Why a ‘Constant Power’ Pump delivers constant flow and can not do as a VSP? Let me example:
A ‘Constant Power’ pump is defined in the attached network. The pump can deliver 3984 gpm, when option ‘Is Variable Speed Pump’ is ‘False’. But after setting ‘True’ and ‘Flow (Target)’= 1200 for ‘Fixed Flow’ and calculating it, it shows that the pump still delivers 3984 as flow. Why is not decreased to 1200 gpm?
If ‘Pump Definition’ changes to ‘3Point’ (which is a 3 Point type), you will see that the pump delivers 1200 gpm.
If you need to model a variable speed pump, you'll need to enter the full pump curve (using the 3-point or multi-point option for example.)
Constant power pump curves are less accurate and should be avoided whenever possible, as mentioned in the Help.
We will look into adding a validation message for fixed flow VSPs, similar to the one you get when set to fixed flow (reference # 124145)
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Sushma Choure
First let me know why 'Constant Power' Pumps can not considered as a VSP? I need more explanation.
Second what '124145' code is? meanwhile I did not get any message while set VSP Type to 'Fixed Flow'.
The Constant Power pump curve type is a crude approximation that doesn't work very well with the Affinity laws, so it is not supported with variable speed pumps. It has a concave shape, where it goes off to infinity if flow or head approach zero.
This type of pump curve was available in EPANET and KYPIPE, so it has been available in WaterCAD and WaterGEMS to support users who may need to use it for a quick check. Again though, if you need to model a variable speed pump, you will need to enter the real pump curve using one of the other methods.
124145 is the ID in our defect management system for adding a validation message for this case, to inform the user that constant power pump curves are not supported with variable speed pumps. Currently you will see this message for fixed head VSPs, but as you mentioned, the message is currently missing for fixed flow VSPs.