Unbalanced model with VSP

A.S.,

It looks like the model is unbalanced - note the "Network Unbalanced" message in the list of User Notifications. This means that the program was not able to converge on a balanced solution within the maximum number of trials set in the calculation options. When the network is unbalanced, the results cannot be trusted and you'll often see strange results. 

There are a number of reasons why the network may be unbalanced. Try clicking the timestep in the Calculation Summary (which appears after computing the model) and look at the tabs at the bottom for clues, especially "intra-trial status detaails".

If this started happening after setting up a VSP, closely examine the VSP settings, and how the VSP might interact with the hydraulics of the rest of the model.

You can find more troubleshooting information here: Troubleshooting the Network Unbalanced or Cannot solve network hydraulic equations user notification

If this does not help, please provide a copy of the model for review: Sharing Hydraulic Model Files on the OpenFlows Forum

project watercad final update 4-10.wtgAttached  model still not knowing how to solve it 

Hello A.S., 

To open this model, we would also need the .wtg.sqlite file, which is a database file without which model cannot be opened. 

Please upload the .wtg.sqlite file as well. 

https://communities.bentley.com/cfs-file/__key/communityserver-discussions-components-files/5925/_2300_3.rar

sorry about the first file i didn't notice ... kindly find the attached file 

Since this is a separate issue from the original post, I have split this to a new thread.

I see that you are using an older version, 10.00.00.50. I have tried running the model in that version as well as the latest version (10.02.00.43), and it immediately fails with "cannot solve network hydraulic equations". This is different from the issue reported in your screenshot from March 28th, so I assume you have made some changes to the model since then, and this "cannot solve..." issue is what you are also now currently seeing.

I see that you have configured the Motor tab of the pump definition for pumps 1-8 to be variable speed drive, but the "is variable speed pump?" option in the pump properties is set to false for all pumps. This means that the pump will either have a speed of zero when off, or full speed when on (and the initial relative speed factor is set to 1.0, meaning full speed). If you meant to configure the pumps to be VSPs which change speed to maintain a target head or flow, you'll need to configure that in the pump properties.

The "cannot solve..." error seems to be caused by two main issues:

1. A large number of elements  are fully disconnected from a water source. This is due to a portion of the middle part of the model being set to inactive. When I opened the model, these inactive elements do not seem to be colored per the display inactive topology option for some reason (possibly a corrupt .WTG.DWH file), and I had to go to File > Database Utilities > Synchronize Drawing, to see them disappear (or turn gray, depending on the setting). You should then see the elements in the "PODs Room 1" section of the model are inactive and therefore all the elements on the left side are disconnected from the water source on the right side (as well as a few pipes at the top-right side under the annotation "Return Line (Hot Water)".) If the inactive portion of the model represents a future condition, you will need to properly connect the left side of the model to the right side. Otherwise, you may need to make those elements active by using the "clear" button in the Active Topology Selection tool.
   
   
2. The only water source (reservoir R-4) is connected to the system via a 1 mm diameter pipe, but there are very large demands in the system. I see that you have an annotation above it indicating that it is a "fake" reservoir", and I am guessing you have done this because it is a closed loop system and you saw the suggestion in this article. However, the model has some very large demands, inducing very large headlosses not only in this tiny "fake" pipe, but also in the other, relatively small diameter pipes in the model. Did you intend to model water exiting from the system at these demand points? With the inactive elements made active, if you remove all demands (for example using an Active Demand Adjustment in the calculation options, configured to "set" the demand zero for the entire network), then the model balances and the results look more reasonable. I also noticed that there is a gap in the "Return Line (Hot Water)" at the top-right of the mode; there is no pipe connecting J-866 to J-867 and therefore it is not connected back to the "fake" reservoir per the related article on closed loops. Did you intend to connect this? If you Reconnect the pipe, the model seems to have an even easier time balancing.

Since this is a separate issue from the original post, I have split this to a new thread.

I see that you are using an older version, 10.00.00.50. I have tried running the model in that version as well as the latest version (10.02.00.43), and it immediately fails with "cannot solve network hydraulic equations". This is different from the issue reported in your screenshot from March 28th, so I assume you have made some changes to the model since then, and this "cannot solve..." issue is what you are also now currently seeing.

I see that you have configured the Motor tab of the pump definition for pumps 1-8 to be variable speed drive, but the "is variable speed pump?" option in the pump properties is set to false for all pumps. This means that the pump will either have a speed of zero when off, or full speed when on (and the initial relative speed factor is set to 1.0, meaning full speed). If you meant to configure the pumps to be VSPs which change speed to maintain a target head or flow, you'll need to configure that in the pump properties.

The "cannot solve..." error seems to be caused by two main issues:

1. A large number of elements  are fully disconnected from a water source. This is due to a portion of the middle part of the model being set to inactive. When I opened the model, these inactive elements do not seem to be colored per the display inactive topology option for some reason (possibly a corrupt .WTG.DWH file), and I had to go to File > Database Utilities > Synchronize Drawing, to see them disappear (or turn gray, depending on the setting). You should then see the elements in the "PODs Room 1" section of the model are inactive and therefore all the elements on the left side are disconnected from the water source on the right side (as well as a few pipes at the top-right side under the annotation "Return Line (Hot Water)".) If the inactive portion of the model represents a future condition, you will need to properly connect the left side of the model to the right side. Otherwise, you may need to make those elements active by using the "clear" button in the Active Topology Selection tool.
   
   
2. The only water source (reservoir R-4) is connected to the system via a 1 mm diameter pipe, but there are very large demands in the system. I see that you have an annotation above it indicating that it is a "fake" reservoir", and I am guessing you have done this because it is a closed loop system and you saw the suggestion in this article. However, the model has some very large demands, inducing very large headlosses not only in this tiny "fake" pipe, but also in the other, relatively small diameter pipes in the model. Did you intend to model water exiting from the system at these demand points? With the inactive elements made active, if you remove all demands (for example using an Active Demand Adjustment in the calculation options, configured to "set" the demand zero for the entire network), then the model balances and the results look more reasonable. I also noticed that there is a gap in the "Return Line (Hot Water)" at the top-right of the mode; there is no pipe connecting J-866 to J-867 and therefore it is not connected back to the "fake" reservoir per the related article on closed loops. Did you intend to connect this? If you Reconnect the pipe, the model seems to have an even easier time balancing.