choosing a pump that follows a demand pattern during an EPS simulation. Unless there is something that I am not understanding about your question, which is entirely possible.

In case you need to know, a fixed head VSP will provide a fixed hydraulic grade at the point that you define in the pump properties as the control node. A fixed flow VSP will attempt to provide a constant flow throughout the entire simulation and a pattern based VSP is controlled using a user defined pattern based on time from the start of the simulation vs. multiplier that controls the relative speed factor.

Mark

Mark
Thank you for response.
1- Let me ask my question again. I think it was not enough obvious.
Assume a ‘closed-system ‘ network which has a Pump. Downstream of the pump there is a Junction which has a based Pattern of Demand. (e.g. 10 l/s for 2 hours after starting and 120 l/s for 7 hours after starting).
It is not a good idea to select a non-VSP Pump, because the system is a closed one and changing in demand is very wide. Then if the Pump which is selected be a non-VSP one, it will operate out of operating point. I think it is better to select a VSP. But I do not know which type of VSP can be selected for this situation:
A ‘Fixed Flow’ has not been suggested in Help documents: ‘... This can be a typical control case when a pump is supplying water to an "open" system where a tank is located in the downstream distribution system. It is unlikely that a pump is expected to supply the fixed flow to a "closed" system where no tank is located at the downstream of a pump.’
A ‘Fixed Head’ can do better, but I am not sure whether it is the best choice or not.
A ‘Based Pattern’ is not a choice at all.
What do you think about?

2- another question which was generated along the above question is:
If a ‘Fixed Flow’ Pump be selected for a closed system which downstream Junctions of it follow Patterned demands, then what will happen? I modeled it and could not understand behavior of the pump. What does ‘Flow target’ mean in this situation?
Sim

Simbaa,

When describing your issues in the future please use as much detail as possible, while keeping your questions as succinct and clear as possible, about what you are trying to accomplish. This will ensure that we can provide you with a solution as quickly as possible and help us to better understand what you are doing.

1 - In your case it sounds like what you will have to do is sensitivity analysis where you set up a scenario with a test case for a fixed head pump in your model and then set up another scenario with other possible test case that you think might work for this pump given the system that you are working with. After you do that you will have to use your best engineering judgment based on the results of the tests to decide what will work best for you given your end goal of the project.

Mark

For a closed system, you would typically use a fixed head variable speed pump. Take a look at the section called "Variable Speed Pumps" on page 313 of our Advanced Water Distribution Modeling and Management book.

If you only have fixed demands downstream, a fixed flow VSP would not make sense since the flow through the pump would always be equal to the sum of the demands.